In reading my own messages I see a need for a small correction.
The amount of heat generated via a dissipative force should be
labeled as deltaQ while Q should be used as to indicate the
total amount of thermal energy, for example, 1.5*N*R*T
(for the ideal monoatomic gas).
In other words mhenergy should have been defined as the sum:
KE+PEgrv+PEspr+deltaQ
and deltaQ should be have been called an increment of thermal
energy, not the total thermal energy a body contains at a given T.
Another observation is that Model 2 is a good place to
introduce entropy, S. A change of entropy, deltaS, in an
elementary thermo-mechanical process, is deltaQ/T. The unit of
S is J/K. The significance of S can be explained later but the
positive nature of deltaQ (in Model 2) is a good place to
indicate that S has a natural tendency of growing.
Ludwik Kowalski