S2.10 The centripetal force
[A] About the force
- A body of mass m moving at uniform speed v in a circle of radius r exhibits an acceleration of magnitude v2/r towards the centre (Key Point 1.8).
- By Newton’s 2nd law this acceleration must be attributed to a force
FC where:
- the magnitude of FC is FC=mv2/r
- the direction is towards the centre
- The generic name for this force is centripetal.
Examples
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Examples
mass whirled on string centripetal force: tension |
car on bend in road centripetal force: friction |
planet in circular orbit centripetal force: gravity |

Tip!
Students often go wrong here. You need to be very clear that a centripetal force is, in fact, always ‘provided’ by some specifc (‘real’) force (tension, friction, gravity, electrostatic...). Calling it ‘centripetal’ is just saying that, in the context, the force serves to provide the centripetal acceleration. The trap for the unwary is thinking that (eg in our last example) the body experiences a ‘gravitational force’ and some (other) centripetal force.[B] Example problem:
See S2.11
Learning Resources
![]() | HRW Chapter 6.5 |
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