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Re: Meauring Volts?



Ken Fox wrote:
However mass is but one measurable quantity of the sugar at
hand or needed for cooking, volume is another, weight another.
One could argue that these are properties of the object, the
lump or pile of sugar, which is where I found my quandary to
start.

and Jim Green responded:
Well, Ken, we have convincingly demonstrated here that language is
a fumbling point. But aren't "mass" and "color" and "momentum" and
"entropy" and "energy" properties of a system? If physicists could
agree on anything, maybe it could be the word to use in this
case.: Property? Characteristic? I would agree to any word as
long as it doesn't imply substance or flowability. <g>

Given the history of measurement jargon, I don't believe that Ken needs
to feel the least bit apologetic for using the term "quantity" in
referring to such "things" as mass, length, area, volume, etc. For most
of the 20th century it was common to use the term "quantity" to refer a
class of measurements such as "mass" or "length" or "time".

My textbook library isn't vast nor do I have time to search every text I
do have, but I'll lay a few references on you to document my point.
1955-1964, Charles Dull's famous HS texts from Holt; 1960-62, my
venerable Halliday & Resnick from my college intro courses at Michigan
Tech; 1965, the PSSC text published by Heath; 1972-1982, the Merrill
physics-lite offering from Murphy & Smoot. "As already pointed out,
there is a certain amount of arbitrariness in the choice of fundamental
quantities. For example, length, time, and mass can be chosen as
fundamental quantities; then all other mechanical quantities, such as
force, torque, density, etc., can be expressed in terms of (or derived
from) these fundamental quantities." -- Halliday & Resnick.

In the last HS text published in the 20th century (to my knowledge), the
Serway & Faughn book from Holt, the jargon has changed somewhat although
note the use of the word "quantity" is still inextricably coupled into
their new terminology. "The description of *what kind* of quantity is
represented by a certain measurement is called *dimension*. In the next
several chapters, you will encounter three basic dimensions: length,
mass, and time. Many other measurements can be expressed in terms of
these three dimensions. For example, physical quantities, such as
force, velocity, energy, volume, and acceleration, can all be described
as combinations of length, mass, and time. In later chapters, we will
need to add two other dimensions to our list, for temperature and for
electric current." -- Serway & Faughn.

I suppose you could go with something like "property" or
"characteristic" or "dimension" if you wish, but "quantity" has a long
and strong tradition going for it.

Best wishes,

Larry

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright <exit60@cablespeed.com>
Retired Physics Teacher
Charlotte MI 48813 USA
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Lord, preserve us from the excesses of those
who would do us harm; and preserve us from
the excesses of those who would protect us.
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