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It is clear that if a frictional force must exist on an object that rolls without slipping, it must a static frictional force because the contact point of the object with the ground does not move.
I know that if a ball rolls on a flat surface, once it begins rolling without slipping, the frictional force is 0. I am confused, however, about the case when a ball rolls down a ramp. For the condition of rolling without slipping to hold, there must be a frictional force on the ball up the ramp. I am confused about where this frictional force comes from if the part of the ball touching the ramp isn't actually moving. It doesn't seem to make physical sense because from the ramp's perspective, it is touching a stationary object and thus there shouldn't be a frictional force.