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I read in multiple sources that the speed of sound depends on:

  • density of medium
  • temperature of medium

The sources treated the topic fairly simplified although. Is there more to this?

Does the number of moles of molecules, the size of molecules and other factors also matter or is the speed of sound purely determined by these two factors (to an extent that would allow a formula to be made)?

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  • $\begingroup$ Are you thinking specifically about a gas, a liquid, or a solid? Or looking for general principles that would be starting points for all 3 but then diverge when getting specific? $\endgroup$
    – Bill N
    Commented Dec 11, 2019 at 15:37
  • $\begingroup$ For example, with gases you can eliminate density in a "formula" in favor of temperature and molecular mass by using some gas law such as Ideal or Van der Waals. Bulk modulus is important for solids, but not gases (specifically), but pressure is a gas factor. $\endgroup$
    – Bill N
    Commented Dec 11, 2019 at 15:52

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The speed of sound is found (both mathematically and experimentally) to be: $$ v = \sqrt{\frac{P}{\mu}}$$ . Let's understand this formula a little, it depends on pressure directly (although to $1/2$ power) means if we increase the pressure the speed will be increased because more pressure means that molecules are hitting the walls of container strongly and hence are more energetic. If we make an ideal assumption that molecules can have only the kinetic energy and no potential energy then it's a simple thing to conclude that more pressure means molecules are travelling faster (therefore hitting the walls more often and strongly) and therefore communicates or transfers the disturbance (that's what sound is) more quickly.

The denominator $\mu$ is the mass density ( you can write it as $\rho$ and simply interpret it as density), all it tells us that how bulky our particles are, if they are bulkier then it would be harder to move them and hence the transfer of disturbance will be slower because our disturbance will cause only a little acceleration in them. Therefore, our speed is inversely proportional to th square root of $\mu$.

Now, let's see your thing

I read in multiple sources that the speed of sound depends on:

1.density of medium
2.temperature of medium .

The sources treated the topic fairly simplified although. Is there more to this?

See, the density means mass per unit volume, i.e. how bulky are particles in one unit volume of the medium. If they are bulkier, then they will move slowly.

There are laws for gases and which relate pressure directly to temperature like

  1. Ideal Gas Law $PV = NkT$ .

  2. Van der Waals Eqaution $(P + \frac{an^2}{V^2})(V-nb) = nRT$ .

For the solids, the equation changes a little, it becomes $$ v = \sqrt{\frac{T}{\mu}}$$ where $T$ is the tension under which the solid is kept. Increasing the tension increases the volume which in turn decreases the density and hence the sound travels faster. With the increase in temperature, the solid expands and hence the density goes down, therefore the wave speed goes up. This may help you.

Hope it helps.

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  • $\begingroup$ For a gas the term in the numerator should be $\gamma P$? Another formula for a gas is $\sqrt{\frac{\gamma R T}{M}}.$ $\endgroup$
    – Farcher
    Commented Dec 11, 2019 at 16:38
  • $\begingroup$ @Farcher I would really like to learn it, can you please explain me your formula? What is $\gamma$ ? $\endgroup$
    – user240696
    Commented Dec 12, 2019 at 5:07
  • $\begingroup$ The equation that you quote would be correct if the variation in pressure occurred under isothermal conditions but because the changes in pressure are so rapid there is not enough time for any heat transfer so the changes are adiabatic, There are many pages on the Internet showing the derivation, here is one of them. $\endgroup$
    – Farcher
    Commented Dec 12, 2019 at 11:24
  • $\begingroup$ @Farcher Sir, I think the formula I wrote was $\sqrt{\frac{P}{\mu}}$ and you’re referring to the formula of the form $v = \sqrt{\frac{dP}{d\mu}}$ and thus repleacing the $dP/d\mu $ by $E_v/\mu$ Where $E_v $ is the bulk modulus. $\endgroup$
    – user240696
    Commented Dec 12, 2019 at 12:11

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