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Re: A weighty subject



To Brian,

This is not as much of a flame as it might seem. It is just something
to goad you a little bit.

You managed to think up some clever responses to my e-mail so you
wouldn't have to admit that people really do say that thermometers
measure temperature, and voltmeters measure potential difference, and
balances measure mass.

And all you can come up with for whether an electronic balance will
properly re-calibrate on the moon is to say that we might lose
readership if we get into too many engineering details? What a
wimp-out!

For an electronic null-type balance, there is no mechanical/engineering
limitation that would prevent it from working in any gravitational
field from greater than zero up to slightly above earth-g. That is, if
we have a location where 0 < g < 10 m/s^2 this thing is going to
calibrate and measure mass just fine, unless there is a software check
to prohibit it from working if it appears that g is outside some
narrower range, say 9.7 < g < 9.9 m/s^2.

That is, your statement that "the engineer designing the device is
constrained by practical and cost considerations" just isn't correct
because there aren't any practical or cost considerations involved in
allowing this device to work over the range 0 < g < 10 m/s^2 rather
than over the range 9.7 < g < 9.9 m/s^2.

About the only thing the company might want to do is explain that the
precision will not be as high in low-g environments as it will be in
high-g environments.

I also do not understand your insistence that a device isn't really a
mass-measuring device if it cannot measure mass in a free-fall or in
field-free space. A mercury manometer cannot measure pressure
differences in free-fall or in field-free space. In fact, it cannot
measure pressure differences if it is lying on its side (perfectly
horizontal). Does that mean a mercury manometer does not measure
pressure differences under those conditions in which it does work?
Finding some environmental conditions under which an instrument does
not work does not invalidate the fact that it works under a different
set of conditions.

Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817