1. The problem statement, all variables and given/known data I drew this to make it easier to understand: http://img142.imageshack.us/img142/2729/problemagc0.th.jpg [Broken] E (mass: 400g) can move along the semicircle. ABCD is a plate rotating around (AD) axis at constant speed (14 rad/s). Coefficients of friction are 0.35 (static) and 0.25 (dynamic). I need to find out whether E will move for θ = 80º and for θ = 40º. Also I need to find the module and direction of the friction force for t0. 2. Relevant equations None. 3. The attempt at a solution I applied Newton's second law. Σ Fext = mg + N1 + N2 + f Where: mg is E's weight N1 is the normal force in the (ABC) plane N2 is the normal force perpendicular to the (ABC) plane f is the friction force I did this also so that you understand what I mean -just in case... :) http://img88.imageshack.us/img88/4488/esquemabr8.th.jpg [Broken] Then I think I must use: aE = aO + aE/O + ωx(ωxOE) + αxOE + 2ωxvE/O With: α = dω/dt = 0 ω = 14 j OE = (0.65 - sin(θ)*0.25) i I hope you can help me out here. Thanks a lot!