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On the Lighter Side => New Theories => Topic started by: alancalverd on 01/08/2020 11:28:25
Title: Can heat affect Earth's rotation?
[Mod edit: Topic split from "Can windmills affect Earth's rotation?"]
https://www.thenakedscientists.com/forum/index.php?topic=80136.0
Any windmill extracts kinetic energy which we eventually turn into heat.
Ignoring second-order effects such as thermal winds, the source of kinetic energy is the rotational energy of the planet, so it must eventually stop spinning.
Now that really will induce some climate change!
Title: Re: Can heat affect Earth's rotation?
gnoring second-order effects such as thermal winds, the source of kinetic energy is the rotational energy of the planet, so it must eventually stop spinning.
And there was me thinking that the Sun powered the wind.
so it must eventually stop spinning.
Just as soon as it gets hold of something to which it can impart angular momentum.
Tricky for something in a near vacuum.
Might need to wait until the Sun goes red giant.
Post by: chiralSPO on 01/08/2020 16:54:22
Well, the moon is taking some... but tidally locked to the moon is also not "stopped"
I'm with Bored on this one. Thermal effects (wind) are only secondary to the rotation of the earth if your frame of reference is not tethered to the earth. If you wanna argue that the atmosphere is moving with the earth at several thousand kph, that windmill had better be inbound from outer space!
Not a lot. Solar heating is responsible for the slow, gross convective movement of large air masses towards and away from the poles, but the formation of cyclones is powered by the coriolis displacement of those masses. The wind in the Southern Ocean is almost entirely due to the earth's spin as there is almost no land to produce differential heating, which is why albatrosses live the way they do, reliant on a constant westerly to keep them airborne for years at a time.
Post by: Petrochemicals on 02/08/2020 00:55:22
If you take the energy out of the wind in an eastward direction the waves will not be generated in that direction and trees will not blow thus meaning the earth is slowed more by the windmill but less by the environment.
The spinning Earth has enormous rotational KE.
But it can't transfer that energy without slowing itself down.
And it can't slow itself down without an external torque.
Now, the geothermal energy, and the tides might make small contributions but they really don''t do "weather".
So, the fundamental question for you to answer Alan, is this.
Are you abandoning the conservation of energy, or abandoning the conservation of angular momentum?
Quote from: Petrochemicals on 02/08/2020 00:55:22
It's all very clever, and very grown up, to proclaim that you are ignoring me, but you are also ignoring physics.
Windmills can't slow the Earth.
You need to consider the reaction forces at the foot of the windmill and the conservation laws.
Apologies - I hit "modify" instead of "quote", but I think it's clear what you were referring to.
For the sake of public safety, please publish the registration number of your car, as you say the brakes don't work.
And how sad that James Joule wasted his honeymoon.
I don't drive- it's a public service I offer the rest of the world for free.
But, many years ago I did an O level physics module on the physics of the motor car.
And they did explain things like brakes.
One thing which they didn't need to explain was that, if you hit a bump, and your car leaves the ground, the brakes and steering have no effect (neglecting air resistance) until you hit the ground again.
The Earth is perpetually in flight (well, in orbit...) and in the vacuum of space, it's perfectly sensible to ignore air resistance.
So apart from the Moon's tidal drag, what torque acts on it to alter its angular momentum?
Because, without such a torque, the rate of spin will remain the same.
And, if the rotation rate remains the same, then its rotational kinetic energy remains the same.
And if its energy is the same, it can't be giving up energy to drive the weather.
And- this is England- we have plenty of weather, so something must be driving it.
And - even in England- the Sun provides huge amounts of power, which has to go somewhere somehow.
The world's weather is a giant heat engine driven by the Sun.
So, rather than making silly comments about my (non existent) driving, perhaps you can tell us what provides the torque that slows the Earth?
(Hint; it's not atmospheric drag; there isn't a 1000 MPH wind running round the equator)
The prevailing geostrophic wind is the result of coriolis force making the air move relative to the surface of the earth. The coriolis force is a consequence of the spin of the earth. If we extract kinetic energy from the geostrophic wind and dissipate it as heat, whence came that energy? The only source is the spin of the earth.
The function of a vehicle brake is to convert the kinetic energy of the vehicle to heat. Same thing. Conservation of momentum means that applying the brakes whilst airborne will stop the wheels spinning but won't dissipate much energy, but if they are in contact with the ground (a very large mass) you can generally bring the vehicle to a standstill.
but if they are in contact with the ground (a very large mass) you can generally bring the vehicle to a standstill.
So, what's the corresponding "very large mass" that the Earth is in contact with and which can slow it down?
Essentially you are still ignoring the conservation laws.
Without an externally acting torque, the world keeps spinning.
Now who's being silly? "Wind" is air moving over the ground. The surface air at the equator is moving 1000 mph faster than that at the poles, but neither mass is moving very fast over the ground. Now if we take a sample of equatorial air and adiabatically move it 1 degree north, it will be travelling over the ground at about 11 mph. The same volume of air moving 1 degree southward from a northern latitude will be travelling on the opposite direction. That is the origin of geostrophic wind: the north-south movement of air masses is due to temperature differential (cold dense air sinks below warmer air, so the surface drift is from pole to equator), and the east-west movement is due to coriolis force.
Now who's being silly?
Well, since you are sticking with your idea that the wind can slow down the rotation of the Earth in the long run... you.
Now, for the 3rd or 4th time
perhaps you can tell us what provides the torque that slows the Earth?
Hint: it can't be the atmosphere because that's rotating along with,and is part of, the Earth. If it wasn't then there would be a 1000 mph wind round the equator.
Now if we take a sample of equatorial air and adiabatically move it
What moved it (Hint, it's convection currents driven by the Sun)?
A ship sailing due north has to overcome coriolis forces, but that doesn't mean they can switch off the engine.
The engine has to work harder.
Please don't ascribe irrelevant ideas to me.
You are saying that the wind takes energy from the rotation of the Earth.
If we extract kinetic energy from the geostrophic wind and dissipate it as heat, whence came that energy? The only source is the spin of the earth.
Are you saying it does that without slowing the Earth down?
That's plainly a breach of the conservation of energy.
So Either you are being absurd and ignoring the laws of physics (spoiler alert- you are anyway) or you are saying that "the wind can slow down the rotation of the Earth in the long run" but not being bright enough to recognise that you are saying it.
So I'm not ascribing an irrelevant idea to you.
I'm just pointing out that your idea is absurd.
Post by: David Cooper on 03/08/2020 20:51:19
I'm not sure who's right here, but if you think about the way the equator of the sun rotates at a higher rate than the poles and how the core of the Earth rotates at a higher rate than the crust, it appears that are things that can happen with rotating liquid gas and plasma bodies which are able to cause drag and generate heat, but does that change the angular momentum?
Quote from: David Cooper on 03/08/2020 20:51:19
, but does that change the angular momentum?
Because only an external torque can do that.
There are small effects due to tide and even smaller ones due to radiation pressure
Things like earthquakes alter the distribution of the mass and thus the moment of inertia, and that alters the rate of rotation very slightly.
This isn't hard.
Angular momentum is a conserved quantity
I checked, it's the fifth time of asking.
I guess you could pretend that the world is one of these
https://en.wikipedia.org/wiki/Crookes_radiometer
But fundamentally the winds are driven by the Sun.
Please explain Buys Ballot's rule and the veering of wind direction with altitude.
I am well acquainted with the apparently erroneous mechanism in the meteorology textbooks, but whilst that is adequate for aviators and mariners, it seems that we have been missing the obvious for over 150 years.
A Nobel Prize awaits.
The Sun drives massive convection currents.
https://en.wikipedia.org/wiki/Atmospheric_circulation#/media/File:Earth_Global_Circulation_-_en.svg
The direction of these is somewhat perturbed by the spin of the Earth.
Some of the minor details of the flow patterns are still unclear, but can be predicted empirically.
I'm not going to get a nobel prize for that.
And now, for the 6th time.
Sooner or later, you will find it is easier to accept that you are wrong.
Maybe that understanding will lead to to an explanation of Buys Ballot's rule and a nobel prize.
But you are not going to get one by ignoring the conservation laws.
Post by: gem on 05/08/2020 12:14:16
Hi all could not resist this one,
The short answer to the original question is yes.
The energy that would be converted from kinetic to electrical is Originally from outside the Energy total of the Earth ( solar input) I will explain further at a later date via new theory's the consequences of this fact .
Quote from: gem on 05/08/2020 12:14:16
True, to the extent already explained
Quote from: Halc on 26/07/2020 00:13:45
By conservation of angular momentum, all you need is one windmill with a vertical axis at the north pole, rotating against Earth's spin.
climbing the stairs increases your distance from the rotation axis, so it increases the moment of inertia and this reduces the rotational speed, but not much.
The rest of you post indicates that (like Alan) you don't understand that angular momentum is a conserved quantity.
I will explain further at a later date via new theory's the consequences of this fact .
You don't have a theory
"A scientific theory is an explanation of an aspect of the natural world that can be repeatedly tested and verified in accordance with the scientific method, using accepted protocols of observation, measurement, and evaluation of results."
https://en.wikipedia.org/wiki/Scientific_theory
https://www.grammarly.com/blog/apostrophe/
Hi B/C I'm confident what I posted is correct, however in regards to the consequences and my future explanations We can discuss once posted in new theory's as I don't want to hijack this posting. But in regards for conservation of angular momentum to be appropriate. it requires a closed system ie no energy input
I do indeed understand the conservation of momentum, whether linear or angular. But a system that converts rotational kinetic energy to heat, which is then radiated out of the system, is not closed or conservative.
Post by: Halc on 05/08/2020 16:13:42
Your post demonstrates a complete lack of understanding. Your initial post in this thread was so wrong I thought you were trying to be sarcastic.
Momentum is not energy. It's amazing how many people confuse energy with force, momentum, or power. I'll add you and @gem to that list.
Heat radiates away energy, but not momentum. To change the momentum on a system, torque must be applied from outside the system, and said radiation applies no such torque.
You want to increase the spin of earth by windmill? Get a chainsaw and cut the thing down. That lowers Earth's moment of inertia and increases its rate until somebody erects the thing again. Angular speed is not conserved, but angular momentum is.
The force on a windmill blade is the rate of change of momentum of the air striking it. At least it has been since Newton's day, and fortunately it remains the case for aerofoils and propellors.
Angular speed is not conserved, but angular momentum is.
Angular momentum = I ω. So if you change angular speed ω and conserve momentum, you must change the moment of inertia I of the planet. If the mass remains constant (and nobody is suggesting otherwise) you have to alter its distribution. Are you suggesting that windmills cause earthquakes? That would really upset the green lobby!
Quote from: Bored chemist on Yesterday at 23:13:48
Seventh time.
What do you think is providing the external torque needed to change the angular momentum of the Earth?
So if you change angular speed ω and conserve momentum, you must change the moment of inertia I of the planet.
But- to a very good approximation the moment of inertia of the Earth is fixed. In principle, it rises slightly when I go upstairs and falls when I come back down again.
So the only way to change the rotation rate would be to apply a torque.
So either there is a torque, or there isn't a change in rotation rate.
And since there isn't a torque, there can't be a change in the rotation rate (we aren't talking about tidal drag here).
And since there isn't a change in rotation rate there can't be a change in rotational kinetic energy.
And since there isn't a change in that energy, it can't be being picked off rto drive the wind.
None of this is complicated.
It's high school physics.
I can recommend the study of basic atmospheric physics. It's a little taxing as it involves spherical geometry as well as Newtonian mechanics but it's more interesting than anything on TV these days.
Or if you have access to an inquisitive 10-year-old, you could ask him what makes air move latitudinally over the oceans.
Are you suggesting that windmills cause earthquakes?
That goes both ways- except I wasn't, but you are.
You are muddling two ideas.
The direction of the wind is influenced by coriolis forces (etc).
But as I already pointed out, the energy driving the wind is not derived from those forces.
If I walk North or South I am forced left or right by the coriolis force. But it is at right angles to my path and so it does no work.
And so, for the 8th time...
Halc, I don't know what list you're putting me on 💋💋or what I've posted you disagree with, but am quite happy to discuss the points I have posted.
Ie is the earth a closed system/ does the suns energy input provide the kinetic energy of the weather/wind
So although you're drifting away from the original question, there are several external torque forces that are accepted by mainstream science that affects the length of day and there is active research in regards to the coupling between the various layers of the planet.
Yes, there are. But, they are small; the weather is essentially driven by the wind.
And what Alan was saying was that the spin of the Earth powered the weather.
In that regard, he has mistaken the rudder for the engine.
But as I already pointed out
There's a difference between "asserted" and "pointed out". One of them has a scientific basis.
And here's the scientific basis
I think we are now up to the ninth time of asking.
Why don't you simply answer the question?
What supplies the external torque (that slows the Earth) against which work is done to provide the energy that you think is fed into the weather?
It's a simple enough bit of physics; which part do you not agree with?
In order for any of the Earth's rotational energy to be transferred to the winds, the Earth's rotation must be slowed down
That's just the conservation of energy.
It's not controversial.
And in order for the Earth to slow down, either the moment of inertia must change, or the angular momentum must change.
That's just the definition of angular momentum- again, it's not open to much debate.
And since the Earth's moment of inertia is fixed by the mass and structure of the Earth, a change in rotation would require an external torque to act on it (like tidal drag).
Again, it's a conservation law, so it's hard to see how you can dispute it.
So which bit are you not getting?
Or do you accept the conservation laws etc, in which case, where do you think the torque is from?
You are unteachable.
Quite possibly, but it's not relevant. I was taught before, so now I know.
The fact that you are not even trying to pretend to answer the question shows that you know I'm right.
If you thought I was actually wrong, you would have pointed out the error.
Hi B/C in regards to the effects being small, I assume you are referring to the positive/negative frictional coupling Effect between the Atmosphere and earth's surface, as per the original question.
So just to put a comparison value to reiterate that point and I think you posted previously in regards to how large the earth's angular momentum is.
As a fraction of the Total solar radiation Received by Earth for one day allowing around 30% reflection vs Earth's rotational Kinect energy gives :
Solar energy per day is 0.000005% of Earths rotational Kinect energy
I thought my explanation to Alan was pretty clear.
That rotational energy is big, more importantly, it's not going anywhere (except due to tidal drag).
But many thanks for doing the maths for us.
As you say:
"Solar energy per day is 0.000005% of Earths rotational Kinetic energy"
That means that the energy of rotation is equivalent to about 55000 years' radiation from the Sun .
So, if the weather was taking more energy from the spin than from the sun (as Alan originally said) then (simplistically) over about 55,000 years, the energy would be gone.
But the Earth is still spinning. And we know it's been spinning at pretty much the same rate for since they built Stonehenge.
That's about 5000 years ago.
A 10% change in the Earth's rotational energy would correspond to about a 5% change in rotation rate (The energy varies as the square of the rate).
And if the length of the day had varied by 5%, Stonehenge just wouldn't be aligned any more.
So that's another convincing argument that Alan is wrong.
Yes what your saying makes perfect sense and is aligned with mainstream science, and in regards to your dispute with Alan, I believe it's well accepted that the weather cycle is powered by the solar energy received.
Its also currently known that the weather patterns have a direct impact on length of day.
Which raises the question why does it appear that although there are known fluctuations To LOD due to the frictional couplings Due to weather patterns, the overall effects overtime is neutral. As per your post above.
On a slightly separate note I believe LOD is believed to have been around 20 hrs in the Devonian period but that is postulated that rotational energy has been transferred to the moons orbit.
There's really rather a lot of science about it. I found more than I expected here
https://en.wikipedia.org/wiki/Day_length_fluctuations
But the atmospheric contribution- apart from the even smaller effect of airborne tides*- averages to zero.
*"even smaller" compared to the very small effect of oceanic tidal drag.
Blazing sunshine today, no wind. If the sun powers the wind, why not?
If the sun is the principal determinant of wind, why is the prevailing wind westerly in high latitudes and easterly in low latitudes?
Sun heats earth, earth heats air, so there is more solar-derived energy in the lower atmosphere. But wind speed increases with altitude. And not just over mountains, but in the middle of the oceans, deserts and prairies. How come?
Why do we get more gales in the winter, when there is less sun?
Was it some other Alan Calverd then?
The prevailing geostrophic wind is the result of coriolis force making the air move relative to the surface of the earth. If we extract kinetic energy from the geostrophic wind and dissipate it as heat, whence came that energy? The only source is the spin of the earth.
The wind in the Southern Ocean is almost entirely due to the earth's spin
Just stop being silly and admit you got it utterly wrong.
Earth is rotating today.
No wind.
If the rotation of th...
I don't see the word "weather" in that sentence.
I will pass your comment to the meteorological department of the International Civil Aviation Organisation, with a recommendation to modify the examination syllabus in line with such qualified expertise.
The word popliteal is also missing.
Or are you somehow seeking to pretend that the wind isn't part of weather or some such?
Fundamentally, the windmill still doesn't get its energy from the rotation of the Earth.
Well, that's not a bad idea- if they are teaching that the wind gets its energy from the rotation of the Earth- but I suspect they are not.
As I said; you have mistaken the rudder for the engine.
I doubt the ICAO would be happy to find pilots making that error.
The geostrophic wind is crucial to understanding major weather systems.
Sea breezes are great fun for gliding and dinghy sailing, but if you want to travel long distances or at high altitude, or extract useful electricity from the wind, you need to look beyond the primary school textbooks.
This isn't new stuff. Prehistoric mariners understood trade winds and westerlies and were able to sail on oceans (where there is no differential heating even at midday) in the absence of sunshine.
This isn't new stuff.
Well, I'm glad you accept that.
Because it helps demonstrate why you are mistaken.
If the Earth had been putting lots of energy into the weather for a long time, then the Earth would have slowed down since, for example, Stonehenge was built.
You still haven't actually answered the fundamental question.
What supplies the external torque that slows down the Earth's spin?
Surely you accept that , for a given moment of inertia, and a conserved angular momentum, the rotation rate , and thus the rotational energy of the Earth is conserved (pace tides buffs) .
Did you notice how nobody ever said they weren't?
Nor has anyone said that their direction is not due to the spin of the Earth.
That's my point.
You keep thinking the rudder is the engine.
I refer the hon gent to reply #8 above, and the laws of physics.
The dominant geostrophic component of wind arises from the rotation of the planet. Windmills extract kinetic energy from the wind. We turn that energy into heat which is ultimately radiated away from the planet.
I refer the hon gent to reply #8 above
Either that post agrees with the conservation laws, in which case it's redundant, or it disagrees, in which case it's wrong.
Are you saying that we can extract energy from the rotation of the Earth without slowing that rotation down?
Or are you saying you can slow down the Earth's rotation without an external torque?
Yes I would agree oceanic tidal drag is probably an even greater frictional source of energy loss to the kinetic rotational energy of Earth, also shearing of various layers Believed to be occurring within the earth.
However It could be viewed that these energy transfers are not small, given the 0.2 of a milli second daily fluctuations occurring to the LOD equates to approximately
10 x10 ^20 joules variation in kinetic energy, raises the question how does it appear that over time the length of day stays within such a tight range ??
It's about 30 seconds drift in about 60 years
https://en.wikipedia.org/wiki/Day_length_fluctuations#/media/File:Deviation_of_day_length_from_SI_day.svg
Alan seems to have realised he's wrong, but isn't prepared to admit it.
Did you notice the 3 milli second daily variation annual range On the link you provided.
On the data I have it looks like it's peak this Hemispheres, summer is - 1.4599 milli seconds, and will anticipate a plus figure similar in early January.
Or approximately equivalent to Plus or minus 70% of the solar energy received just to put a scale on the variations in the energy to earth's rotation.
It would be interesting to calculate the effect of our orbit.
When we are near the Sun we are, I guess, hotter. That will slightly expand the atmosphere and temporarily alter the moment of inertia.It should mean the Earth spins slightly slow when we are nearest to the Sun (Early Jan, I think)
And I thought there was a problem with my Mickey Mouse watch. Thanks for that. Skipper to navigator: synchronise the chronometer, please - we don't want to miss The Archers again.
Oh but I am. Every time I plot a course, descend through the predicted wind shear, and find myself lined up with the runway I think "This can't be true, because BC says I don't know what I'm doing". Nothing to do with physics - aviation is the triumph of wishful thinking.
Plenty of people drive cars with little or no understanding of what makes them work.
It seems you ride the wind while thinking it's provided by fairies.
That's fine- as long as the fairies produce the same wind as actual physics does.
(Sorry, my mistake; not fairies, but a non existent torque on the Earth- the argument is the same.)
Incidentally, I presume you think that they typically launch balloons at dawn because that's when the world stops spinning and there is consequently little wind. Similarly you presumably imagine that the winter storm season coincides with when the Earth speeds up and we all need to reset our clocks.
OK, so it's the conservation of angular momentum that you don't accept.
Well, please yourself, but this is a science site so you might get laughed at.
Angular momentum is conserved in a closed system.
Consider a spinning electric motor. Disconnect the supply current and connect the motor terminals via a resistor. The kinetic energy of the armature Iω2 is dissipated as heat (the simple electromagnetic brake) and ω→0.
Does the angular momentum Iω remain constant?
Like the Earth.
Because it's a conserved quantity.
If the motor is floating in space with you watching it from a distance lets simplify things by saying that the stator starts off stationery from your PoV and the rotor is spinning.
The fact that it is a motor dissipating heat in a resistor is irrelevant.
Because the bearings are imperfect, the rotor will apply a torque to the stator and will cause it to accelerate.
The stator will speed up and the rotor will slow down until they are both rotating at the same rate.
If you use the motor to generate current and feed that into a resistor then the magnetic field does the same as a bad bearing. It transfers energy quicker.
The outcome is the same, the rotor and stator will come to rest WRT each other, but they will be spinning from your point of view.
And the angular momentum of the system as a whole- the rotor and stator will remain constant.
If you want to change it then you need to apply an external torque.
So, for the (about) twelfth time, what do you think applies an external torque to the Earth in order to change its angular momentum?
I understand your logic B/C given the plus or minus 1.5 milli seconds is nailed on every year related to earth's orbit and yes the increase/decrease in energy is
1316.75/1407.88 watts m^2 of cross sectional area so a delta of 6.5%. Of solar energy received.
However the length of day is taken from Earth's surface and the atmosphere is uncoupled from earth, apart from its frictional coupling at the earth's surface.
Therefore not a satisfactory explanation.
There are similar contradictions in the current explanations as to this effect.
That's all it takes to couple them . It might take a short while to catch up, but the air moves pretty much with the Earth.
If it didn't there would be the 1000 MPH wind at the equator.
There's only 1 contradiction in Alan's explanation.
He says the Earth is slowing down and thereby coupling energy onto the wind and weather, but without an external torque, that's impossible.
just like the ice skater moving his/her arms further out from the axis of rotation.
When the (idealised) skater stops waving their arms about, they are spinning at exactly the same rate as when they started.
You are beginning to get the idea. Because the equator is moving at 1000 mph, and the poles at 0 mph, an equatorial air mass moving north or south will move over the surface (i.e. generate wind) at the initial rate of about 11 mph per degree thanks to the conservation of its momentum.
And you too are beginning to get it.
The important thing to realise is that the air doesn't all stay at the pole.
The air, on the way back, it accelerates sideways again, exactly compensating for the change in angular momentum on the pole-ward journey- which is HOW momentum is conserved.
And, you also forgot the important thing.
Why would the air be moving Northwards?
Clue- it's a convection cell driven by a hot thing nearby.
So, while the Earth's spin affects the direction of the wind, the actual power behind is is solar.
As I said, you have mistaken the rudder for the engine.
And so, for the 13th time, what causes the external torque needed to change the rotation rate of the Earth?
David, as I discovered along time ago that in the long term the only way to affect the earths ;
position in space
Orbital speed
Is you
have to exeed the maximum surface escape velocity of the earth moon system
In a very real sense.
But, in a rather more real sense, the Moon is one of the few things that is having a measurable effect on the spin of the Earth and, since it's still here, it can't exceed escape velocity.
But at some point in its journey, the air mass has transferred some momentum to the windmill, one hopes.
Though it has been admitted that some small windmills actually consume electricity when there is no wind, because the public object to stationary windmills!
It doesn't matter if the drag on the air is caused by friction at the Earth's surface or a windmill.
