# Pure rolling

1. Nov 28, 2009

### sArGe99

When an object is said to be under pure rolling, what friction does it experience? Static, kinetic or rolling friction?
If its not rolling but rather just rotating and translating, what friction does it experience?

If a rolling body is kept on a surface of certain friction constant, does the friction force on it vary with changing angular velocity? Is the friction force still given by f = k * Normal reaction, which in the case mentioned is mg?

I appreciate any help.

2. Nov 28, 2009

### kuruman

If by "pure rolling" you mean "rolling without slipping", then it is static friction. I am not sure what "rolling friction" is.
Kinetic friction if it rolls with slipping (like a car "laying on the rubber" as it starts moving).

Yes if it rolls without slipping. The force of static friction will be whatever is necessary to provide the observed linear and angular acceleration.
Yes but only if there is rolling with slipping, i.e. if the instantaneous point of contact on the rolling object is not at rest with respect to the surface on which it rolls.
Good luck.