An analysis program is presented for rigid part mechanisms, such as feeders, locks and brakes. The program performs a kinematic simulation of driving motions and part contacts, with a limited dynamic simulation of gravity, springs and friction. It produces a realistic, 3D animation and a concise, symbolic interpretation of the simulation. It derives the kinematic motion equations for a large class of mechanisms, including ones with complex part shape, varying part contacts, and multiple driving motions. It avoids collision detection during simulation by precomputing pairwise part interactions. It uses a simple model of dynamics that captures the steady-state effect of forces without the conceptual and computational cost of full dynamic simulation. It is demonstrated that the simulation algorithm captures the workings of most mechanisms via a survey of 2500 mechanisms from an engineering encyclopedia.