For second law forget the change to leave it out and end up with half Newton’s don’t phrase ‘rate of’ – it’s easy marks. To Show that F = ma is a special case of Second Law Newton’s From Newton II: Force is proportional to the rate of change of momentum F = k (ma) F = ma Note: k = 1 because of how we define the newton: (a force of 1 N gives a mass of 1 kg an acceleration of 1 m s-2)* Impulse Change in momentum is also known as ‘impulse’ Impulse = mv mu – at the derivation above: Let’s look again but k = 1 as above Ft = (mv mu)* – This relationship is important when trying to improve performance in ball games; when you want to change the momentum of a ball you need to either increase the force applied (not always easy to do) or else increase the time for which the force is applied (this can come with practice. This formula was required to answer a question in 2008 and 2014. Why use the term impulse? Because the force associated with this change in momentum (due to a collision of some sort) is exerted over a very short period of time, and Newton wanted to distinguish this from a longer-acting force which causes an object to accelerate over a long period of time, for which he was more likely to use F = ma The relationship between mass and weight The weight of an object is a measure of the force of the gravitational force acting on it. Earth’s Because weight is a force, it follows that the unit of weight is also the newton. Mathematically weight = mass × gravitational field strength (where is a measure of the strength of the gravitational field at that point). gravitational field strength Earth’s
For Newton’s second law don’t forget the phrase ‘rate of’ change – it’s easy to leave it out and end up with half marks. To Show that F = ma is a special case of Newton’s Second Law From Newton II: Force is proportional to the rate of change of momentum F = k (ma) F = ma Note: k = 1 because of how we define the newton: (a force of 1 N gives a mass of 1 kg an acceleration of 1 m s-2)* Impulse Change in momentum is also known as ‘impulse’ Impulse = mv – mu Let’s look again at the derivation above: but k = 1 as above Ft = (mv – mu)* This relationship is important when trying to improve performance in ball games; when you want to change the momentum of a ball you need to either increase the force applied (not always easy to do) or else increase the time for which the force is applied (this can come with practice. This formula was required to answer a question in 2008 and 2014. Why use the term impulse? Because the force associated with this change in momentum (due to a collision of some sort) is exerted over a very short period of time, and Newton wanted to distinguish this from a longer-acting force which causes an object to accelerate over a long period of time, for which he was more likely to use F = ma The relationship between mass and weight The weight of an object is a measure of the force of the Earth’s gravitational force acting on it. Because weight is a force, it follows that the unit of weight is also the newton. Mathematically weight = mass × gravitational field strength (where gravitational field strength is a measure of the strength of the Earth’s gravitational field at that point).
9.%20Force,%20Mass%20and%20Momentum.docx