That is because its principal mode of vibration is symmetric, with the two prongs always moving in opposite directions, so that at the base where the two prongs meet there is a node (point of no vibratory motion) which can therefore be handled without removing energy from the oscillation (damping). It is easier to tune other instruments with this pure tone.Īnother reason for using the fork shape is that it can then be held at the base without damping the oscillation. 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. By comparison, the first overtone of a vibrating string or metal bar is one octave above (twice) the fundamental, so when the string is plucked or the bar is struck, its vibrations tend to mix the fundamental and overtone frequencies. The reason for this is that the frequency of the first overtone is about 5 2 / 2 2 = 25 / 4 = 6 + 1⁄ 4 times the fundamental (about 2 + 1⁄ 2 octaves above it). 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. Motion of an A-440 tuning fork (greatly exaggerated) vibrating in its principal modeĪ tuning fork is a fork-shaped acoustic resonator used in many applications to produce a fixed tone.
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