# Two Potentially Easy Kinematics Problems (sliding/rotation)

Chestermiller
Mentor

In post #20, I don't think you meant "normal" force acting on the bug. I think you meant force "tangent to the disk surface." This is what keeps it from slipping. The force tangent to the disk surface is comprised of two components, the component in the radial direction (centripetal force) and the component in the circumferential direction. The component in the circumferential direction is the result of 2 factors: (1) the fact that the circumferential velocity of the bug is increasing as it moves out radially and (2) the fact that the radial component of velocity is changing as the but moves circumferentially.

Chet

jbriggs444
Homework Helper
2019 Award
I think you meant to say that the "radial component of mass times acceleration is the centripetal force." I don't think you meant to say that the force of static friction is the centripetal force in this case.
I had struggled with the wording. The static friction is the only radial force there is. So if there is a centripetal force, it is the force of static friction.

Chestermiller
Mentor
I had struggled with the wording. The static friction is the only radial force there is. So if there is a centripetal force, it is the force of static friction.
I see what you are getting at. Terminology is always a difficult issue.

Chet