# Eli5: How does centripetal force work?

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Eli5: How does centripetal force work?

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Centripetal force is just a force that is pulling something toward the center of a circle. Depending on what you’re talking about, that force can be gravity (in the case of planets in orbit) or something like the tension in a rope (if you’re swinging something around on a rope). In either case, there is a force pulling toward the center of the circle, and centripetal force is just the word that describes that concept.

Centripetal force is a force that pushes your inwards/towards the center of something.

So say you go on the carnival ride where you stand against the wall and then the ride spins really fast and you feel stuck against the wall.

When that’s happening, your body’s momentum doesn’t want to keep spinning, it wants to just fling out of the ride, but the wall is keeping you in, exerting a force on your body.

That force is directed towards the center of the ride, that’s the centripetal force, the wall keeping you in

If you’ve learned it, remember Newton’s First Law – “An object in motion stays in motion, unless acted upon by an outside force”.

That boils down to objects move in straight lines until they pushed or stopped.

The straight line part is the key here – objects don’t spin in circles naturally, they want to move in a straight line. In order to make an object spin in a circle it needs a constant “come back here!” force to counter act the “flying away” desire from Newton’s First Law. If the come-back-here perfectly cancels out the flying-away-desire, the object *doesn’t* fly away, and you essentially get an “orbit”, a perfect spinning motion around a central point.

So if you spin a ball around on a string, the ball constantly wants to fly off, if the string snaps or if you let go it’ll do just that. The string is the source the constant “Come back here force” that keeps the ball spinning in a circle.

How Does it Work – The strength of the force required to keep the ball from flying off can be calculated and measured. The equation has 3 factors –

1. the mass of the object (sort of like the weight of the ball in layman’s terms, but that’s not a perfect definition)
2. The length of the “string”
3. The speed the object moves.

In order words, the heavier the object, the faster it moves, and the shorter the length, the stronger the centripetal force.

“Centripetal force” just means any force that happens to be causing an object to move along a more-or-less circular path by pulling that object toward the center of the circle. It’s not a *type* of force, it’s just a *direction* in which any type of force can pull.

In the case of the Earth’s orbit around the Sun, the centripetal force acting on the Earth is the Sun’s gravity. If you put a bucket on a rope and then spin it around in a circle, the centripetal force acting on the bucket is the tension from the rope that’s pulling on it. If you put water in the bucket, the centripetal force acting on the water is the force being applied to it by the bottom of the bucket. etc.

These different forces don’t really have much in common with one another than the direction in which they are pulling. If you want to understand one of them, you should ask about it individually (e.g. “Eli5: How does gravitational force work?”).