Anyay, none of that can transfer any angular momentum off the planet, so it can't affect the rate of rotation of the Earth.
So, for the 14th time what causes the external torque needed to change the rotation rate of the Earth?
Hi all, David's analogy re the rotation of a satellite clearly describes the fundamentals of conservation of momentum, however there is the counter argument of rather than losing gas to gain an external torque force, you could have a external energy source to gain propulsion, think solar sails work on this principle.
clearly describes the fundamentals of conservation of momentum,
Not entirely clear.
If you have a satellite that's rotating slightly, you can presumably stop that using the gyroscopes, but only at the cost of having to run them continually. To stop the rotation so that you don't have to run motors all the time
If the bearings are good (and they are) you don't need to run motor to keep the gyro spinning.
I don't know much about the efficiency of the bearings, but the analogy with the caveat I posted, demonstrates the counter argument of energy gain having to be considered, in a non closed system, can also ultimately effect, positively or negatively, the rotational Kinect energy
Rather than just the loss to the system.
You can't change the rotation rate unless you change the moment of inertia or you add (or subtract) angular momentum.
And we are waiting for Alan to explain where that angular momentum goes to, or comes from.
You can move some to or from the atmosphere, but not for long because viscous drag shifts it back to the ground.
And that's the point.
Like the skater who stops waving their arms about, in the long run, there's no change in spin rate.
And if there's no change in spin rate (and no change in I) there can't be a change in rotational energy.
And if there's no change in rotational energy then no energy can be coupled into the weather.
We are now all waiting for Alan to get to grips with that simple physics, and accept that he was mistaken.
I believe if you have inelastic collisions between the atmosphere and earth's surface, rotational energy can be reduced/increased And energy transferred in to other forms.
As per the laws of conservation of energy..
The biannual +- 1.5 milli second variation we were discussing earlier is causing active research Because once atomic clocks came into service to monitor LOD, it was proven weather patterns especially near mountain ranges gave a measurable effect to length of day
(variation of velocity in the x direction)
However currently there is a known shortfall in the calculations of angular momentum in the atmosphere to correlate with this phenomenon.
Which brings us back to the crux of the original question of should we have to give any consideration to the aspect to the design positions and increasing numbers of wind turbines.
I believe if you have inelastic collisions between the atmosphere and earth's surface, rotational energy can be reduced/increased
Yes, once, until the atmosphere is rotating at the same rate as the Earth.
It's like the case of the motor and stator.
Once they are rotating at the same rate (and they are) there's no longer a net transfer of momentum or energy.
Given the continuing and constant dynamics of the atmosphere due to earth's weather patterns moving the molecules at varying velocities within the atmosphere due to variations in temperature and pressure, due to suns energy input, therefore variations in the atmospheres velocity relative to the earth's surface, that we can observe pretty much on a daily basis.
Which is known to still effect the LOD (Angular momentum) and given that the atmospheres interaction with the earth's surface is not elastic, how is angular moment kept separate from these transfers of energy to other forms .
It's high school physics to know that the requirement for momentum and energy to be conserved implies that some collisions must be inelastic.
The same is true of connecting a charged capacitor and an uncharged one- conservation of charge means that some energy has to be dissipated.
But it still remains the case that Alan needs to explain an external torque if he wants the world to slow down.
So far, he hasn't tried and I suspect that's because, for all his bluster, he knows he was wrong.
Just in case any high school pupils or teachers read this, the requirement for momentum and kinetic energy to be conserved is, all collisions have be to be elastic, however momentum is conserved in inelastic collisions, in a isolated/closed system.
Therefore the criteria for conservation Of momentum being Relevant and an outside torque force required to alter earths overall angular momentum are,
a physical system so far removed from other systems that it does not interact with them.
a thermodynamic system enclosed by rigid immovable walls through which neither mass nor energy can pass.
Therefore earth's rotational energy and momentum cannot be conserved.
That's correct, but I got tired of repeating the phrase "apart from the tidal drag effects of the Moon etc" or words to that effect.
And it's also true in that there can be an exchange of momentum between the atmosphere (or bits of it) and the Earth, but that's going to average out to zero. What is gained by 1 is lost by the other. The sum is constant. Angular momentum of "the planet + its atmosphere" is conserved.
There's also the change in angular velocity which takes place when I climb the stairs.
But that's reversed when I come back down again.
I'm happy to discuss things like the Earth's emission of gravity waves, but I think it's a stretch to say they drive the weather.
The Earth's motion round the Sun must have a tidal effect on both bodies and thus dissipate kinetic energy, but again, that's not what couples energy from the rotation of the Earth into our weather.
If you are saying they are not conserved then there has to be an interaction of the Earth with something else.
That interaction will be a torque (or it won't affect the angular momentum).
So, like Alan, you are left trying to explain what the source of that external torque might be
In regards to Earth's interaction with something else, just concentrating on the electromagnetic energy received and we have already quantified this value relative to the rotational Kinect energy,
we know this energy input contravenes the conditions required for the laws of conservation of momentum
We can observe these chains of events of various energy transfers that the Suns energy induces, for example the variations in pressure/temperature generating velocity and number of collisions of the molecules of the atmosphere fluctuations.
The friction of the millions of metric tons of water dropped down to the surface at velocity's not in accordance with conservation of momentum, the dynamics of the waves of the oceans.
The wind passing across earth's surface with varying degrees of friction, depending on the type of surface, all start chains of events that can and does impact on the sum total of earth's Momentum through transfer of earth's rotational energy to other forms , that are not compatible with conservation of momentum.
It is high school physics, and B-C seems to be one of the few that remembers any of it.
This is nonsense. Energy certainly pours into the Earth system and pours out just as fast, making it sort of an equilibrium. OK, there's somewhat more incoming solar energy around January and less in July, so that equilibrium fluctuates regularly year over year, but it has pretty much negligible effect on the angular momentum on Earth. You can't radiate away momentum, angular or otherwise, given uniform radiation.
The friction of the millions of metric tons of water dropped down to the surface at velocity's not in accordance with conservation of momentum
The energy of all that water falling has no effect on the momentum of Earth. It is part of Earth. Rain does not apply external torque to the system, and only external torque can transfer momentum to something else.
Torque is what you need to look for. Tides do that, and pretty much nothing else. Earth used to spin once every 10 hours. It's almost 24 hours now, and all due to tides, not to wind, sunlight, or dissipation of rotational kinetic energy. The momentum has to go somewhere, which is almost entirely into orbital energy of either Earth or the moon. Momentum is conserved.
You forgot the only important thing you need to explain.
Where is the external torque?
Hi, so in regards to the point regarding an outside torque force, I covered that in previous posts with the laws of conservation of energy/momentum.
In regards to the 3 milli second annual range in the LOD, you misunderstand me, I am not attributing that to the variation in solar flux.
And yes huge amounts of energy do (pour in as solar radiation) and huge amounts exit in different forms of energy as per the laws of conservation of energy due to the various energy dynamics occurring here on Earth on a approximate balance between input/output, some of these transfers have been empirically been linked to variation to LOD
So the question at this point should be why you believe momentum is protected from these transfers of energy.
Because it is a conserved quantity.
To change it, you need to apply a torque.
That really is high school maths.
The proof (which I accept isn't high school maths) was worked ou a hundred years ago.
https://en.wikipedia.org/wiki/Noether%27s_theorem
So the question is, why don't you accept it?
Because of the laws of conservation of energy and ironically the mathematical proof you refer to links from the same pages below.
https://en.m.wikipedia.org/wiki/Closed_system
https://en.m.wikipedia.org/wiki/Isolated_system
As the requirement That underpins Noether Theorem is a closed/ isolated system.
In classical physics.
And...?
What it says is "a physical system so far removed from other systems that it does not interact with them."
And, unless you can show the means by which the Earth interacts (in a relevant way) with anything you have proved my point for me.
You seem to be conflating two different sets of criteria which are not as well defined here as you seem to think.
A system is isolated enough for angular momentum to be conserved , provided that it is isolated from any torque.Imagine we put a pair of huge lasers on opposite sides of the equator, both pointing west.
They would provide a torque and alter the spin of the Earth.
And they would also apply a torque to the rest of the universe.
The angular momentum of the universe as a whole would be conserved.
If you turn one of the lasers round so it faces east, then they would provide a net force on the Earth and would change its linear momentum.
And again, the rest of the universe would be pushed the other way so the linear momentum of the whole universe would be conserved.
Now imagine that we put a big black box round the Earth.
The lasers still alter the angular or linear momentum of the Earth.
They also alter the momentum of the box such that the sum of the momentum of the Earth and the box stays the same.
Now imaging tethering the box to the Earth so it can't translate or rotate with respect to Earth- obviously, that would involve spinning it at 1 rev per day.
All the lasers would do would be to put a force on the tether ropes. They wouldn't actually make anything move, would they?
I looked through and didn't see anything that did that. Sure, you mention momentum, but then seem to equivocate it with energy. Energy comes and goes, so momentum must come and go with it. That seems to be your logic, and it's wrong.
And yes huge amounts of energy do (pour in as solar radiation) and huge amounts exit in different forms of energy as per the laws of conservation of energy due to the various energy dynamics occurring here on Earth on a approximate balance between input/output,
Irrelevant. This is what I mean. If you talk about momentum, then you need to discuss huge amounts of momentum pouring in or out. Earth is indeed a not a closed system in this respect, but it all has to do with tides and nothing else. The energy pouring in and out, the weather, wind, rain, etc do not exert torque, so they're irrelevant.
some of these transfers have been empirically been linked to variation to LOD
LoD is not momentum. LoD is effected by a change in moment (by an earthquake say). Angular momentum of Earth is not.
What energy transfers have been thus 'empirically linked'? In the earthquake example, it is the moment change, not the energy released, that changes the LoD.
I didn't say otherwise.
Because they're different things. Both are conserved, but neither is the other. I put up a windmill and power a bunch of houses. Great, but that has zero effect on the total angular momentum of Earth since zero net torque is applied to the Earth system by the windmill.
Post after post, you ignore requests to identify torque other than tides being applied to the system. Tides do transfer angular momentum to other forms (mostly to an increase in orbital distance and decrease of orbital speed of moon), but I can think of no other mechanism that exerts any but trivial amount of torque, immeasurable in any empirical way.
Hi all so in regards to conflating the criteria, let's start with the first couple of paragraphs of the laws of conservation of momentum
https://en.m.wikipedia.org/wiki/Conservation_of_momentum
It states the momentum of an isolated system remains constant.
And if you follow the links for definitions of closed and isolated you get the clarification of this not my words just the laws of conservation
(classical mechanics
In nonrelativistic classical mechanics, a closed system is a physical system that doesn't exchange any matter with its surroundings, and isn't subject to any net force whose source is external to the system.[1][2] A closed system in classical mechanics would be equivalent to an isolated system in thermodynamics. )
And this states for an isolated system
(An isolated system cannot exchange any heat, work, or matter with the surroundings,)
Therefore as stated by the previous posts Regarding the solar energy received, Earth does not meet the criteria in regards to conservation of momentum. As stated by the laws of conservation of energy with no mention of an outside torque force required, just the transfer of energy is sufficient.
Maybe your mixing up closed and isolated.
My phone is sat on the table in front of me.
It is neither an isolated, nor a closed system.
And yet, it will not suddenly start spinning.
What you need to have, to get it spinning, is a torque.
As stated by the laws of conservation of energy with no mention of an outside torque force required, just the transfer of energy is sufficient.
They do not say that.
Show me how it could work.
Show me how something could start (or stop) spinning without a torque.
And then show me any sort of calculation for the rate at which the angular momentum changes.
That's going to trip you up.
The rate of change of angular momentum is the torque divided by the moment of inertia.
If the torque is zero then the change in angular momentum is also zero.
And yet you will switch to energy before this post is over. Energy has nothing to do with conservation of momentum.
No mention of energy I see.
Therefore as stated by the previous posts Regarding the solar energy received, Earth does not meet the criteria in regards to conservation of momentum.
No, because there are external forces acting on Earth. It has nothing to do with the solar energy, since that itself applies neither force nor torque to the planet. Gravity on the other hand exerts a force, therefore the momentum of Earth is not constant, and that momentum necessarily is transferred to other objects. Tides exert a significant torque, therefore the momentum is transferred via reaction-torque to other forms. There is no other significant torque. Gravity waves exert a torque, and thus radiate away some of Earth's orbital momentum, so the angular momentum of Earth's orbital energy is actually radiating away at a rate of about 200w, which is less than some of my light-bulbs. That is an awful lot of significant digits less than the torque from the tides, which work in the opposite direction (increasing the orbit).
Only net force has an effect on momentum. Not energy. Yes, from an energy standpoint, the solar system is a completely open system, radiating energy at a furious pace into space. That has no effect on either the momentum or the angular momentum of the solar system.
The energy laws are irrelevant to momentum laws. Indeed, no force need be applied to change the energy of a system any more than energy needs to be applied to change the momentum of a system. B-C's phone is not only on the table, but it's charging there, and that input of energy doesn't get it sliding or spinning now, does it? There is no torque between it and the table, so no change in angular momentum, regardless of its status of receiving energy.
There is no torque between it and the table, so no change in angular momentum, regardless of its status of receiving energy.
(Unless its kinetic energy)
Even then, there's no guarantee.
I could install a pair of contra-rotating flywheels in my phone. As long as they are a matched pair there's no net exchange of angular momentum.
So it is stated an isolated system is a requirement for conservation of momentum
https://upload.wikimedia.org/wikipedia/commons/8/8f/Diagram_Systems.png
And Halc states the energy laws are irrelevant to the momentum laws
Do you realise that the conservation laws are laws of nature and the terms " isolated" and "closed" are entirely arbitrary?
There are no isolated systems, not any closed ones.
We can not put a box round something to block gravity waves. Nor can we stop things tunnelling.
Even black holes evaporate.
So stop trying to use "lies we tell to children" concepts to overturn maths.
They are entirely independent quantities,
I can impart kinetic energy to a system without any external application of force from outside the system, so this is wrong.
In the case of momentum, the system needs to be isolated from external force. Isolation from energy and other things is not required at all.
Come up with an counterexample if you disagree. Change the momentum of a system without application of external force. I can change its kinetic energy, but not its momentum.
A big reason not to equivocate energy and momentum like you're all doing is that energy is a scalar, and momentum is a vector quantity. Neither can, in isolation, be a direct function of the other.
Not entirely. I don't think I can change the momentum of a system without transfer of some kind of energy. But something like kinetic energy is not absolute, but frame dependent, so a change in the linear momentum of a rock might require positive input of energy in one frame but negative in another, and zero in some frames. So there is a relation there, but not a direct one. Energy can change without any change to momentum, but momentum cannot so easily change without energy being involved.
Nuh huh.
I can impart kinetic energy{ via acceleration from outside the system ?} to a system without any external application of force from outside the system ???
https://en.m.wikipedia.org/wiki/Kinetic_energy
That doesn't actually make much sense.
Are you trying to say that you don't understand how wireless charging could drive a fan?
I'm still waiting for someone to explain how there's a change in angular momentum without a torque .
How do you get round this ?
Thanks petrochemicals, I made that point in my first post in this thread #38
BC every time you see trees bending in the wind. think about what age you were when you learnt about momentum.
In a practical sense, whatever age I was when I first ran into something.
Stop posting drivel and answer the question.
I made that point in my first post in this thread #38
The "point" you made back then was wrong.
Yep treat every post as if the poster has the starting sentence
Quote from:
i believe yet am not sure, i think this is how it works, ...........
Hi all, thanks for the advice on the etiquette petrochemicals.
Halc I believe your final part of your post
( but momentum cannot so easily change without energy being involved.)
Is more in line with conservation laws previously stated. https://upload.wikimedia.org/wikipedia/commons/8/8f/Diagram_Systems.png
Also in post 110 you state LOD is not momentum, no it isn't but it is the very accurate measure of angular velocity which is required to calculate the value of momentum, and rotational Kinect energy.
B/C I believe you're familiar with the method of calculating changes in pressure/volume using gas laws due to an energy input, and we are all capable of observing the kinetic dynamics input to the earth's surface.
Which has been measured to impact on LOD
Related, but not the same thing.
There's also no dispute that the tides transfer angular momentum between the Earth and the Moon.
None of that is relevant.
If the rotational kinetic energy of the Earth was being dissipated by the weather at anything like the rate that the weather picks up energy from the Sun, then the Earth would be slowing down a lot more.
Stonehenge wouldn't work.
But the energy coupled by the tides is much smaller so the rate of slowing is much smaller.
All the stuff about isolated systems and so on is just an illusion brought about by the fact that isolated systems are generally considered as thermodynamics and thermodynamics doesn't normally bother with angular momentum.
And the only reason you don't even try to answer the important question is that you know that you can't- because you know that you are fundamentally wrong and you are trolling.
If you aren't a troll, you should be able to answer this question:
Hi all, we do appear to be repeating ourselves, but if you read back I am not arguing against the majority of what is stated, previously I mentioned there appear to be contradictory facts in regards in this aspect of the original question, in the science world, which you disregarded and put any contradictions at Alan's door, but I have continued to explore some of the contradictions, to some people's frustration, by way of the dynamics we can observe and put some values to within the conservation laws.
So revisiting the fact that angular velocity and therefore momentum has stayed within such a tight range even though it skips about between 0.1 and 0.2 milli seconds daily, and has this 3 milli second range annually, could have several explanations yours above being one of them.
However to move the discussion forward, do you accept that a proportion of these changes to LOD is due to frictional coupling of the atmosphere with the earth's surface.
but I have continued to explore some of the contradictions,
There are none.
On a day by day basis the earth's atmosphere moves about with respect to the Earth.
In simple terms if the air moves up (on average) then the Earth slows down and if the air moves down then the Earth speeds up (like the overused analogy of the skater pulling their arms in).
So, on a short term basis (and If I remember rightly Wiki says the relaxation time is a few days) then yes the air has an effect.
But in the long term, it can't.
In the long term the air and the ground are coupled together. They spin once a day.
Indeed to a good approximation both the angular momentum of the ground (and sea) and the angular momentum of the atmosphere are pretty constant.
There are formulae for the moment of inertia of a rigid sphere and for a rigid spherical shell.
And yes, I am calling the atmosphere rigid- because it rotates as if it is. Essentially all of it goes round once a day. The weather adds "noise" to that rotation rate.
For every wind that's blowing the ground clockwise, there's another (on a long term average) blowing it counterclockwise.
But fundamentally, if you think the air is slowing the world down, you still have to deal with this
If you really think the Earth is slowing down because of the weather, just tell me where the torque comes from.
It can't be the air.
Or do you think the man on the truck is helping his mates?
[ Invalid Attachment ]
Are his mates pulling or pushing 👁
Am assuming the yes part of (yes and no) is covered by your statement
(For every wind that's blowing the ground clockwise, there's another (on a long term average) blowing it counterclockwise.)
Then if you apply that logic to the original question you can alter the LOD by altering the coefficient of friction in one directions favour.
Do you understand why the man on the truck isn't helping?
If you push the truck, the truck pushes back on you.
So, to achieve much, you need to brace yourself against something.
The man isn't helping because his feet are braced against the same thing that he is pushing.
Now, think about it; when air pushes a windmill, what is it "braced" against? What pushed the air to get it moving?
Well the only possible answer is "the ground" because that's the only thing it touches.
So, like the man on the truck, the air must push the ground forward just as much as it pushes back.
You don't even need the high school physics version. The middle school science version of Newton's laws of motion will do.
If the air pushes the Earth then the Earth must push back on the air just as hard.
If the Earth pushes the air then the air must push back on the Earth just as hard.
Since they are the only things pushing eachother, the net effect is zero
Which brings us back to energy input from outside the system as you state
(Now, think about it; when air pushes a windmill, what is it "braced" against? What pushed the air to get it moving?)
What did push the air to get it moving ???
Post by: Colin2B on 21/08/2020 09:51:05
Not pushed, pulled - by gravity.
Cool air, heavier than warm air, falls to displace the air near ground which is warmed by sun.
What did push the air to get it moving
The ground. That's my point.
The only thing the air can push is exactly the same ground that is the only thing it can brace itself against.
It's like the man on the truck.
He's not making it go faster.
The air is not making the earth fo faster (or slower).
Quote from: Colin2B on 21/08/2020 09:51:05
That drives the big convection cells.
But those winds run North and South.
The rotation of the Earth pushed them out of line via Coriolis forces, but those affect the direction of the wind, They don't couple energy into it- not least because they act in the opposite direction when the wind returns. There isn't a vacuum at the equator. The air goes back to where it came from.
Like a ship sailing north or south the coriolis forces act sideways . That's at right angles to the direction of travel. So they don't do work and don't transfer energy.
That is the bit where Alan had mistaken the rudder for the engine.
I was rather expecting him (maybe expecting too much) to work that out for himself.
He doesn't seem good at realising things, or he would work out that there's no torque, so there's no change in rotation rate.
Colin you state
Which I believe is a reasonable description of an energy input to a system (the atmosphere ) that by Excitation of the air molecules changes the density and through these dynamics occurring you described changes it's velocity, and therefore it's momentum.
......through these dynamics occurring you described changes it's velocity, and therefore it's momentum.
What goes up .....
It changed velocity on the way up (+) and on the way down (-), mass of air displaced must equal mass doing displacing, nett effect ?
I haven't been following this thread but I suspect this is what @Bored chemist is saying to you, you are dealing with a circulating system.
The surface winds in depressions (anticyclones) and cyclones also experience friction with the ground changing their velocity and causing them to back, but again circulating system, what goes one way returns the opposite way.
What goes up one day comes down another day.
And going up and down does not affect angular momentum.
So, once again...
My bold. These dynamics do not change the velocity or momentum of the air. Momentum and velocity are vector quantities, but you're treating them like they are scalars. If you add the collective momentums of all the moving bits of atmosphere using vector addition, they add up to essentially a small fixed constant (relative to the rotating reference frame of the surface of Earth) at all times. That means they exert negligible torque on Earth, and even the momentary variations have to average to zero over time else the atmosphere would have to accelerate over time to a very different speed than the surface of Earth.
Hi all, so a couple of things
B/C you said.
And then Colin said.
Which contradicts your action/reaction pairing, for the air striking any potential wind turbines as per the question.
In regards to the change in momentum of the atmosphere receiving electro magnetic radiation not being angular momentum, is precisely the point, therefore angular momentum is not conserved as stated by the laws of conservation.
Halc regarding whether the atmosphere should be behaving differently to how it is, if it's angular momentum is disturbed by solar input I will address later.
No it does not.
Do you understand how up and down is different from side to side?
That's what Halc was referring to here
Momentum and velocity are vector quantities, but you're treating them like they are scalars.
Now, it seems I have been reasonably patient in rebutting your assertions and answering your questions.
Could you please return the compliment and address this which I have asked a dozen or more times
What provides the torque required to change the angular momentum (and thus the spin speed) of the Earth?
That can't be right. Start with the whole system with zero relative motion. Sun heats air. It pushes against other air to get moving. The ground is stationary, so cannot get air moving east. So for every eastbound gob of air, there is an equal and opposite westbound gob somewhere. Each eventually hits a windmill or tree, and yes, that puts a bit of torque on the ground, but torque is a vector quantity, and all those east and westbound torques add up to pretty much nothing, especially over time. There is only imperceptible wiggles in the momentum of the atmosphere as those winds experience friction with the ground at different times.
Air mostly touches other air, which is what gets it moving. The ground can't, because it is essentially stationary relative to the rotating frame. Coriolis force can't do it because it only works if the air is already moving. It just turns you (again, relative to the rotating frame), but it doesn't accelerate anything.
Quote from: Colin
But there is an opposite reaction where the wind going the other way hits another turbine or tree or dune.
If there is only the one turbine pushing continuously in one direction, the whole atmosphere would eventually be moving at arbitrarily high speed in the opposite direction. This doesn't happen, but you seem to envision this strange singular point of force with no reaction force anywhere, in total violation of Newton's laws.
You say EM imparts no momentum (correct), therefore you conclude momentum is not conserved. That's right on par for you at least.
It is disturbed, just not in a way that involves wind turbines. Solar 'input' as you call it applies friction to the spin of the planet, which mostly transfers angular momentum from its rotation to its revolution. This mechanism, if left undisturbed, will eventually (long time, heap big zeros) transfer enough of that momentum that the moon will eventual collide with the planet. There's a fair chance that the planet will be destroyed before that happens, depending on how much mass the sun retains before it grows to 1au in radius.
