# Rotational Dynamics

1. Apr 14, 2009

### zcdfhn

A uniform solid sphere of mass M and radius R rolls, without slipping, down a ramp that makes an angle θ with the horizontal.

The question ask for me to find the force of friction between the ramp and the sphere.

My attempt at the problem was to utilize the x-component of the force of gravity of the sphere and then the friction must be greater than that component.

I also have a feeling to use final energy - initial energy = nonconservative work, but I can't seem to find a velocity, whether its linear or angular, which is necessary to find the energy.

Note: when a ball rolls without slipping, v=R * $$\omega$$

2. Apr 15, 2009

### Beam me down

This is rolling without slipping. So at the point of contact between the ball and plane is the ball moving or stationary?

3. Apr 15, 2009

### Staff: Mentor

That's certainly true, but not enough. Hint: Apply Newton's 2nd law to both the translational and rotational motion and solve for the friction force.

You'll definitely need that to relate the translational and rotational quantities.