Re: [Phys-L] work versus mechanical transfer of energy

[Diego Saravia <dsa@unsa.edu.ar>]

> Here's another version, where the radiation has been replaced
> by a filament with some small but nonzero thermal conductivity.
> Assume the energy and entropy stored in the filament at any
> given moment are negligible.


I use another mail because in this case we have a "material" system between
the first two, so we have 3 systems, and the filament is not in
equilibrium, so you cannot use our equation, even splited in 3.

Its not clear if I can describe the state of that system even with an
infinite number of temperatures.

if you ignore the entropy in the filament, you cannot explain the
generation of entropy* or even the transport of the "heat", sorry for
speaking about heat.

  * a very important function in irreversible thermodynamics

but the important thing to study, I think, is that in all the process
covered by mi thermostatics is that heat is Tds and work pdV

if they are not, yo need another variables involved, or the variables you
use do not describe the system.

for example if you have a pad mixing a fluid with T and P, V fixed

you will need the angle, but the angle is not the function that appears in
U, could be the modulus integral of the angle, and then you have
irreversibility, but that variable is "irreversible by itself" it always
goes
in one direction.

ok, you have an example, U exists as function of V y S, but no variable in
U accounts for the work, another kind of systems.

I think its very hard to think about energy in thermodynamics without heat
and work.