Factors Which Affect the Speed of Sound in Air

Isaac Newton showed that the speed of sound in a gas is proportional to the square root of pressuredivided by density:

This relationship implies that the speed of sound in air is independent of the pressure, since if the pressure is doubled, Boyle's Law - pressure times Volume = constant - tells us that the volume is halved, so that the same mass of gas is concentrated into half the volume and the density is doubled. The expressionremains constant, and the velocity remains unchanged.

On the other hand the speed of sound does depend on temperature. The sound is carried by the air molecules. If the temperature increases, the air molecules have more kinetic energy and so travel faster. The speed of sound should therefore increases with increasing temperature. Thought of another way, if the temperature increases at constant volume, the pressure will increase and hence so will the speed of sound. Conversely if the pressure remains constant, then Charles's Law (or) tells us that the density will decrease, and the speed will increase.

Pitch and loudness have no effect on the speed of sound. Reflect that when at a concert, notes from the various instruments and voices are heard at the same time no matter what the distance from the source.

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