2.4 Analysing Momentum

Chapter 2 Force and Motion

You can catch a fast moving ping-pong ball easily with your bare hand.A softball keeper must wear a glove to catch a hard and fast moving softball.Why is a slow moving softball much easier to catch?

If a loaded lorry and a car are moving at the same speed, it is more difficult for the lorry to stop.

This is because the lorry possesses a physical quantity, momentum, more than the car.

All moving objects possess momentum.

Activity 2.2To compare the effects of stopping two objects in motion

The steel ball released from a greater height strikes the plasticine at a greater velocity.

Although both balls have the same diameter, the steel ball has greater mass than the wooden ball.

Observation: Two balls at the same

mass moving at different velocities

The depth and size of cavity caused by the steel ball released from a greater height is deeper and larger

Two balls of different masses moving at the same velocity

The depth and size of cavity formed by the steel ball is deeper and larger.

Conclusion

The moving balls produce an effect on the plasticine which is to stop the motion.

The greater the mass or velocity of the moving object is, the greater is the effect (the depth and size of cavity), the greater is the momentum.

Linear MomentumThe linear momentum is defined as the

product of mass and velocity.Momentum = Mass × velocityp = mvunit: kg ms-1

Vector quantity

A billiard ball A of mass 0.5 kg is moving from left to right with a velocity of 2 m s-1 while another billiard ball B of equal mass is moving from right to left with the same speed. Calculate the momentum for both balls.

Conservation of Momentum