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[Phys-L] Re: Animated Math - comments



On Monday 04 July 2005 19:05, jbellina wrote:
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.

To hone the point finely, that is incorrect. The name of the unit is "degree
Celsius", not "Celsius degree". At least in English. In other languages:
French: degré Celsius
German: Grad Celsius
Spanish: grado Celsius
Italian: grado Celsius
Russian: see http://www.cofc.edu/~frysingj/SI_russian.htm
(roughly, "gradus Tsel'ciya")
Greek: see http://www.cofc.edu/~frysingj/SI_greek.htm
(roughly, "bathmos Kelsios")
Japanese: see http://www.cofc.edu/~frysingj/SI_japanese.htm
(roughly, "sesshi")
Chinese: see http://www.cofc.edu/~frysingj/SI_chinese.htm
(roughly, "shèshìdù" or "shèdù")

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

Joe is precisely right in pointing out that altering the unit symbol to
indicate the nature of the quantity is pedagogically unwise. But so is
altering the unit name.

One of the hardest things we find to teach to engineers is the distinction
between quantities and units. Quantities of the same type may be added or
subtracted. To do so, one should put them in the same units, to facilitate
that operation. Thus, using T for thermodynamic temperatures, in
Delta T = T_f - T_i
all three quantities are of the same type and they are measured in the same
units, kelvins. Likewise, in
Delta t = t_f - t_i
where t is used to indicate Celsius temperatures, all three quantities are
measured in the same units, degrees Celsius. Note that I put "Celsius" up
front to modify the quantity "temperature" but I did not do that to modify
the unit.

Caveat: The use of the same unit to measure two quantities does not mean that
they are of the same type. For example, one cannot add a heat capacity value
to an entropy value, though both are measured in joules per kelvin.

The SI explicity states that units will not be modified to indicate the
nature or attributes of the quantity. That's how the SI got it down to so few
units! In America we have used ton for air conditioners, horsepower for
motors, Btus per hour for heating, kilowatts for electrical power and so
forth. But those are all units of one quantity: power. The only distinction
is the attribute. We measure the mass of gold in Troy ounces and the mass of
iron pyrite in ounces Avoirdupois. That is how we got ourselves into the
sorry mess of having over 2000 units in active use in this country.

Please, leave the units alone and unmolested. Teach the differences between
and the distinctions among the quantities.

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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