1. The problem statement, all variables and given/known data When the converyor belt was first installed safety checks were carried out to determine the limit of angle for safety. It was found that at an angle of 30 degrees the crates start to slip down. Calculate the coefficient of friction between the crates and the belt? (Diagram as shown in the question attached) I also assume they are looking for the static coefficient not the slipping as the question isn't very clear? 2. Relevant equations Friction = Pressing Force x Constant or μ= Pressing Force/Friction 3. The attempt at a solution Vertical force acting on the crate (H in my free body diagram) H = Gravity x mass H = 9.81 x 200 H = 1962N Parallel downwards to the surface of the plane force acting on the crate (O in my free body digram) O = H x Sin θ O = 1962 x Sin 30 O = 981N Therefore i can assume the friction force acting in the opposite direction to 'O' is 981N Force acting into the surface of the plane (A in my free body diagram) A = H x Cos θ A = 1962 x Cos 30 A = 1699.14N This is my pressing force. To calculate the coefficient of friction between the crates and belt is μ = 1699.14 / 981 μ = 1.73 This is my first attempt at calculating a coefficient do would really appreciate if someone could review this and check i'm on the right lines.