What is sound wave?

A sound wave in air consists of alternating zones of low and high density. The vibrating diaphragm of a loudspeaker generates such zones of alternating density. The alternating zones of low density and high-density travel to the right away from the source. However, although these density disturbances travel, the air as a whole does not travel, the air molecules merely oscillate back and forth.

The pushes of the loudspeaker or of the tuning fork on the air are longitudinal, and the sound wave itself is also longitudinal. The air molecules oscillate back and forth along the direction of propagation of the sound wave. The restoring force that drives these oscillations is the pressure of air. Wherever the density of molecules is higher than normal, the pressure also is higher than normal and pushes the molecules apart; wherever the density of molecules is lower than normal, the pressure also is lower than normal, and therefore the higher pressure of the adjacent regions pushes these molecules together. Thus, the pressure in air plays the same role as the tension in a string.

Velocity of sound in air is 330 m/s.

The frequency of the sound wave determines the pitch we hear; that is, it determines whether our ear perceives the tone as high or low.


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