Re: ENERGY WITH Q

["Carl E. Mungan" <mungan@USNA.EDU>]

> Your #2 was "Heat is internal energy, or possibly just
> certain forms of internal energy called thermal energy."
>
> Replace "certain forms" with "certain part" and the
> discrepancy between your #1 and #2 will disappear.

I disagree. Either heat is energy "in" a system (defn 2) or it is
energy "in transit" from one system to another (defn 1). This
discrepancy is irreconcilable in the definitions.

Consider two systems A and B which possess internal energy (and let's
say no mechanical energy, for convenience of discussion).

Some interaction occurs and as a result the energy of A decreases and
that of B increases.

eg. - Say A is me and B is an ideal gas and the interaction is the
adiabatic compression of B by A.

According to defn 1, no heat is involved in the description of this
process at any point. Work was done. The gas gained internal energy.
I lost internal energy. Heat is a name of a kind of process. That
kind of process did not occur here. Specifically, there was no
conduction, convection, or radiation.

According to defn 2, system B increased in heat. Heat is a name of a
kind of internal energy. But careful! It is time dependent, as things
slowly thermalize. I find this troubling. I would rather say there is
an equivalent heating process which results in the same change in
internal energy of A. It is equivalent because it results in the same
final state but it is not identical operationally. I distinguish the
operation with a heat/work nomenclature and the final result with an
internal energy nomenclature.

You can only go with one view or the other, and your choice will
affect the way you teach thermo. Attempting to teach both views in
some kind of "unified" manner is futile and misleading.
--
Carl E. Mungan, Asst. Prof. of Physics  410-293-6680 (O) -3729 (F)
      U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu    http://physics.usna.edu/physics/faculty/mungan/