Halc I believe if you read back you attributing quotes to me from other members, therefore I cannot respond fairly.
Especially as your disagreements with the points I was disagreeing with also.
All quotes above are from you in your post earlier today, the way you posted them.
Perhaps the bit where "Colin said", but I left that in. You didn't delimit what Colin said, so I didn't know where his words stop and your reply starts (something I since have fixed). You should learn to quote people properly yourself, which happens automatically if you used 'quote selected'.
I fully agree with what Colin said. My comment applied to the part you said.
There is a reaction to any air movement which you seem to refuse to take into account. If something goes south, something else necessarily goes north to fill its place. Almost all wind is cyclic motion, with negligible momentum difference from air stationary relative to the planet surface. Friction with the surface (in the form of turbines, trees, water, or whatever) thus exerts a net torque of negligible magnitude.
Ok apologies accepted even though it came with a but😀 you may like to review your post as some of the points raised are for others to address.
B/C, Halc says your reasonably patient rebuttals are wrong.
For example when you stated.
The quote function sometimes screws up nested quotes so, so, for example, the text that says "Well the only possible answer is "the ground" because that's the only thing it touches." is from me and that's not clear.
There's a distinction between "the air" as a whole and "the air" referring to the bit of it hitting a windmill.
I'm sure that Halc agrees that, if you consider the air as a whole then the only thing it pushes against is the ground.
It should be easy enough to check.
Halc, Do you agree with my view that the idea of the atmosphere, as a whole, pushing the Earth is like the man standing on the back of the truck trying to push it.?
even if he and I never come to agree about that, it doesn't detract from your basic rudeness in not answering my question.
Why not just admit that your view is at odds with the laws of physics, ad stop wasting everyone's time?
It does nested quotes just fine for me, as evidenced above. The text is unclear what part is yours because again, gem refused to delimit your quote. He's the one repeatedly making it unclear whose words are whose, not even using quote marks like you had to add there.
I also don't recall saying that your patient rebuttals are wrong. The ground is the only thing it touches, and the only thing that could possibly transfer momentum to or from the atmosphere, but that seems unlikely since the sum total of the momentum transferred to the ground is essentially zero.
Yes, but I'm not sure gem ever figured out why that picture is funny.
Yes, gem, in refusing the repeated requests to identify a source of torque, seems to be taking the troll approach. If not, this would have been resolved about 120 posts ago.
To be fair, in that regard he's just copying Alan (who seems to have gone rather quiet).
So in regards to being rude, I don't believe I have, but will let others decide as to who's being rude.
Hal as far as the conditions set out in the original question how does your statement below not allow for a greater torque force favouring one direction to alter LOD
So for every eastbound gob of air, there is an equal and opposite westbound gob somewhere. Each eventually hits a windmill or tree, and yes, that puts a bit of torque on the ground,
As far as the conditions set out in the original question how does your statement below not allow for a greater torque force favouring one direction to alter LOD
The words 'equal and opposite' might have something to do with it. That refers to angular momentum (torque * time), not torque by itself.
If there is a persistent favoured torque one way or the other, momentum would be perpetually transferred the same way between ground and atmosphere, and the atmosphere would soon be moving at greater than the speed of sound relative to the ground. It follows from the lack of such arbitrarily high prevailing winds that there is no persistent favoured torque in any direction.
Repeatedly refusing to answer a question is a breach of the rules of the site.
Most people would, I think, agree that signing up to the site rules, but not following them is rude.
Why not just admit that your view is at odds with the laws of physics, and stop wasting everyone's time?
So Halc and BC I believe the question is answered accordingly following the logic of Halcs post, the kinetic energy that's driving the weather system and changing the energy it possesses due to its acceleration in motion and change in direction, and therefore change in velocity and therefore momentum.
which is the delta under discussion in regards as to what is moving air in relation to earths surface can apply a torque as it exchanges its kinetic energy gained from the solar input via frictional drag with wind turbine designed to favour one direction, by way of a reduction in kinetic energy of the atmosphere, as per the original question.
in an action/reaction pairing
Momentum = Mass X Velocity
https://en.wikipedia.org/wiki/Kinetic_energy#:~:text=In%20physics%2C%20the%20kinetic%20energy,energy%20unless%20its%20speed%20changes.
As to whether this would alter wind speed in one direction overall is your interpretation.
It seems we need to sort out a few things.
Firstly, do you recognize that there are three conserved quantities and they are all conserved independently?
(1) Energy is conserved - but the Sun provides lots of it. The Earth isn't an isolated system.
(2) Angular momentum is conserved - To change this you need to supply an external torque (and it's bit of semantics but you can do that by throwing something away from the Earth along a line that is not a radius)
(3) linear momentum is conserved. To change it you would need to apply a force to the Earth which is not compensated by some other force.
OK, once you get to grips with that, let's imagine one small bit of the Earth's surface getting heated by the Sun- don't worry, it's representative of the whole surface.
OK, let's say it is black tarmac and surrounded by fields.
So, when the Sun heats it it gets hotter than the fields.
It warms the air above it. That warm air rises and is replaced by air coming in from all around it.
It is cylindrically symmetrical.
It can not generate a net force along a line tangential to the Earth's surface (though it does generate lift)
The air rises and cools http://apollo.lsc.vsc.edu/classes/met130/notes/chapter6/adiab_cool.html In effect, it exchanges thermal energy for gravitational potential energy.
And it's still cylindrically symmetrical.
The hot air that has risen and cools, spreads out because it is pushed away by the air underneath it.
And this cool air falls.
The whole thing now forms a convection cell.
It is still cylindrically symmetrical.
Now, I think the mistake you are making is that, because a windmill near the tarmac will turn (pushed round by the air flowing into fill the "gap" left as the hot air rises), you think that will affect the momentum transfer.
At one level you are right- the sum of the angular momentum of the windmill and the rest of the planet is constant. if one spins one way, then the other spins the other way to compensate.
But that effect is small and not cumulative. When the windmill stops, the Earth goes back to its original axis and rate.
That's not going to extract energy from the spin of the planet.
Now there are two things you might mean by this phrase
"wind turbine designed to favour one direction"
It might be that you fix the axis of the windmill so it only ever spins when the wind blows along that axis.
Or you might put a brake of some sort on the mill so that, if the wind blows east, you let it turn, but if it blows west, you stall it.
It doesn't actually matter much which version you choose.
The wind, in the absence of the windmill doesn't get infinitely fast, even if the Sun keeps shining.
It reaches an equilibrium where the updraft dissipates as much energy by friction/ viscosity as it gains from the hot tarmac.
So we need to think about where that energy goes.
Well, it can't all go into heating the air by viscous drag.
If it heats that air, that just make it expand, and it rises faster. So the kinetic energy of the upward moving column is still in that column of air. And it's still symmetrical so it's not providing any torque on the Earth
It's not gone anywhere.
(Part of it goes into warming the air, but again, it's clear that it doesn't get hotter indefinitely. It's also irrelevant, since it is symmetrical)
The only place that it can dump energy is in frictional drag as the downgoing cold air hits the ground and travels across it. It can then dissipate energy as heat, a warming the ground.
OK, now imagine that you put your windmill in the way.
You extract energy from that air.
You also transfer momentum (though not angular momentum along any useful axis).
As far as I understand it, you are saying that the wind pushes the windmill and so the footings of the windmill push the ground and that provides a torque.
Well, yes it does.
(It would also do the same if it was a tree)
And here's the bit that you seem to ignore.
You slow down the bit of air that goes past the windmill.
So the bit of air that would have blown along the ground, pushing on it is not going so fast.
And- because of Newton's 3rd law, the extent to which the wind pushes on the windmill (or a tree) is exactly the same as the extent to which the mill (or tree) pushes back on the air.
And that "push" is no longer available to push on the ground, so there is a slightly smaller force acting on the ground in the lee of the windmill.
And, again, by Newton's 3rd law, that exactly compensates for the forces acting at the foot of the mill.
and it therefore exactly offsets the torque produced by the mill.
So the net effect of the mill is to provide zero torque on the Earth as a whole.
Now, given that the windmill's torques is exactly compensated by the lack of wind force acting on the ground,
(which Halc explained ages ago*)...
Will you please tell us what is providing the torque which you are saying changes the speed of the Earth?
He really did explain this; you just didn't pay attention.
Each eventually hits a windmill or tree, and yes, that puts a bit of torque on the ground, but torque is a vector quantity, and all those east and westbound torques add up to pretty much nothing, especially over time
I posted no such logic.
The weather is driven by solar energy, not kinetic energy. That does change the kinetic energy of the atmosphere, but acceleration doesn't describe that since acceleration is a change in velocity, not a change in kinetic energy. The atmosphere cannot have a change in velocity since if it did, it would exit Earth. It is always centered on Earth and has essentially zero velocity relative to Earth. It thus has zero momentum relative to Earth.
I've not been talking about momentum, but rather angular momentum, which can in principle deviate from zero relative to Earth for short periods of time, but not in the long run. The solar energy stirring it all around doesn't change any of that.
moving air in relation to earths surface can apply a torque as it exchanges its kinetic energy gained from the solar input via frictional drag with wind turbine designed to favour one direction
The drag cannot favour one direction since the equal an opposite air mass will drag on something else. A tree or a lake will do. Any push by the turbine will be opposed by an equal and opposite torque somewhere else, or else you get the faster-than-sound wind speeds I mentioned. But here I am explaining it again. No turbine exerting force in one direction can have a significant effect on the momentum of the atmosphere since there is no way to isolate the air movement created from further friction with the ground. If the turbine pushes the ground eastward, then somewhere a tree pushes the ground westward. That's why BC posted the picture of the guy pushing the truck from the truck bed. You can't change the momentum of an object by force exerted from within the object. It has to come from outside. You need to identify that outside torque.
But your posts are all about kinetic energy, not velocity. You even give a link to an irrelevant kinetic energy page on wiki. And the topic is not about momentum either, but rather angular momentum. The momentum of the sun is very much affected by the sun since its gravity exerts a continuous force on Earth that gives it a constant accelration of about .0006g. That's an external force, so momentum of Earth is constantly changing.
Angular momentum of Earth is unaffected by the sun's radiant energy and by the kinetic energy of the atmosphere.
Actually, if the windmill stopped when the wind blew from the opposite direction it would actually exert more torque on the ground, not less, and I don't think gem realizes this since he thinks only in terms of energy. It would be more like a tree and less like a generator that intentionally lets the flow go through. Mining energy from the wind exerts less force on everything than just blocking it.
I suppose to favour the wind as described, the best strategy would be to put up a sail when the wind blew one way, and take the whole thing down when it blew the other. Of course, all this is useless because of the reaction forces I describe above. You can't push one way without an equal and opposite push being exerted somewhere else.
Nice post BTW.
What baffles me was that you can show why the weather can't (permanently) affect the angular momentum of the Earth by giving a number of arguments
(1) simple symmetry
(2) analysis of the energy involved- if the rotation of the Earth was contributing more energy to the weather than the Sun, then we would see the change in rotation rate; Stonehenge wouldn't line up any more.
(3) The law of conservation of angular momentum says it's impossible without an external torque.
(4) the definition of angular momentum in terms of torque time and moment of inertia means that without a torque, the change in angular momentum (and thus rotational kinetic energy is zero.
(5) straightforward analogies in the form of "when the skater stops waving their arms about they are still spinning at the same rate as when they started and the man on the truck who thinks he's helping.
And, though nobody has in any way refuted those, they still don't actually accept a simple fact. The Sun drives the weather.
Stopping following this threeeeeeeead. . Now
Hi all, I believe we have already covered a lot of what is contained in your responses, however just to reiterate a couple of points, we may have misunderstood each other on.
Halc you stated in response to my statement
The weather is driven by solar energy, not kinetic energy.
In which I stated
the delta under discussion in regards as to what is moving air in relation to earths surface can apply a torque as it exchanges its kinetic energy gained from the solar input
so not sure where we disagree on that point. (that goes for BC also, as he stating disagreements about earth rotation generating the weather)
Halc you then went on to say.
That does change the kinetic energy of the atmosphere, but acceleration doesn't describe that since acceleration is a change in velocity, not a change in kinetic energy.
I believe that statement is incorrect as demonstrated by the following opening paragraph from the earlier link provided, which you dismissed as irrelevant
In physics, the kinetic energy (KE) of an object is the energy that it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body when decelerating from its current speed to a state of rest
You also stated
No turbine exerting force in one direction can have a significant effect on the momentum of the atmosphere since there is no way to isolate the air movement created from further friction with the ground. If the turbine pushes the ground eastward, then somewhere a tree pushes the ground westward.
which I don't disagree with, but in regards to the principle of the original question, by designing a turbine or retractable barrier as per your posting to favour one direction on what was originally a flat level surface will not only alter the amount of surface area the atmosphere comes into contact with, and the coefficient of friction at that point, it will therefore increase the amount of torque applied to that area, indeed when designing wind turbines the height above the ground is a key consideration, so a percentage of the air in question may not have been destined to contact the surface at all, which I believe addresses B/C point below
Also BC I believe you seriously are mistaken in this statement regarding the atmosphere.
The only place that it can dump energy is in frictional drag
I believe the atmosphere is credited with approximate emission of energy back out to space of around 200 watts per metre square in the infrared spectrum.
quite windy today where i was :)
so not sure where we disagree on that point.
I disagree with this because it's a breach of the conservation of angular momentum.
At least, I think it does.
It's impossible to be sure because it's too badly written.
It certainly appears to say "energy can change momentum" which is wrong.
I also think you have misunderstood Halc's statement that "That does change the kinetic energy of the atmosphere, but acceleration doesn't describe that since acceleration is a change in velocity, not a change in kinetic energy."
You do not seem to grasp the fact that rotation is a change in velocity, and thus an acceleration, but without a change in speed and thus not a change in KE.
I ignored that, because it's obviously irrelevant and the thread is long enough.
But since you seem to need me to point it out for you, that doesn't produce a torque.
It also doesn't produce any (meaningful) push. There's the tiny effect of radiation pressure, but it's symmetrical anyway so it has no net effect on an air parcel.
You don't seem to realise that you just said you don't agree with Newton's 3rd law.
Is that what you intended to say?
Do you know what viscosity is?
It's the way that a layer of moving fluid transfers momentum to the layers adjacent to it, even if there is no material flux.
The high up air pushes the lower air and the lower air pushes that which is lower still and so on.
And eventually it reaches the ground.
Because there's nowhere else for it to go.
And, once again.
What provides the torque needed to change the angular momentum.
"energy" can't provide a torque (other than the effects of radiation pressure).
quite windy today where i was
It was here too.
But it has calmed done a lot now.
Presumably, you think the Earth must have stopped turning.
(that goes for BC also, as he stating disagreements about earth rotation generating the weather)
If you have a planet in isolation (no moon, no sun), and it is thermally closed (nothing allowed to radiate into space) and it is rotating, the atmosphere would have no wind. There is no way to harvest the kinetic energy of the Earth's spin to make the air move. Alan seems to disagree on this point, but Alan has left.
Quote from: Halc
[Solar energy does indirectly] change the kinetic energy of the atmosphere, but acceleration doesn't describe that since acceleration is a change in velocity, not a change in kinetic energy.
Quote from: wiki KE
My statement is entirely consistent with that paragraph. Consider a hand grenade in space. Put it at rest in some frame. It has zero KE and momentum in that frame. Now it explodes, which performs work on the bits. All the bits are moving at high speed and it has transformed much chemical energy into significant kinetic energy. But KE is a scalar, and thus is the scalar sum of the KE of each of the bits. The momentum (the part that is relevant) is a vector, and thus is a vector sum of the momentum of all the bits. That sum is still zero. This is why energy is irrelevant when discussing momentum.
My quote said acceleration is a change in velocity, but what is the velocity of the grenade now? It's center of gravity is still where it was before, so it still has zero velocity despite all the bits having significant speed. This is why acceleration is not a change in kinetic energy.
If the turbine pushes the ground eastward, then somewhere a tree pushes the ground westward.
which I don't disagree with, but in regards to the principle of the original question, by designing a turbine or retractable barrier as per your posting to favour one direction on what was originally a flat level surface will not only alter the amount of surface area the atmosphere comes into contact with, and the coefficient of friction at that point
There's your problem. Yes, you change the friction at that point, which just leaves faster air to hit the tree over yonder. It's going to exert friction with the ground whether or not you put up a barrier at favorable times. It just does it somewhere else. Yes, the changed timing of that friction makes a small temporary wiggle in the momentums of the atmosphere and ground as separate systems (BC and I have both acknowledged that in several prior posts), but the sum of the momentum of the two cannot change. The average of that different in momentum over time must be zero despite your efforts with the retractable tree.
it will therefore increase the amount of torque applied to that area
Yes, to that area. That small area is an open system from a momentum standpoint. There is external force (incoming air) being exerted, and you're apparently choosing to discount any external force entering the system via the ground. I'm looking at Earth as an isolated momentum system, not looking at one area. Yes, the wind pushes the tree, but something needed to push the air to get it moving like that, and you're ignoring the equal and opposite reaction to wherever that happened.
Halc thanks for that response.
But think that grenade analogy only works from the centre of an isolated system.
I really struggle to visualise any scenario on Earth Or it's atmosphere where this statement can be applied.
( This is why acceleration is not a change in kinetic energy.)
Just to use your grenade analogy, if we suspended a grenade at say 100m above the ground and chemical energy was converted to kinetic energy via an explosion (Similar to the solar input )
breaking the grenade shell in to two Identically equal parts initially going level in opposite directions (East/West) at equally high speeds, could you design a scenario where one piece transferred more of its kinetic energy via a torque force applied to the Earths surface, and the other transfers more of its kinetic energy to heat.
Again you make the mistake. You don't want to learn.
More correct to say the grenade analogy only works in an isolated system, which is why I specified that it was floating in space. There is not 'from the center' about it since the momentum doesn't have a location.
To illustrate (yet again), suppose I have a brick strapped to one end of a long thin pole and a grenade at the other end, all stationary in some frame. That's the best I could do for the explosion not happening at the center of mass of the system (which does have a location).
It has zero KE and momentum in that frame. Now it explodes, which performs work on the bits. All the bits are moving at high speed and it has transformed much chemical energy into significant kinetic energy. The momentum of the system (the part that is relevant) is a vector, and thus is a vector sum of the momentum of all the bits. That sum is still zero despite the explosion taking place well to one side. This is why the 'location' of the vector is irrelevant when discussing momentum.
Apparently you do, but then you shouldn't go on making assertions about topics where your understanding lacks.
OK. Sun heats the air (indirectly mostly) and that causes it to expand, similar to a grenade expanding, but with less abruptness to it.
Kinetic energy cannot be converted to torque. Force does, not energy. Energy is totally irrelevant here.
No, the two parts have equal and opposite momentum per your description, so the will (when each hits the ground and stops) impart identical momentum (force * time it takes to stop) to the ground. Net effect is zero. Some (most?) of the momentum of each is actually transferred to the air if there is air friction. While the parts are in-flight, each has a gravitational effect which exerts a tiny tidal torque, but that always cancels since it is a closed system as far as momentum goes.
Per conservation laws, there cannot be a scenario where it imparts net torque to the ground unless at least one of the fragments is blown permanently away from Earth at escape velocity.
could you design a scenario where one piece transferred more of its kinetic energy via a torque force applied to the Earths surface, and the other transfers more of its kinetic energy to heat.
Because you can't "transfer kinetic energy via torque" It's like trying to change the flavour of something by altering its position.
You could get the exploding grenade to change the rotation of the Earth- as long as one part of the grenade was thrown clear of the Earth- completely clear. If it remained in orbit the angular momentum of the shrapnel/ Earth system would remain the same as before the bang.
But the problem you seem to have is that you think angular momentum can be "created" from energy.
It can't.
How do you find it difficult to visualise a rock tied to a string swinging round in a circle?
Or the fairground big wheel or roundabout, lots and lots of visualisations - some real gems.
//www.youtube.com/watch?v=e_04ZrNroTo
yes very funny, must admit, had a little chuckle and a wry smile at the fun had, even if it was at my expense, at a comment taken out of context. as I was meaning in relation to the grenade analogy when I stated,
ie grenade exploding is not uniform circular motion
Halc you stated
which I believe I covered below
more of its kinetic energy via a torque force
in regards as to energy being irrelevant, I would disagree, if say you had one half of the grenade with a
velocity of 972.31 m per sec immediately after the explosion and it had
a mass of 100 grams it would have
a kinetic energy of 47.3 x 10³ joules
and momentum of 97.23 kg m per sec
and if said energy was immediately converted into a force via a collision with say a vertical cliff face it would result in
a force equal to ≈ 1.6 x10 to the 6 Newtons and a resulting kinetic energy of zero.
Nobody said it was. I was hoping you'd actually get the point of that example instead of posting an irrelevant comment like that.
First, you did the math wrong. You computed mass * speed, not mass * velocity. The difference is important.
That said the momentum of the one half did very much change since it was subjected to an external force from the other half which received and equal and opposite force. But the total momentum of the entire grenade (sum of the momentum of all the pieces) is zero. The sum of the momentums computed as you did above (mass * speed) would not be zero, which is why it's important to compute momentum correctly as mass * velocity.
Same problem with the cliff face: That's a force from outside the system, which yes, changes the momentum of the system. You've not identified a torque on Earth that comes from outside the system of the Earth, a system that includes all its parts like air, water, bicycle wheels and female skaters and such. Earth is not blasting away the other half of a grenade, or hitting a cliff.
We can take the idea of half the grenade hitting a cliff a bit further. We can fix the grenade to the cliff wall, then detonate it.
If the wall is strong,then essentially the whole of the grenade ends up moving away from the cliff and, for an instant the kick that it delivers to the rock starts the world turning (very slightly) away from the cliff face.
But the bits of the grenade don't stay moving forever.
They slow down and fall to the ground.
And when they do that, the impart a counter-torque and bring the Earth back to its original spin.
Obviously, some of the force is transferred by air resistance but still, after a while the air slows down due to the only thing it's in contact with- the ground- and, in doing so, it pushes on the Earth. (Once again, we are talking about viscosity)
After a short while the spin of the Earth is back to what it was.
That's the conservation of angular momentum.
The leftward moving bits of the grenade are brought to a halt by the Earth, pushing the earth left
The rightward moving bits of the grenade are brought to a halt by the earth, pushing the Earth right.
And the two things exactly cancel.
Imagine that we move the grenade a few cm from the cliff.
It does not "know" which side the cliff is on, so it explodes symmetrically.
So there must be as mush momentum transferred left as right.
So the sum of those is zero. (Once you remember they are vectors).
So BC following your analogy below.
using the data I posted would give values in one direction
a force equal to ≈ 1.6 x10 to the 6 Newtons and a resulting kinetic energy of zero
and if say we place another cliff face directly opposite at a distance of 274.32 metres
would result in
velocity of 737.62 metres
kinetic energy of 27.2 x 10 ^3 Joules
momentum of 73.76 Kgm per sec
a force equal to ≈ 0.91 x10 to the 6 Newtons and a resulting kinetic energy of zero
which represents a reduction in direct force applied of aprox 43%
one other factor which will be pertinent would be the drop in height which occurs during its flight time of 0.509 of a metre when calculating the resulting torque force
Then your data (or your calculation) is wrong.
In particular, you are calculating forces when you should be calculating impulses.
A force of a million Newtons acting for a week will make more difference than the same force acting for a second.
You have't taken that into account.
Yes, you need to account for that 0.5 metres of height in the about about 6,371,000 m radius of teh earth.
But, if you do the arithmetic correctly, you discover that it cancels.
Because angular momentum is always a conserved quantity.
Why are you trying to argue that a mathematically proven thing is wrong?
I forgot Noether's theorem when I drew up that list of reasons why you are plainly wrong.
So BC you stated
So just to be clear on the data, I got the mass and speed and reduction in speed due to drag over set distances from ballistics tables, (bullets that are designed to minimise drag.)
Therefore I believe the reduction in velocity under consideration is realistic.
