For other uses, see Pendulum (disambiguation). For torsion pendulums, see torsion spring. For the mathematics involved with pendulums, see 'Pendulum (mathematics)''.

A simple gravity pendulum or bob pendulum (plural pendulums or pendula), is a weight on the end of a rigid rod (or a string/rope), which, when given an initial push, will swing back and forth under the influence of gravity over its central (lowest) point.

The pendulum was discovered by Ibn Yunus al-Masri during the 10th century, who was the first to study and document its oscillatory motion. Its value for use in clocks was introduced by physicists during the 15th century, following observations from Galileo.

Pendulums for divination and dowsing

Pendulums (these may be a crystal suspended on a chain, or a metal weight) are often used for divination and dowsing. There exist many different techniques. One widely used form is the following. The user will first determine which direction (left-right, up-down) determines "yes" and which "no," before proceeding to ask the pendulum specific questions. In another form of divination, the pendulum is used with a pad or cloth that may have yes and no, but also other words written in a circle. The person holding the pendulum aims to hold it as steadily as possible over the center. An interviewer may pose questions to the person holding the pendulum, and it swings by minute unconscious bodily movement in the direction of the answer. In the practice of radiesthesia a pendulum is used for medical diagnosis. However all these uses of pendulums are not scientifically tested or supported.

Applications

As first explained by M. 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.

The presence of g in the 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%.

Two coupled pendulums form a double pendulum. A pendulum whose time period is two seconds is called the second pendulum.

A pendulum is also used for finding acceleration due to gravity(g), formula is T² = 4π²l/g. It is also used in seismographs.

See also

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

External links

• A more general explanation of pendulums

Classical mechanics

Махало | Matematisk pendul | Pendel | péndulo | آونگ | Pendule (physique) | Pendolo | מטוטלת מתמטית | Bandul | Slinger (natuurkunde) | Wahadło | Pêndulo simples | Математический маятник | Nihalo | Pendel