# Quick question about rolling without slipping

1. Dec 9, 2012

### izelkay

If a ball is rolling without slipping up an incline, would the static frictional force also be up the incline?

2. Dec 9, 2012

### Staff: Mentor

Something has to slow the rotation rate of the ball as its increase in height slows its linear speed (KE traded for PE), otherwise it would start slipping. What direction must the force act (think torque) in order to slow the rotation?

3. Dec 9, 2012

### CWatters

More info required (eg do you mean rolling or being pulled up the slope?).

For it to roll up a slope at a constant speed there must be other forces acting on it. I believe the other force will effect the direction friction takes.

If you mean rolling and slowing down see gneill's reply.

4. Dec 9, 2012

### izelkay

Oh, ok. The force would need to be in the direction the ball's moving if the ball's moving uphill, but in the opposite direction of motion of the ball if the ball's moving downhill?

5. Dec 9, 2012

### rcgldr

For most rolling on incline problems, there are two forces acting on a ball (or cylinder), gravity and friction force (the force the incline exerts on the ball). The friction force from the incline will always oppose gravity, and it doesn't matter if the ball is initially rolling uphill or downhill (or the moment between when the ball is at rest).

6. Dec 9, 2012

### izelkay

Thank you, that's easier to remember.