# What is this formula for?/What is it called?

1. Jun 1, 2014

### Latsabb

I have a formula, S*r=1/2*m*r^2*a/r

The problem is that it is unlabeled, and I am not 100% sure what this is supposed to be for. As near as I can tell, it is for something with inertia, and involving tension on a wire coiled around a cylinder. Is this correct? Does anyone know if this is simply a derived equation for a specific problem, or a general use equation? Thank you.

2. Jun 1, 2014

### Staff: Mentor

r cancels out.

3. Jun 1, 2014

### Latsabb

I know, but this is a formula that was supplied for a problem, and I am attempting to figure out what everything is. I think I have it narrowed down that S*r is supposed to be torque, and everything else on the right is supposed to represent inertia times the angular momentum, but I am not sure.

4. Jun 4, 2014

### cosmosmike

You are on the right track, I see it as torque = (moment of inertia) x angular acceleration.
S is force, r is radius, 1/2 m rsq is moment of inertia, and a is linear acceleration, a/r is angular acceleration.