Pendulum

Pendulum, rigid body mounted on a fixed horizontal axis that is free to rotate under the influence of gravity. Many types of pendulum exist, the most common consisting of a large weight (the bob) supported at the end of a light string or bar. An idealized simple pendulum, with a string of negligible weight and length, l, the weight of its bob concentrated at a point, and a small swing amplitude, executes simple harmonic motion. The time, T, for a complete swing (to and fro) is given by Huygens' formula T=2π√l/g, depending only on the string length and the local value of the gravitational acceleration, g. Actual physical or compound pendulums approximate this behavior if they have a small angle of swing. They are used for measuring absolute values of g or its variation with geographical position and as control elements in clocks (Huygens, 1673).

See also: Foucault, Jean Bernard Leon; Galileo Galilei.