What is centripetal force and where might you find an example?

When there is no force acting on a moving object, it just

keeps on moving in a straight line. It takes force to pull

the object away from a straight line.

Whenever anything moves in a curve, there's a force on it,

pulling it toward the center of the curve. That's called a

"centripetal" force.

I think the easiest example to understand is spinning a stone

or a yo-yo around your head on the end of a string. The object

is moving in a circle, and the force that's keeping it on the circle

is the tension in the string. If the string suddenly breaks, then

that force suddenly goes away, and the object suddenly stops

moving in a circle ... it takes off in a straight line, in the direction

it was moving on the circle at the instant when the string broke

and the centripetal force stopped.

But examples are everywhere ... wherever you see something

that's moving in a curve and not in a straight line.

A fun one to talk about is things in orbit ... the Earth around the

Sun, the Moon around the Earth, Jupiter's moons around Jupiter,

and TV satellites and the International Space Station around the

Earth. An orbiting object might not exactly move in a circle, but it

moves in a path that's always curved, so there's a centripetal force

acting on it all the time. Where does that force come from?

Where?

Why, it's the force of gravity between the two objects, always

trying to pull them together!