page_title: Pendulum
section_title: Use for time measurement
hierarchical_section_title: Pendulum / Use for time measurement
caption_attribution_description: English: Drawing of a pendulum with anchor escapement, from a 1906 physics book. Labeled parts:(a) pendulum rod, (b) pendulum bob, (c) rate adjustment nut, (d) pendulum suspension spring, (e) crutch, (f) fork, (g) escape wheel, (h) anchor. Alterations to image: altered brightness slightly to optimise contrast, replaced original part labels with colored labels in different order, and added labels a, b, c, and d Français&#160;: Balancier avec son échappement à ancre. Légende&#160;: (a) tige de la pendule, (b) balancier, (c) écrou de réglage d'oscillation, (d) ressort de suspension du balancier, (e) béquille, (f) fourche, (g) rouage d'échappement, (h) ancre. Italiano: schema di pendolo con scappamento ad ancora
context_page_description: A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that 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, is called the period. The period depends on the length of the pendulum and also to a slight degree on the amplitude, the width of the pendulum's swing.
  From the first scientific investigations of the pendulum around 1602 by Galileo Galilei, the regular motion of pendulums was used for timekeeping, and was the world's most accurate timekeeping technology until the 1930s. The pendulum clock invented by Christian Huygens in 1658 became the world's standard timekeeper, used in homes and offices for 270 years, and achieved accuracy of about one second per year before it was superseded as a time standard by the quartz clock in the 1930s.
context_section_description: For 300 years, from its discovery around 1582 until development of the quartz clock in the 1930s, the pendulum was the world's standard for accurate timekeeping.  In addition to clock pendulums, freeswinging seconds pendulums were widely used as precision timers in scientific experiments in the 17th and 18th centuries. Pendulums require great mechanical stability: a length change of only 0.02%, 0.2 mm in a grandfather clock pendulum, will cause an error of a minute per week.
caption: Pendulum and anchor escapement from a grandfather clock
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