Physics - The speed of sound
The speed of sound
A day spent at an athletics carnival provides strong evidence that sound
takes a finite time to travel a set distance. If you were at the end of a
100 metre track you would see the smoke emerge from the starter's pistol
before you heard the familiar 'bang'. This is evidence that although light
travels quickly to your eyes, the speed of sound is somewhat slower. Since
the seventeenth century we have known that the speed of sound in air is
roughly 340 metres per second, depending upon the temperature of the air.
The speed at which a particular medium can conduct sound is determined by
how quickly the molecules of the medium can pass on the vibrations.
It therefore makes sense that sound travels fastest in solids, slightly
slower in liquids and slower again in gases. Solids allow a faster rate of
transfer of the vibrations due to the proximity of the molecules. You
should familiarise yourself with some typical speeds of sound. In metals
the speed of sound is above 3000 metres per second. In water the speed of
sound is around 1400 to 1500 metres per second. In air at 20 Celsius the
speed of sound is 340 metres per second .
The table below shows the speed of sound in a range of different
substances. Remember that these values do not refer to the speed at which
the molecules are moving. The molecules merely vibrate around a mean
position. The speed of sound refers to the speed at which the vibrations
are transferred. Note that the speed of sound is not at all affected by the
frequency of the soundwave. It is purely a property of the medium itself.
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