This experiment is great fun, and can be done out of doors. You can use almost any balls and a selection of different surfaces on which to bounce them.
Encourage students to think about different types of balls, and the different games they are used for.
Ask them to design an experiment to test the bounciness of a selection of different balls. How will they ensure that their test is fair?
There are several ways the children might devise for this experiment, but most of them will depend on bouncing the ball from a set height and noting either how far it bounces back or how many times it bounces.
To measure the height of the bounce they could make a graded scale as a backdrop to the experiment, or bounce the ball in a transparent graded tube.
They may wish to try bouncing the balls on different surfaces. When a ball hits the ground, its kinetic energy is converted to elastic potential energy as the ball is deformed. As the ball returns to its original shape, this energy is released and converted back to kinetic energy.
These transformations cause energy to be lost, and the ball does not bounce back to the height from which it was dropped.
For a dramatic conclusion to your experiments, take a large ball and a smaller, lighter one. Place the smaller ball on top of the large one and drop them on the ground. Ask students to predict what might happen to the two balls.
They should find that the small ball is sent high into the air - far higher than the height from which it is dropped. As the balls fall they become separated. The larger ball bounces on the ground and starts travelling upwards while the smaller ball is still progressing downwards.
When they collide, a lot of energy is transferred to the smaller ball, which bounces much higher than expected.