An argument has been travelling in amongst my friends around this matter and after listening about it for 3 whole days I decided to ask it here.

The Question is: Would a high atmospheric pressure slow sound that travels through it- due to there being more matter that the waves need to travel through- or would the overall speed be un-effected?

My thoughts to begin with were that sound would be slowed down, some others involved though think it would be the opposite, the denser atmosphere in-fact working to increase as well as maintain the speed and distance sound waves traveled- due to there being more closely compacted matter [oxygen/gas molecules] for the waves to be passed on through- making it easier for it to move faster and further!

The problem with this theory (as I thought it) is that the sound waves would loose momentum quicker- it using more energy for movement to continue hence slowing it down and reducing travel distance.

The opposite view posed to this is that less atmospheric pressure would allow for sound to travel further at a faster rate, the reduced air pressure causing less energy loss as waves travelled through it.

The problem with this theory (As I believe) is that if sparse atmosphere [having less pressure and gasses] made sound go further and quicker why then wouldn't it do so in an environment such as space- where there is almost no pressure or gasses at all to slow sound? (It being a near perfect vacuum.)

So I now find myself on the fence asking which of the above is correct: sound travelling faster and further in sparse atmosphere or in dense atmosphere?

-Harry David

  • 2
    $\begingroup$ Have a look at en.wikipedia.org/wiki/Speed_of_sound $\endgroup$
    – akrasia
    Aug 31 '14 at 13:39
  • $\begingroup$ Welcome to Physics SE! Consider marking the question as answered by clicking the check mark near an answer. In that way the question disappears from the list of unanswered questions. :) $\endgroup$ Oct 9 '14 at 11:41

According to the MTU webpage Speed of Sound in Air, some things to consider:

if the ideal gas model is a good model for a real gas, then you can expect, for any specific gas, that there will be no pressure dependence for the speed of sound. This is because as you change the pressure of the gas, you will also change its density by the same factor.

However, the atmosphere is a mixture of chemicals with some varying, especially water vapour (hence, humidity), hence not an ideal gas - from the Wikipedia Speed of Sound page:

Sound speed in air varies slightly with pressure only because air is not quite an ideal gas.

This variation in speed of sound according to the MTU webpage is extremely minimal at most (see vertical scale below) for the range of atmospheric pressures at low humidity and a slight bit more pronounced at extreme humidity (see graph below):

enter image description here

Compositional changes (mainly water vapour) and especially air temperature has the greatest effect.


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