# Question about Centripetal Force

1. Jun 29, 2012

### theintarnets

So in a physics experiment, we used a motor to rotate a mass connected to a spring by a string and pulley until it's radius of rotation increased to a certain point. My question is, why did rotating it faster increase the radius of rotation? Centripetal force pulls objects inward, but the mass looked like it was being pulled outward the faster it rotated. I have a feeling that it has to do with the magnitude and direction of velocity as it increased, but I'm not sure. When the mass was being pulled outward, it also pulled on the string and caused the spring to stretch, but I don't understand why that happened either. Can someone explain this to me please?

The picture I have shows the setup before removing the hanging mass and pulley on the left and before rotating. When you remove the hanging weights, the spring pulls the suspended mass towards itself, I guess because the tension in the string is reduced and can no longer counter the tension in the spring.

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2. Jun 29, 2012

### karlzr

The centrifugal force should not be considered as some usual force like electrostatic force or gravity, rather, it refers to the composition of some forces.
When it rotates faster, the velocity increases. In this case, we need to increase the centrifugal force to stop it from flying away. Actually,the radial velocity tends to pull the string outwards until the tension is strong enough to keep it in a circular orbit.

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