# Homework Help: Rotational conceptual problem?

1. Sep 29, 2011

### sulabh64

1. The problem statement, all variables and given/known data
a disk is rolling on a flat horizontal surface.only rolling friction will act on the body.(true/false).ans false WHY?a body rolls.therefore sliding friction can't act on body.(true/false).ans. false WHY?

2. Relevant equations

3. The attempt at a solution
since the point of contact is at rest with respect to the surface (rolling condition) therefore no sliding friction must be there.

2. Sep 29, 2011

### Staff: Mentor

The question seems to be relying on vagueness and technicalities to trick you

Technically, a rolling disk may also be sliding if it has an initial rotational speed that differs from the linear tangential speed; The speeds would eventually match as friction worked to equalize them.

Technically, a rolling disk may also be sliding perpendicularly to the rolling motion (think of a car tire negotiating a curve when the car is traveling to fast -- lateral road friction is too small to impart sufficient centripetal force and the rolling tire slides sideways).

Technically, air friction will also operate on the moving disk...