This problem has been driving me crazy. There is spherical ball of mass M and radius R. It is in a sphererical bowl with radius 10R. What is its frequency if pure rolling motion is assumed? I figured it out if there is no friction so it slips. Sum of Torque = I ddz/ddt = Mg10RsinZ I = 1/2 MR^2 + M(9R)^2 W^2 = MG10R/(163/2MR^2) = (20 G)/(163 R) I am at a loss in figuring it out if the ball rolls.