<p>In the book <em><a href="https://books.google.de/books/about/Horizons_Exploring_the_Universe.html?id=QO25DQAAQBAJ&amp;redir_esc=y" rel="nofollow noreferrer">Horizons: Exploring the Universe</a></em> (2018) by M.Seeds and D.Backman, chapter 9, page 170-171, it states that:</p>
<blockquote>
<p>At least four factors resist the
compression of an interstellar gas cloud, and those factors must
be overcome by gravity before star formation can begin. [...]</p>
<p>Third, everything in the Universe rotates. As a gas cloud begins
to contract, it spins more and more rapidly, just as ice-skaters
spin faster as they pull in their arms. This rotation can become
so rapid that it resists further contraction of the cloud.</p>
</blockquote>
<p>Which bring the question of why does rotation prevent the further contraction of the cloud? Doesn't the rotation create a centripetal force that pointed inside, thus make the matters become denser, therefore it shouldn't be a reason that interstellar have to overcome in order to form stars?</p>

CC BY-SA 4.0
2021-04-16T08:18:37.503Z
Gravity has to supply that centripetal force. Also see https://xkcd.com/123/ ;)
PM 2Ring
CC BY-SA 4.0
2021-04-16T11:19:53.487Z
@PM2Ring So the spinning created a centrifugal force, which is like Shot put, is that correct? And then I was wondering, why aren't we flying to the sky, due to the spinning of the earth? Is it due to gravity is greater?
Jack the Ranger
CC BY-SA 4.0
2021-04-16T13:50:40.277Z
Yes, the centripetal force required to keep an object spinning with the Earth is very small. Its maximum is at the equator, where it has a value around 0.3% of the gravitational force. https://en.wikipedia.org/wiki/Centrifugal_force is pretty good, but also see https://physics.stackexchange.com/q/109500/123208
PM 2Ring
<star><star-formation><interstellar-medium>
Why does rotation prevent the further contraction of the cloud?
Jack the Ranger
# Why does rotation prevent the further contraction of the cloud?

(Asked by: username_0 on 2021-04-16)

In the book *[Horizons: Exploring the Universe](https://books.google.de/books/about/Horizons_Exploring_the_Universe.html?id=QO25DQAAQBAJ&redir_esc=y)* (2018) by M.Seeds and D.Backman, chapter 9, page 170-171, it states that:

> At least four factors resist the
> compression of an interstellar gas cloud, and those factors must
> be overcome by gravity before star formation can begin. [...]
>
> Third, everything in the Universe rotates. As a gas cloud begins
> to contract, it spins more and more rapidly, just as ice-skaters
> spin faster as they pull in their arms. This rotation can become
> so rapid that it resists further contraction of the cloud.

Which bring the question of why does rotation prevent the further contraction of the cloud? Doesn't the rotation create a centripetal force that pointed inside, thus make the matters become denser, therefore it shouldn't be a reason that interstellar have to overcome in order to form stars?

**Tags:** star, star-formation, interstellar-medium
> **Comments:**
> **username_1**: Gravity has to supply that centripetal force. Also see https://xkcd.com/123/ ;)  
> **username_0**: @PM2Ring So the spinning created a centrifugal force, which is like Shot put, is that correct? And then I was wondering, why aren't we flying to the sky, due to the spinning of the earth? Is it due to gravity is greater?  
> **username_1**: Yes, the centripetal force required to keep an object spinning with the Earth is very small. Its maximum is at the equator, where it has a value around 0.3% of the gravitational force. https://en.wikipedia.org/wiki/Centrifugal_force is pretty good, but also see https://physics.stackexchange.com/q/109500/123208  

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