### Filmed at 1000 fps, balls can be seen to compress as they are kicked.

WATCH VIDEO

Teachable Topics:

• Conservation of Energy
• Newton's Laws
• Sports

Theory:

The collision of a rugby ball and a foot is elastic, meaning the kinetic energy of the swinging foot will be conserved to some extent (but not fully). Before the kinetic energy of the foot translates into the kinetic energy of the ball, there is some compression, meaning the energy first translates to elastic potential energy. The reason why this energy exists in the compression of the ball has to do with a couple things.

Firstly, the balls used in this demo are filled with air. When the balls are kicked, the air is compressed. This compressed air pushes out on the ball, resulting in the motion of the ball and the return to it's regular state.

Also, there is the elasticity of the material the ball is made of. How elastic it is defines how well it returns to it's original shape after it is struck or put under stress. If it is more resistant to stress, then it will be more resistant to the compression and more of the energy will be conserved.

In the end, the less compression there is, the higher the amount of energy conserved will be. Think about bouncing a flat ball versus bouncing an inflated ball. There is more air in the inflated ball, which can't be compressed as much as the flat ball. With less compression, there is more energy being conserved.

Apparatus:

• various balls (i.e. soccer ball, rugby ball, basketball, etc.)
• high-speed camera
• foot

Procedure:

1. Kick the balls and observe the compression.