Also the method of calculating the average collision force I used the equation
½ x (mass x velocity^2/stopping distance) given I would have been guessing at what time to place on the collision but did have knowledge of bullet length, so stopping distance I used at 30mm on the figures provided, but if you double the stopping distance, the reduction in the collision force is still around 43%.
However given the average collision force value from that calc just to get an approximate value for the stopping time by rearranging the force time equation, gives a time around 8 x 10^ - 5 seconds
In regards to your following statement
So I plug in the numbers and Cliff face one nearest the explosion transfering a torque force of
620 x10^6 Nm for aprox 8 x 10^ - 5 seconds
Cliff face two opposite at a distance 274.32 m applying an opposite torque force of
470 Nm for aprox 8 x 10^ - 5 seconds
So I believe the values given are a reasonable demonstration of the direct forces applied to the surface of Earth,
could you give a brief description of the dynamics that you allude to in the statement below, to make up the shortfall in one direction applied to the surface ?
Obviously, some of the force is transferred by air resistance but still, after a while the air slows down due to the only thing it's in contact with- the ground- and, in doing so, it pushes on the Earth.
As it seems very vague.
Question 1) How were these forces computed? I don't get those numbers.
The force and energy computations seem irrelevant to the discussion, since the discussion is about momentum, which brings up:
Question 2) What's your point here? You just let everything drop and fail to complete the total momentum calculation, which should add up to zero if you're doing it right. All I see is you trying to bury this calculation in complexity, adding motion in a second dimension, drag, gravity, blah blah blah.
You address question 1 here:
½ x (mass x velocity^2/stopping distance) given I would have been guessing at what time to place on the collision but did have knowledge of bullet length, so stopping distance I used at 30mm
You said 'immediately' above, not '30 mm'. You're leaving an awful lot out of your calculations.
Anyway, as I said, the force (and energy) is irrelevant. What counts is the momentum transferred, and you haven't completed the calculation, so question 2 was: What's your point? That total momentum is not zero? Then you need to do the complete computation, not just pick a few random components of it. You choosing all these complications just makes that task harder, but that's your choice.
Given these choices, you seem to be trolling us. You know they're wrong, yet you persist.
You wave away the missing parts as being 'vague', but they're entirely quantifiable.
So I believe the values given are a reasonable demonstration of the direct forces applied to the surface of Earth, could you give a brief description of the dynamics that you allude to in the statement below, to make up the shortfall in one direction applied to the surface ?
Computations are not complete, and they're done as scalars, not vectors. Do the whole thing. Your 2nd projectile slowed down. Where did that momentum go?
The 2nd projectile isn't moving horizontal anymore. Where's the vector adjustments for that. How about the momentum transfer via gravity while it was in flight? You're missing all this. You wanted to make it complicated, so you need to include all this stuff.
Your computations of 'torque force' are completely wrong. 620e6 Nm of torque? How did you arrive at that figure? You just posted this random number that doesn't seem to be computable from the prior figures.
It seems that way to you because you don't realise it's absolutely clear that it must e right- due to the conservation of momentum.
I got the mass and speed and reduction in speed due to drag over set distances from ballistics tables, (bullets that are designed to minimise drag.)
So the tables you used say the bullets slow down.
And, obviously, that's because they transfer momentum (and energy) to the air.
But then you ignored that momentum.
So it wasn't there when you calculated the momentum of the fragments.
Well of course it wasn't.
You forgot to add it.
You think it's vague that the only thing that momentum can be imparted to (in the long run) is the Earth.
It seems pretty concrete to me that, since there's nowhere else for it to go, that's where it goes.
If not, then where?
I posted that the grenade analogy wouldn't work, on earth or in its atmosphere, because it does not meet the criteria for an isolated system, and am highlighting that.
BC posted
So Momentum values at the point of explosion and several points along the way are
0.0 m = 97.23 Kg M per sec (point of explosion and 3.1 x 10 ^ minus 5 sec later collision one )
91.44 m = 89.00 Kg M per sec
182.88 m = 81.1 Kg M per sec
274.32 m = 73.76 Kg M per sec (point of collision two aprox 0.32 sec after collision one)
given that kinetic energy is lost continuously via frictional drag there is less and less momentum available to the body in flight to be continuously be transferred to the air, therefore the sums cannot add up to zero.
Which results in an unequal momentum transfer overall, combining in the air and and the amount to the solid that is earth's surface.
Therefore resulting in an unequal torque applied to the earth's surface.
given that kinetic energy is lost continuously via frictional drag there is less and less momentum available to the body in flight to be continuously be transferred to the air,
There is less momentum carried by the body, precisely because the momentum is transferred to the air.
Once you stop ignoring that, and add together ALL the contributions to the momentum, you find it comes to zero.
So, BC given your statement
and given some of this momentum is directly from collision with the casing these won't be perfectly elastic or inelastic collisions, so heat generated as work is done
So once that momentum is transferred, to the molecules of the air mostly N2 with mass of 4.65 x 10^ - 26 Kg
the average speed of the nitrogen molecules N2 at say a temperature of 20° C (293 K) results in a mean speed of about 470 ms.
On average, the air particles move at speed greater than the speed of sound, however, significantly higher speeds are also present. About 1 % of the molecules have a speed of more than 1000 m/sec.
So at a atmospheric pressure (1 bar) gives a collision frequency of aprox 7.0 x 10 ^9 per sec
i.e. within one second a nitrogen molecule will collide on average with 7 billion other molecules in what is probably best described as very high speed three dimensional snooker,
So the question is "I believe i asked this before" how does the momentum transferred to the air keep itself separate from the high speed dynamics its mixed in with, to then transfer an equal amount of momentum half a meter lower down the opposite cliff face.
Indeed the difficulty lies in the fact that the molecules will permanently collide with other particles and change their direction of motion in a random way, let's say you applied a indicator like a smell to track the momentums progress. it would go out in all directions, it would be more influenced by the fact that the smell is conveyed mainly due to air currents (convections), which carry the particles over greater distances.
Note that convection is no longer a completely random motion. In this case, the molecules are moved over macroscopic distances in a certain direction.
when I stated previously the conservation laws and isolated systems in regards to what conditions are not being met,
it was dismissed as lies we tell to children.
So let's further explore some similar examples
below is an extract from
https://en.wikipedia.org/wiki/Momentum
Newton's second law of motion states that the rate of change of a body's momentum is equal to the net force acting on it. Momentum depends on the frame of reference, but in any inertial frame it is a conserved quantity, meaning that if a closed system is not affected by external forces, its total linear momentum does not change.
https://en.wikipedia.org/wiki/Inertial_frame_of_reference#:~:text=An%20inertial%20frame%20of%20reference,moving%20at%20a%20constant%20velocity.
Inertial and non-inertial reference frames can be distinguished by the absence or presence of fictitious forces, as explained shortly.[8][9]
The effect of this being in the noninertial frame is to require the observer to introduce a fictitious force into his calculations….
— Sidney Borowitz and Lawrence A Bornstein in A Contemporary View of Elementary Physics, p. 138
Given the coriolis force dynamics occurring between earths surface and the atmosphere it cannot be argued they are a inertial reference frame to each other, and therefore fail on that criteria.
Indeed the analogy with hand grenade applying Newtons first law
In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force
given the flight of the ballistic doesn't maintain a straight line it would be reasonable to say it failed on that criteria for conservation of momentum also.
mean while we still have an imbalance in momentum
I believe this was answered before
Don't you see how, because in every single one of those 7 billion collisions, the momentum is conserved it must be conserved overall?
way, let's say you applied a indicator like a smell to track the momentums progress. it would go out in all directions,
No. it would not, because every single time a molecule hit another molecule, the momentum would be conserved.
Momentum depends on the frame of reference, but in any inertial frame it is a conserved quantity,
And the footings of a windmill are as good an inertial frame as any on Earth.
And, you seem to be trying to invoke relativistic effects for something only travelling at about a millionth of the speed of light.
That pretty much gives the game away. You don't know what you are talking about.
BC states
Not to the atmosphere they aren't
What do you suddenly disagree with regarding non inertial reference frames and the coriolis effect, it its occuring due to the earth's rotation and the weather patterns tending to go more in straight lines north and south, from the equator, due to the atmosphere being uncoupled from the solid earth.
You seemed to understand it previously,
So seem to be contradicting your own point.
you also state
you seem to be trying to invoke relativistic effects for something only travelling at about a millionth of the speed of light.
Newtons laws are more than sufficient.
this from
The equations of motion in a non-inertial system differ from the equations in an inertial system by additional terms called inertial forces. This allows us to detect experimentally the non-inertial nature of a system.
— V. I. Arnol'd: Mathematical Methods of Classical Mechanics Second Edition, p. 129
Yes, and conserved conserved overall has to account for the dynamics we call the weather and the readily observable resulting motions deviating away from a conserved angular momentum path of the atmosphere, due to the solar input causing transfers of energy which causes a chain of events which are constantly changing the speed and direction of large parts of the atmosphere resulting in observable net changes in the momentum of the atmosphere.
Because by itself, the law of conservation of momentum is not enough to determine the motion of particles after a collision. Another property of the motion, kinetic energy, must be known.
Excuse me? It seems you are claiming (in bold no less) observable net changes in the momentum of the atmosphere.
Where can I observe this? What is its angular momentum (relative to the Earth below it) now? All I see is the little bits that are immediately around me. At no point can I look at the entire thing and discern a deviation of momentum from zero. It might be there temporarily, but only when balance by equal and opposite temporary deviations at other times.
Here's a reasonably live shot of surface wind just for your observation purposes:
https://earth.nullschool.net/#current/wind/surface/level/orthographic=17.35,57.43,569/loc=-34.263,51.134
Momentum admittedly cannot be determined from this due to lack of data for air not at the surface, something readily apparent by the existence of points where wind comes from all directions with no way out except up.
OK, what is a better inertial frame for the atmosphere?
Glad to hear it.
One of those laws- every action has an equal and opposite reaction- is the root of the conservation of momentum.If something pushes to the left then it is pushed to the right.
You seem determined to ignore this.
readily observable resulting motions deviating away from a conserved angular momentum path of the atmosphere,
Where that this deviation from the conservation of momentum been observed?
You have claimed it, but not demonstrated it.
Are you saying that the momentum of the atmosphere is not equal to the sum of the momenta of every particle of which the atmosphere is made?
Because, you accept that momentum is conserved for each molecular collision, but somehow don't accept that it is conserved when you add them all together.
so in regards to what would be better as a reference frame,
quote author=Bored chemist link=topic=80136.msg613221#msg613221 date=1599302257]OK, what is a better inertial frame for the atmosphere?[/quote]
I believe the question is flawed, due to the atmosphere cannot maintain a inertial reference frame, given the constant changes to velocity and dynamics occurring due to the energy inputs and losses and gravitational force applied to it.
For example buoyancy is a major aspect to the dynamics under discussion
https://en.wikipedia.org/wiki/Buoyancy
which states about buoyancy,
This can occur only in a non-inertial reference frame, which either has a gravitational field or is accelerating due to a force other than gravity defining a "downward" direction
In regards to the conservation of Kinetic momentum of the atmosphere which is continually energy gaining and dissipative through various energy transfers, you would have to consider its accepted a change in momentum occurs due to the energy transfers processes so described
https://en.wikipedia.org/wiki/Momentum#Conservation
this from the above link
Forces that can change the momentum of a droplet include the gradient of the pressure
and given the gradient of the pressure is temperature dependent it is therefore in constant state of pressure changes and constant momentum changes.
I believe the question is flawed
Possibly, but it's implicit in your assertion.
I said the footings of a windmill are as good a reference frame as any.
You said I was wrong.
That leads to the question; if the footings of a windmill are not as good a reference as any, then what is?
And you say that question's meaningless.
Well, OK, fair enough, but you framed it.
I can sit at the foot of the windmill and watch air molecules collide in much the same way that I can sit in a bar and watch snooker balls.
Momentum is conserved from my PoV.
Now, please address the important issue:
We're discussing the constant angular momentum of the Earth as a system, so the effectively inertial frame of the Earth (effectively because we're ignoring the fact that it is in orbit and thus not actually inertial) is a far better reference frame than the local accelerated reference frame of the windmill footing.
In that local system, there is definitely torque being applied since the foot of the windmill and the height at which the force of the wind is applied are separated by say 100m. That's a long lever, and considerable torque. But use the inertial frame of the entire Earth as a system, and there is no net torque at all since there are no forces coming from outside.
I'm still wondering how Gem is going to explain away the fact that addition works.
So when I stated
and your response was
To be clear it is not my assertion it is an explicit condition of the laws of conservation of momentum.
Newton's second law of motion states that the rate of change of a body's momentum is equal to the net force acting on it. Momentum depends on the frame of reference, but in any inertial frame it is a conserved quantity, meaning that if a closed system/isolated system is not affected by external forces,
a closed system is a physical system that doesn't exchange any matter with its surroundings, and isn't subject to any net force whose source is external to the system.[1][2] A closed system in classical mechanics would be equivalent to an isolated system in thermodynamics. An isolated system cannot exchange any heat, work, or matter with the surroundings,
violating the conservation laws gives physical consequences like a change in momentum as previously stated
gradient pressure constantly changing due to energy received by the earth affecting atmospheres density, therefore resulting in,
Forces that can and do change the momentum of a droplet vai the gradient of the pressure changes.
this resulting acceleration because of the constant changes to the pressure gradient, is a major mechanism of the earth's weather system, due to the energy received from outside the earth to its atmosphere combined with the violation of the conservation of momentum laws (non inertial reference frame)
(buoyancy law)
resulting in net forces and the subsequent variations in velocity (speed and direction ) within the atmosphere.
changing where you chose to view these dynamics from wont stop the physical reality of them occurring.
If you are saying that the conservation laws don't work with accelerating objects then you have a different problem.
All collisions obviously require that things accelerate.
So the law should never apply- yet, by observation, it always does.
So BC not sure where you got the idea I stated this
So just to repeat.
the conservation laws for momentum would not allow buoyancy effect to occur within its closed/isolated system
Momentum depends on the frame of reference, but in any inertial frame it is a conserved quantity, meaning that if a closed system is not affected by external forces,
and this from
and the resulting consequences, this from
Forces that can change the momentum of a droplet include the gradient of the pressure and gravity,
So BC in reply number 17 as you stated yourself
https://en.wikipedia.org/wiki/Heat_engine#:~:text=In%20thermodynamics%20and%20engineering%2C%20a,to%20a%20lower%20state%20temperature.
which relies on the expansion and contraction of gases therefore constantly changing the gradient of pressure through changes to the density of the atmosphere and therefore constantly changing the kinetic energy of the atmosphere and its momentum (direction and speed)
So the problem is the earth's atmosphere cannot achieve conservation of momentum if its being altered by the dynamics described.
Due to not being a closed/isolated system
Every time you say that the angular momentum of the Earth can change without an external torque acting on it.
It is, as you keep stressing the importance of the fact, an isolated system.
The atmosphere can't push the world for the same reason that the man on the truck bed can't push the truck.
You seem to be trying to elevate the terms isolated and closed to the status of holy writ.
It's not magical.
Classically:
(1) A system to which you can't add or remove stuff will not change mass
(2) A system to which you can't add or remove energy will change energy
(3)A system to which you can not apply a force will not change momentum.
(4) A system to which you can't apply a torque will not change angular momentum.
Those are pretty much tautologically true.
Since Einstein's day the first pair of those are a bit more flexible, but only in a very clearly defined way.
Historically, in thermodynamics it was important to lump together some of those statements of the obvious.
If you have a system to which you can add or subtract matter then you can't sensibly define what it will do- because it depends on the matter you might add.The same goes for applying forces to it. Those forces just complicate the issue.
So, they invented the "closed system" where tautologies 1 and 3 apply.
Similarly, for some calculations, you want to prevent energy entering or leaving the system.
And that's why they invented the "isolated system"- as a shorthand for a system where tautology 2 also applies.
If thermodynamics dealt with angular momentum they would have invented another term for systems where tautology 4 also applied. They didn't.
But, if they had done, the Earth would be on the list.
I'm still waiting for youto explain where the torque comes from.
And then there are these.
And then, of course, there's Noether's theorem.
so BC you previously stated
you seem to be contradicting yourself again.
Also for your information this from
https://en.wikipedia.org/wiki/Tautology_(logic)
In logic, a tautology (from Greek: ταυτολογία) is a formula or assertion that is true in every possible interpretation.
So does the solar energy received change the momentum of the mass of the atmosphere or not ?.
Also your up against mainstream thinking if you believe the man on the truck represents the atmosphere.
which states
fluctuations are very probably generated by the interaction between the solid Earth and the atmosphere.
Also you may need to add "not" to your point 2
In what way?
Not in any circumstance (apart from by photon pressure which we have already pointed out is too small to be responsible for the weather)
It remains tautologically thrue that you can not change the momentum without adding or subtracting momentum.
Why would I do that?
No, I'm the one on the side with mainstream physics.
If the man runs around on the truck bed he can produce (small) movements of the truck, but theses are temporary and stop when he does
They are fluctuations, but they don't impart a long term change to the momentum of the truck.
I'm still waiting for you to explain where the torque comes from.
Quote from: gem on Today at 01:31:49
to which you reply
So you are arguing that the solar input of electromagnetic radiation to the earth does not provide any change to the momentum (speed and direction ) of the earth's atmosphere via absorption of thermal radiation and electromagnetic radiation and consequential energy transfers to various kinds that we can observe as the weather (wind and rain)that causes the motion of the masses of air within the atmosphere.
your statement seems to contradict this from the above link
this occurs due to a change/decrease in density of warmed air displaced by colder more dense air.
In regards to your man on the truck analogy to represent the roles of the atmosphere (man) and the truck (earths surface) where you state
To be a correct representation of the atmosphere the man should arrive on the back of the truck already in possession of a speed and direction heading from the rear to the front (kinetic momentum) gained from an action reaction away from the truck which he then transfers via a deceleration/collision ethier with the bed of the truck or a abrupt stop when he stops at position he was pictured in.
To be a correct representation of the atmosphere the man should arrive on the back
About 4.5 billion years ago,.
Since then he has been break-dancing on the bed of the truck.
The point is that he's no longer pushing it along the road.
I have pointed out at what I thought was tedious length that I'm ignoring photon pressure- the momentum of the EM radiation itself (though the effect is, to a first order approximation, zero). I'm not saying that doesn't exist; I'm saying it's far too small to drive the weather.
Setting that side...
For a start, it's not me saying it, it's the conservation law saying it.
Two qualifications you missed.
First I'm saying it provides no NET change in momentum and also I'm actually talking about angular (rather than linear) momentum.
It's like saying the explosion of a grenade provides momentum to the bits of shrapnel (obviously- were you trying to straw-man this?) but it doesn't chance the momentum of the CoG of the grenade.
On average the momentum transfer to all the bits is zero.
What I'm really saying is that the Earth's rotation does not provide the energy for the weather.,
However that statement is a consequence of the same conservation laws.
Now, will you stop pussyfooting about and answer the damned question.
If the angular momentum is changing, what is providing the external torque.
ok when I stated
and your response
Funny :) but wrong, the mass of air (the man) after colliding with the truck and transferring some of its momentum will then be displaced by his colder denser mates (displaced, due to friction of the collision and change in density )whilst also being warmed further from the solar input due to proximity to earth's surface, will rise in the atmosphere and regain fresh momentum to potentially transfer to the earth's surface again and again and again. (renewable)
which brings this point you raised
Which quite a while ago I compared the total solar input over that time scale to the rotational kinetic energy of the earth,
which makes for an interesting comparison, similar to the stonehenge example.
Which brings us to your statement,
I believe the question is flawed, if you follow the logic that the atmosphere is changing momentum continually (therefore not conserved) and is able to transfer momentum with the earth's surface via collision/friction, which is observed in the data of LOD, we have several options to consider.
1, No change in momentum has occurred
2, The forces of the trade winds and polar winds 0-30 and 60-90 degree regions, are exactly matched by the prevailing winds in the 30-60 degree regions so LOD is maintained.
3, , The forces of the trade winds and polar winds 0-30 and 60-90 degree regions, that have frictional contact with the surface, are NOT exactly matched by the prevailing winds in the 30-60 degree regions, would require a external torque force. (ie the LOD is the earth's terminal velocity, balance between all frictional drag and external force)
Post by: Jaaanosik on 17/09/2020 19:36:33
I am wondering, what is the external torque causing Venus to slow down the rotation:
http://www.esa.int/Science_Exploration/Space_Science/Venus_Express/Could_Venus_be_shifting_gear (http://www.esa.int/Science_Exploration/Space_Science/Venus_Express/Could_Venus_be_shifting_gear)
However, surface features seen by Venus Express some 16 years later could only be lined up with those observed by Magellan if the length of the Venus day is on average 6.5 minutes longer than Magellan measured.
If no change in angular momentum has occurred then we are still spinning at the same rate (which is good- ask the people who built stonehenge).
But that in turn means that the rotational kinetic energy also has not change.
Which means that the Earth has not transferred energy to the weather (which was the original point that Alan messed up) and it also means that there's no net transfer of rotational energy to or from the atmosphere.
That says that the atmosphere does not produce a net torque on teh earth 9or vice versa)
Also, since the definition of a torque is that it changes angular momentum,
There is no torque.
And, since a windmill has a radius (wrt the centre of the Earth) any net force would produce a net torque.
But there isn't one so there isn't a net torque provided to the atmosphere via the windmill (or, indeed, a tree).
So the answer to the OP is "No"
(as it always clearly was).
Congratulations on finally working out what Halc, others and I said ages ago.
The torques all balance out.
his colder denser mates (displaced, due to friction of the collision and change in density )
The problem there is that the Earth is a very big truck and his colder mates were also already on it.
You have converted the break dance to a square dance, but otherwise changed nothing.
(https://i.imgur.com/qudSSFf.png)
//www.youtube.com/watch?v=WR7hqUq7aNQ
Windmills do affect the Earth rotation.
Windmills are gyros and they are prevented from doing the precession therefore they torque the Earth.
Quote from: Jaaanosik on 17/09/2020 21:30:09
Sorry Jano, but that would only work if all the windmills faced the same way, but, as has been pointed out previously, the winds go round in circles so nett effect = 0
Or to put it another way
I went by OP:
If all windmills on earth are designed to catch only eastward wind, while westward wind can blow freely, will it accelerate earth rotation?
I am not sure what was changed and discussed.
Just saying that under right conditions a windmill torques the Earth.
Among other things , this:
The question seemed to be about a cumulative effect- where a mill running for 2 days changed the speed of the Earth more than running it for 1 day.
Ok, Jaaanosik, you are raising something related, there, of great importance
http://www.esa.int/Science_Exploration/Space_Science/Venus_Express/Could_Venus_be_shifting_gear
To a phenomena I was aware of, only because I believed it should be occurring and so when I Looked it turns out we have data to confirm it,
Similar to the underlying annual changes to LOD, so you have skipped a long way ahead of the narrative, and as alluded to in my first post on this matter will have to be addressed in new theories but is something I intended to use, but will expect data to show another contradiction the opposite way also (a speeding up) Fluctuating.
However to prepare the ground, BC when I stated
These are separate explanations/options that the merits (truth) of each would have to be considered as to the sustainability of wind energy electrical generation for man's use long term.
ie 1 & 3 should be ok 2 would require coefficient of friction balance
Under right conditions 2 days effect can be bigger than 1 day effect.
The Sun heats the ground, the air, there is a wind caused by the external energy input.
If all is aligned well then yes, 2 days effect can be bigger than 1 day effect due to the external energy input.
It would be interesting to align the Earth LoD variation with the Sun's 22 year cycle.
Just for fun. ;)
Under the right conditions maybe, but not due to locking precession around the tower axis. Go back to basic gyroscope theory and tell me why that is.
I focussed on the one that is correct.
Try posting the others on an anti-science forum.
Are you deliberately missing the point?
In your world, would the third day produce an even bigger effect and so on?
//www.youtube.com/watch?v=tLMpdBjA2SU
Are you saying there is no counter torque required to prevent the precession?
Video at 2:47.
No, even more basic than that.
If the wind blows in a correct direction all the time.
The wind does not stop because it has a continuous energy input from the heat.
The effect has to accumulate, no?
I suggest an experiment.
Take the toy gyro, spin it, hold it between your fingers at one end/on one side and see if it takes any torque to prevent the precession.
Been there, done that, got the faded tee shirt.
