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Re: W+Q deprecated



For what it may be worth:

The first law of thermodynamics asserts:
A.) The Principle:
1.) For every well defined system there exists an energy state function
E(x1,x2 ...), a scalar quantity, where the xi are the appropriate state
variables.
2.) The value of the state function E may change by means of energy
transfers between the system and objects in its environment.
3.) These transfers are always such that the total energy E_tot of a
closed super-system of such systems is conserved (fixed in numerical
value).

I dare to think that no physicist will quarrel with the above.

B) Calculational Implementation:
4.) It is suggested that, where possible, each of these energy transfers
might be usefully expressed in terms of the system's state variables in
the general form dWi = Yi*dxi, where Yi is the partial derivative of E wrt
xi. Note that this quantity dWi is not an exact ("perfect")
differential - it is not the differential of a function. It is simply a
numerical evaluation of the amount the system energy E was changed by the
( i )th interaction of the system with its environment (electrical,
mechanical, gravitational, etc.) Often it is more convenient to evaluate
a quantity dWi by evaluating the energy gain/loss of the environmental
object involved in this energy transfer with the system.

5.) The taxonomy of partitioning changes in E among several dWi terms is
driven by the ad hoc model which produced the state energy function E(xi),
a model detailing the energy transfer possibilities between the system and
its environment.

6.) Experimental verification requires that one must include heat transfer
as a possible system/environment interaction. If one is describing a
reversible process, then the heat transfer can be included as a term of
the type described in (5) with dW = Y*dx becoming dQ = T* dS. This
notation (dQ vs dW) is simply to emphasize the special role played by heat
transfer in our choice of taxonomy. Note that dQ is also an inexact
differential.

7.) If we are describing an irreversible process, then we must seek an ad
hoc evaluation of dQ appropriate to each situation (e.g., in terms of a
heat transfer diffusion equation, heat capacities and temperature changes,
electrical Ohmic heat generation parameters, etc.

8.) The suggested calculational statement of the FLT is then summarized as
dE = dQ + dW. Note that once one has filled in the particulars of the LHS
of this equality for a particular process, the dW vs dQ distinction is
gone and irrelevant, and it matters not which appellation the writer was
assigning to an item from (7) above, so long as a consistent energy
conservation is effected. Otherwise the dW vs dQ distinction is only to
serve our human conceptualizing and calculating, wide variations often
being permitted without offending any testable physical "laws".

Of course there's more, but let's pause for any comments.

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor