Physics

Why a small ball on a big ball shoots up nine times higher: the two-step bounce

A small green ball resting on a larger grey ball, with an arrow showing it rising far above the dashed drop-height line
30seconds
The 30-second version

Drop a tennis ball on top of a basketball and the small ball can fly far above the height it fell from. Nothing is cheating: it is a two-step bounce. The floor flips the big ball upward while the small one is still falling, and a bouncy collision between the two sends the light ball away three times faster than it arrived.

Speed three times higher means nine times the height. Stack a third ball on top and the ideal limit is seven times the speed and forty-nine times the height. Build the stack, change the mass ratio and bounciness, and watch the energy trade.

Deep dive · 4 min
Deep dive · 4 min

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