# Friction force in rolling motion

In rolling without slipping motion we know that the friction acting is static friction and so we treat it as an unknown while solving equations of dynamics.

Question: Is the static friction during pure rolling the same as rolling friction?

• – ja72 Nov 11 '14 at 15:06

Rolling friction result from for example small changes in the surface or in the wheel material (the rubber in a tire).

The surface is not perfectly flat and rigid so there will be some small forces trying to stop the rotating motion:

(source: davidson.edu)

On the contrary, the static friction is not trying to stop the rotation of the wheel.

Static and rolling friction are different things.

No.

Rolling friction is the fraction of resistive force to normal load. It is a fudge factor, lumping all rolling related resistances into one dimensionless value. This applies to rolling only.

Static friction is a measurable quantity relating to the maximum resistance an interface provides before sliding occurs. This applies to sticking only.