I have some related questions about a body moving in uniform horizontal circular motion:
The body moves with a constant angular velocity on a rough horizontal surface. It is attached to a string that is attached to a fixed point on the surface. The body revolves around that fixed point. If the body is continuously in contact with the surface, in which direction will friction act and what type will it be (static or kinetic)?
Now what if it moves with constant angular acceleration? In which direction will friction act?
What if the body is on a rough inclined plane undergoing circular motion?
Best Answer
Since the object is moving and not at rest, it is undergoing kinetic friction. The force of kinetic friction will always be directly opposite the instantaneous direction of motion of the object. This does not depend on the angle of the surface or the value of angular acceleration. The force of kinetic friction will point directly opposite the direction of motion of the object.
Friction can only oppose motion in the contacting object, it does not create motion in that object. If the force of friction points anywhere other than directly opposite the direction of motion, then it has the effect of creating motion along a separate direction.