Momentum Learning objectives Know Newtons third Law Know

Momentum

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

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)

Starter 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

a car hits a tree 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 Action Reaction force on car due to tree force on tree due to car

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 force on A due to B, spheres, A and B, are towards B near each other force on Sita due to Sita is standing on the gravitational attraction of ground Earth, downwards force on Earth due to the Earth orbits the Sun gravitational attraction of Sun, towards Sun Reza pushes against a wall force on B due to A, towards A force on Earth due to gravitational attraction of Sita, upwards force on Sun due to gravitational attraction of Earth, towards Earth force on wall due to Reza, force on Reza due to towards wall, towards Reza two north-seeking poles of a magnet, A and B, force on A due to B, away force on B due to A, are placed near each from B away from A other

Newton’s 3 rd 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. Newton 16421727

Newton’s 3 rd Law of Motion What will happen if I push this satellite away from me? 24/02/2021

Momentum Any object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula: P Momentum = Mass x Velocity (in kgms-1) (in kg) (in ms-1) What is the momentum of the following? 1) A 1 kg football travelling at 10 ms-1 2) A 1000 kg Ford Capri travelling at 30 ms-1 3) A 20 g pen being thrown across the room at 5 ms-1 4) A 70 kg bungi-jumper falling at 40 ms-1 M V

Task: 1. Calculate the momentum of a toy train of mass 1. 5 kg travelling at 0. 2 m/s due west. 2. 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? 3. 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 (250 000 kilograms) which is moving west at a speed of 20 m/s?

Answers 1. 2. 3. 4 5 a b 0. 3 kg m/s due west Van 720 kg m/s due north 720 kg m/s due east 3 kg m/s due north 5 × 106 kg m/s due west (or 5 million kg m/s due west)

Higher only – foundation do q 1 -5 page 186 -187 - old course Newton’s 2 nd 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… Force = Change in momentum (kg m/s) (in N) Time (in s) F = mv – mu t Also called “impulse” For example, David Beckham takes a free kick by kicking a stationary football with a force of 40 N. If the ball has a mass of 0. 5 kg and his foot is in contact with the ball for 0. 1 s calculate: 1) The change in momentum of the ball (its impulse), 24/02/2021 2) The speed the ball moves away with

Answers 1. 4 kg m/s 2. 8 m/s

Example questions 1) Ben likes playing golf. He strikes a golf ball with a force of 80 N. If the ball has a mass of 200 g and the club is in contact with it for 0. 2 s calculate a) the change in momentum of the golf ball, b) its speed. a) 16 kg m/s b) 80 m/s 2) Nick thinks it’s funny to hit tennis balls at Tom. He strikes a serve with a force of 30 N. If the ball has a mass of 250 g and the racket is in contact with it for 0. 15 s calculate a) the ball’s change in momentum and b) its speed. a) 4. 5 kg m/s b) 18 m/s 3) Dan takes a dropkick by kicking a 0. 4 kg rugby ball away at 10 m/s. If his foot was in contact with the ball for 0. 1 seconds calculate the force he applied to the ball. 40 N 4) Simon strikes a 200 g golf ball away at 50 m/s. If he applied a force of 50 N calculate how long his club was in contact with the ball for. 0. 2 s

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

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)

Plenary • Matching pairs (technicians notes P 5 d 1 – old course)