  If the assumption that the center of mass(CM) and the center of charge(CC) of
the electron are two different points was stated 100 years ago, our conceptual
ideas about elementary particles would be different. This assumption is only
compatible with a relativistic description. It suggests, from the classical
point of view, that the angular momentum of the electron has to have a unique
value. In the free motion, the CC follows a helix at the speed of light. The
spin with respect to CC and to CM satisfy two different dynamical equations
which shows that Dirac spin operator in the quantum case satisfies the same
dynamical equation as the classical spin with respect to the CC. This means,
among other things, that the addition of the three Dirac's spin operators of
the three quarks can never give rise to the spin of the proton, so that the
proton spin crisis could be related to this incompleteness in the addition of
the quark's angular momenta. Some other effects related to spinning particles
like the concept of gyromagnetic ratio, a classical description of tunneling
and the formation of bound pairs of electrons, are analized.
