Re: ENERGY WITH Q

["John S. Denker" <jsd@MONMOUTH.COM>]

At 10:07 PM 10/26/01 -0400, Ludwik Kowalski wrote:

>        deltaU=Q+W            (The First Law)

This is a bad idea for reasons discussed previously.  See also
  http://www.monmouth.com/~jsd/physics/thermo-laws.htm#sec-eschew-w+q

> where deltaU is a finite change in Esys while Q and W (with
> appropriate signs, according to a convention) are heat and work.

Not according to any conventional definition of "heat" or "work".

> Suppose I push a box along a floor with a rigid stick. Some
> chemical energy is lost by my body while thermal energy is added
> to the box and floor. The stick is not a thermal conductor, no
> energy travels through the stick.

Huh?  Energy must be travelling through the stick.

> On the other hand, ... In [another] interpretation the mechanical energy
> does travel through my non-conducting stick.

I should think so!  This is the only reasonable interpretation.

> If this is a correct then we should replace W by mechanical energy X
> (deltaU=Q+X). In that context both Q and X flow except that no randomness is
> involved in the rapid flow of X.

This is symptomatic of the impossibility of giving a consistent
interpretation to the W+Q equation.

> The traditional First Law tells us that energy is conserved in
> a closed system (U=constant). That is it.

If U=constant is the first law, call it the first law.  Don't call the
deprecated W+Q equation the first law, as was done above.

> In my opinion learning of physics (in an introductory course)
> would be easier if the energy conservation idea was presented in
> the spirit of Denis the Menace, as described by Feynman.

I agree.

> Why do need W in the First Law?

Beats me.

> The Second Law, I think, does not need it either.

I agree.