  The dynamics of wavepackets in a relativistic Dirac oscillator (DO) is
considered. A comparison to nonrelativistic spin-orbit pendulum effect is
discussed. Particular relativistic effects, like Zitterbewegung in spin motion,
are found in Dirac representation. This trembling motion disappears in
Foldy-Wouthuysen representation. A substantial difference between the dynamics
of wavepackets corresponding to circular and linear orbits of a particle is
obtained and discussed.
