1. The problem statement, all variables and given/known data the ball has a mass M and is fixed to a rod having a negligible mass and length L. If it's released from rest when theta=0, determine the angle theta at which the compression force in the rod becomes zero. 2. Relevant equations A(tangent) = dv/dt = vdv/ds A (normal) = v^2p ...where p is radius of curvature, or L. 3. The attempt at a solution well, I'm stumped. This is dynamics problem moreso than physics, but still. I have a FBD with mg down and the C force. I used tangent-normal coordinates, and have the Compression force in the normal direction. So I get A=V^2 / L I guess I just don't get conceptually why the force would ever need to become zero? PS....so theta is from the vertical axis down. So it starts completely vertical and makes its way down clockwise.