Physical significance of U
For arbitrary T(?), Uunits is a minimum with respect to variations that keep N(?) and T(?) constant. But actual perturbations may not conserve N and T.
U is not the free energy.
The true conservation law K+W=constant satisfied by the linearized electron fluid momentum equation has the potential energy W:
Is W minimized in equilibrium with respect to physical perturbations? Work in progress.
Numerical equilibrium solutions provide a clue.
The “U” principle can be expressed in physical units as: