# Homework Help: A friction conundrum

1. Nov 29, 2004

### Ravnus9

You have a wheel that is rolling without slipping on the ground, it is being subjected to no outside tourque or pulling force..... which way is friction acting and why.
I thought that this would be easy but it turns out to be tricky, if the wheel isn't slipping the velocity equals omega times the radius, and you solve and get a direction of the friction.... using work kenetic energy theorem.... but that direction always seems to be in the opposite direction itd have to be according to the angular velocity, can anyone help?

2. Nov 29, 2004

### e(ho0n3

Friction always (I'm not 100% sure on this though) opposes motion. If a wheel is rolling right, the part of the wheel making contact with the ground is moving left so the friction vector is pointing to the right.

3. Nov 29, 2004

### Ravnus9

Ok yeah but then the angular acceleration is to the left because the wheel is slowing down..... which means that friction should be is the opposite direction right? but angular velcocity should agree with the direction of friction.... which means you have two frictions opposing eachother

Last edited: Nov 29, 2004
4. Nov 29, 2004

### e(ho0n3

Why are you saying that the angular velocity should agree with the direction of friction? The direction of the angular velocity vector for a wheel is parallel to the axis of rotation. Right?

5. Nov 29, 2004

### Ravnus9

yeah i don't know..... you are correct, i think it was one of those things where i was making it harder in my head than it has to be, thanks for your help :)