Huygens turned swinging weights into the clock standard
A pendulum hangs a mass from a pivot so it can swing; displaced, gravity restores it through regular arcs. Christiaan Huygens invented the pendulum clock in 1656, and for about 270 years it set the world's timekeeping standard, cutting clock errors from minutes a day to seconds.
A pendulum is a weight hung from a pivot so that it can swing freely. Pushed aside, it feels a restoring pull from gravity that sends it back toward the bottom, where momentum carries it past, and it keeps swinging to and fro. Its period depends on its length and on local gravity, barely on how wide it swings, and not at all on the mass of the bob. For small swings the timing hardly changes even as the arc shrinks, a property called isochronism that makes pendulums ideal for clocks; at a swing of about 23 degrees the period runs only 1 percent longer.
Among the earliest uses was a first-century seismometer built by the Han dynasty scientist Zhang Heng, in which a swaying pendulum tripped levers when a distant earthquake struck. A popular claim that the tenth-century Egyptian astronomer Ibn Yunus timed things with a pendulum is an error begun by the historian Edward Bernard in 1684. Galileo started studying pendulums around 1602, having first noted their behaviour in notes from about 1588.
In 1656 Christiaan Huygens built the first pendulum clock, improving the best clocks from roughly 15 minutes of error a day to about 15 seconds, and in 1673 he proved that a pendulum's pivot and its centre of oscillation can swap places without changing the period. Robert Hooke used a conical pendulum around 1666 to model planetary orbits, and in 1671 Jean Richer found a clock losing two and a half minutes a day in Cayenne compared with Paris, evidence of weaker gravity there. Pendulum clocks kept time in homes and offices for some 270 years, and the Shortt-Synchronome reached about one second a year.
Pendulums have also served as gravimeters, as a standard of length, and inside accelerometers and seismometers. A rigid rod swung from one end keeps the same time as a simple pendulum two-thirds as long, and a pendulum hung from another pendulum behaves chaotically. The word comes from Latin pendulus, hanging.
Source: Pendulum
