30.2: Introduction


All waves begin as a vibration.  For the vibration to produce sound, there must be a material through which the vibration may travel.  The vibrations of atoms and molecules in air create compressions and rarefactions in the air.

Sound travels at an average speed of 343 m/s in air; this speed varies because it depends on the atmospheric pressure and temperature of the air.  It takes time for the sound wave to travel.  Light travels at a speed of 299,702,547 m/s in air.  Light waves also take time to travel.

$\text {speed} = \dfrac {\text{distance}}{\text{time}} \nonumber$