1. Momentum

2. Learning objectives Know Newton’s third Law
Know what is meant by momentum
Understand how to calculate momentum
Understand how to calculate change in momentum

3. Success criteria
Describe every day examples Newton’s third law. (Grade C)
Be able to calculate momentum
(Grade C)
Be able to calculate change in momentum (Grade A)

4. Starter Complete the following table Information:
Newton’s Third Law states that ‘to every action there is an equal but opposite reaction’
This means that when object A exerts a force on object B, then object B exerts an equal but opposite force on object A.
Complete the following table

5. Action
Reaction
a car hits a tree
force on car due to tree
force on tree due to car
Jan pushes Joe to the left
two oppositely charged spheres, A and B, are near each other
Sita is standing on the ground
the Earth orbits the Sun
Reza pushes against a wall
two north-seeking poles of a magnet, A and B, are placed near each other

6. Action
Reaction
a car hits a tree
force on car due to tree
force on tree due to car
Jan pushes Joe to the left
force on Joe due to Jan, to left
force on Jan due to Joe, to right
two oppositely charged spheres, A and B, are near each other
force on A due to B, towards B
force on B due to A, towards A
Sita is standing on the ground
force on Sita due to gravitational attraction of Earth, downwards
force on Earth due to gravitational attraction of Sita, upwards
the Earth orbits the Sun
force on Earth due to gravitational attraction of Sun, towards Sun
force on Sun due to gravitational attraction of Earth, towards Earth
Reza pushes against a wall
force on wall due to Reza, towards wall
force on Reza due to wall, towards Reza
two north-seeking poles of a magnet, A and B, are placed near each other
force on A due to B, away from B
force on B due to A, away from A

7. Newton’s 3rd Law of Motion
When body A exerts a force on body B, body B exerts an equal and opposite force on body A.
My third law says that if I push to the right I will move backwards as well.

8. Newton’s 3rd Law of Motion
What will happen if I push this satellite away from me?
19/09/2018

9. Momentum
Any object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula: P V M
Momentum = Mass x Velocity
(in kgms-1) (in kg) (in ms-1)
What is the momentum of the following?
A 1kg football travelling at 10ms-1
A 1000kg Ford Capri travelling at 30ms-1
A 20g pen being thrown across the room at 5ms-1
A 70kg bungi-jumper falling at 40ms-1

10. Task:
Calculate the momentum of a toy train of mass 1.5 kg travelling at 0.2 m/s due west.
Which has greater momentum – a car of mass 1000 kg travelling at 32 m/s or a van of mass 1800 kg travelling at 20 m/s?
a. What is the momentum of a boy of mass 60 kg running on a circular track at a steady speed of 12 m/s when he is running due north?
b. What is his momentum when he is travelling at the same speed due east?
4. Calculate the momentum of a bullet of mass 15 g travelling north at 200 m/s.
5. What is the momentum of an oil tanker of mass 250 tonnes ( kilograms) which is moving west at a speed of 20 m/s?

11. Answers 1. 0.3 kg m/s due west 2. Van a 720 kg m/s due north
b 720 kg m/s due east
4 3 kg m/s due north
5 5 × 106 kg m/s due west (or 5 million kg m/s due west)

12. Newton’s 2nd Law and Impulse
Higher only – foundation do q1-5 page old course
Newton’s 2nd Law and Impulse
Instead of F=ma Newton actually said that the force acting on an object is that object’s rate of change of momentum. In other words…
F = mv – mu t
Force = Change in momentum
Time
(in N)
(kg m/s)
(in s)
Also called “impulse”
For example, David Beckham takes a free kick by kicking a stationary football with a force of 40N. If the ball has a mass of 0.5kg and his foot is in contact with the ball for 0.1s calculate:
The change in momentum of the ball (its impulse),
The speed the ball moves away with
19/09/2018

13. Answers
4kg m/s
8 m/s

14. Example questions
Ben likes playing golf. He strikes a golf ball with a force of 80N. If the ball has a mass of 200g and the club is in contact with it for 0.2s calculate a) the change in momentum of the golf ball, b) its speed.
Nick thinks it’s funny to hit tennis balls at Tom. He strikes a serve with a force of 30N. If the ball has a mass of 250g and the racket is in contact with it for 0.15s calculate a) the ball’s change in momentum and b) its speed.
Dan takes a dropkick by kicking a 0.4kg rugby ball away at 10m/s. If his foot was in contact with the ball for 0.1 seconds calculate the force he applied to the ball.
Simon strikes a 200g golf ball away at 50m/s. If he applied a force of 50N calculate how long his club was in contact with the ball for.
a) 16 kg m/s b) 80m/s
a) 4.5 kg m/s b) 18m/s
40N
0.2s

15. Learning objectives Know Newton’s third Law
Know what is meant by momentum
Understand how to calculate momentum
Understand how to calculate change in momentum

16. Success criteria
Describe every day examples Newton’s third law. (Grade C)
Be able to calculate momentum
(Grade C)
Be able to calculate change in momentum (Grade A)

17. Plenary
Matching pairs (technicians notes P5d1 – old course)