Yeah BC, that's the one I was thinking of, no space suit.Imagine you had a lung full of air, You scream. The air is forced past your vocal chords which vibrate, modulating the air leaving your mouth and producing alternating waves of air compressions. These compressions are further propagated by the air outside your body.
But it is molecules particles 'vibrating', right? Gaining energy by me shouting, exiting them?
Now, what happens if there were no air outside of your body.
The air inside your lungs is made up of molecules which are themselves traveling at something like 340 m/sec. The air molecules are close enough together that they can't travel very far before bumping into another molecule (the mean free path). This distance is very small compared to the wavelength of a sound wave. which is why air at standard pressure can carry sound waves for long distances.
So when the air which has been modulated by your vocal chords leaves your mouth, there are no air molecules out there to "contain" them. Instead of bumping into other molecules and creating sound waves, they scatter and spread out a 340 m/sec.
So the "energy" from the sound is rapidly being spread out thinner and thinner over this expanding volume.
Not only that, but the mean free path of the molecules increase; they individually travel further and further before encountering another molecule. Thus the mean free path becomes long compared to the wavelength of the "sound", eventually surpassing it.
The upshot is that the "sound energy" becomes more and more just a matter of the average kinetic energy of the molecules which is randomly distributed and no longer takes the form of discernible sound waves.
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