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[Phys-L] Re: Animated Math - comments



I'll just jump in briefly. If you want to describe a temperature
change you would say it is so many Celsius degrees. If you want to
describe a temperature,you would say it is so many degrees Celsius.
Sadly that gets abbreviated into symbols that are not clearly defined.
The intent is correct, the symbolism is easily missinterpreted.

Further, students often have difficulty distinquishing temperature from
change in temperature. So having a symbolism that easily confuses
these is not pedagogically wise.

cheers,

joe
On Jul 4, 2005, at 5:35 PM, James R. Frysinger wrote:

On Monday 04 July 2005 17:37, Bernard Cleyet wrote:
"The SI derived temperature scale is the Celsius scale now, no longer
called the Centigrade scale. The symbol is °C and the space comes
between
the number
and the raised circle, not between the raised circle and the number. A
raised
circle immediately after the number (especially with a "C" following)
would
indicate a plane angle value given in degrees."


Yes. Furthermore, I was taught that a number followed by a space and
degrees C. is a temperature while a number followed by a space and C.
deg. is a temp. difference or change.
bc

If I understand you correctly, Bernard, you are saying that
you were taught
to use
5 ¡C to indicate a temperature of 5 degrees Celsius and
5 C¡ to indicate a temperature change of 5 degrees
Celsius.
I have seen a textbook somewhere in recent history where the author
created or
used that format. It is, however, not proper SI to do so. In the SI
there is
no symbol C¡ and it represents nothing (unless one can imagine coulomb
degrees [of arc]). The SI is a creation of an international committee
structure that arises from an international treaty. It is not "up" for
adaptation by users except as its rules provide. It is defined and
"owned" by
that committee structure --- or, if you will, by the many, many
nations that
signed the treaty.

Anyone who would propose to make this part of the SI can
contact the
Consultative Committee on Units (CCU) to propose it, perhaps by going
through
IUPAP. I think that the odds of that making it all the way to CIPM
would be
about as good as a proposal to use
5 Pa to indicate a pressure of 5 pascals and
5 aP to indicate a pressure change of 5 pascals.
But that's just a guess on my part.

The SI is a very concise set of units, prefixes, and rules.
The tradeoff one
must make for such a tersely defined system is strict adherence to the
rules.
That upsets lay people because lay people have always been cavalier
with
units. It also upsets scientists who delight in forming their own
"local
definitions", which perhaps plays to their creative spirits. Alas, both
instincts detract from the universal comprehension that the SI brings.

One therefore must vent creativity on definitions of
quantities and leave the
small set of units (and their symbols) unmolested. Good bye to Vac and
Vdc,
folks! It's the voltage that changes, not the volt. There is only one
volt.

Likewise, there is only one degree Celsius. The SI brochure
(see below) says
in Table 3, that ¡C = K. It also says, in note d, "This unit may be
used in
combination with SI prefixes, e.g. millidegree Celsius, m¡C." Now that
blows
a lot of people's minds! Thus, the triple point of water occurs at a
temperature of 10 m¡C.

Thus the degree Celsius is a special name for the kelvin, one
that is used on
a derived temperature scale. Conveniently or confusingly, that is
called the
Celsius temperature scale and the values on that scale are stated in
terms of
the degree Celsius, just as the values on the thermodynamic
temperature scale
(nee Kelvin scale) are given in kelvins. (By the way, the degree
Kelvin is no
more; now it is just the kelvin.)

Another characteristic that folks have, be it lay or
professional, is a
propensity to follow the examples of others instead of checking the
source
documentation. That perpetuates a lot of bad information. For example,
I was
amazed when I read Milliken's original papers and found out what he
actually
concluded, in contrast to what what the textbooks all said that he had
concluded. Fortunately textbook writers today are more inclined to go
to the
primary sources rather than "averaging" what existing textbooks say.

Below are some links to references you might find handy for
your reading
pleasure:
The defining document, commonly referred to as the "SI brochure", for
the SI
in its authorized English translation:
http://www.bipm.org/utils/en/pdf/si-brochure.pdf
The online version of the above:
http://www.bipm.org/en/publications/brochure/online.html
The authorized U.S. adaptation of the SI, approved by the CIPM; this
is what
authorizes -er endings instead of -re endings and L instead of l for
the
symbol for the liter in the U.S.:
http://physics.nist.gov/Pubs/SP330/sp330.html
A very handy guide that provides a bit more verbosity to clarify
issues on how
one should use the SI; it is aimed at federal agencies but it is nicely
done!:
http://physics.nist.gov/Pubs/SP811/sp811.html

Jim

--
James R. Frysinger
Lifetime Certified Advanced Metrication Specialist
Senior Member, IEEE

http://www.cofc.edu/~frysingj
frysingerj@cofc.edu
j.frysinger@ieee.org

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Joseph J. Bellina, Jr. Ph.D.
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556
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