Pat,
I'm concerned about your inclusion of voltage in your recent, interesting
email post to the USMA list.
Pat Naughtin wrote (tongue in cheek):
> (To delay SI, one should) Encourage the use of
> words like footage, mileage, and yardage where you use the name of the
> measuring unit as if it were the name of a physical quantity. This always
> was an inferior and confusing practice. The words amperage, tonneage,
> voltage, and wattage should be enough to get you started.
I agree totally with what you; it is indeed an inferior and confusing
practice. I have taught that to my students for years (decades, really).
But I have a problem with expecting people not to use "voltage" (and even
with trying not to use it myself) because the alternative CORRECT terms are
fraught with their own problems.
The most common "correct" term for the word voltage is "potential
difference". I find that an awkwardly long name for a useful quantity. In
technical situations it is also possible to confuse "potential difference"
with just plain "potential", a different though related concept. (That is
why, if one uses the term "potential difference" at all, one must insist
upon calling it by its full name and not shortening it to "potential".)
The other meaning that can be ascribed to "voltage" is "electromotive force"
(often shortened to emf, pronounced as E-M-. That name is even worse
(awkwardly long) than is "potential difference". Also, it is not a force at
all and one could question whether "motive" is appropriate since motion (of
electrons or ions) is not always involved.
Furthermore, "potential difference" and "elecromotive force" are not
interchangable. The difference may be subtle but it is real. (A voltage of
12 V across a battery is its emf and is not necessarily equal to the
potential difference across it's terminals. A voltage of 12 V across a
current carrying resistor is always a potential difference but is not an emf
under any circumstances.)
So, if we don't call it "voltage", what do we call it? The difficulty with
the two correct terms (the only ones that I know of) are so great that I
find myself concluding that the term voltage should be allowed; that it
should be considered the one (and only) exception to the rule that
measureable quantities NOT be named by adding "-age to their unit names.
One of the practical reasons for not using terms like footage, mileage, and
yardage, amperage, tonneage, and wattage (which you cited) is that doing so
seems to prohibit using other correct units for the same measurement. Surely
any length can be measured in either feet or yards or miles (and others,
including metric units). If you call that length "the yardage", it suggests
that it CAN'T (or shouldn't) be measured in feet or miles (or metric). It is
one of the stumbling blocks to converting to metric when one doesn't
understand how you can measure yardage in metres.
I recognize this problem with my decision to use "voltage". I tell my class
about it and advise them to be aware that, although I call the quantity
"voltage", it is not always measured in volts! It may be measured in
millivolts, kilovolts, megavolts, etc. At least all of these end in the name
"volt" which make the word "voltage" not seem too awkward when applied to
them.
I'd be interested in your reaction to my position:
(1) regarding what name to call voltage if one does not want to use the word
"voltage", and
(2) whether making this one exception (with appropriate caveats) is
reasonable.
Regards,
Bill Hooper
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Keep It Simple!
Make It Metric!
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