The Stacked-Ball Trick

A tennis ball launched by a basketball

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• A light ball on a heavy one rebounds at up to 3v, rising up to 9 times as high.
• Elastic rebound speed: $v' = \frac{3M - m}{M + m}v$.
• The energy comes from the bottom ball, which barely bounces.

Steps

1. Drop them together
2. Three times as fast
3. Mass matters
4. Where does the energy come from?
5. From one metre
6. Three in a stack