Why Does Sound Travel at a Constant Speed in a Medium?

[Frillth]

I know from my physics course that sound has a particular speed in any medium that it is traveling through, much like light. I have not learned, however, why this is so. I know that sound is simply a pressure wave traveling through air (or water or steel or whatever), but it doesn't seem obvious to me why this pressure wave should have one and only one speed per medium.

Can somebody please explain why sound travels at one particular speed per medium? Thanks!

 

[chroot]

A pretty good approximation to the speed of sound in a medium can obtained with only the molecular weight of its constituent molecules, and its density.

Density and pressure are usually inversely related, so together they have little effect on the speed of sound.

- Warren