In music, a bow (/boʊ/) is a tensioned stick which has hair (usually horse-tail hair) coated in rosin (to facilitate friction) affixed to it. It is moved across some part (generally some type of strings) of a musical instrument to cause vibration, which the instrument emits as sound. The vast majority of bows are used with string instruments, such as the violin, viola, cello, and bass, although some bows are used with musical saws and other bowed idiophones.