Why do balls bounce?

The longer answer

A falling ball is full of movement. When it lands, the ground stops it, and all that movement goes into squashing the ball. A springy ball pushes back out right away and launches itself up again.

Not all of the movement comes back. Some of it turns into the thud you hear and a tiny bit of warmth in the ball and the ground. That is why a ball dropped from your hand never bounces back above your hand.

Springier balls lose less each time, so they bounce higher and longer. A soft beanbag hardly springs back at all, which is why it just lands with a flop.

Three things to know

• A tennis ball is filled with air to help it spring back. When it squashes, the air inside pushes back. An old ball with a leak has less push, so it bounces low and flat.
• A ball on the Moon would bounce much higher. The Moon pulls things down much more weakly, so the same ball would rise far higher, though it would still settle in the end.
• A cold ball bounces lower than a warm one. Cold rubber is stiff, so it squashes less and gives back less. Warm rubber is springier.

Try it at home: a bounce test

1. Hold a ball at the height of your shoulder and let it drop. Do not throw it.
2. Watch how high the first bounce comes back. Does it reach your hand?
3. Count how many bounces it makes before it stops.
4. Try different balls: a tennis ball, a bouncy ball, a soccer ball. Which bounces highest?

Put one ball in the fridge and one in a warm spot, then drop both from the same height and compare.