I am doing a physics project whose purpose involves describing the physics behind a toy. The toy I have selected is a "decision maker" which is composed of a pendulum which has a magnetically charged ball on it that swings side to side, while having a force exerted on it by magnets which change the direction and momentum of the pendulum. Could anybody direct me to a resource that explains the theory behind calculating external forces acting on a swinging pendulum, or if possible, explain it in this thread? Any help would be appreciated, and for reference, the toy looks like this http://prntscr.com/5qyefo Thank you!!!