On Aug 27 , at 10:27 AM, Stanislav Jakuba wrote:
> ... BIPM is neither infallible nor keen on removing its own contradictions.
> Several of those concern temperature and Celsius, particularly the
> thermodynamic temperature.
>
> Why the adjective thermodynamic with the temperature in the main table? What
> are the other temperatures and what are their units? Some justify the
> adjective on the basis of the existence of the “Celsius temperature” (see
> SI10). But it is not in any table.
> For decades I have been fighting for the simple statement:
> “Temperature – its unit is the kelvin in SI, symbol K.”
>
> Some (SI10 included) claim that degree Celsius is a derived unit. This cannot
> be true if one believes the definition of SI derived units and how they are
> formed. One or the other must be incorrect.
Stan,
I agree that there is something wrong ith the logic here and I think I have a
reasonable alternative view of the situation that may be helpful.
My view is that kelvins and degrees Celsius are NOT two different units for
measuring the same thing.
They are two IDENTICAL units used to measure DIFFERENT things.
The two different things are
(1) the elevation of temperature above absolute zero
and
(2) the elevation of temperature above (or below) freezing.
(Throughout this note, when I write "freezing" I mean the freezing point of
water with all the usual conditions that are normally prescribed.)
Using the terminology "the temperature is 30 kelvins above freezing" is
identical to the practice of measuring altitudes of geographic features or
things in the Earth's atmosphere (or even above). One commonly measures the
elevation above (or below) mean sea level. It would certainly be possible in
this day and age to measure "absolute" elevations, meaning distance from the
center of the Earth. No one would consider measuring both of these in metres
but calling the unit by one name if the elevation is from the center of the
planet while calling it by a DIFFERENT name when it is measured above sea
level. The measures, both in metres, are measures of two different things
(height above sea level vs. distance form Earth's center).
My suggestion would be to emphasize that the phrase "degree Celsius" MEANS
"kelvins above freezing". The proper usage would be to state "Today's high
temperature was 30 kelvins above freezing" or writing "Today's high temperature
was 30 K afw". I just invented the abbreviation "afw" to mean "above freezing
water". This would be similar to using ASL to mean "above sea level" as in "The
height of that mountain is 2224 m ASL", as is already done in some places.
I would be the first to point out that it is improper (by SI rules) to combine
the metre symbol with the sea level abbreviation (as it indeed is done in some
places) so that it should not be written "The height of that mountain is 2224
mASL". So also it would be improper to write "The temperature is 30 Kafw"; it
must be "The temperature is 30 K afw".
Bill Hooper
Temperature 37 K apf
Fernandina Beach, Florida, USA
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SImplification Begins With SI.
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