Day 143

The Speed of Sound

Sound travels much slower than electromagnetic waves and its speed depends on the medium through which it passes. The greater the density of the material, the greater the speed of sound. This is actually opposite to what happens with light waves, but remember sound is a compressional wave, whereas light is a transverse wave. Since sound needs a medium to propagate, it is compressing material particles together to transmit the energy of the wave.

  • vsteel > vwater > vair


  • Speed of sound in steel is approximately 5200 m/s, in water about 1500 m/s and in air 331 m/s at 0°C.


  • Objects which travel at less than the speed of sound are called subsonic.


  • Objects which travel at greater than the speed of sound are called supersonic.

Planes which are traveling at Mach speeds are actually traveling at multiples of the speed of sound. For example, Mach 3 means the plane is traveling at three times the speed of sound in air at that temperature.