  It is believed that the first law of black-hole mechanics has no independent
physical significance and acquires it only after identifying with the first law
of thermodynamics. It is argued here that the first law of black-hole mechanics
has a direct physical significance: not only the term $\Omega dJ$ but all its
terms have the same mechanical meaning - the rotational kinetic energy of a
black hole in real or in an internal space. Moreover, it is shown that the
Kerr-Newman black hole is a system of non-degenerate plane rotators represented
by the corresponding terms in the first law of black-hole mechanics. It is
found that a degeneracy arises because the energy of a black hole does not
depend on where an internal angular momentum of a black hole associated with
the black hole area is determined on the horizon.
