I want to ask about the direction of frictional force in smooth rolling motion which means the rolling object doesn't slide on the surface.
Here is the first case, the wheel rolls to the right so the rotation is clockwise. At the point P, velocity is zero. To make the wheel rolls faster, it bottom must rotate to the left faster and the frictional force direct to the right to oppose its tendency to slide as to keep v=0
However, in this case it's also smooth rolling motion but the direction is different. It is explained in the book that if the object slide, it will slide down the ramp so the frictional force must be up to the ramp
So, in the first case the frictional force have the same direction with the acceleration of the center of mass but it's not in the latter one. Can someone explain the difference between those 2.
If the object want to slide, it first must rolls faster with very big acceleration. I can understand the first case, the force act ton the point P direct to the left to make the wheel rolling faster so the frictional force must direct to the right. In the second case, the object rolls to the left so the force acting on P must direct to the right so why the frictional force direct to the right. Isn't its direction must be to the left.
Also, in both cases above, considering accelerating object but not considering object which move very fast. If the object is rolling very fast at a direction, to which direction will the frictional force be?