  Stimulated generally by recent interest in the novel spin Hall effect, the
nonrelativistic quantum mechanical conserved currents, taken into account of
spin-orbit coupling, are rigorously formulated based on the symmetries of
system and Noether' theorem. The quantum mechanical force on the spin as well
as the torque associated with the variance of angular momentum are obtained.
Consequently, the kinetic interpretation of the variances of spin and orbit
angular momentum currents implies a torque on the "electric dipole" associated
with the moving spin. The bearing of the force and the torque on the properties
of spin current in a two-dimensional electron gas with the Rashba spin-orbit
interaction is discussed.
