The following is a direct scan from Bridgman's 1941 " The Nature of
Thermodynamics":
*********************************
58 THE NATURE OF THERMODYNAMICS
. . . it is convenient to write the law in the conventional
differ-
ential form
dE = dW + dQ.
If the changes for any actual body are not small and the
material of the body is not under homogeneous conditions,
we assume that we can split the body or the process into
parts small enough so that the differential form will apply.
The essence of the first law is now contained in the mathe-
matically different character of dE on the one hand and
dW and. dQ on the other; dE is a perfect differential, as
distinguished from dQ and dW. Strictly, these two sorts
of small quantities should not be written in the same way,
and some careful authors do actually use a different nota-
tion for them. The statement that dE is a perfect differen-
tial implies that there are certain variables of “state” of the
body such that when these are brought from fixed initial
to fixed final values the sum of the heat and the work for
the change is always the same, whatever the precise method
of change. Or, expressed in another way, whenever the
body (or the interior of the region) is brought back to its
initial “state” the sum of heat and work absorbed during
the complete cycle of change will be found to be zero.
It is the statement that dE is a perfect differential in the
parameters of state that removes from dE the character of
a pure convention, defined by the equation. Under these
conditions the equation formulating the first law really
says something.
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The left hand side of the above FLT is expressly written as the genuine
differential dE in order to stress that we are postulating the existence
of a state function E. The right hand side of this general statement is
then to enumerate in some general fashion the infinitesimal quantities
which may sum to produce the infinitesimal increment dE: different forms
in which infinitesimal quantities of energy (E) may be added to the
system. The infinitesimal character of these energy additions is the
motivation for the "delta" notation, whatever form one might adopt. The
desire to distinguish heat as a "special" type of energy transfer is the
motivation for distinguishing the two general types of quantities of
energy. Once a particular system is specified and understood, these
quantities may be written in terms of specific state variables.
Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net http://www.velocity.net/~trebor
----- Original Message -----
From: "John S. Denker" <jsd@MONMOUTH.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Monday, May 12, 2003 2:11 PM
Subject: Re: TdS is not dQ or d(anything)
| . . . Please clarify:
|
| If dbar(W) is a "long-time honored notation meaning ... a
| quantity of something", what is the "something" here?
| Is dbar(W) a quantity of W? If so, what is W?
|
| P is a function of state
| V is a function of state
| P dV is a function of state ???????
| W is not a function of state . . .