# Why is speed of sound constant?

## Main Question or Discussion Point

This just occurred to me a few minutes ago, sorry if it's a dumb question:'

Why is the speed of sound constant in an ideal gas?

Suppose you have a box with an ideal mono atomic gas and a diaphragm that can oscillate. The diaphragm busts one move at ~3000 m/s. Since collisions with ideal gas particles are modeled elastically, the RMS speed of the particles that were in contact with the diaphragm while moving is ~3000m/s. Consequently, the neighboring particles will be bumped to ~3000m/s also, and so on until the end of the box is reached. Since no energy is lost and the RMS speed in the other two dimensions is zero, won't the pressure wave be traveling at ~3000m/s?

Related Other Physics Topics News on Phys.org
The analysis is a little more complex.

http://www.grc.nasa.gov/WWW/K-12/airplane/snddrv.html" [Broken]

Last edited by a moderator:
By the way, the speed of sound is of the same order as the RMS speed of molecules in the gas, but the original RMS speed of molecules due to thermal motion is going to be much greater than the speed at which the diaphragm is moving.

thank you (teşekkür ederim)