I'm thinking about how this sphere would move down the ramp and through the loop at the bottom of the ramp. I'm mostly interested in whats going on at the very top point of the loop. If I were to draw a free-body diagram of the sphere at that point, what forces would be present? I'm guessing that there would be weight directed downwards, and then the centripetal force pointing upwards. Is this correct? The centripetal force appearing on a FBD of the sphere at this point would be a force pair? As in, the centripetal force is provided by the loop surface on the sphere directed towards the center of the loop, so with equal and opposite force pairs, the sphere would exert the same but opposite force on the loop? I'm just trying to straighten out in my head where the normal force from the surface is. I always thought that if there is contact between a surface and object, there would be a normal force. Where is it in this case? If i were trying to solve for something like the minimum height needed for the sphere to pass through the loop, I'm solving for when the centripetal force equals the weight...but again, where is the normal force during all of this?