From: The Lahrs (JohnJan@lahr.org)
Date: Wed Feb 23 2000 - 07:18:22 PST
Message-Id: <4.2.0.58.20000223080040.00ae5be0@netmail.home.com> Date: Wed, 23 Feb 2000 08:18:22 -0700 From: The Lahrs <JohnJan@lahr.org> Subject: Re: Pinhole Digest #359 - 02/23/00
Dear Adam,
These are great questions. Here are my thoughts on them. The boundary between
the vacuum of space and the Earth's atmosphere is not a sharp
line. Rather, the
"ocean of air" that is held by gravity to the earth gets thinner and
thinner (fewer
molecules per unit volume) the higher one goes, due to the decrease in air
pressure
with elevation. The air pressure at any given elevation is caused by the
column of
air above that elevation pressing down with its weight on the air below.
A loud sound made at sea level expands outward in all directions, including
upwards.
The sound volume is reduced as it expands because the energy is distributed
over
a larger area (the area of a hemisphere) and because some of the energy is
converted
to heat along the way. If the sound reaches the outer atmosphere before it is
weaker than the random motion of the molecules there, then it would indeed bump
a few molecules farther out into space. Then gravity would pull them back down
again.
What do others think about this question?
Cheers,
John
>Subject: Sound waves
>From: "Adam Singer" <adamsinger@earthlink.net>
>
>One of my sharper 8th grade students asked further about why sound waves
>cannot travel through a vacuum. He had reminded me that I
>had described sound waves as a longitudinal (or compression) type
>wave. He wanted to know why the last layer of atoms don't fly
>off into the vacuum and span the gap. If they cannot, what happens to the
>sound energy? Can anyone clarify this?
>
>-- Adam Singer
> Marina Middle School
John C. Lahr
1925 Foothills Road
Golden, CO 80402
(303) 215-9913
http://lahr.org/john-jan
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