Sound travels faster in dense materials since the atoms are more closely packed together - the medium to propogate the wave. However, cooler air is more dense than warmer air; yet, air travels faster in warmer air. What explains this apparent paradox? Should it matter that one medium is solid vs. gas?
I have to run some number crunching about air at different temps to verify, but let’s assume the air pressure remains constant. (Unless this assumption precludes the above results from being possible.) - Jinx
where
d is adiabatic constant
r is gas constant
t is absolute temperature
m is molecular mass of gas
So the warmer the gas, the faster sound is in it.
This also explains squeaky-voice-syndrome with helium. Its molecular mass is less, so everything else being equal makes the speed of sound faster in it. If it’s the gas that’s filling your lungs and throat, your voice is going faster and makes your pitch go up.
Actually, sound travels more slowly in dense materials. The hitch is that denser materials are usually much stiffer, and that overcomes the retardation of the increased density.
Speed of sound =K (stiffness/density)[sup]1/2[/sup]
My brother and I were discussing this very thing yesterday. It’s funny how often the Straight Dope chases up our conversations.
I always thought of it as a result of how fast the molecules in the gas were moving. The faster they are moving, the faster they can communicate any disturbance to their neighbors.
Yes, I found this general equation in my Gas Dynamics book. It explains, that for ideal gases, the collisions between molecules is isentropic which allows other gas properties to stay constant. Because of this, it can be shown that the density doesn’t matter and the above equation can be manipulated to (almost) become the equation posted above by AWB. My equation applies “k” the ratio of the specific heats for any given gas.
It is not as intuitive as people try to theorize (as seen in posts above)…
