sound transmission

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From: Marc Afifi (marc_afifi@yahoo.com)
Date: Mon Nov 22 1999 - 07:47:29 PST 

Message-ID: <19991122154729.11067.rocketmail@web218.mail.yahoo.com>
Date: Mon, 22 Nov 1999 07:47:29 -0800 (PST)
From: Marc Afifi <marc_afifi@yahoo.com>
Subject: sound transmission

Hi all,

We often say that sound is not transmitted in space.
The explanation offered is that this is because there
are no molecules to propagate the disturbance and a
bell jar with a ringing bell is sometimes shown to
become silent when the air is pumped out of the jar.
My question is, at what point does the sound cease to
be transmitted? I know we are not establishing a
vacuum in the jar, just lower pressure. In fact, the
lowest pressures I have seen in a lab are on the order
of a picotorr to a nanotorr. Even at this low
pressure, there are many molecules per liter. My
calculation shows there to be about 30 billion
molecules per liter at standard temperature and one
picotorr. So, is sound actually being scattered at
this pressure (by random motion of molecules) rather
than propagated? At what mean free path does the
propagation cease? If it is being propagated but at
too low an intensity to be measured, then wouldn't the
same be true for outer space since there are many
particles out there that are capable of transmitting
sound (even if it is only one molecule per cubic
meter)?

Just wondering.

=====
Marc Afifi
Chemistry, AP chemistry
Pacific Grove High School
Pacific Grove, CA

email: marc_afifi@yahoo.com

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