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 made of 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 generated pitch from a particular tuning fork depends on the length of the two prongs. Its main use is as a standard pitch to tune other musical instruments.