The hurdy-gurdy is a string instrument that produces sound by a hand-crank-turned, rosined wheel rubbing against the strings. The wheel functions much like a violin bow, and single notes played on the instrument sound similar to those of a violin. Melodies are played on a keyboard that presses tangents—small wedges, typically made of wood—against one or more of the strings to change their pitch. Like most other acoustic stringed instruments, it has a sound board and hollow cavity to make the vibration of the strings audible.