he strands of the rubber band, also the prongs of the tuning fork, were moving back and forth rapidly while they were producing sound. This back and forth motion of a substance is called vibration.
When a substance is producing sound, it is vibrating. The strings of a violin are set in vibration by means of a bow. A reed in the mouthpiece of a saxophone is set in vibration by a player’s breath. The sounds made by wind instruments like the pipe organ are produced by vibrating columns of air. Any sound, no matter how it is produced, is caused by a vibrating substance.