Iron Pendulum Bob1 Inch DiameterWeight (Approximate): 2.440 Oz.Brass hook on bob for attachment to pendulum arm The iron pendulum bob provides one of the necessary tools for studying the physics of pendulum motion (tension force, gravity force, centripetal force, potential energy, kinetic energy, etc.). When used with a full pendulum set up, it provides a visually and kinesthetically affective method by which to study pendulum physics.