Re: There's work, and then there's work

[Bob LaMontagne <rlamont@POSTOFFICE.PROVIDENCE.EDU>]

Bob Sciamanda wrote:

> As a spin-off from another thread, let me explain my appreciation of the
> differences in the use of the term "work" between
>
> (1)the CM Work/KE theorem of mechanics, and
> (2)the First Law of Thermodynamics.
>
> (snip)
>
> Much confusion has resulted from using the word "work" to describe both Fdx
> of (1) and Ydz of (2)
> Some have even written that the CM Work/KE theorem of (1) is invalid and
> should not be used because its Fdx work does not always describe an energy
> transfer, as Ydz in (2) necessarily does by design.  The CM Work/KE theorem
> is a very useful calculational tool of Mechanics - it should not be asked to
> do what it knows nothing of.  Its work, Fdx, may in fact be useful in the
> First Law of thermodynamics as a Ydz, evaluating an energy transfer; but
> this is a separate question and must be answered by an ad hoc energy
> transfer model of the phenomenon at hand.

Your comments are very helpful - I have a class on this same topic later today.

In terms of Ydz, the electrical contribution to the "work" term of (2) is a good
example. Here Ydz is Vdq.  There certainly is no analogy here to CM work/KE for
the case of a constant current - yet energy changes occur.

Bob at PC