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[Phys-L] Re: Acoustics question about popped balloons - try 2



----- Original Message -----
From: "John SOHL" <jsohl@WEBER.EDU>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Wednesday, August 24, 2005 11:24 PM
Subject: Acoustics question about popped balloons - try 2


<cutting>

They are saying that the "extra molecules" that pressurize the air
inside the balloon are what you "hear" when the air expands outward
rapidly with the release of the air. (PV=NRT, increase N and you
increase P and slightly increase V.) I.e., this pressure moves outward
and your ears respond by giving the sensation of a "bang." This is a
conservation of air molecules argument that implies that the extra air
molecules that are released have to go somewhere and as they escape they
cause a local increase in air pressure that your ears hear since the air
pressure momentarily increases at your ears as the molecules in the
surrounding air adapt to the extra molecules you just released.
This argument makes no sense to me and without actually calculating the
increase in the air pressure 100 meters away, I just don't see that it
would be a very loud pressure sensation to your ear.

I guess it comes down to how sensitive our ears are to pressure changes and
where the threshold for discernment of sound occurs. "Loud" or "soft" are
our brain's interpretation and probably vary from one individual to another.
Someone with mechanically impaired hearing doesn't receive a different
stimulus, but has less sensitivity TO that stimulus. What is clear is that
our ears are remarkably sensitive to VERY small pressure changes, thus
accounting for the loudness of something 100 meters away. Is it really any
more unlikely than being able to detect a minute number of airborne
molecules (smelling) over very long distances (not so much for us, but for
some animals)?