Pendulum

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A pendulum is a mechanical device consisting of a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting mechanical equilibrium position, it is subject to a restoring force due to gravity, which will accelerate it back toward the equilibrium position. When released, the restoring force acting on the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one complete cycle, a left swing and a right swing, or frequency, is commonly known as its "period". The period depends both on the length of the pendulum and, somewhat, on the amplitude (the width of the pendulum's swing). The SI unit of the period of a pendulum is the second (s). The regular motion of a pendulum lends itself to timekeeping. The pendulum clock was invented by Christiaan Huygens in 1656. It became the world's standard manner of timekeeping for several centuries. The Shortt-Synchronome clock achieved accuracy of about one second per year before it was superseded as a time standard by the quartz clock in the 1930s. Pendulums are also used in scientific instruments such as accelerometers and seismometers. Historically, pendulums were used as gravimeters to measure the acceleration of gravity in geo-physical surveys, and as a standard of length. The word pendulum is Neo-Latin, from the Latin pendulus, meaning 'hanging'.