What is centripetal force?

Why doesn't a spinning ball fly away from your hand?

Imagine swinging a ball on a string in a circle. The string keeps pulling the ball toward your hand.

That pull toward the center is called centripetal force. The word means center seeking. Without this pull, the ball would not turn at all. It would just go straight. Newton said things move straight unless a force pushes or pulls them. Turning needs a force.

• Centripetal = center seeking
• Turning needs a force

Here is the key. The force always points to the center, and the ball moves sideways to it. The same idea works for a car turning a corner. Friction from the road pulls the car toward the middle of the curve.

In space, gravity does the job. The Earth pulls the Moon, so the Moon keeps circling us.

So centripetal force is not a new kind of force. It is whatever force pulls toward the center.

A bigger force, a faster ball, or a smaller circle all change how hard the pull must be. Here is an example. If you spin the ball twice as fast, the string must pull four times harder.

• Twice as fast = four times pull

That is why a fast spin can snap a string. The pull needed gets too big.

Time for a quick check. If the string breaks, which way does the ball fly? Centripetal force is the inward pull toward the center that keeps anything moving in a circle.