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Re: CONSERVATION OF ENERGY



On Sun, 13 Jul 1997 Leigh <palmer@sfu.ca> wrote:

There is a work-energy theorem by means of which the two quantities may
be seen to be related, much as the height of a water column is related
to the pressure at its base. Height and pressure are not the same thing,
however, even if the latter is expressed in the units of the former,
a [still] common practice.

Aside from the current topic I find this interesting. One of the arguments
in favor of SI, when it was debated, was that each quanity will have a
distingushable unit (see "A Short History of the SI in Electromagnetism",
TPT, February 1986). A common unit, joule, for "heat, work and energy" was
viewed as an improvement over a situation in which calories were used for
heat and ergs for work and energy. By the way, the CGSE unit of capacitance
was centimeter.

And here is a loosly related "aside" from another list.

........ two quotation from Hans U. Fuchs (A.J.P. March 1987).
The article refers to the innovative German way of teaching energy at
the introductory level.

1) In 1970s, Falk et al. came up with a concept of teaching physics based
on "substancelike" quantities ... as the carriers of energy in physical
processes. Entropy is the carrier of energy in thermal phenomena. This
is a very simple picture which helps us to .....

2) Clausius gave the name of "entropy" and defined it as an integral of
dQ/T. Such a definition appeals to a mathematician only. In justice
to Carnot, it should be called caloric, and be defined directly from
his equation W = A*Q*(T-To), which any schoolboy could understand.
[Here, W is the work done by a quantity Q of caloric falling from a
temperature T to To; A is a convestion factor ...].

The second quotation is itself a quote from a 1911 paper. Schoolboys were
very knowledgable in those days. As you probably know, Carnot's model of
a heat engine was a water wheel. This explains the terminology of
"falling" from one temperature to another.

Note that in SI A would be equal to 1 and the unit of Q would be J/K, as
for entropy. Interesting! But do we really want to resurect caloric and
give it a new interpretation? I am not automatically agains this. But I
want to hear good arguments favoring this approach. Why is it better than
what has been developed since then. [A conservative approach based on
"If it ain't broke don't fix it".]

Is anybody on this list familiar with the new German approach to which
Fuchs is referring? Can it be summarized for us briefly? I heard that the
concept of work, as "force time distance", has been eliminated.

Ludwik Kowalski

P.S. Leigh, how should dU=c*m*dt be called? We used to call it "heat" but
this was in conflict with how heat is defined in thermodynamics. What is
wrong with the name "thermal energy"? It is now used by many authors.