If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

## High school physics

### Course: High school physics>Unit 4

Lesson 3: Centripetal forces

# Centripetal forces review

Review the key concepts, equations, and skills for centripetal forces, including that centripetal force is the net force in the radial direction.

## Key terms

Term (symbol)Meaning
Centripetal force (F, start subscript, c, end subscript)Net force acting in the direction towards the center of a circular path, causing centripetal acceleration. Direction is perpendicular to the object’s linear velocity. Also sometimes called radial force.

## Equations

EquationSymbol breakdownMeaning in words
\Sigma, F, start subscript, R, end subscript, equals, m, a, start subscript, c, end subscripta, start subscript, c, end subscript is centripetal acceleration, m is mass, and \Sigma, F, start subscript, R, end subscript is net force in radial direction (or centripetal force)Net radial force is directly proportional to the product of the object's mass and centripetal acceleration.

## Common mistakes and misconceptions

• Centripetal force is not a type of force. Centripetal force is a net force is the sum of the force vectors pointing in the radial direction. It could be the component of a force, the sum of multiple forces, or the difference of two radial vectors.
• People mistakenly think objects moving in a circular path are acted upon by an outwards pointing force. When you turn in a circle, it may feel like something is pulling you outwards from the turn, but that’s your inertia trying to resist a change in motion.

For deeper explanations of centripetal force, see our video introducing centripetal force using flaming test balls.
To check your understanding and work toward mastering these concepts, check out the exercise on centripetal forces.

## Want to join the conversation?

• ΣF r is net force in radial direction, then it could be the difference of two radial vectors that are pointing in opposite directions? (such as the difference between force of tension and gravitational force) Also, I noticed how the object attached to a string wouldn't actually rotate unless you exert a force that could spin up the string, so it there a notion to explain this? thank you!