# Mechanics what force causes a ball rotate up an incline

1. Nov 14, 2009

### ronaldor9

When a ball rolls down an incline without slipping friction causes the ball to rotate CCW
When a ball with an initial velocity climbs up an incline friction is now in the opposite direction as in the previous case, the problem now is which force causes the ball to rotate CW. It cant be friction because that would cause it to rotate CCW but the ball is rolling CW, could the component of gravity be causing the torque to rotate the ball CW?

2. Nov 15, 2009

### willem2

Apparently you have a slope that goes upwards to the right, so the ball will go CCW if it rolls down, and CW if it rolls up.

If you launch the ball upslope and rightwards without it rotating, then the friction force on the bottom part of the ball points to the left, this will make the ball rotate more and more CW until the ball is rolling without slipping.

Once the ball is rolling without slipping, gravity will slow down the ball, so CW rotation decreases. The friction force that causes this will indeed make the ball CCW, but until the ball has stopped it will only decrease the CW rotation.