Read my post https://www.thenakedscientists.com/forum/index.php?topic=80399.msg614353#msg614353
See if it gives you a clue.
Think very, very basic
Sorry, think very, very, very basic
Imagine 1kg weight on a table.
Imagine two Earth like planets next to each other, no rotation, just being next to each other in an intergalactic space.
Are they going to start to crumble/collapse after some time?
The 1kg weight has an effect on the Earth just not the same as the other planet.
Holding the toy gyro in fingers and preventing the precession cannot be done without a counter torque.
All the windmill can hope to do is (infinitesimally) change the axis of the Earth's rotation ( and only while it's running; the axis returns to where it was when the mill stops).
Making the windmill bigger doesn't help much. The effect is still temporary and tiny.
A bunch of windmills all round the Earth all facing West (or East or whatever) doesn't help- they cancel out.
Then it runs out of puff.
There is an external energy input from the Sun.
If we simplify the scenario and we assume the energy input goes only to generating the wind.
The wind passes energy to windmill rotation but it never stops because of more energy input from the Sun.
Question, what happens with all energy input assuming the energy cannot escape anywhere else, the energy just goes into rotating the windmill?
It's not as if anyone has disputed it.
Is it because you don't understand that conservation of energy is independent of the conservation of momentum and that both are independent of the conservation of angular momentum?
Did you read the OP:
It's about the real world.
Obviously the answer was that the windmill breaks long before it makes a measurable difference to the angular momentum of the rest of the Earth.
Why did you think that was worth asking?
Do you understand work energy principle and rigid bodies?
Do you understand Newton's second law?
An increase in kinetic energy will lead to an increase of momentum.
The momentum is conserved for a closed system.
I did not described a closed system.
The answer to the OP is yes.
No matter how small change it is if the wind is considered to be cause by the Sun's energy then the system is not closed.
Real life has other energy flows but this one is into the system.
Just look at Venus measurements.
I explained this earlier.
At least read the thread before you rehash the same errors.
Please, check this video:
//www.youtube.com/watch?v=1VPfZ_XzisU
At around 8:20 the explanation starts to describe a small displacement of the disc.
So, if the Earth system is like the perfect disc, ...
but the first event is the air displacement from the Sun's input energy then there could be a cascade of events leading to big angular momentum changes.
The windmills could be part of the 'chain reaction', not important.
The point is that the Sun's heat can trigger big changes.
What is slowing down the Venus?
So BC when I stated,
on point 2 you stated
Congratulations on finally working out what Halc,others and I said ages ago, The torques all balance out.
You then contradict yourself
So which scenario is correct in your view 1 or 2 as with point one there can be no torque
Colin given your statement about torque applied to the solid earth via a windmill,
Under the right conditions maybe,
what do you believe would be the outcome of placing windmills at 15 degrees north and south latitude given the north easterly and south easterly trade winds
https://commons.wikimedia.org/wiki/File:Earth_Global_Circulation_-_en.svg#/media/File:Earth_Global_Circulation_-_en.svg
It would mean that rather than the trade winds spending their energy warming the air via viscosity against the ground, they would dissipate that energy via a windmill.
But the forces would be the same. Instead of pushing a windmill, they would push against the ground. Why are you asking this? I have already told you what the answer is.
And the change in net torque would be zero.
That's to say that it would change from zero to zero.
And, at 4:30, he explains that it won't work with a sphere- like the Earth so... it's not going to be very relevant.
When does it show the mathematical falsification of Noether's theorem?
Because if it doesn't do that, it's not relevant.
Noether"s theorem cannot apply to the dynamics of the earth's atmosphere, whilst it is effected by the gravitational field and solar input, It's conditional On meeting certain criteria to be applied. So not relevant.
So BC you're plumping for scenario 2,
Which is the friction applied to earth's surface, balances.
Therefore let's consider If we treat the earths surface as a anemometer
https://en.m.wikipedia.org/wiki/Anemometer
The coefficient of friction will come into consideration to different latitudes.
Apologies for slow response, out and about a lot with poor wifi, so priority is on spammers rather than following threads. Also, apologies if you've already covered this as I haven't been following.
Firstly, congratulations on knowing about precession torque, many people don't.
I didn't say they don't torque the earth, but perhaps being unfair in the interpretation of the OP you quote, perhaps winding you up a bit ;D
Let's assume a single east facing windmill on the equator. The only way this will try to precess around the tower (as in the diagram on your post) is if the axis of rotor spin is torqued or rotated in the vertical plane. This will happen as the earth spins, giving a torque vector for the tower pointing out vertically from the earth centre (all very idealised), but 180° later this vector is pointed in the opposite direction so cancels out. So assuming random distribution of all windmills on earth then all those windmill's towers are trying to torque on different axes and over all the earth will cancel out (apologies to BC if he's already pointed this out, but short on time at moment).
However, here's an alternative to consider (again apologies if you already have).
What if you put a single windmill on latitude 45°N 0°E what happens; then add another 45°N 180°E what happens; you can go on adding. Of course you still have to contend with halc's point about what happens when the force is removed https://www.thenakedscientists.com/forum/index.php?topic=80136.msg609359#msg609359, so you are back to continuing discussion.
I'm lot looking at any of your scenarios in particular (except #1 by default).
I'm just pointing out the fact that angular momentum is a conserved quantity.
No torque implies no change in rotation.
There's nothing more to say.
It is relevant, if you watch it till the end. It is being explained why.
A system is defined by boundaries.
The OP does not define any boundaries of the Earth rotation acceleration question.
It is OK to assume only the current axis of rotation is considered.
The video shows that rotation around one axis can be transformed to rotation around another axis.
The total angular momentum is the same, still individual axis of rotation have different angular momentum.
The answer to OP is yes, when one axis is considered without breaking the total angular momentum.
What is slowing down the rotation of the Venus anyway?
How is Noether's theorem holding there?
We are all correct, nobody defined boundaries of the system in the OP, we can go home now. :)
Like the question if the effect is the same after day one, day two or it is changing?
If the Sun's external energy input is not going anywhere else (waves, the wind losing energy creating waves, ... any other 'leakage'), just to increase the wind speed then under right conditions (good distribution of the windmills) is going to keep increasing the effect.
This is a hypothetical talk, it can go for long, very long, based on 'endless' possibilities of the boundary conditions.
The real life, apparently measured, what is slowing down the Venus?
Talking about "the Earth" defines a boundary of... the Earth.
The video explains, in some detail, why that "flip" will not, and can not happen to the Earth.
If you watch to the end, it explains why it is not relevant to the Earth.
It's an interesting phenomenon- which the Earth will never exhibit.
We are all correct, nobody defined boundaries of the system in the OP, we can go home now.
"The Earth" - as in the OP- defines a boundary.
But if you want to use that as an excuse to go away without admitting you were wrong, that's fine.
I am not saying the flip is going to happen. The torquing and the small acceleration change is a fact under right conditions, that's all.
Let us take out the windmills and the Earth out of it for now.
What slows down the Venus rotation?
What is happening to the theorem there?
Please, explain the Venus rotation slow down.
You really haven't got the hang of the fact that talking about "the Earth" puts a boundary round the problem, have you?
Such a boundary excludes Venus.
Feel free to start a thread about it.
Not windmills.
I am not saying the flip is going to happen.
Then it's kind of tricky to see why you insisted that a video about the flip is relevant...
First of all, tidal forces put a net external torque on Venus, as they do on all planets except Mercury. That is going to reduce the angular momentum in most cases. Venus is soon slated to be an exception to that, when it accelerates from a state of zero angular momentum.
5 minutes is a difference of about 1/70000 which is admittedly quite a bit. Contrast that with Earth where a 5 minute change to the spin period would be a difference of over 1/300.
Earth is similarly slowing, since the day is no longer some single-digit of hours in length like it used to be. Solar energy has nothing to do with this. It's all tidal forces, which happen whether the sun shines (and makes the wind move) or not.
Secondly, due to the inability to see the surface, it has never been easy to measure the rate of spin, and there is considerable room for error in the measurements.
Thirdly, a change to the spin rate of part of the mass is not necessarily a change to its momentum. The Earth's spin certainly has measurably changed due to melt of polar ice for instance. The man-made dam in China has had a measurable impact. These things don't change the total momentum of the system. Do not confuse angular velocity with angular momentum.
So with Venus, the wind and the weather might very much contribute to convection of material from here to there, changing the moment of the system, which affects angular velocity but not angular momentum since it cannot involve external torque. There is much to be learned about what kind of impact is made by such a dynamic system.
There is nothing tricky. Just pointing out about the angular momentum has to be studied carefully.
Is the Earth's 'dynamo' flipping when the north and south magnetic poles flip?
The Sun heats up a planet.
If the radiation and planet cooling is slower compared to the input then the inner temperature of the planet goes up.
The inner parts will start to move faster due to the Sun's external energy input.
This will change the angular momentum.
The change in total energy of the planet will show in the change of the angular momentum.
The temperature change works both ways.
If the planet cooling is higher, the inner core gets colder, it 'freezes' then the angular momentum will change as well.
This will apply both clockwise and anticlockwise.
No it won't.
No. By simple symmetry.
You would need to explain what you think that means.
Yes, and you are steadfastly refusing to do that.
You're just repeating the same fallacious argument over and over without addressing the repeated posts over why it is wrong.
Your argument is a non sequitur, equating 'more wind' with altered angular momentum of the system. You've identified zero net torque to the system, so this cannot be. If the wind blows harder, it does so in all directions, or it pushes on something to move the other way. None of those actions changes the angular momentum of the system.
https://www.nasa.gov/topics/earth/features/2012-poleReversal.html
When the iron core is flipping it is changing the outside crust angular momentum as well.
OK, we know the magnetic field flips from time to time.
But that can't mean the core suddenly spins in the opposite direction.
That would tear the Earth apart. There would be mass extinctions etc that would make the end of the dinosaurs look trivial.
So, via interactions with the Sun's and Moon's magnetic fields, the flip of the Earth's magnetic field would produce a small change in spin, but it would be reversed when the spin flipped back.
Just saying this does not make it true.
My apologies, in my post https://www.thenakedscientists.com/forum/index.php?topic=80136.msg614647#msg614647 (https://www.thenakedscientists.com/forum/index.php?topic=80136.msg614647#msg614647) I started to talk about the scenario without windmills.
If the planet heats up internally from the Sun's external energy then the inner parts of the planet start to rearrange and the acceleration/deceleration follows.
If there is the Earth crust (outer shell) and the inner core.
What is going to change the magnetic poles if not the change of the inner core rotation?
How else can the magnetic poles change happen?
so colin thanks for your post in response to Jaanosik"s point about precession torque.
However given the fact that occurs once the blades are in motion, we need to consider the initial frictional drag that occurs in the direction of the air flow, that then creates the lift to the turbine blades, and the subsequent force that the said drag applies to the tower and its foundations.
Now given it is being argued that although there is torque the average net torque is zero to the system because, If the wind blows harder, it does so in all directions, or it pushes on something to move the other way.
Also the wind blows/moves in cycles/cells so does not favour a net force/change in momentum in one direction.
So in regards to what the mass of the air pushes against this is mostly the mass of other air especially when increasing momentum through the dynamics of changes in density occurring within the atmosphere, and as is well understood these changes in kinetic momentum are happening continually. (renewable) due to solar input to a fluid in a gravitational field creating the change/increase in kinetic momentum, through buoyancy effects.
So consider the design of a anemometer which simultaneously rotates into and away from the wind of equal speed to both halfs in relation to itself, whilst still transferring momentum to favour one direction.
Therefore the coefficient of friction will/should come into consideration to different latitudes. given the established wind patterns, and the conditions as set out as per the OP .
Simple physics.
It's one of the interesting fact about the "self excited dynamo"- it can start up with a current either way.
It's also possible to flip it. without changing the direction of rotation.
We make that argument because, if it wasn't true, the air would need to "Pile up" somewhere- and obviously, it doesn't do that.
You seem to have forgotten that the only other thing the air can "brace itself" against is that atmosphere.
You are still the man dancing on the truck bed.
The physics is far from simple on this topic.
The only thing that is sure is that there are huge relative motion changes beneath the crust because that's the only explanation of the magnetic flip.
The details of this motions are unknown to us.
We have only hypotheses.
The fact is that the angular velocity of the Earth crust rotation is pretty stable compare to what is happening beneath.
The rearrangement of the rotational inertia beneath the crust will lead to angular velocity changes beneath the crust and it will affect the crust as well.
The stuff beneath the crust can take/give rotational energy to the crust.
There is nothing simple about that!
Hmm, the Earth must be hollow. ;)
... I forgot, it is flat! :)
That's still not true.
You still haven't bothered to look up how a self excited dynamo works (or you haven't understood it)
The rearrangement of the rotational inertia beneath the crust
Assuming you are talking about the angular momentum, it's a single vector.
How do you "rearrange" it?
You are going too fast.
There are so many pieces to the puzzle of the Earth magnetic field and you act like you know it all.
One of many questions. How many 'dynamos' down there, their shapes, sizes?
I'll leave it with you if you really think you know it all, there is no point to discuss it.
The wing nut flips and changes angular momentum vector orientation in the linked video.
Is the angular momentum constant in this case?
This is a tiny rigid body compare to the Earth.
The Earth is not a simple rigid body.
The Earth is a complex system and the external heat can change the internal heat flux, influencing the whole system.
The Earth is a sum of countless parts, many of them have own angular momentum, what is the total angular momentum?
Do you really think we are dealing with one vector? Really?
I am checking out,
Do you really think we are dealing with one vector?
The angular momentum of the Earth is a single vector.
Your question is like saying "The Earth is really complicated- do you think it has only one mass? Really?"
Well, Obviously, yes.
And, if you understood that, you would stop wittering on about this.
The angular momentum of the nut is fixed- it's roughly aligned with the axis that the nut is moving along.
That's the axis around which it spins.
The rate changes a bit as it flips because that alters the moment of inertia.
Yes; but only a torque can change its angular momentum.
Do you really not understand that?
Go to the library; check out some text books.
I'll leave it with you if you really think you know it all,
I'm not claiming to know "it all"
I'm pointing out one thing which is known by all.
Angular momentum is a conserved quantity.
So BC, you statement below seems a little misplaced
in response to this statement in relation to the dynamics of the mass that is uncoupled from earth's surface contained within the atmosphere.
BC You also state quite correctly
which is not disputed, as energy is a conserved quantity also, but for both to be conserved to the earth requires certain conditions, and the earth's atmosphere does not fulfil the criteria of conditions for energy or momentum conservation, indeed given the friction occuring and subsequent transfer of momentum to the freedoms of movement we define as heat, which is then converted to radiation and emitted out to space is well understood.
https://commons.wikimedia.org/wiki/File:AtmosphCircNT.png#/media/File:AtmosphCircNT.png
and the earth's atmosphere does not fulfil the criteria of conditions for energy or momentum conservation
I never said it did.
Let's start by just reminding you that your obsession with energy is annoyingly irrelevant.
Momentum and energy are independently conserved.
Do you understand that?
One changes if you transfer energy to or from a system.
The other changes if you transfer momentum to or from a system.
So there's probably never going to be any call for you to mention energy in this thread ever again.
Can you agree to stop wasting time on it?
so looks like we may agree on something;
Quote from: gem on Yesterday at 00:39:51
Good so far
yes still pretty much in agreement apart from the
and I am afraid we part company again on this:
So given the close relationship between kinetic energy and momentum of a system it would be difficult to have any meaningful discussion on momentum if you exclude the consideration of energy, as is clearly demonstrated in your previous posts, where you have referred to conservation of energy and sun's energy heat engine etc etc.
Indeed energy is the currency of the physical world
Therefore;
we need to consider the initial frictional drag that occurs in the direction of the air flow, that then creates the lift to the turbine blades, and the subsequent force that the said drag applies to the tower and its foundations.
Let me know when you learn enough to realise that the universe has three different currencies which are not interconvertible.
You can't make energy into angular momentum.
If you could it would break both conservation laws.
Until you understand this, you are never going to realise why you are wrong about the windmills.
I am not sure how much you know about pseudovectors/bivectors.
That's what the angular momentum is.
To simplify for readers here, we can say it is a vector.
Vector has magnitude and direction.
It is easy to show that adding energy to a rigid body can change the axis of rotation, changing the direction of the rotation.
It will change the angular velocity as well.
The angular momentum is not 'the same' as before,
It is easy to show that adding energy to a rigid body can change the axis of rotation,
Then show it.
But no cheating.
You have to do it without applying a torque.
Only add energy.
You need to understand this part first, 11:25min of the linked video.
The fact is the rotation changed in the video.
(https://i.imgur.com/hBxlVs3.png)
Imagine a bean can/cylinder with 'infinitely' strong walls.
The can is filled with ice, no empty space in the can, rigid body.
It will rotate 'forever' around the axis as in that video.
Applying heat will melt the ice.
We have water and steam/gas in the can with a right amount of heat.
The water moves to the walls the steam stays in the middle, close to the axis of rotation.
The moment of inertia 'I' changed.
That leads to the angular velocity 'w (omega)' change because L=I*w and L is 'constant'.
The angular velocity change is an angular acceleration change.
That leads to the axis of rotation change through the right hand rule.
There was no contact, no external torque applied to the can, just heat,
There is an error in this video at about 10:10 where the angular momentum of Earth is depicted as reversing, due to a poor editing job of somebody just rotating a gif of the spinning Earth, which isn't how the motion would progress.
If you watch any of the real objects or actual computer simulations, the angular momentum of the various objects (wing nut, racket, soap bottle, etc) never change one bit. It goes down in magnitude a bit due to friction since most of these objects are not spinning in a vacuum, but the direction of the momentum vector never changes (except in the one at 10:10).
You (Jano and gem) are seemingly claiming a change in momentum of these systems, which violates conservation laws. Energy input (without input of force or torque) has nothing to do with it, as BC and I repeatedly point out.
then there could be a cascade of events leading to big angular momentum changes.
Nonsense. The angular momentum of these systems is fixed at all times, or it would be if done in a vacuum. Our poorly shaved friend never asserts a change in any momentum vectors (again, excepting the one place where it does it in error).
And, like the legendary skater putting their arms out, the speed of rotation falls.
However, the moment of inertia rises. (More of the mass is further from the axis). For a given mass and length, a tube has a higher moment of inertia than a solid cylinder.
The two effects cancel out and the angular momentum stays exactly the same.
So, once again:
You have accepted that L is constant, as part of your "proof" that L changes.
Were you expecting to be taken seriously?
You just showed your ignorance (not understanding the analysis).
I'll have to leave you in your ignorance,
That doesn't make sense.
Not from my point of view., nor from that of, for example, an ant on the bean tin.
If he sees the axis of rotation of his tin is lined up with a distant star then, even if the material inside melts + tumbles (like the water bottle in in the video) the axis of rotation will still point at the star.
The rotation rate will also change but, if our clever ant calculates the moment of inertia of his bean tin world and multiplies it by the rate of rotation, he always get the same answer even though the axis of rotation changes (wrt the tin's axis)
So Halc states
You (Jano and gem) are seemingly claiming a change in momentum of these systems, which violates conservation laws. Energy input (without input of force or torque) has nothing to do with it, as BC and I repeatedly point out
If you read what I have stated I believe it is quite clear how the change in momentum of the mass of the fluid atmosphere occurs,
ie; due to the energy input from the sun via electromagnetic radiation to a fluid in a gravitational field converts that energy to kinetic energy, and how that changes the momentum of the atmosphere due to buoyancy effect results in the transfer of said kinetic momentum to the earth's surface.
Due to frictional drag, therefore applying a force and torque to the solid of the earth's crust, subsequently means a transferring of some of the momentum gained in this process to the earth's crust, and some to the momentum we observe as heat.
which can ultimately be lost to the system via radiation to space.
Therefore the coefficient of friction will/should come into consideration to different latitudes. given the established wind patterns, and the conditions as set out as per the OP
I believe all of the above are correct in regards to the conservation laws and its naive to argue for the atmosphere to fulfil the criteria of conservation of momentum when its clearly stated momentum can change due to the pressure gradient/buoyancy.
indeed BC agrees
Due to frictional drag, therefore applying a force and torque to the solid of the earth's crust,
Just like the man on the truck bed.
But the point remains. The atmosphere may "borrow" angular momentum from the solid Earth (Though, even for a hurricane, the effect is tiny) but, the sum of their momenta is still the same as it was. And when the hurricane stops, it returns exactly the same angular momentum as it "borrowed.
For the planet earth, as a whole, including the atmosphere, the angular momentum is constant.
the momentum we observe as heat.
Learn to read...
If we go with three planes and three axes of rotation.
The angular velocity change caused by melted water will generate angular acceleration due to change of the rotational inertia in one of the axis.
This angular acceleration leads to angular velocity changes in other rotational axes.
The total net angular momentum is conserved but individual axes have big changes.
The ant, accelerated observer, will undergo acceleration changes.
The acceleration during the flip/transition is not constant as it was before melting.
The inertial observer agrees, the individual axes undergo changes during the transition.
Yes, the axis will be there but the angular velocity around this axis will be changing during the flip/transition.
Yes it will
And so will the moment of inertia; it will also change; in lock step with the rotation rate.
But the product or the two, which is the angular momentum, will be constant.
The angular momentum is a conserved quantity. The angular velocity and the moment of inertia are not conserved.
Which is what the science has said all along.
How do boundary conditions work?
Let us say the ice can transition/flip lasts 10s.
The ant lives 50 microseconds sometimes during the flip.
The ant will observer big changes not knowing where they come from.
The changes in the 50 microseconds span are dependent on the boundary conditions.
Where and when the ant lives.
Going to the OP. The same applies.
We are ants and the windmill is a tiny factor in all the big changes and it can under the right conditions influence the Earth acceleration.
That was the question, about the rotation and specifically acceleration.
There could be an angular velocity change (an angular acceleration) even though 'the total big angular momentum would be conserved'.
You draw a boundary round the relevant thing- in this case the tin, its contents and the ant. And say that's the system under consideration
And then you measure the total angular momentum of the system
And you find it is constant.
You cannot measure it with high enough precession therefore it is not going to be constant. ;)
So BC
I agree,
however thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation.
Given the gas laws and momentum of a particle and subsequent pressure are temperature dependent,(PV=nRT)
as radiation is emitted to space temperature decreases as does momentum.
Now given the atmosphere does not fulfil the criteria for conservation of energy or momentum.
there appears to be a contradiction in this statement
Now BC this is not a criticism it is one of the contradictions I referred to when i joined this thread.
So if you consider option 3 you get the same effect for opposite reasons.
"If you follow the logic that the atmosphere is changing momentum continually (therefore not conserved) and is able to transfer exchange momentum with the earth's surface via collision/friction, which is observed in the data of LOD, we have several options to consider.
and I edit your statement to read;
But the point remains. The atmosphere transfers to and borrows angular momentum from the solid Earth (Though, even for a hurricane, the effect is tiny) but, the sum of their momenta is still the same as it was. when the hurricane stops, it returns to exactly the same angular momentum.
Actually, in context, I can.
I can point out that Stonehenge is still lined up with the solstice.
You seem to be forgetting to address this issue:
Whoa there.
That particular logical fallacy is called "begging the question"; don't do it again.
Who says it doesn't.
Again you seem to be linking momentum with energy.
The atmosphere picks up energy from the Sun.
But it can't pick up angular momentum from anything but the planet Earth.
And it will, in the long run, always return that so, overall, it has conserved angular momentum.
No, there isn't.
You just think there is because you do not accept that momentum and energy are separate.
What I said was"But the point remains. The atmosphere may "borrow" angular momentum from the solid Earth (Though, even for a hurricane, the effect is tiny) but, the sum of their momenta is still the same as it was. And when the hurricane stops, it returns exactly the same angular momentum as it "borrowed.
For the planet earth, as a whole, including the atmosphere, the angular momentum is constant."
If you edit it and still say it's my statement then you are lying.
If you need to lie to prove your "point" then you have accepted that you can't do it honestly.
If you can't honestly prove your point, you know your point isn't true.
You seem not to accept that the atmosphere is part of the Earth and that the Earth as a whole must, at all times, have a constant angular momentum.
So BC not sure where the misunderstanding came from for this
Your statement;
So to repeat the point, and to make clear this is coming to very similar results for very different reasons as stated in the previous post.
