# Centripetal acceleration

The inward acceleration that keeps something on a circle, a = v squared / r. It changes direction, not speed.

Physics (university) · Part 04: Rotation and gravity · Card 2 of 11 · Last updated 2026-10-19

## Analogy

The pull of the string when you swing a ball round your head.

## Example

**Car on a bend**

a = v^2 / r
a = 225 / 50
a = 4.5 m/s^2

## In practice

A car at 15 m/s on a 50 m radius bend accelerates inward at 4.5 m/s squared.

## Practice

### Flashcards

- **What is the formula for centripetal acceleration?** a = v^2 / r, pointing toward the centre.

## Questions people ask

### Is centripetal acceleration different from centrifugal force?

Centripetal means centre-seeking and describes the real inward acceleration. Centrifugal force is an apparent outward push felt inside a rotating frame, like being pressed against a car door in a turn. In an outside, non-rotating view, no outward force acts on you.

### Does constant speed on a circle mean zero acceleration?

No. Velocity is a vector, and its direction keeps changing on a circle. A change in direction is an acceleration even if speed is steady. That acceleration points toward the centre and has a size of v squared over r.

## Related concepts

- [Angular velocity](https://studyvisually.com/learn/science/physics-university/physics-university-part-4/physics-university-part-4-concept-1)
- [Centripetal force](https://studyvisually.com/learn/science/physics-university/physics-university-part-4/physics-university-part-4-concept-3)
- [Torque](https://studyvisually.com/learn/science/physics-university/physics-university-part-4/physics-university-part-4-concept-4)
- [Moment of inertia](https://studyvisually.com/learn/science/physics-university/physics-university-part-4/physics-university-part-4-concept-5)

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