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
combined with 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. A pendulum swings with a specific period which
depends (mainly) on its length. From its discovery 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. Pendulums are used to regulate
pendulum clocks, and are used in scientific instruments such as
accelerometers and seismometers. Historically they were used as
gravimeters to measure the acceleration of gravity in
geophysical surveys, and even as a standard of len