Tuning fork
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 and mass of the two prongs. It is frequently used as a standard of pitch to tune musical instruments.
The tuning fork was invented in 1711 by British musician John Shore, Sergeant Trumpeter and Lutenist to the court.
A tuning fork is a fork-shaped acoustic resonator used in many applications to produce a fixed tone. 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. The reason for this is that the frequency of the first overtone is about 52/22 = 25/4 = 6 1⁄4 times the fundamental (about 2 1⁄2 octaves above it). By comparison, the first overtone of a vibrating string or metal bar is only one octave above (twice) the fundamental, so when the string is plucked or the bar is struck, its vibrations tend to be a mixture of the fundamental and overtone frequencies. When the tuning fork is struck, little of the energy goes into the overtone modes; they also die out correspondingly faster, leaving a pure sine wave at the fundamental frequency. It is easier to tune other instruments with this pure tone.
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