Energy Transfer

Gravitational Potential Energy to Kinetic Energy - Bouncing Ball.

What are the Energy Changes when a Ball Bounces?

1. A falling ball transfers  GPE into KE.

2. When the ball hits the ground,
its shape changes and the KE is transferred into EPE.

3. As its shape is restored, the EPE changes back into KE.

4. As the bouncing ball gets higher in the air,
KE is transferred back into GPE.

Bouncing Ball

When the ball bounces back up into the air,
it does not go up to the same height at which it started.
With each of the above transfers of energy,
some of the energy is wasted as heat.

In stage 1 energy is lost because of air resistance.
When the ball collides with the air molecules,
both the ball and the air are made a little warmer.

In stage 2 energy is lost when the ball changes its shape
and the ball becomes warmer. Those of you
who play squash will be familiar with this. Stage 2 also
loses energy as sound when the ball hits the ground.

Stage 3 loses energy for the same reason as stage 2.

Stage 4 loses energy for the same reason as stage 1.

If the energy transfers were perfect and there were
no energy losses, the bouncing ball would always return
to the same height at which it started. It would carry on
bouncing like this forever. This would be called
"perpetual motion". Perpetual motion does not exist
because there are always energy losses during transfers.

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