tapping two objects together causes the particles in those objects to vibrate & glass is a kind of object & a fork is a kind of object ->  tapping a fork against a glass causes the particles in the objects to vibrate  tapping a fork against a glass causes the particles in the objects to vibrate & vibrations are a source of sound ->  the vibration of the particles caused by tapping the fork on a glass is a source of sound  the vibration of the particles caused by tapping the fork on a glass is a source of sound & a source of something produces that something -> the vibration of the particles caused by tapping the fork on a glass produces sound