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Re: CONSERVATION OF ENERGY



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

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

I did not mean to say that Q is a state function and something better than
"thermal energy" would be appropriate because energy is a state variable.
I did not invent "thermal energy"; many authors are now using this term
where older textbooks used to say "heat".

It is my understanding that heat, in the first law, is defined as that
part of internal energy which is transfered (driven by?) a difference
in temetratures. The dT, in the formula above, is a difference between
the initial and final temperature of a body (in a process). In the
example I used dQ is due to friction. If I am correct (that c*m*dT is not
heat, as defined in thermodynamics) then what name should be given to it?
We need distinct names for distinct physical quantities.

Treating heat, work, and energy as though they are all the same thing
is [wrong].

I agree. And that is why I was asking how a common statemet "energy =
ability to do work" should be interpreted. Or what does it mean that
"work by friction is done at the expense of kinetic energy"? If these
questions can be clearly answerd (for a specific situation invented
to discuss the issue) then some progress will be made.

1) Can somebody describe the process under consideration using the terms
on which we can agree?
2) Can somebody explain the meaning of "work at the expense of energy"
and "energy is an ability to do work"? Are these phrases acceptable?
Why yes? why no?

I an not against generalizations but I suggest we begin with the concrete
situation at hand. This will help us to understand each other better.

Ludwik Kowalski