# Angular Momentum and Forces

1. Oct 20, 2005

### No Name Required

I have this question im having trouble with.
A massless rectangular parallelepiped with sides $$a, a$$ and $$\sqrt{a}$$ has equal masses attached to its vertices. It is rotating around its major diagonal with a constant velocity $$\Omega$$. Find the forces acting on the two vertices on the axis of rotation.
I'm confused by the fact that im trying to find a force even though its rotating with a constant angular velocity. Would this force not create a torque hence changing the angular velocity.
A hint or bit of explanation to get me going would be very helpful please

2. Oct 20, 2005

### Fermat

Can you say what forces are acting on any of the masses ?

3. Oct 20, 2005

### No Name Required

Centripetal forces? But if that is the case, why does it say find the force acting on the two VERTICES. That confuses me... Or is vertices correct? If so then the problem is basicall one of finding the distance of each particle from axis of rotation yea?

4. Oct 20, 2005

### Fermat

Yes. It's centripetal forces that are acting on the masses that are not on the axis of rotation.

I'm asssuming that the parallelepiped is a wire-frame composed of massless wires where the centripetal force on each rotating mass is resolved along the three wires attached to each vertex/"rotating mass."
These resolved forces will then "meet up" at one of the non-rotating masses.

In addition, you will need to find that distance you mentioned.

This parallelepiped. It is an orthogaonal one, yes ? i.e. a cuboid.

Last edited: Oct 20, 2005