Re: CONSERVATION OF ENERGY

[Leigh Palmer <palmer@sfu.ca>]

> 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.

As you state, it should properly be called heat, since a process, though
not a uniquely specified one, is implicit. It is certainly not an energy.
Use of the symbol dU (by which I infer you mean the change in U) is most
improper; heat is not the change in anything. You should use Q instead:

                        Q = m c dT

where m is the mass of a homogeneous system having heat capacity per
unit mass c (some modifier is appropriate here) and dt is the change in
temperature that occurs in the process of heating.

Some may think I am being terribly picky; I believe that I am not. This
particular error (which we physicists all understand completely, of
course - nudge nudge) completely baffles students. Treating heat, work,
and energy as though they are all the same thing is as quick a way to
lose a student as any I know. If they were all the same thing why would
we have three different terms for them, and why would we have a law which
treats them as separate entities!?

Leigh

Leigh Hunt Palmer                                  Phone: 604 291 4844
Department of Physics                                FAX: 604 291 3592
Simon Fraser University                             Home: 604 299 3731
Burnaby, BC  V5A 1S6                              email: palmer@sfu.ca
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