From: Steven Eiger (eiger@montana.edu)
Date: Wed Nov 24 1999 - 01:10:00 PST
Message-Id: <l03102802b4615b2c7275@[153.90.241.107]> Date: Wed, 24 Nov 1999 03:10:00 -0600 From: Steven Eiger <eiger@montana.edu> Subject: RE: Pinhole Digest #296 - 11/23/99
Regarding this vacuum and sound transmission business; isn't a vacuum full
of particles? virtual ones, can these transmit sound? Is sound kind of
like temperature in that it takes a collection of a certain size to be
meaningful? Eiger
>This sounds like the perfect opportunity for an experiment! Use two
>transducers in a large class tube (2 to 3 cm diameter) . Arrange one
>transducer on long leads so that it's position can be changed in the tube.
>Have a pump-down nipple and another nipple leading to a manometer (slant
>type with Hg) or other fairly precise indicator.
>
>Somewhere, there is information on the minimum pressure or maximum height in
>the atmosphere for sound transmission.
>
>John
>
>
>|| Subject: sound transmission
>|| From: "Marc Afifi" <marc_afifi@yahoo.com>
>|| Date: Mon, 22 Nov 1999 07:47:29 -0800 (PST)
>||
>|| 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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Steven Eiger, Ph.D.
Departments of Biology and the WWAMI Medical Education Program
Montana State University - Bozeman
Bozeman, MT 59717-3460
Voice: (406) 994-5672
E-mail: eiger@montana.edu
FAX: (406) 994-3190
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