If you consider option 3 you get the same effect for opposite reasons.
It would be reasonable to expect the atmosphere transfers to and borrows angular momentum from the solid Earth (Though, even for a hurricane, or extreme winds especially near mountain ranges with a east or west net force the effect is tiny but measurable) but, the sum of their momenta returns to approximately the same as it was. when the hurricane/extreme weather stops, it returns to approximately the same angular momentum.
For the planet earth, as a whole, including the atmosphere.
Now given you now state quite correctly that the atmosphere transfers momentum to the solid earth and the solid earth transfers momentum back, and this is stated to be done by frictional coupling, brings us back to heat and to my statement from the last post
So How does your statement;
And when the hurricane stops, it returns exactly the same angular momentum as it "borrowed.
Allow for this loss of momentum due to the continual exchange of momentum between the earth's surface and the atmosphere due to the conversion of kinetic momentum to heat momentum due to frictional coupling and subsequent radiation and temperature decrease resulting in decrease in the thermal motion of particles. (PV=nRT)
Therefore a reduction in the momentum available to return to whence it was borrowed.
You really need to get to grips with the fact that you can not convert a scalar quantity like energy into a vector quantity like angular momentum.
You have forgotten that what started the hurricane spinning in the first place is that it was pushed by the earth- that's why they spin in opposite directions either side of the equator.
So, as the winds die down and are slowed by friction with the Earth's surface, they return the same angular momentum they borrowed earlier; neither more not less.
but, the sum of their momenta returns to approximately the same as it was
No; it's exactly the same angular momentum.
Do you not accept that angular (and linear) momentum is conserved during every single collision between molecules in the air?
And since it is conserved in all those huge numbers of collisions, it is also conserved for the sum of all of them?
Or are you saying that arithmetic does not work?
Are you saying that you can not add things up to get a sum of the individual things?
what started the hurricane spinning in the first place is that it was pushed by the earth- that's why they spin in opposite directions either side of the equator.
yes quite agree we covered the coriolis effect previously
https://en.wikipedia.org/wiki/Coriolis_force
However on this point;
So if there is friction, for both linear and angular momentum means the collision is not perfectly elastic, and therefore a percentage of momentum is transferred to the thermal motion of particles, whether within the earth's surface or the gas particles of the atmosphere.
So if calculated at that instance of transfer, it would be calculated momentum is conserved, overall but the linear/angular
momentum will have altered.
Indeed it would not be possible to determine any difference from this thermal aspect of momentum due to frictional coupling and the thermal momentum occuring because of solar radiation.
We have discussed at length the process that occur due to the conditions of earth's atmosphere having a pressure gradient and energy input, momentum is constantly changing, and that thermal momentum can be reduced via radiation
to space. (due to reduction in temperature and gas laws PV=nRT )
which means this statement
cannot be correct.
Given friction occurs, momentum is transferred in both processes of borrowing/returning when frictional coupling with the earth's surface occurs, means a percentage of momentum of the earth is continuously being transferred to thermal motion of particles.
And you have ignored a simple fact.
Friction "degrades" kinetic energy to heat.
But it doesn't destroy momentum; it just transfers it.
means a percentage of momentum of the earth is continuously being transferred to thermal motion of particles.
And vice versa.
You still don't seem to have got to grips with the fact that momentum is a conserved quantity unless there's an external torque.
You also don't seem to have grasped the fact that momentum and energy are different.
At least Jaaanosik has recognised that he was wrong to say this, and gone away.
So BC when I stated
So if there is friction, for both linear and angular momentum means the collision is not perfectly elastic, and therefore a percentage of momentum is transferred to the thermal motion of particles,
your response;
now given I stated this in the same post;
what is the mechanism that discriminates/separates the thermal motion of particles generated by,
1. frictional coupling
2. solar radiation
to allow this statement to be correct;
So if there is no friction, for both linear and angular momentum means the collision is not perfectly elastic, and therefore a percentage of
no momentum is transferred to the thermal motion of particles,
You can't turn a scalar quantity into a vector one.
You can't make energy into momentum.
If I wrote something that said otherwise then I was mistaken. Opps!, Sorry about that.
But the fact remains that the quantities are all independently conserved.
Symmetry.
So in regards to; if there is no friction, for both linear and angular momentum means the collision is perfectly elastic, and therefore
no momentum is transferred to the thermal motion of particles.
Yes think we can all agree on that.
However you seem to be backing away from your statement below, which quite correctly highlights there is frictional coupling between the earth's surface and the atmosphere;
are you now saying there is no friction between the atmosphere and the earth's surface and therefore no transfer of momentum to the thermal motion of particles ?
Friction refers to the conversion of mechanical energy to heat energy.
It is not magic.
It still obeys the conservation of angular and linear momentum.
You can not convert energy into momentum.
At the level of individual molecules of gas hitting eachother there is no friction- energy and momenta are conserved.
This is also true for gas molecules hitting the solid earth or the sea surface.
Since energy and momentum are conserved in absolutely every one of these tiny collisions. it follows that energy and momentum must be (exactly) conserved over all.
Why do you not see that you are trying to claim that addition does not work?
BC, yes agreed
I believe we already covered this.
However it is possible to increase/change momentum of the atmosphere due to the conditions/dynamics occurring ie solar input to a fluid changing density in a gravity field creating buoyancy force and subsequent acceleration.
Below is a quote with the link given;
If the forces are not balanced, the droplet accelerates. This acceleration is not simply the partial derivative
∂v
∂t
because the fluid in a given volume changes with time.
Applied to any physical quantity, the material derivative includes the rate of change at a point and the changes due to advection as fluid is carried past the point. Per unit volume, the rate of change in momentum is equal to
ρ Dv/Dt (ρ density)
This is equal to the net force on the droplet.
Forces that can change the momentum of a droplet include the gradient of the pressure and gravity, as above.
Now given the above states quite clearly the atmosphere is capable of changing momentum, and one such cause is change in density due to the solar input constantly changing the balance of the forces,
Therefore addition doesn't doesnt work if the numbers keep changing.
Now this statement ;
In regards to "At the level of individual molecules of gas hitting each other there is no friction- energy and momenta are conserved"
yes agreed, but I would have stated At the level of individual molecules of gas hitting each other they are elastic collisions
In regards to this part;
"This is also true for gas molecules hitting the solid earth or the sea surface."
agreed that energy and momentum conserved overall, but given the collision with the surface is not 100% elastic
some kinetic energy is transformed to heat/thermal energy and sound waves and similarly some momentum is transferred to the thermal motion of particles and also momentum carried away in the sound waves emanating out in all directions as per the inverse square law.
when considering the exchange that occurs with the atmosphere and the sea similarly you get heat and thermal motion of particles and also momentum carried by the waves.
Therefore not a 100% exchange rate of the solid earth's or atmospheres, rotational kinetic or angular momentum.
And as covered previously if some momentum is transferred to thermal motion this is now in the same category as the thermal motion due to solar input and open to the same dynamics going forward in time.
The numbers only change when "something happens" and momentum is conserved during every "something".
So it is conserved overall.
If I explained to the man on the truck that his hands were pushing the truck forward but his feet were pushing it back just as hard, he would probably accept that.
You, on the overhand would say that because he's working really hard - burning lots of calories + sweating, he must be achieving something.
Sometimes, even in physics, it's not the energy you need to look at.
but given the collision with the surface is not 100% elastic
some kinetic energy is transformed to heat/thermal energy
Momentum is conserved during inelastic collisions.
That's how we can still do maths with them.
Keep dreaming :), it is about the boundary conditions.
We cannot have right/wrong if were are not talking about the same observers and boundary conditions.
The boundary is perfectly clear and has been obvious all along from the thread title and the OP.
It's the planet Earth and its atmosphere.
Now, once again, since you said it was easy...
It was already pointed out to you that the rotation and rotational acceleration changes have to happen to conserve the total angular momentum.
The cause of the rotational inertia changes could be an energy of the Sun's heat.
The answer to the OP is yes, the windmills can affect the Earth's rotation.
The windmills are one piece of the complex friction layer between the atmosphere and the rigid ground.
Whatever tiny part the windmills play, it still will affect the Earth's rotation.
You do not stop with re-posting this and you fail to understand 'the boundaries' of what I was saying.
Please, stop being annoying.
I will stop posting this when you either show that it was easy as you claim, or accept that it's impossible because the laws of physics prevent it.
In the end, the windmill will fall into disrepair and be scrapped.
Do you accept that, at that time, the Earth will return to exactly the same rotation as it started with?
(All other things being equal)
So BC when you stated:
I already covered that momentum is conserved overall, In my last post.
However I also stated some of the angular momentum is transferred to momentum of other kinds, such as the momentum carried by sound waves and water waves.
Therefore for angular momentum to be conserved overall requires a mechanism that converts this said momentum back to angular momentum of the solid earth or the angular momentum of the atmosphere, for your position to be credible.
The trouble there is that what you stated is wrong.
Angular momentum is conserved.
You don't convert linear to angular (or vice versa).
It's a bit like the fact that you can't convert energy to momentum.
Do you actually understand what "Conserved" means?
I was talking about the 3 axes of rotation and how the total angular momentum is being conserved even though the individual axis are changing, as per the video.
The angular velocity changes along the 3 axes.
An accelerometer on such body will not measure a constant acceleration/rotation during these changes.
No, because, it depends...
Well, OK, we are back to the thing you said was easy, but failed to do.
The fact that you didn't answer the question.
You seem to think that resolving the angular momentum into 3 components matters.
It doesn't.
The cat walked past; I stroked it.
From my point of view, it was stroked left to right.
From the cat's perspective it was front to back.
A passing boy scout consulted his compass and concluded that it was North westerly.
A flea on the cat thought it was bottom to top
But, no matter what coordinates you pick, the actual event was the same.
And if you got any of the observers to do the maths they would all agree that from the point of view of a bee that was circling the cat's body, the stroke was a spiral.
The angular momentum of the Earth is also a thing that's fixed.
You can pick any set of coordinates and you can, if you wish, resolve it onto a set of cartesian ones.
But it's still conserved.
Obviously, if you change the coordinate system then the numbers you assign to the component vectors will change, but the momentum is still conserved.
How fortunate, then, that nobody asked what an accelerometer would say.
Ok BC you state:
So it is stated and you have stated also angular momentum is transferred between the earth's surface/atmosphere due to frictional coupling.
Are you now arguing this is done silently and therefore no momentum is transferred outward in all directions from the points of friction.?
What I have said (well, it's not me saying it; it's physics) is that linear momentum is conserved, angular momentum is conserved and energy is conserved. They are all conserved quantities
You seem to have become muddled.
It is possible to convert energy from one form to another- for example you can convert light energy into kinetic energy
But it is not possible to interconvert any of the three conserved quantities,
So, for example, you can not convert linear momentum into angular momentum.
Obviously, I didn't say that.
You just made it up and it's a bit silly.
The OP question is about rotation and acceleration.
Why are you talking about the angular momentum?
Imagine, you are floating inside of the International Space Station.
Not moving, no rotation, nothing.
Can you flip 180 degrees without touching anything, just with your motion?
Just pointing out some continued mistakes being continuously asserted by one or the other of you, none of which has been backed by anything other than empty assertions.
Cats are legendary for being able to do this in well under a second, but they don't change their angular momentum in doing so. Neither do the objects in the video change their axis of rotation (except one, and that one depicts a violation of physics). The angular momentum vector in each example wavers neither in magnitude nor direction.
As B-C has repeatedly pointed out, this statement is just plain wrong, and yes, we've both noticed that despite the claimed ease of showing this, you've not shown it. That makes you full of hot air, but said hot air doesn't change the momentum of your argument.
However I also stated some of the angular momentum is transferred to momentum of other kinds
All of these assertions violate the laws of momentum conservation. A collision between two masses has the exact same momentum (both linear and angular) as before the collision, whether the collision is elastic or not. The latter case ends up with warmer masses perhaps, but no difference in the momentum of the system.
Did I say that the total angular momentum is not conserved?
Yet, consider the following, if an astronaut can rotate 180 degrees then what stops him from rotating continuously without stopping?
In the beginning, no rotation, no motion and then continuous rotation.
The rotation changed but the total angular momentum is conserved.
If the direction of rotation is changed, the angular momentum is not conserved now, is it? So yes, you've been asserting just that.
It also is not confined to rigid bodies. A system of masses connected with pool noodles or not connected at all will still maintain both linear and angular momentum, absent external forces. Energy input (in a form other than external force/torque over distance) makes no difference. I can also apply an external force or torque (and change the respective momentum) without application of external energy, so the momentum is simply not a function of energy input.
Well, for a more or less rigid body like the Earth they are so closely related that it doesn't matter.
Are you considering that idea that someone might move enormous quantities of rock from the equator to the poles?
That's what it would need before that interesting but irrelevant video of the flipping wingnut applied to our planet.
It's also important to recognise that during its flight the angular momentum of the wingnut is conserved.
The reason for choosing angular momentum is ironically illustrated by Gem who pointed out that energy is the currency of physics or some such.
Well, it's only one of the currencies in use.
You choose the conserved property that best fits the situation and, in this case it's angular momentum.
A much better question is why are you ignoring it?
In particular, why are you ignoring the fact that angular momentum is conserved.
If the Earth doesn't change its shape or the distribution of its mass then the moment of inertia , and thus the rotation rate, will be constant.
Windmills don't do that (or, rather they do, but less so than a block of flats or a grain silo; it's not "being a windmill" that makes the difference).
You just don't seem to understand that you did so.
Any change in the rotation of the Earth is a change in angular momentum.
Your failure to understand this simple bit of physics is also shown by you asking this
Position is not a conserved quantity
The conservation of angular momentum.
He starts with zero, so he must end up with zero.
During the maneuver, he imparts equal and opposite angular momenta to his leg and to the rest of his body. but the sum remains zero.
He can do this because he is flexible and has muscles which apply forces.
Cats are also noted for the ability to do it, and for their flexibility.
However the Earth is , for all practical purposes, rigid.
(It's interesting to note that, in principle, it's possible to make the change of direction in which you face without expending energy).
The rotation changed .
Not really. It remains zero at all times.
The clever bit is that his leg(s) rotates in the opposite direction to the rest of him.
https://space.stackexchange.com/questions/2954/how-do-astronauts-turn-in-space
So , once again...
You keep on saying you can perform this miracle and that it's easy.
Why don't you do it?
So Halc you state:
A collision between two masses has the exact same momentum (both linear and angular) as before the collision, whether the collision is elastic or not. The latter case ends up with warmer masses perhaps, but no difference in the momentum of the system.
So to be clear is the momentum of the said matter effected by the collisions that is the vibrations and movement within a particles freedom of movement, included in your version of the sum of conservation ?
Also is the momentum carried Out in all directions by the sound waves included in your calculations?
By symmetry, that sums to zero anyway.
is the momentum of the said matter effected by the collisions that is the vibrations and movement within a particles freedom of movement, included in your version of the sum of conservation ?
So, that's a "no" then. You do not know what "conserved" means or you would not have asked that.
A cold 1kg mass moving at 2 m/sec north has the exact same momentum as a hot 1kg mass moving at 2 m/sec north, so the difference is only thermal energy. Yes, the particles in the latter are moving at a higher average speed, but not at a higher average velocity, and momentum is a function of velocity, not speed.
One is a scalar quantity, and one a vector quantity, and you cannot substitute one for the other, as B-C has already pointed out, but if you don't listen to him, why should you listen to me?
Sound waves carry energy but not momentum. That means a perfectly elastic collision between objects cannot make any sound. The inelastic collision can, but if the system is moving through a medium which carries sound (air), they're probably losing momentum due to friction with the air. That would constitute an external force upon the system.
This is not the case with Earth as a system. It makes no sound as it travels through space.
The bold part, I am talking about three axes of rotation.
These axes are defined with relation to the body.
The angular momentum changes between them but there is no total sum gain.
Like the cats rotation, applying energy within the system can be a cause of such rotation.
This is a quote from that video description:
This, together with the centrifugal effects, means that the components of momentum DO change.
The analysis of 'one of the best mathematicians' of our time, as per the video, switched to a non-inertial observer.
We started to talk about the Sun's energy input.
That's the point when we should stop thinking about the Earth as a rigid body.
The boundaries...
When we consider the Earth's crust as the most visible part of a bigger system then the OP question can be understood as 'do windmills affect the Earth's crust rotation?'
The answer to the OP is clear, yes.
If the rotation of the crust changes then something happens to the stuff beneath (mantle, ... ) to compensate and to keep the total angular momentum conserved (ignoring the stuff outside the crust: water, ...)
I can also apply an external force or torque (and change the respective momentum) without application of external energy, so the momentum is simply not a function of energy input.
Well, it depends, ...
... who is looking, the reference frame and the boundaries.
'The momentum is a function of energy input.' is a true statement as well.
Also, applying an external force or torque by contact is applying an external kinetic energy.
Applying an external force or torque by field requires a question where is the field coming from.
Still, the momentum could be a function of energy input as well.
I am not sure what you were trying to say.
I tried to explain why that's not helpful with the comments about the cat.
You can resolve the rotation of the earth onto any set of axes you like.
But, as long as you maintain the same set of axes, the projections of the angular momentum onto those axes will remain constant because the angular momentum remains constant/
There's a lamp behind me.
If I turn round the lamp is in front of me.
That's not because the lamp has moved, it's because I have changed the reference.
As I pointed out, technically, you don't need to supply energy to do this.
However, what you fail to take account of is that the cat's angular momentum is constant throughout the process.
The cat never spins. Bits of it do, and other bits spin the opposite way.
If the Earth did that, we would be dead,
Yes we did.
God knows why.
It's not got anything to do with rotation.
The answer to the OP is clear, yes no.
OK, I take a rock and heat it up, thereby changing its energy.
Does it somehow suddenly have to start spinning or moving through space?
So neither angular nor linear momentum is a function of energy.
Just as well really, since they are vectors, not scalars.
And there was me thinking I could make an electric motor.
Will you please think about stuff before you post it.
Just try to remember that everything you post will be looked at critically by people who do science for a living.
So, you should really try to imagine what our reaction to a post will be and, if that reaction is to trivially show that you are clearly wrong, don't post it.
You should be checking your own work before you post it, otherwise you may mislead other people who look at this to think that there's actually a controversy here.
The relativity says the lamp moved for the non-inertial observer.
There is a dr/dt change for the non-inertial reference frame.
The bold part, I am saying the same thing, components change, the total sum of angular momentum is conserved.
I said the same thing with the ice can example.
Yes, people die, when a bad earthquake happens, hence the importance of the boundary conditions, space and time.
It can generate a flip, as per the ice can example.
So the flip is not a rotation now?
You keep pulling my quotes out of context.
It is impossible to have a reasonable discussion.
For example: "Also, applying an external force or torque by contact is applying an external kinetic energy."
How you came to conclusion that I am saying an electric motor cannot be made?
Where is the electric motor coming from? Why?
It's not a change in angular momentum nor does it give rise to a rate of rotation.
Not with the earth.
Also, it's important to recognise that the energy added does not cause the flip.
The change from a solid to a liquid does that.
There are materials which liquefy when cooled.
You could spin a warm can of that in zero gravity and as it cooled it would give out energy and start to change the axis of rotation as it lost energy, cooled and "melted".
The change isn't caused by energy, it's caused by a change in the moment of inertia.
It's true that moving rocks around to turn the earth into a huge donut shape would change the rotation rate and need energy.
But it's not the energy that changes the rotation rate.
You can get one on amazon. That's hardly the point.
An electric motor spins the rotor by contact- that's why they have brushes.
And yet it does not add kinetic energy to the rotor.
The motor just sits there; it has no kinetic energy to transfer.
is incorrect- as shown by an electric motor which applies a torque, but does not apply external kinetic energy.
So Halc in regards to your 1kg mass moving at 2m/s you need to do that change in temperature and change in momentum Calculations after a collision. Else you give the impression momentum/ LoD value Is unaltered after frictional coupling.
Also Halc where you stated:
"Sound waves carry energy but not momentum."
That is incorrect, for your and subsequent readers information it can be calculated using
Momentum = energy/phase velocity
BC you stated:
"So, for example, you can not convert linear momentum into angular momentum"
Not sure that's correct either
https://en.m.wikipedia.org/wiki/Crankshaft
So in regards to symmetry yes the sound waves leaving the angular Momentum motion sum to zero but the Total value of them individually is subtracted from the angular momentum total.
That's OK, I am sure it is.
What I'm puzzled about is why you think that something so obvious could invalidate a well known law of physics.
Would you like to speculate on that?
Here's a clue.
Imagine building a petrol engine with all the cylinders + spark plugs and valves etc.
But not including the bearings etc that hold the crankshaft in place.
Would it work?
As Halc pointed out, the momentum carried by them is zero.
The symmetry argument has the advantage of being quick and obvious, which is why I used it.
Halc clarified that, a wave carries energy away from the system
In an elastic collision, no energy is lost so there can be no wave.
A wave that does not exist can not carry momentum
For some reason you have brought it up again.
Wooow :)
The energy melted the ice in the ice can example.
The primary factor is energy. There would not be any change of the moment of inertia if not for the energy.
I said that pages ago, it appears you are starting the grasp it now. :)
Starting... the last step is to agree the energy is the primary factor.
... and this is a domino effect.
The change of the moment of inertia leads to the change of the angular velocity around that one specific axis.
The change of the angular velocity is the angular acceleration.
The right hand rule and there you go ... there is a rotation around another axis.
The components are changing but the total sum of the angular momentum is conserved.
Look, please, start reading the posts and stop shooting from your hips right away.
I said this:
Also, applying an external force or torque by contact is applying an external kinetic energy. - like a hamster wheel.
Applying an external force or torque by field requires a question where is the field coming from. - like the electric motor.
Your example of the brushes and contacts has nothing to do with what I meant by contact.
This is a physics basics question.
What are the options to transfer kinetic energy?
The answer: contact or field.
Note: the contact is 'field' as well; when we zoom in down deep... friction, contact is a field as well, just atoms are very close to each other and they interact through their field.
Do you remember 'boundaries'? Think about them when you watch this video.
https://www.khanacademy.org/science/high-school-physics/torque-and-angular-momentum/conservation-of-angular-momentum/v/ball-hits-rod-angular-momentum-example
I am sorry for thinking that you meant contact when you said contact.
And energy moving in the opposite direction would have the same effect in a can of thermosetting material.
So energy going in has the same outcome as energy going out.
That pretty much proves that it' not the transfer of energy that makes the difference.
I can even manage the same thing with a vanishingly small energy transfer.
Do you know how they make liqueur chocolates?
So. we can get the can to change from one stable state to another by
(1) adding energy
(2) removing energy
(3) doing neither.
and yet you still think it's energy that changes it.
I don't think many would agree with you.
And, as I said, if you rebuilt the planet and turned it into a donut you would alter the rate of rotation.
But windmills don't do that, do they?
So it's irrelevant.
Also, applying an external force or torque by contact is applying an external kinetic energy
That would be relevant if someone put a big spanner on the Earth or something and applied a torque.
Since nobody is doing that , it's irrelevant.
Why mention it?
Do you think the Sun is transferring kinetic energy ?
Or is that just more gish gallop?
I'm not the one who forgets the boundary.
Unless a force acts from outside the earth (i.e outside the boundary) the angular momentum within the boundary (i.e. of the Earth) will remain the same.
Sorry, I've not been able to keep up, and there's a lot of nonsense that doesn't warrant a reply, but I'll chime in for some blatant wrong assertions:
OK, I have a system with say linear momentum of 100 kg.m/sec in the x direction relative to inertial frame F.
I add 1 KJoule of energy to the system. What is its momentum after I do that?
You can have anybody you like 'looking' at the system.
More specifically, how much kinetic energy does it have if I add 1 KJoule of heat to the system? That question actually can be answered.
This is what I mean by momentum not being a function of energy. The first question would have an answer if it was. Sure, energy can be employed to exert an external force on said system, but a boat load of energy isn't going to make that mass change its momentum by itself. NASA would love a reactionless drive, but such a thing violates Newton's 3rd law. They have space ships with plenty of energy, but they can't use it to propel the ship. I can build a reactionless drive with the physics gem describes. He should patent it.
You need to read reply 320 where B-C asks you to consider the most simple counterexamples before posting (and even repeating) blanket statements like that, although admittedly I didn't didn't think the electric motor thingy illustrated the point clearly.
