I was reading the chapter Sound Waves from my textbook and I came across this line that I am unable to comprehend properly.
Here's how it goes -
The speed of an mechanical, transverse or longitudinal, depends on both an inertial property of the medium (to store kinetic energy) and an elastic property of the medium (to store potential energy). Thus, we can generalise $v = \sqrt{\tau\over{\mu}}$ which gives the speed of a transverse wave along a stretched string, by writing $v = \sqrt{\tau\over{\mu}} = \sqrt{\frac{ \text{elastic property}}{\text{inertial property}}}$, where (for transverse wave) $\tau$ is the tension in the string and $\mu$ is the string's linear density. If the medium is air and the wave is longitudinal, we can guess that the inertial property, corresponding to $\mu$, is the volume density $\rho$ of air. What shall we put for the elastic property?
I want to know the meaning of inertial property, elastic property, how that relates to the formula given for $v$ and the answer to the question in the very last line of the paragraph.