# Homework Help: Definition of centripetal force

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1. Sep 18, 2016

### MBBphys

1. The problem statement, all variables and given/known data
Hi,
If an object is undergoing uniform circular motion, then the net force is acting perpendicular to the instantaneous velocity, and this is called the centripetal force.

However, if the object is moving in a circle but the magnitude of its instantaneous velocity is not constant, then there must be a net force parallel to the instantaneous velocity, in addition to a net force perpendicular to the instantaneous velocity which makes it go in a circle.
My question is: in the second scenario, is the centripetal force the net force perpendicular to the instantaneous velocity, or is it the resultant force of adding the parallel and perpendicular "net forces", and so the centripetal force would not be wholly perpendicular to the instantaneous velocity?
Which is it?
In essence, is the centripetal force always perpendicular to the instantaneous velocity, or if the object is undergoing non-uniform circular motion, would the centripetal force not be wholly perpendicular to the instantaneous velocity?

2. Relevant equations

F=(mv2/r)
3. The attempt at a solution
N/A

2. Sep 18, 2016

### PeroK

Centripetal means "towards the centre" so it's only that component.

3. Sep 18, 2016

### MBBphys

Thank you!

4. Sep 18, 2016

### haruspex

It might also help to bear in mind that the centripetal force is not an applied force; it is the force that would be required to keep the object at a constant distance from a given axis (even if it is not staying at a constant distance).