Consider a gas at very low temperature(lower than critical) and pressure . Upon increasing pressure it will transform to liquid state.

I know that speed of sound is independent of pressure, and also speed of sound is more in solids than in liquids than in gases.

So if I increase pressure of the gas will the velocity of sound increase or remains same in other state?

  • $\begingroup$ Can you increase the pressure and still be at the triple point? I thought it was just that - a point - on the pressure vs. temperature graph. $\endgroup$ – M. Enns May 21 '16 at 16:35
  • $\begingroup$ @M.Enns No. That is a mistake $\endgroup$ – user117954 May 21 '16 at 16:39
  • $\begingroup$ @M.Enns Please have a look at edited question $\endgroup$ – user117954 May 21 '16 at 16:44
  • $\begingroup$ $c=\sqrt\frac{K}{\rho}$ where density $\rho$ is weakly dependent on pressure. So it is incorrect to say that the speed of sound is independent on pressure. $\endgroup$ – Feyre May 21 '16 at 17:15
  • $\begingroup$ The speed of sound directly depends upon pressure. See for instance http://physics.stackexchange.com/a/179057/59023. $\endgroup$ – honeste_vivere May 21 '16 at 18:12

I know that speed of sound is independent of pressure

No, it isn't. It's just not directly dependent on it so it's said that the speed of sound in gases depends on the temperature, molecular composition, and heat capacity ratio of the gas. But temperature and heat capacity ratio depend on pressure. Furthermore, the dependencies on temperature don't always cancel each other out.

If the state changes to a liquid, the speed of sound depends on the medium's compressibility and its density. The latter of which you change by changing its pressure.

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  • $\begingroup$ So the velocity in both states remain constant at a given temperature because compressibility decreases and density increases? $\endgroup$ – user117954 May 22 '16 at 2:31
  • $\begingroup$ No. The speed of sound starts to depend on different things when going from a gas to a liquid. You can easily see that this can't be true because density is monotonous with pressure but compressibility isn't. However, your assumption that the speed of sound doesn't depend on the pressure when still in the gas state is wrong from the beginning. $\endgroup$ – UTF-8 May 22 '16 at 11:19

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