# Sliding vs. rolling ball

1. Nov 28, 2008

### Marin

hi there!

I considered the following problem:

a ball of radius R on a horizontal plain is at first in rest. Then it receives a horizontal force for a very short time at a point placed 1/3R from the plain and the ball starts moving with initial velocity v_0. There is also a friction when the ball slides.

the question is: at which velocity v will the ball start rolling?

here´s what I figured out:

the force initiates a torque such that the ball gets initial angular velocity w_0, counter clockwise. But the velocity v initiates another angular velocity w in clockwise direction. My assumption is that the ball will start rolling counter clockwise when the velocity v becomes 0.

what do you think?

2. Nov 29, 2008