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[DPRG] Measuring Speed of sound in a liquid

Subject: [DPRG] Measuring Speed of sound in a liquid
From: Ken Comer me at kencomer.com
Date: Fri Sep 3 15:50:53 CDT 2004

> >Why measure speed
> >Are you looking to id what the liquid is or the purity or
> >Or do you just need to measure the presence of liquid?
> >A u-shaped fiber optic will give you a "distressed Liquid"
> >sensor with some accuracy or transmittance, and somewhat
> >inert to acids, etc.!
> >Could you measure light to get the results, and use glass
> >or crystal windowed pvc fittings?
> >Brain storming.

Let me preface this with a clear warning that I only have two
semesters of college physics, that it was 20 years ago, and that my
interests were less to do with mechanics at a macro scale that wasn't
at least hundreds of light-seconds worth of "macro" than the
dark-haired woman in the third row. I remember as much about her as I
do about physics, and I can't even recall her name. YHBW.

That being said, how's this for a brainstorm: when all's said and
done, a "sound wave" is nothing but a bunch of compression waves
back-to-back. In its basic form, just one oscillation has the same
properties as a sound wave. It seems to me that you could have a
chamber with a fixed end and an end that can could move, and a blade
that chop down. The blade goes spl-thunk, the liquid goes sloosh,
then the movable end moves a finite amount of time later. The
distance from the blade and the initial position of the movable end
is known. Measure the amount of time that it takes for the movable
end to move, divide by distance; et voilá, the quotient is the speed
of sound. All of the pieces involved in this method are pretty
minimalist and can be as durable as you like without sacrificing

The shape of the tank and initial stillness might throw slop into the
measurement, but a little more sophistication in tank and
wave-generator can help dampen errors and increase accuracy. The
reason this might be better than measuring real sounds is that the
waveforms for sound are necessarily going to be more complex and, to
get the maximum gross movement to match my "single wave" method in a
sound pulse, the energy of my single wave would have to be the
highest energy in a waveform that rose from zero energy a rapid
to/fro sequence with a net energy near zero.

As previously noted, I am not a physics guru and the two books that I
would resort to in hopes of getting further inspiration are in
storage. If you have access to a copy of _The Way Things Work_, there
is almost certainly at least two designs that would meet your needs,
and the things in TWTW are always concrete,
they've-been-built-and-tested-in-non-laboratory conditions. Another
good general reference to check for ideas on this stuff is Van
Nostrand's Scientific Encyclopedia, and if you have the option, look
first for a copy that is pre-'85. They stopped using English around

The UN, the CDC and the WHO all say in blunt, unequivocal terms, "A
flu pandemic is inevitable." Maybe not to your town and maybe not
this year; but history shows us to expect three per century. The
important hallmarks have already appeared this summer. Get a disaster
kit. Twenty-first century cultures are highly mobile and
Avian/Swine/Human flu hybrids kill even young, healthy people. Get
masks, gloves, no-cook food for 3 days, and easily prepared food for
3 weeks. Do it today. The worst that can happen is you end up with
spare groceries.

The life you save will be someone you kiss, someone you hug, or
someone you see every day. (If your life is so bad you hate all the
people you see every day, then pray for plague.)

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