My example is a simple precessing wheel which has external torque applied to it by physical contact (visualize a top spinning at a tilt on a level table) yet has zero kinetic energy applied to it. Its KE will remain unchanged except for losses to friction, which don't exist in an ideal environment, but the external torque applied necessitates its perpetual change in angular momentum.
For linear momentum, a ball twirling on a string is a nice example, which has force continuously acted on it by contact with the string, necessarily changing its momentum, yet without gain or loss of kinetic energy relative to frame F in which the center of rotation is stationary.
No, the post-collision momentum calculation does not involve any thermal calculations. You simply add the momentum of the two objects together. As simple as A+B. Geez, I learned this when I was 13 in middle school intro physics class.
Quote from: B-C
for example, you can not convert linear momentum into angular momentum
You do realize that a crankshaft spins due to an external torque being applied to it, not due to it converting its own linear momentum to angular momentum, right? No, apparently you don't realize even this. Unbelievable.
You are here not to learn but simply to contradict at all costs rather than admit that you didn't know something.
Post by: hamdani yusuf on 08/10/2020 08:24:40
A 1 kg ball is attached by a 1 meter string to a 2 kg ball. The system is rotating at 1 rps in space far away from any other mass. At t1 the string breaks.
Is there any change in angular momentum?
Is there any change in linear momentum?
Quote from: hamdani yusuf on 08/10/2020 08:24:40
No and No.
Because no torque acts on it there is no change in angular momentum
Because no force acts on it, there is no change in linear momentum.
So in response to my statement of;
Halc states:
To which I respond
To which BC states
So what Halc stated is clearly wrong as he believes sound waves don't transfer momentum, and what BC states is disingenuous and incorrect given the dynamics under discussion are the frictional coupling of the atmosphere and the surface of the earth which are not perfectly elastic coupling therefore sound waves do exist and are transferring momentum out symmetrically, which as stated previously under the laws of conservation, a percentage of said momentum came from the angular momentum of the solid earth/atmosphere total.
So as I stated before, for you position to be credible you need to address this continuous transfer away from the angular momentum budget.
Now in regards to my example of a direct conversion of linear momentum to angular momentum using pistons and crankshafts and flywheel in response to BC statement of;
Neither BC or Halc thought it was a correct example and wanted to take the engine apart, or move the boundaries of the system
So you have made clear what you consider the boundaries in earlier posts so try this heat engine for an example of linear to rotational/angular momentum.
https://www.cnbc.com/2016/10/07/heres-why-hurricanes-spin-counterclockwise-in-the-north.html
And still, at every stage where a molecule hits a molecule, momentum is conserved so the momentum overall is conserved.
So you still can't convert a scalar (like energy) to a vector (like momentum) this way.
You still can't convert linear to angular momentum and you still can't convert angular to linear.
So the Earth's angular momentum is conserved and the earth just keeps turning.
As Stonehenge proves it has been doing for millennia.
Which of those don't you understand?
The coriolis force happens because momenta are conserved.
Post by: nathmaheshmp on 09/10/2020 18:55:53
Quote from: nathmaheshmp on 09/10/2020 18:55:53
That is a second (third?) order effect.
The first order is that it just keeps turning.
So given the dynamics under discussion are not dissimilar,
//www.youtube.com/watch?v=zwjoycoEQWw
BC you state
The key word there is "overall",
which still leaves outstanding an explanation or comment as to this aspect;
the frictional coupling of the atmosphere and the surface of the earth which are not perfectly elastic coupling therefore sound waves do exist and are transferring momentum out symmetrically, which as stated previously under the laws of conservation, a percentage of said momentum came from the angular momentum of the solid earth/atmosphere total.
Also BC when you state
yes agreed but it starts out as linear momentum and ends up with rotation/angular momentum
https://en.wikipedia.org/wiki/Coriolis_force#/media/File:Coriolis_effect14.png
Also in ideal gas laws one of the freedoms of movement of a gas molecule is rotation and if a molecule with zero spin has a linear collision "off center" spin/rotation is a consequence.
Now your stonehenge analogy is a most relevant point and similarly will require addressing.
BC just seen your most recent post stating the first order is it just keeps turning, which is quite relevant to the stonehenge comment i just wrote.
So keeps turning yes but not as consistently/smoothly as you might think, for example
28 th sept LOD was - 0.5142 milli sec
which is a pretty standard daily fluctuation, which represents Δ of approximately 6.55 x 10^20 Joules of kinetic energy
there is, absolutely, no stage during the whole process where the total angular or linear momentum -measured in any sensible way- will actually change.
And the same is true of the Earth.
No, it does not.
because the momenta are conserved at every scale.
Congratulations on spotting something we all accepted ages ago.
There's a tidal drag from the Moon etc.
But that's a different effect from the ones you are talking about where the atmosphere slows the Earth down. (notably it is different because it is real).
You can't say if that's a change in momentum or moment of inertia.
(Obviously, it's not a sudden change in momentum, because that's impossible- but you seem to have dispensed with logic)
So BC you raise one good point
Just for clarity for those that may not understand your point below is quite a good demonstration.
//www.youtube.com/watch?v=64t-dVtDwkQ
I believe there are some quite sophisticated gps tech that monitors the solid earth's flexing so along with that data and length of day and weather patterns there is good reference points, However as mentioned earlier this is an area of active research, and there are obviously very difficult aspects to getting a handle on the dynamic atmospheres momentum total at any one time but there is noted discrepancies.
But it is currently postulated most of daily variations are credited to exchanges of momentum between the solid earth and the atmosphere.
Heat can generate rotational kinetic energy, angular momentum in a closed system (no mass in/out, just heat energy in/out).
It depends on the efficiency of the system how much rotational kinetic energy the system would have.
Perhaps most, or perhaps not. I don't know. The Earth below is hardly a solid thing, and magma currents within must have an incredible inertial effect, compared to an atmosphere that masses only a millionth of the planetary mass.
My point has been that the total momentum cannot be affected by this at all, and such variations between one component of the system and another are temporary fluctuations and cannot be cumulative. If the atmosphere loses momentum to the ground one day, it must gain it back another day, else eventually one would move at a significantly higher or lower angular rate than the other, and the friction would be imbalanced.
Real torque on the other has IS cumulative, which is why Earth has been slowing down for billions of years, relinquishing its spin momentum to orbital momentum. The energy from the sun has nothing to do with that. The process does generate its own heat, heat that doesn't come from the sun. Yes, this heat is radiated away, but not the momentum.
Kinetic energy yes. Momentum, no. An internal combustion engine gets its rotational kinetic energy basically by turning chemical energy into heat, and that heat into kinetic energy. But that doesn't change the momentum of the engine one bit. The angular momentum gained by a revving engine comes from external torque applied to it by the engine mounts.
It is the other way around.
There is no external torque. If engine is not running then where is the external torque? Doing what exactly?
Nothing. No external torque. There is nothing external spinning the engine, is there?
The torque comes from the engine itself.
Why car engines have the torque as their specification?
It is action and reaction. The first action is engine running then the reaction is engine mounts 'counter-torque', preventing the engine block from spinning.
Here is the problem that might be in the way of agreeing what we say.
We start an electric motor on ISS, floating, stator and rotor spin opposite way.
The total net angular momentum is going to be zero.
Does the motor have an angular momentum as a system?
Would the system behave differently upon application of an external force when motor is not spinning compared to when the motor is spinning?
It's not a very good demonstration of how the Earth behaves, is it?
Would you like to demonstrate that?
Don't forget that I will be adding together the angular momentum of all the parts of the system before and after.
It is action and reaction.
Congratulation on spotting this.
It is the reaction against the Earth which provides the torque.
The effect is, perhaps, more apparent in helicopters which either need contrarotating blades or a tail rotor in order to fly.
I already said that- weeks or months ago.
Not a well defined question.
Do you mean "if we took the wheel out of a child's toy gyroscope and replaced it with the motor with the its rotor going one way, and its stator going the other, would it act like a gyroscope?".
If so then the answer is no.
It wouldn't (neglecting friction, air resistance etc).
Because, overall, the combination would have zero angular momentum
Again, it's like having contrarotating blades on a helicopter (though that's not the only reason they do it).
I split this topic, since the vast majority of the discussion going on has no business being in the mainstream physics section. I pretty much put all the posts from those advocating violations of conservation of angular momentum in this topic.
If the engine isn't running, there is no change in angular momentum of the engine, so there cannot be external torque beinging applied. Do you think I said otherwise?
An engine (revving or not) in a closed system cannot put external torque on itself, and thus cannot change its angular momentum one bit. So if the momentum of the engine is changing, there must be an external torque being applied to it, and the mounts are the only place applying such a force.
The energy comes from the engine. The external torque comes from, well, external.
There are a few examples of engines running without mounts, such as the one on a Sopwith Camel. The drive shaft of the engine is bolted to the fuselage, with no actual connects to the engine itself. In that case, positive torque is applied only through the drive shaft, making the momentum of the engine negative. The propeller blades are bolted to the engine block which allows the air to apply positive torque to the engine preventing it from gaining even more negative angular momentum. The positive torque applied to the fuselage is countered by the negative torque via wing flaps.
An isolated engine (a closed system) cannot deliver any torque at all. Nada. Car engines have a torque spec because they're expected to be mounted. A torque spec is pretty useless in isolation. My leaf blower, if hooked to the right transmission, can deliver more torque than a Jaguar engine. A power spec seems a more appropriate measure of an engine's ability to do work.
Very good. So why is it "the other way around" then? Counter-torque is torque, not a different thing with different physical rules. That torque applied by engine mounts changes the angular momentum of a revving engine, something that wouldn't change if it was in a closed system.
You just said it has none, so no. This is consistent with your scenario, since no external torque has been applied, only energy.
It perhaps vibrates when running. It is hard to hold on to when running since the motor is spinning, but any application of identical external force on the stopped motor must have the identical effect on the running one. Same change to linear momentum, and same change to angular momentum. For instance, the running motor will not exhibit any gyroscopic effects since it has zero angular momentum.
I pretty much put all the posts from those advocating violations of conservation of angular momentum in this topic.
Should this stuff be in teh "that can't be true" forum?
There's lots of crap that should go there first then. Dave's threads are high on the list, but at least he had the sense to post here from the beginning, and not post his assertions in the main sections.
The thread title doesn't explicitly call out momentum, but I put the posts here from people that at some point assert non-conservation stances. I probably should have entitled it "Can energy affect..." rather than 'heat'.
Energy, or windmills, or any tall tower for that matter, can affect the spin rate of a rotating thing, so it isn't entirely 'not true'. A windmill spins, and thus absorbs more than its share of the angular momentum of the system. The tower on which it stands changes the moment of the system. None of these touch the system angular momentum, but they do wiggle length of day by a few picoseconds or so.
On a totally unrelated note: Three of us are all coming up on posting milestones:
Alan is close to 10K, you to 20K, and me to (just) 2K.
Perhaps Alan will come back and either explain where the torque is from, or admit that he was wrong.
Perhaps he won't.
We have been here before. :)
We discussed it, never came to a conclusion a few months back.
//www.youtube.com/watch?v=1RkBwvuF80I
First thing to recognize is the difference.
The 3 CD players at 0:49s when the CDs are not spinning inside.
There is an external impulse to the system of connected 3 CD players when they are not running.
The system starts to rotate/spin.
The system center of mass moves/translates at velocity v1.
The CDs are spinning inside at 0:55s.
There is an external impulse (it appears to be the same magnitude, but off center) to the system of connected 3 CD players when the are running (CDs are spinning inside).
The system does not start to rotate. The system wobbles.
The system center of mass does not move/translates at velocity v1 (magnitude).
The system center of mass is resisting the straight line motion/translation.
Do we have an agreement that the system demonstrates different attributes, the system behaves differently due to the internal motion of inner parts even thought the total net angular momentum is the same before the external impulse?
(Am I The only one who worries about anyone in zero G who thinks that taping 3 CD players together at right angles is ter than taping them together with the axes aligned?)
Anyay, you are missing the point, and I suspect it's deliberate.
Imagine that the CD player has an IR remote control and is running on batteries.
You set it in front of you in zero G then, using the remote control, you press "play".
What happens?
If all is well balanced (ideal) then the discs will spin inside and the structure of CD players stays as is.
Now, do you agree there is a difference in the system response to the impulse as I described it?
Yes, but what is the relevance of this to this topic? The other topic was a sort of denial of angular momentum conservation, so since you've been doing that here, I suppose it is related.
As it should given an external force that you describe. The force is off center, so the 'brick' acquires nonzero angular momentum. No surprises.
This is the part BC gets at in his reply. They don't show the external torque being applied to the assembly. The thing has angular momentum at 0.57s, so it cannot have gone from the prior scene to the one at 0:57 without an external torque being applied. You're not denying this (yet), but I want to explicitly point this out.
The impulse applies a small torque to the assembly and thus must alter its angular momentum, which yes, results in the wobble you see.
Every tap changes the linear velocity of the center of mass of the thing. Are you denying that here?
Nonsense. That is a denial of Newton's second law.
No, because both linear and angular momentums are changed by each tap done by the guy. Those changes are the same magnitude whether or not the devices are spinning or not.
do you agree there is a difference in the system response to the impulse as I described it?
Yes. One tumbles due to the change in angular momentum, and the other wobbles due to the same change in angular momentum. I do not agree that the changes in momentum are any different given identical input taps.
Would you like a second guess?
It's related to this bit
(Am I The only one who worries about anyone in zero G who thinks that taping 3 CD players together at right angles is better than taping them together with the axes aligned?)
Post by: puppypower on 13/10/2020 15:18:02
One observation that nobody has mentioned, is that the earth's core spins faster than the surface of the earth. This was discovered in 1996 but has been ignored by the status quo, since too much credit would have required a complete revision of current earth theory. Below is an article from the NSF in 2004 after the first wave of dust settled and the status quo fought off a threat to their livelihood. This was attempt two, which by lack of mention in this discussion was also bottled away by the science swamp.
https://nsf.gov/discoveries/disc_summ.jsp?cntn_id=100044&org=NSF (https://nsf.gov/discoveries/disc_summ.jsp?cntn_id=100044&org=NSF)
The implications of the core rotating faster than the crust, is the earth's surface rotation may well be driven by the core, through visco-plastic friction. This outer core friction should also be producing heat, which then flows into the outer core and lower mantle, which is being convect toward the surface. It is a global warming wild card.
If we accept this data as true, then we need to revise the earth sciences since no models anticipated this, nor do many take it into account. We have a moon sized object, inside the earth, rotating faster than the surface. This is a very dominate earth feature, that cannot be ignored by any theory that claims to be valid.
I have pondered this and the wild card variable appears to be water. Water is continuous from the atmosphere, to the oceans, through the crust, into the mantle and theoretically to the core. The water placement is not driven by gravity, old asteroids, and density differences, but by chemical potential based on enhanced phase solubility at various conditions. As water gets hotter and higher in pressure it gets increasingly aggressive to minerals inside the earth. This is accelerated by the second law of entropy.
Experiments with extreme pressure and temperature water; at US National Labs, show new phases of water that appear to correspond to the layering within the earth; atmosphere is water vapor, oceans are liquid water, inner crust=hydrothermal water, upper mantle=superionic water, lower mantle=ionic water, outer core and core=metallic water. The phases of water define the layers of the outer and inner earth.
This layering of water would imply that the ionic water near the outer core; O-2, H+, is rusting the iron core and extracting energy and electrons. This driven by the sun evaporating the surface water and the continuity of water to the core. The movement of positive charge upward by solar evaporation causes a potential for electrons to move upward. Along with this electron movement are other sources of deep ocean heat.
The maximum solar heating occurs along the equator, which has more material; bulge. This is the main source and vectors for electrons This east-west, helps too direct the north-south magnetic field.
Can heat impact the rotation of the earth? If the core is driving the rotation, then the question becomes does heat increase reaction rate and thereby speed core rotation and the secondary affect this will cause?
Quote from: puppypower on 13/10/2020 15:18:02
One observation that nobody has mentioned, is that the earth's core spins faster than the surface of the earth. This was discovered in 1996 but has been ignored by the status quo, since too much credit would have required a complete revision of current earth theory.
The theory actually predicted that the core spins faster in 1995.
This was then measured in 1996.
If we accept this data as true, then we need to revise the earth sciences since no models anticipated this,
Just not true.
" A 1995 model of Earth's dynamo predicted super-rotations of up to 3 degrees per year; the following year, this prediction was supported by observed discrepancies in the time that p-waves take to travel through the inner and outer core."
https://en.wikipedia.org/wiki/Inner_core_super-rotation
The rest of your post makes no more sense than would be expected, given that it's based on errors.
What happens when 3 torque pseudovectors of different direction meet in one point and the magnitude is the same?
The 3 pseudovectors need to form a plane. The arrangement is possible.
For the 3d space 4 torque pseudovectors are required. The ISS uses 4 CMGs.
They add together to form a single (pseudo) vector.
Which is the same as
taping them together with the axes aligned
Except that the magnitude is smaller.
If you stacked the CD players like coins then you could get three times as much angular momentum as just one.
With the 3 at right angles they give a vector sum of (I think) root 3 along the diagonal of the cube
So, anyway, you forgot to answer this bit
The 3 pseudovectors need to form a plane.
That's about the one thing that three orthogonal vectors can't possibly do.
When you asked the question I said "well balanced (ideal)".
That means the CD players would be in 3 planes of the triangular prism with 60 degree angles, axes forming a plane.
The better solution is 4 CMGs (CD players) at tetrahedron vertex corners (or planes/faces) formed by equilateral triangles.
The 4 axes would point to the center of the tetrahedron.
So we turn on CD players of an ideal setup, what happens?
Well, four CD players forming a tetrahedron would be even funnier.
But I would still like you to answer the question you keep ignoring.
I answered in the post #333.
He did indeed answer the question, albeit a very wrong one. Jano apparently has no clue how to do vector arithmetic. Lacking his literacy in the language of mathematics, I'm not bothering to continue. Have fun.
Some errors:
His 4-CD tetrahedron would have zero net angular momentum and would thus exhibit zero gyroscopic effects.
No pair of sides of a regular tetrahedron meet at a 60° angle, nor do the axes passing through their centers.
The angle (called a dihedral angle) is about 70.5°.
60 degrees was for the triangular prism, 3 CD players, not the tetrahedron and the 4 CD players.
I did not talk about any angles in regards to the tetrahedron.
My apologies: You did say prism. My mistake there. What's the point of arranging them in that pattern? Why do you think the guy in the video didn't choose to do that? Why is something with no angular momentum 'ideal'? What benefit do you expect from it, or from the tetrahedral arrangement? You'd not be able to tell if they were running or not in either case. Might as well just tape three decks of cards together in a prism arrangement.
OK, I made a second mistake in reading what you said. You didn't answer BC's question in post 333 since it is preceded by 'if ideal', which apparently means a different arrangement than the 1-CD or 3-orthogonal cases that he was asking about. So you answered a different question. My apologies to BC this time for that mis-read.
No, you did not.
I was talking about just one single CD player.
You were talking about more than one.
the discs will spin inside and the structure of CD players
No please stop trying to evade the question.
I imagine it will take ages to get a sensible answer to this from Jaaanosik , but it's an interesting question so here goes.
Jaaanosik
Imagine that I got a huge number of CD players- a few cubic metres of them.
And I arranged them randomly in a big rigid box.
They are packed in the box so they can't move with respect to each other.
What happens when I press the remote and set them all spinning? (I'm ignoring the practicality that the one sin the middle will overheat).
From what you have acid before I think you will say that the combination will act like a gyroscope because all the angular momenta of the disks will act together.
Have I understood you correctly?
When you said:
"Am I The only one who worries about anyone in zero G who thinks that taping 3 CD players together at right angles is ter than taping them together with the axes aligned?"
I replied with what I said to point out there is a difference based on the arrangement of the CD players.
Three CD players would behave as one CD player if the axes are aligned and they spin in the same direction.
The CDs would spin inside and the CD players would spin in the opposite direction in ideal conditions.
The total net momentum would be 0.
No they would not, because the angular momentum would be three times higher.
But it seems you have more or less answered the right question
OK, so the total angular momentum would be zero.
So, if you tapped on it like in the video, what would happen?
(Imagine that the finger tapping it is moving at the same speed tangentially as the player so it doesn't impart a torque.)
Do you agree that , because the overall angular momentum is zero, it will tumble and there will be no "gyroscope" effect?
The most intuitive explanation without going into detail is the axes do not meet at the center of the mass for the 3 CD players system built as in the video.
The tetrahedron the axes meet at the center of the mass.
The simplest system where the overall angular momentum is zero would be two players stuck together "feet to feet".
Tetrahedra, prisms etc just add to the complexity.
Do you think that a pair of players stuck together in this way would have any gyroscopic effect?
If you pushed them would they tumble or wobble?
I am not sure what you mean by tumble, no "gyroscope" effect, please, be more specific.
That's essentially what I'm asking about.
"Tumbling" is rotating in a disorganised way.
Imagine I have two pairs of players taped together feet to feet so that (as long as the disk speeds are the same) the angular moment sum to zero.
I set both disks in one pair spinning.
I leave the other pair switched off.
And, since I'm in zero gravity Ican just put the two pairs in front of me and watch them.
They do nothing, because no (significant) external force is action on them.
Imagine I tap both of the pairs on the corresponding corners.
Do you think they will behave differently (because one of the pairs contains spinning things, and the other pair does not)?
They will behave differently.
Considering we are applying an external momentum, the distribution to all parts of these two systems is not going to be the same therefore they will behave differently.
If one is 'rigid' body and the other has moving parts, they have to behave differently.
I am not saying the external momentum will 'get lost', I am saying it will distribute through the system differently and therefore the systems will move (translate/rotate) differently.
They are not "rigid". The CDs are still in the players and can rotate. Switching them off doesn't stop the bearings working.
I am really rather sure that they will not behave differently.
If their axes are all aligned, then the system won't resist spinning of the player caused by external force which is perpendicular to (but doesn't intersect with) that axis.
Multiple axis rotation has been explored extensively in game programming. Here is a good example.
https://gamedev.stackexchange.com/questions/136174/im-rotating-an-object-on-two-axes-so-why-does-it-keep-twisting-around-the-thir
(https://i.stack.imgur.com/So2HM.gif)
So when the disc rotates in one direction, the disc player rotates in opposite direction to compensate for the angular momentum. Combining the second disc player orthogonally to the first can create rotation on third axis. If the directions are correct, it is possible to cancel out combined rotation on two axes by applying rotation on third axis.
The question I asked and tried to answer was, how does the observation that the core of the earth is spinning faster than the surface, impact the rest of earth science, all the way to global warming? And why hasn't the status quo altered the rest of the theory to accommodate the implication of a moon sized object within the earth spinning faster than the surface? At the very least we now have a huge object creating viscoelastic friction, which creates heat, eddies, convection and a moving phase boundary. Why is current earth theory not banished to alternate theory until it ups its game with the new data? Dies science has a grandfather clause?
The explanation for the core's higher rotation is supposedly based on the cooling of the fluid outer core. This causes this fluid iron material to contract into the solid inner core. Like the skating pulling in their arms, the angular momentum is conserved, so the result is faster spin.
The problem with this model is why isn't the surface and mantle contracting to fill in the space left behind by the contracting outer core? This global wide contraction should amply the friction. Has anyone thought this through, and are surface observations consistent with these extras? When a liquid changes phase into a solid, there is heat of fusion given off. Where is this extra heat going?
I developed an integrated model that goes from sun to core via the continuity of water, since the current theory does make all the needed connections. Should existing theory be sent to alternate theory, since it lacks the core observations and implications as part of its model?
Another observation, that was noted, at about the same time, was the earth is denser north to south compared to east to west. The earth bulges at the equator, but that average density is lower east to west. The earth is shorter north to south, but denser north to south. This was proven measuring the speed of seismic waves in various directions. Why is the extra material at the equator not packing the earth denser east to west via gravity? Does it have to do with maximum electron flow and the induced phase characteristics at the equator?
Mars does not rotate very fast and it is called the red planet due to the iron. What happened to its iron core rotation? Has the surface water been commandeered to the iron core?
