Newton's Laws of Motion | A-Level Physics | Doodle Science

A Level Physics

Doodle Science teaches you high school and College physics in a less boring way in almost no time!

Script:
Newton’s first law of motion states that a body will remain at rest or continue to move with constant velocity unless acted on by a resultant force. For example, if you threw a ball in space, it would continue to move with a constant velocity until it collided with something.

Newton’s second law states that the resultant force on an object is proportional to the rate of change of momentum and acts in the same direction as the change of momentum. This gives us the formula F = change in momentum/ change in time. For objects of constant mass this formula can be rearranged like so to give the much more familiar F=ma.

Momentum is the quantity of motion of a moving body. It is defined as the product of mass x velocity. Since velocity is a vector quantity, meaning it has both magnitude and direction, momentum must be a vector quantity too.

For example, a lorry of mass 10000kg is initially travelling at 20m/s. The lorry driver applies the brakes and slows down to 5m/s, which takes 5 seconds. From this we can work out the initial momentum of the lorry to be 200,000kgm/s. The final momentum to be 50,000kgm/s and the average braking force can be calculated using Newton’s second law, which turns out to be -30,000N. The negative sign shows that the force acts in the opposite direction to the direction of motion because it is decelerating the lorry.

Newton’s third law states that when one body exerts a force on a second body, the second body exerts a force on the first body, which is equal in magnitude but opposite in direction. This is the reason why your hand hurts when you punch a wall or why there is no skill in a game of conkers. The force one conker exerts on another will experience the same force exerted on it; so the skill lies only in picking the strongest conker.

Impulse is the force x the time for which the force acts. Since force is a vector quantity, impulse must also be a vector. By rearranging the formula for newton’s second law you can see that Impulse also equals the change in momentum and is therefore measured in kgm/s or Ns. You can plot a force-time graph to show how the force varies with time; the area under this graph is the impulse of the force. For example, this curve of the force acting on a football being kicked can be approximated to a triangle; this makes it a lot easier to work out the area, which is 10Ns. If the ball had a mass of 0.6kg and was kicked from rest, then since Impulse = change in momentum, you can work out the speed of the ball when it leaves your foot to be 16.7m/s.

References:
1. CGP AS & A2 Physics for OCR A, ISBN: 9781847624192

[aentropy]

I love crash course, but your videos are straightforward which makes it better.

[AnjaliMishra-bfnu]

please upload more Alevel related videos. these are simply amazing! thanks a lot.🙏

[brashid]

At 2:53 y did he multiply it by 10 inverse 3

[-ruth-]

Wow, these videos are so helpful and amazing! Thank you, and great job

[kellygirls]

THANK YOU SO MUCH OH MY GOSH YOU JUST SAVED 1 PUND OF TEARS 😭 THANK

[dylanparker]

your videos are really good - great job!

[jeetanand]

how momentum got defined the way it is defined. Laws of motion is understandable completely independent of mass. Even acceleration is easy to understand as rate of change of velocity .

But it is quite puzzing to know the necessity of force concept.Why force concept was even needed. What event led people to take mass into account?

[Manish_Rai]

Thx exam coming soon learned more here then in class

[akondikiranmai]

Plzzz sir... try to make video in maths too they are really very helpful

[lakshman.n]

sir demonstrate Newton third when two persons are pushing each other. Understand the question completely, my question is not when A pushing and B is just standing simply, my question is when both are pushing each other. Explain by drawing individual FREE BODY DIAGRAM sir . pls

[burakb]

Great videos, but if you make longer videos I would enjoy more.

[Kurzux]

What am i doing here. I'm only doing gcse lmao