Sounds can be made by twanging a string or an elastic band, blowing down a pipe, banging something together, and scraping or shaking something. There are three families of musical instruments - string, wind and percussion. When a string is plucked on an instrument such as a guitar, the vibration is passed into the air and you hear a sound. Blowing into panpipes or a horn makes the air inside the pipes vibrate. Bongos and other percussion instruments produce vibrations when you bang them.