Why does a soft ball squash on landing?

A soft ball drops onto the floor and goes plop. For a little moment, its round shape looks flatter, almost like a tiny pancake. Why does a soft ball squash on landing?

Let's follow a foam ball, made of soft, spongy stuff you can squeeze. Squash means to press something into a flatter shape. Your hands can squash this ball because its soft foam changes shape when you push on it.

When you let go of the ball, gravity pulls it down toward the ground. Gravity is the pull that brings things toward Earth. Your hands no longer hold the ball up, so it starts to fall.

As the ball falls, gravity keeps pulling it down. The ball gathers speed on its short trip to the floor. Now the whole ball is moving downward, from its rounded top to its rounded bottom.

The bottom of the ball touches the floor first. The firm floor pushes up against the ball and stops its bottom from moving farther down. But the rest of the ball still has some downward movement.

Can you guess what happens when the bottom stops but the top keeps moving down for a moment? The top moves closer to the bottom. That makes the ball shorter and flatter: a squash!

The foam can squash because it bends and squeezes together under a push. Tiny spaces inside the foam get smaller as the ball flattens. A hard ball changes shape much less, so you usually cannot see its squash.

That little squash helps slow the falling ball over a short moment, instead of stopping every part at once. The ball may spread a little wider while it gets shorter. It is still the same ball, just with a different shape.

After the squash, the foam springs back toward its round shape. As it springs back, the ball might push against the floor and bounce a little. Some foam balls bounce only a little, then settle down.

Gravity pulls the ball down, the floor pushes up, and its soft foam squashes, then springs round again. A soft ball squashes on landing because the floor pushes on it while it is moving down, and its foam can change shape.

Now you know the little story inside a soft ball's plop, ready for the next time you play.