A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs (tines) formed from a U-shaped bar of elastic metal (usually steel). It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and emits a pure musical tone after waiting a moment to allow some high overtones to die out. The pitch that a particular tuning fork generates depends on the length of the two prongs. Its main use is as a standard of pitch to tune other musical instruments.
The tuning fork was invented in 1711 by British musician John Shore.
The main reason for using the fork shape is that, unlike many other types of resonators, it produces a very pure tone, with most of the vibrational energy at the fundamental frequency, and little at the overtones (harmonics).
An alternative to the usual A440 diatonic scale is that of philosophical or scientific pitch with standard pitch of C512. According to Rayleigh, the scale was used by physicists and acoustic instrument makers. The tuning fork that John Shore gave to Handel gives a pitch of C512.
Tuning forks, usually C512, are used by medical practitioners to assess a patient's hearing. Lower-pitched ones (usually C128) are also used to check vibration sense as part of the examination of the peripheral nervous system.
Tuning forks also play a role in several alternative medicine modalities, such as Biosonics, Acutonics, sonopuncture and polarity therapy.