My textbook says, "for an object rolling without slipping down an incline, the frictional force fs is less than or equal to its maximum value. fs < μsFn Why is that? What happen it's greater than?? When do we have static friction in rotational motion? (for rolling object) Then in an example problem about rolling with slipping, it says "there is slipping so the friction is kinetic (not static).? Same question. ==> Why?