Applications

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The most widespread application is for timekeeping. A pendulum whose time period is two seconds is called the second pendulum since most clock escapements move the seconds hands on each swing.

Gravimetry

The presence of g as a variable in the above equation means that the pendulum frequency is different at different places on Earth. So for example if you have an accurate pendulum clock in Glasgow (g = 9.815 63 m/s²) and you take it to Cairo (g = 9.793 17 m/s²), you must shorten the pendulum by 0.23%. g = 9.8 m/s² is a safe standard for acceleration due to gravity if locational accuracy is not a concern.

Seismology

A pendulum in which the rod is not vertical but almost horizontal was used in early seismometers for measuring earth tremors. The bob of the pendulum does not move when its mounting does and the difference in the movements is recorded on a drum chart.

Schuler tuning

As first explained by Maximilian Schuler in his classic 1923 paper, a pendulum whose period exactly equals the orbital period of a hypothetical satellite orbiting just above the surface of the earth (about 84 minutes) will tend to remain pointing at the center of the earth when its support is suddenly displaced. This is the basic principle of Schuler tuning that must be included in the design of any inertial guidance system that will be operated near the earth, such as in ships and aircraft.

Coupled pendulums

Two coupled pendulums form a double pendulum. Many physical systems can be mathematically described as coupled pendulums. Under certain conditions these systems can also demonstrate chaotic motion.

Pendulums for divination and dowsing

Pendulums (these may be a crystal suspended on a chain, or a metal weight) can also be used in divination and dowsing. See Pendulums for divination and dowsing for a more detailed discussion.

See also

• Pendulum clock
• Simple harmonic motion
• Foucault pendulum
• Spherical pendulum
• Double pendulum
• Kater's pendulum
• Harmonograph
• Metronome