Ken Fox asked about calibrating spring scales for mass (see below).
It would be inconvenient to recalibrate a spring scale for different
g-fields or for various non-inertial frames if it is a simple spring scale
and re-calibration would involve re-painting the dial.
But modern computerized chemical "balances" are actually spring scales.
They work just fine for mass and will work in any g-field or non-inertial
frame if the conditions are stable enough to allow a calibration. Indeed,
they can be called a balance in the sense they do use a standard mass for
calibration, and the reading is indeed a comparison of the subject to the
standard. Unlike the equal-arm balance, the standard is not in use
simultaneously with the subject being massed, but the calibration can be
made as often as necessary, including just before doing the actual desired
massing.
A year or so ago I described (on this list) how some computerized
balance/scales can be tricked by using incorrect calibration masses, proving
that the balance could be easily calibrated to work properly on the moon.
Calibration would be as easy and as quick as doing the calibration on
earth... you just follow the same exact calibration procedure.
Some computerized scales/balances will not work on the moon because their
software contains code to sense an "incorrect calibration mass" if it is
asking for a 100-g calibration mass and the pan deflection is significantly
more/less than expected. But lacking this software, or given sufficient
latitude, the balance can be calibrated anywhere except for a zero-gravity
inertial frame.
In conclusion... if "balance" implies a "comparison to a standard" then the
distinction between a balance and a scales has been wiped out by
computerized scales. We even have nice analytical balance/scales with
internal motor-driven calibration masses that self calibrates every time you
turn it on.
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
We cannot calibrate a spring scale in mass units that will work in all
reference frames as the acceleration or strength of the field will change
the elongation of the spring as it achieves equilibrium.