Centripetal Force

When you swing a ball on a string in a circle, the string pulls the ball inward. This inward pull is called centripetal force. Without it, the ball would fly off in a straight line. Centripetal force is what keeps anything moving in a circle, from a car turning a corner to the Moon orbiting Earth.

How It Works

Objects naturally move in straight lines. To make something move in a circle, you need a force pulling it toward the center. When you swing a ball on a string, the string provides centripetal force. For a car turning a corner, friction between the tires and the road provides the force. For the Moon, gravity from Earth provides the centripetal force.

Centripetal Force in Action

You feel centripetal force on amusement park rides. On a merry-go-round, you feel pushed outward, but the ride is actually pulling you inward. On a roller coaster loop, centripetal force keeps you in your seat even when you are upside down. Water stays in a bucket if you swing it fast enough overhead.

Fun Facts

• The International Space Station stays in orbit because Earth's gravity provides centripetal force.
• Race car tracks are often tilted on curves to help provide centripetal force for the cars.
• A washing machine's spin cycle uses centripetal force to squeeze water out of clothes.

Did You Know?

If you spin a bucket of water over your head fast enough, the water will not fall out. The centripetal force pushing the water to the bottom of the bucket is stronger than gravity trying to pull it down!