The question I asked and tried to answer was, how does the observation that the core of the earth is spinning faster than the surface, impact the rest of earth science, all the way to global warming?
The questions you actually asked were.
The answers are
Not directly
"If the core is driving the rotation..."
It isn't.
And why hasn't the status quo altered the rest of the theory to accommodate the implication of a moon sized object within the earth spinning faster than the surface?
Because it doesn't actually make a difference to us here on the surface.
You would need to explain exactly what "theory" you think needs updating.
Obviously the theory that they used to predict the rotation of the core does not need to be updated due to the rotation of the core.
What do you think they have got wrong?
There's no implication to global warming. The core has been rotating faster since forever, and global warming is a new thing in the last century. The core dynamics has not changed in the last century.
What theory needs alteration? What implications have you envisioned that were not always there?
At the very least we now have a huge object creating viscoelastic friction, which creates heat, eddies, convection and a moving phase boundary.
The model has always known about the heat generated within. Where do you think geothermal energy comes from? This thermal energy drives all the processes including the core rotation, so that rotation can't create new heat. It rotates because of the heat.
Exactly. You put a pot of water on simmer, and the water moves around as it heats at the burner (the core), and cools at the surface. The result is convection motion. Add spin to it and you'll get the rotation predicted due to Coriolis force.
A hurricane works the same way: Heat input causes convection (upward) of warm air, with colder air moving downward. The effect makes a hurricane spin very fast in the middle without any torque being applied in that direction. The friction from the spin doesn't make the heat. The heat drives the spin.
The problem with this model is why isn't the surface and mantle contracting to fill in the space left behind by the contracting outer core?
Why would the outer core be contracting when there's a stove cooking it from below? That doesn't sound like an equilibrium state to me. This contraction is something you're making up. The Earth isn't losing mass so it maintains its size. There's no empty space being 'left behind'.
Has anyone thought this through, and are surface observations consistent with these extras?
Try thinking it through yourself first.
When a liquid changes phase into a solid, there is heat of fusion given off. Where is this extra heat going?
Probably into the melting of other solids back into liquid. It's in equilibrium, remember?
Mars does not rotate very fast
Pretty much same rotation rate as Earth, so we must not rotate very fast either. Not sure where the threshold of 'very fast' is. It you want one that rotates slowly, try Venus.
Has the surface water been commandeered to the iron core?
Why would low density water find its way below higher density materials?
No, they will behave differently!
(https://media1.tenor.com/images/af865243e0cc23dd20d552c8c67dcf4a/tenor.gif?itemid=5927868)
Jano, you really need to be more precise, since there is no context left to criticise.
So what systems are you talking about (one running, one not presumably). What state are they in, and what force is being applied? Just force? Torque? In what way does the running system behave differently than the non-running one?
I mean, I agree with you. The running one probably has a little yellow light on and has a display that counts the time where it is in the music, and the not-running one doesn't have these. I don't think you're talking about those kind of differences, but with a childish response like that, it's all I have to go on.
So if you assert that it behaves differently, say how exactly, and if it can be shown to violate a known conservation law, you're probably very very wrong.
Considering that the attachements are feet to feet, the discs inside the pair will rotate in the opposite direction, hence cancelling their angular momenta. So although the pair has two rotating discs inside, the angular momentum of the system is 0. Which is the same as the pair with non-rotating discs. Practically, it is still possible to notice the difference, which can be caused by flexibility of the mechanical connections such as the bearings, motor supports, wrapping tapes, etc.
The other case shown in the video where there is only one player with a rotating disc inside, the angular momentum of the disc is not canceled. Hence it will resist torque which would change the direction of its rotation axis. Similar case would happen if the pairs are attached feet to top.
I just checked; a CD has a mass of about 16 grams or 0.016Kg
0.06 M diameter
spins at 5 revs per second.
I = 1/2 M r^2
1.152 x10^-4 Kg m2
The angular velocity is 2* pi * 5 radians per second
31.4 rad/s
So the angular momentum of the rotating CD is
3.61 *10^-3 kg m^2 /s
Now that CD is made up of lots of protons, neutrons and electrons.
Each of those has its own angular momentum (You might realise now , why I was asking about a tonne of randomly oriented CD players in a box).
The mementa of those particles are tiny.
For the each particle , I is ½ ħ
1.58 x 10^-24
But there are lots of them
Thankfully, it hardly matters what elements the CD is made from.
The neutrons and protons have very similar weights- about 1.7 X10^-27 Kg and they make up most of the mass (0.016 Kg)
So the disk has about 9.4 * 10^24 protons and neutrons
And it's got roughly half that many electrons.
So that's about 1.5 * 10^25 particles
So, if you are right about the momenta of components having an effect on the whole body, the subatomic particles in a CD have a total angular momentum of
1.5 * 10^25 * 1.58 x 10^-24
About 22 kg m^2 /s
And that's about 6000 times higher than the angular momentum of the CD due to its rotation as a rigid body.
So, if you were right, a CD would be a very effective gyroscope, even lying on teh table before you started spinning it (and, indeed, for any practical speed, rotating it wouldn't make much difference).
On the other hand, my contention is that the angular momentum of a composite body is the vector sum of the momenta of the components of a the body. Unless those are carefully aligned, they usually sum to zero.
And so, for the pair of CD players, just like for the non rotating CD, there's no "gyroscope" effect.
You should have answered my question about a box full of CD players.
Halc,
yes, I do not have time to write long responses every day.
I found some time, here it is.
Let us consider two CD players with feet sides attached, taped, CDs not spinning.
CDs are either locked as a rigid body or they have friction-less bearings.
We apply the external forces as per the image, in the CDs parallel plane.
The plane goes through the feet touching points.
(https://i.imgur.com/jsXVoTq.png)
The CD players start to rotate, the CDs either rotate with the CD players if they are locked or they are not if the friction-less bearings are used.
This is the first example where the CD players with locked disks will rotate with smaller angular velocity compared to friction-less bearings setup where CDs will not start to rotate inside.
This is what I meant when I said: "The external momentum will distribute through the system differently and therefore the systems will move (translate/rotate) differently."
When the CD players are ON then we need to consider the 'elasticity' of EM field of the motors.
One CD will be accelerated and the other will be decelerated when we apply the same external momentum as per the image.
The electric motor EM fields are not going to respond in the same way.
What I mean is that if stepper motors were used then we might observe steps 'skipping' based on the load being applied in the opposite direction of the running.
The skipping is not going to be the same on both motors because the external momentum is accelerating one CD and decelerating the second one.
Again: "The external momentum will distribute through the system differently and therefore the systems will move (translate/rotate) differently."
My post above shows what you missed.
Just think how different "gyroscope" effect is going to be for the spinning analysis.
The CDs are not going to have the same gyro effect.
Once the disks are spinning then the motors have no work to do (apart from overcoming bearing losses which, in principle could be practically zero).
So you can switch the motors off at that stage.
There's no EM field needed.
So there's no need to consider any elasticity it might have.
It shows that you do not understand physics.
Why did you talk about that?
The question was about what happens after the disks are spinning.
There's a difference between the case of having the disks locked in place or not.
But since we are talking about CD players, and since I talked about being able topers play on the remote control, and get the disks spinning, it is clear that we are talking about the case where the discs can rotate.
Why are you talking about some nonsensical system where the discs won't play?
You say: "Once the disks are spinning then the motors have no work to do (apart from overcoming bearing losses which, in principle could be practically zero).
There's no EM field needed."
That shows: "No
It shows that you do not understand physics."
It is you that does not understand the real world physics.
Escaping to unrealistic assumptions, really?
You started this two CD players taped together ON/OFF analysis.
When the CD players are OFF I split that scenario to two options because...
... the first time we discussed this I used term 'rigid' body and you mentioned the bearings in your post #357.
I made it an extreme, two scenarios for the simplicity, rigid body and friction-less bearings to point out the difference in the system.
So what are you talking about?
I am all for making the OFF scenario realistic as well. When bearings generate random friction each time we apply the external momentum.
Each time the system will respond differently.
They are called simplifications- like the one where you have not mentioned air resistance.
Or is it only "escaping" when I do it?
So, let's try to agree a simple system that actually addresses the point.
There is no air resistance.
The bearings are frictionless and the motors are ideal so that, once they are up to speed the back emf exactly balances the applied voltage, no current flows and they draw no power. As a consequence, they produce no torque once the disks are spinning at 5 revs per second. The disks "coast" after that.
The two players are identical.
They are taped rigidly together feet to feet so that the angular momentum of the disks (and motors, for what it's worth) are identical in magnitude, but opposite in direction.
The cd players are (nearly) perfectly rigid (A perfectly rigid material would breach relativity).
We are doing the experiment in microgravity, so the effect of gravity from surrounding objects is small enough to ignore.
The players have remote controls which use IR or some such and which lets you start or stop them remotely without applying a significant force to them (we can ignore photon pressure from the IR).
The "stop" button on the remote actually drives the motor in reverse to apply a breaking force until the disk stops WRT the player and then switches off the drive power.
No other significant forces act on the players except those explicitly stated as part of the experiment.
Anything else we need to clarify?
Post by: Kryptid on 16/10/2020 17:29:03
Said the guy who thinks conservation of angular momentum can be violated.
OK, what's next?
Quote from: Kryptid on 16/10/2020 17:29:03
Not really, it is all about the space and time boundaries of the system discussed.
That's where the problems are.
Whatever BC comes up with in his ideal scenario I am going to ask what happens when the external momentum is going to applied during the time the motors are accelerating/decelerating the discs.
Are we going to claim EM fields are so perfect there are not going to be any 'skipped' steps?
That goes against randomness of the quantum physics.
I have seen you argue that linear momentum and angular momentum can be interconverted. That leads to violations of both conservation of linear momentum and angular momentum.
They can, because they are system boundaries dependent.
Just check the video.
The beginning, CD player off and there is an external momentum.
The CD player rotates and the center of mass translates.
What momentum was applied? Angular or linear?
OK, you presumably remember asking this
And saying this
Now, imagine wto pairs (as discussed) of CD players.
One has the two disks spinning and the other does not.
You apply a similar impulse to the two pairs
As you put it "There is an external impulse (it appears to be the same magnitude, but off center)"
But let's' be clear; in this case it is exactly similar, the same push in the same place on the shell of the CD player.
Do you believe that the motion of the two systems would be different.
To sum up, the only difference is that the disks are (contra) rotating in one, but stationary in the other.
Both unless the direction of the push happened to be directed exactly towards the centre of gravity of the object.
Was that meant to be a serious question?
They can
And thus you prove my original point.
If the bearings are friction-less then CDs are not part of the system in this exact scenario.
There is no interaction between CD players and CDs when the external momentum is applied as I described.
This is what I mean, the boundaries are important.
So I agree with you that we would not see the difference under these ideal conditions in the example I described.
If we change time boundaries during the CDs acceleration then we need to specify ideal EM field (no skipping), again some unrealistic stuff.
Seriously? Since when did friction define whether or not something was a part of a system or not?
Did the momentum of the CD player system changed when the external momentum was applied?
Where is the conservation? What boundaries are we talking about?
That may be true in the case where the impulse is exactly tangential to the rotation axis, but it is not true in general.
Hence what I am trying to get across. The devil is in the detail.
I don't know the specifics of this CD player system you are talking about, but conservation of angular momentum is proven by Noether's theorem. It isn't up for debate. If you think it isn't conserved, then you are the one who is mistaken.
Just think about this exact scenario and tell us how you can change the rotation of the CDs inside?
It may be a language thing,but that makes no sense.
No EM field is involved.
Time isn't good at obeying boundaries.
And yet, when I Tried to nail down the details I got told I was
I can grab hold of the pair of players and rotate it so that the axis of rotation moves by 90 degrees.
Rather Than us defining the system and you wriggling out of it, perhaps we could look at it the other way round.
Please show us what impulse you could apply to the two pairs of players which would give rise to them following different motions
What happens when the external momentum would be applied at the time when the CD players are turned on and the CDs are accelerating.
Exactly the same as when they were stationary, or at full speed.
At all time the total angular momentum is zero.
One example, let us consider the there is a bearing friction.
The CD players are off.
There is a random transfer of the momentum to the CDs inside of the CD players.
Therefore the CD players will have random angular velocity each time the same external momentum is applied.
The same random transfer of the momentum to the CDs applies to the running CD players as well.
We added an external momentum, we are analyzing a delta.
There is a change.
By symmetry, whatever you added to one disk, you subtracted from the other, and so the effects cancel.
No, that's my point about the random friction. There is no symmetry.
First, there's no friction in the system under discussion,
Second, random stuff cancels out on average.
Nonsense. This violates momentum conservation laws. I can build a reactionless spaceship drive if this ludicrous statement is true.
Secondly, there's no random stuff in a classic system. Formulas for coefficient of friction do not involve probabilities.
Any friction in a CD player is countered by a motor keeping the CD rotating at a constant relative speed, required for the music to play properly.
You asked in #395, I answered in #398, friction is considered.
Do you agree with a delta per instance?
Please, check the setup. How do we spin the CDs that are on the friction-less bearings?
The external momentum applied to the CD players as per the image.
Wait, wait, wait, ... I claimed that first. :)
Do you remember this?
(https://i.imgur.com/6ubvKhG.png)
How do we spin the CDs that are on the friction-less bearings?
By the CD player applying torque to the CD.
The drawing you posted looks a bit like a diagram of automobile disk brakes, which isn't very representative of a frictionless system. No bearings are depicted at all that I can see.
You continue to post complications to a simple scenario, seemingly in attempt to either obfuscate the fact that your physics doesn't work, or to resist giving a direct answer to any question. You're a troll. You don't want to learn, you only want to contradict.
To be fair, I wrote that out of the discussion by saying we were considering a model where friction must be so small you can ignore it.
On the other hand, the thread is about the earth and atmosphere where friction - like the wind - is pretty much random.
If there's a motor compensating for friction, even very high friction can be ignored, since it is internal and generates only heat, not net torque. But the motor in the CD player cannot be ignored.
The CD player will spin the CD at a constant relative RPM, which is different than a box with a frictionless wheel in it and no motor. The latter will have a smaller moment along the spin axis. So if I spin the CD player in the direction the CD is spinning, the motor has to add RPM to the CD to compensate. The motor performs work. That's different behavior than a box with a wheel in it.
That said, strap two CD players face to face an despite the two motors doing work, you cannot tell if the things are running or not. The internal torque by the two motors always cancel each other and there is no external effect.
Not so with the 3 players strapped orthogonally, which behaves differently than three boxes with free spinning wheels inside. Keep that in mind. Jano of course has no clue what he's talking about and has not explicitly spelled out a single scenario with an explicit statement about the difference in behavior between a pair of zero-momentum devices running or not. He's adding needless complication in effort to never have to actually make such a statement.
Let's go slowly.
Two CD players taped together, CDs inside, not spinning, friction-less bearings.
The external momentum as per the image.
The CD players rotate, the CDs inside do not rotate.
Any translation?
This phrase does not make sense in English,
He's adding needless complication in effort to never have to actually make such a statement.
That's why I'm going for frictionless bearings and disk that coasts.
It's one more thing he can't talk bollocks about
Jano of course has no clue what he's talking about and has not explicitly spelled out a single scenario with an explicit statement about the difference in behavior between a pair of zero-momentum devices running or not.
I know that.
You know that .
Reality knows that.
But the more idealised we make the system, the fewer things he can hide behind, so...
let's solve the problem for the spherical horse in a vacuum.
(and then watch him explain how the 6000 fold bigger angular momentum that the disk has because of the subatomic particles,doesn't make a difference because... magic)
Slowly is probably less needed than being precise, and you are being anything but in this post.
Two CD players taped together (or for that matter, any system of components, connected or not) can only have one angular momentum vector and one linear momentum vector. I can only guess that the picture shows one of each, but lacking labels, I'm left guessing.
So let's say the top vector is the angular momentum vector, which means the assembly is tumbling forward (rolling away from the point of view (PoV). If that's the case, the CDs are also spinning with the players just like the seatbelted occupant of a tumbling car must rotate with the car. So saying the player has angular momentum but the disks do not (are not spinning) is a contradiction. It could be done if the player angular momentum was parallel to the disk rotation axis, but the picture shows a vector perpendicular to it.
The lower vector is then the linear momentum vector, which means the thing is moving to the right.
Impossible. The CDs are not free to remain stationary if the case is tumbling like that. Perhaps you need to attempt a more precise description of what you have in mind. It would also help if you say if the CD players are facing the same way or opposite each other. The picture shows only one of them, not two taped together.
The vector at the bottom indicates a translation to the right. If I guessed wrong which was which, then the top vector indicates a translation to the left, and the bottom vector indicates rolling towards the PoV.
I would think for simplicity you'd have the thing start with zero linear momentum, but in fact you didn't specify it at all except for the hints from the unlabeled vectors in the picture. If they mean different things, you should make them different colors. If you meant them both to be angular momentum, then it's wrong since an object can have only one angular momentum vector.
This is what I wrote in the post #369:
I want to create as simple scenario as possible.
Let us assume friction-less bearings.
The red arrows are the external momentum, in the plane as described.
Only CD players will rotate there is no friction to start CDs rotation.
The system is 'ideal', well balanced, no tumbling.
Is this understandable?
OK, that's like over 40 posts ago, and plenty of suggestions from you since then of different scenarios.
You need to spin the case then along the axis of rotation of the bearing then, not tumble it end over end as your vectors indicate.
You identified those vectors and momentum vectors in the prior post. Now they're external force vectors. This is what I mean about being precise.
OK, so you're imparting a spin to the thing counterclockwise, and the CDs do not spin with the case. Fine. That's just not what you said at all in the prior post. The thing spins faster than it would if the CDs moved with the case since the moment is lower.
Now we're back to momentum again. You said force just above. The two are not the same. I'm assuming force since two forces can be applied, but a thing cannot have two angular momentum vectors.
I see little hope of this going far enough to make your point if you cannot speak the language. The red arrows are not momentum if the thing spins counterclockwise. The momentum points at the PoV (at you).
Yes, if I ignore the parts about the arrows being momentum, which is just wrong.
There is presumably no linear momentum, but you don't say that. The center of gravity (CoG) stays put. The thing has angular momentum pointing at the PoV due to the torque applied to it. No net linear force is applied since the red FORCE arrows are equal and opposite. The angular momentum vector is not depicted.
A CD player doesn't work like that, but a simple device with a disk on a frictionless bearing does. A real CD player (unlike an LP player) always maintains a constant linear velocity, which means it runs fast at first, and slows as the music plays. It's pretty complicated, and thus a poor choice for an example. We're going with your simple frictionless disk.
I envision the rotation of the huge and heavy iron core, dragging the rest of the earth through viscoelastic friction. If I placed a drill mixer in the center of a bucket of fluid, the friction at the center will cause the entire bucket of liquid to move with the mixer. If I rotate the bucket at the same time, as log as the bucket is going slower than the mixer, it will be dragged along by the mixer.
This would not be the case, if we assume there is zero friction between the mixer and fluid, which is not a good assumption at the pressures assumed at the earth's core. The pressure is what is allowing the iron to be a solid at the core temperatures. If there was no pressure, iron should be a gas at core temperatures. Pressure induced friction allows torque to be transmitted.
One additional feature for the water continuity model of the earth; water phase boundaries define the various layers of the inner and outer earth, is the oxygen; O2, in the atmosphere. This is induced by solar energy via photosynthesis. The O2 creates a powerful oxidation potential for electrons to flow toward the atmosphere; global oxidation potential. This potential integrates life with the core dynamics, via the continuity of water from atmosphere to core.
At the water phase boundary near the outer core, water is ionic and then becomes metallic at the condtions at the core core. The ionic water phase is a matrix of O-2 and H+. The oxygen accepts electrons as the hydrogen proton strips them from iron. The atmospheric oxygen is O+2. The result is an election flow upward, through the continuity of water; various phase combinations of oxygen and hydrogen.
If you look at oxygen, it can accept two more electrons than it has protons; O-2. The affinity of oxygen for these two extra electrons is not based on the electrostatic force since the charge becomes imbalanced. It is based on the magnetic side of the EM force; electron orbital addition via the magnetic force. The oxidation of the iron core, via ionic water; hydrogen and oxygen, shifts the EM force to the magnetic side; earth's magnetic field.
Only because friction with the Earth stops this happening.
//www.youtube.com/watch?v=JEcTEs5hI4c
And, isolated in space, there's no way that can happen to the \Earth, is there?
It is based on the magnetic side of the EM force
Oxygen atoms and oxide ions are non magnetic.
The oxidation of the iron core, via ionic water; hydrogen and oxygen, shifts the EM force to the magnetic side; earth's magnetic field.
The sort of hogwash we would expect from someone who thinks that a 30% drop in GDP is a sign of a good economy.
https://www.thenakedscientists.com/forum/index.php?topic=80578.msg615231#msg615231
And that homoeopathy works
There is presumably no linear momentum, but you don't say that. The center of gravity (CoG) stays put. The think has angular momentum pointing at the PoV due to the torque applied to it. No net linear force is applied since the red FORCE arrows are equal and opposite. The angular momentum vector is not depicted.
I am glad you are pointing out the difference between the force and the momentum.
Here is my take on it.
It does not meter how the input is described, force or momentum, because what is more important is the output.
We want to analyze the resulting momentum, angular and linear, and for that we need the resulting velocities of all the parts of the system.
The input as force: 'm*a' means we need to find out how long the force was applied, all other details to find out the resulting velocities of all the parts of the system.
The input as momentum: 'm*v' means we need to find out the collisions, what collided, where it went, at what velocities, ... again, all the details to find out the resulting velocities of all the parts of the system.
I said the this:
... and I also asked this:
Because, as you correctly pointed out:
The think has angular momentum pointing at the PoV due to the torque applied to it.
This means there was angular acceleration generating the rotation that ended in the angular momentum.
The CD players system will start to translate in the direction of this angular momentum.
According to conservation laws, both input and output are equally important because they must match each other.
What you apply to the object is an "impulse".
That's the integral of a force WRT time (or force times time if the force is constant).
It is mathematically the same as a change in momentum.
But, it says a lot that you are ignoring the fact that we are talking about rotation, but you are talking about a change in linear momentum.
Why can't you recognise that they are independent?
Apologies - I haven't read all 454 responses to this thread, so this may be covered already. But my small contribution:
Can heat affect Earth's rotation?
As the Earth's atmosphere warms, it expands. This expansion slows down the rotation of the atmosphere, which couples to the rotation of the Earth.
The effect is small but measurable over long periods.
See: https://astronomynow.com/2015/06/30/nasa-explains-why-30-june-will-get-an-extra-leapsecond/
You're confusing linear momentum with angular momentum. No, I do not agree.
The angular momentum of the players is zero at first, and since it is a conserved quantity, the only way it can acquire angular momentum is via external torque, which you say is being applied to it (the presumably force arrows in the picture).
Follow my logic. Oxide is O-2, which means it has two more electrons than protons. If only the electrostatic force was active, this would not be stable due to the charge imbalance. The reason this change imbalance is stable is because moving elections within orbital addition; octet rule, have a magnetic component to balance this out.
A moving electron creates a magnetic field. The magnetic fields of moving electrons, adding via the orbitals, binds the extra two electrons of O-2 together. This enhanced magnetic aspect of the EM force can overcome the electrostatic repulsion, within the same EM force. We do not measure a substantial magnetic field from O-2 since the octet cancels the field via vector addition. This stability holds the extra electrons.
It is not clear how this magnetic affect, needed to stabilize O-2, multiples into the magnetic field. However, a wild card may be a metallic water phase boundary. Metals, including metallic water are excellent conductors. Metallic water may conduct both electrons and protons. This will lower the magnetic ratio of the O-2 matrix, for an external amplification. Surface O2 feels the push and becomes ripe for adding electrons.
Follow my logic.
You don't have any.
You are trying to rewrite the whole of chemistry- without the benefit of understanding it.
It is not clear how this magnetic affect, needed to stabilize O-2, multiples into the magnetic field
The reason that it is "unclear" is that it is tosh you have made up.
Are you saying the CD players system will not move int the direction of the angular acceleration?
Unless something changes the angular momentum, there is no angular acceleration.
The only thing that can change the angular momentum is a torque.
In the absence of pre-existing motion in that direction, or a net force accelerating it in that direction, of course the system will not move in that direction. Such would be a violation of Newton's first law.