We present an analysis program for rigid part mechanisms, such as feeders, locks, and brakes. The program performs a kinematic simulation of driving motions and part contacts along with a limited dynamical simulation of gravity, springs, and friction. It produces a realistic, three-dimensional animation and a concise, symbolic interpretation of the simulation. It derives the kinematic motion equations for a large class of mechanisms, including ones with comlex part shapes, 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 conputational cost of full dynamical simulation. We demonstrate that the simulation algorithm captures the workings of most mechanisms by surveying 2500 mechanisms from an engineering encyclopedia.