Kinetic Energy of a Pendulum Calculator

A swinging pendulum continuously exchanges gravitational potential energy and kinetic energy. At either turning point, the bob pauses for an instant, so its speed and kinetic energy are zero while its gravitational potential energy is greatest. As it falls toward equilibrium, gravity accelerates the bob and converts stored potential energy into motion. At the lowest point, an ideal pendulum reaches its maximum speed and therefore its maximum kinetic energy. This calculator evaluates that energy from the bob's mass and measured instantaneous speed using KE = one half times mass times speed squared. Mass must be entered in kilograms and speed in metres per second, producing energy in joules. Because speed is squared, doubling speed multiplies kinetic energy by four, whereas doubling mass only doubles the result. The equation applies to the translational motion of a compact bob. It does not separately include rotational energy of an extended rigid body, air drag, pivot friction, string elasticity, or motion of a massive rod. For classroom pendulums with a small dense bob and a light string, those omissions usually match the standard simple-pendulum model. The same result can be predicted from release height when mechanical energy is conserved. A bob released from rest loses gravitational potential energy equal to mass times gravitational acceleration times its vertical drop. In an ideal system, that loss equals the kinetic energy at the bottom. Real experiments commonly return a slightly smaller measured value because drag and friction dissipate energy as heat and sound. Comparing the speed-based result with the height-based prediction is therefore a useful way to estimate experimental losses. Use the instantaneous velocity at the position of interest, not average speed over a whole swing. Photogates, video tracking, or motion sensors can provide an appropriate value. Keep units consistent and use the total moving mass, including attachments that travel with the bob. The result is deterministic and suitable for checking homework, planning a laboratory measurement, estimating impact energy, or exploring how mass and velocity affect a pendulum's motion.