A large heavy ball (like a basketball or a football)
A small light ball (like a tennis ball or rubber ball)
Make sure you conduct this experiment outside, in a park or a playground, where there is plenty of space. Choose a place where the ground is even.
Holding one hand under the basketball, carefully place the tennis ball over it with the help of the other hand.
Now, let go of both the balls at the same time and observe.
You will notice that when you drop both the balls at the same time, the tennis ball bounces off the basketball and flies higher.
How does it work?
This happens because of two kinds of energies – Potential and Kinetic. When you lift both the balls, they carry potential energy. The basketball being larger carries more potential energy which gets converted to kinetic energy when the balls hit the ground. Thus, the kinetic energy from the basketball is transferred to the smaller tennis ball, which makes it bounce higher.