From: J. G. Locke (lockejg@redshift.com)
Date: Tue Nov 23 1999 - 06:05:22 PST
From: "J. G. Locke" <lockejg@redshift.com> Subject: RE: Pinhole Digest #296 - 11/23/99 Date: Tue, 23 Nov 1999 06:05:22 -0800 Message-ID: <000301bf35bb$c88e7900$2c30c8d8@daddysmachine>
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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