  On the analytic ground we examine a physical mechanism how particle velocity
can protect an entanglement when quantum system is embedded in Markovian or
non-Markovian environment. In particular the effect of particle velocity is
examined in the entanglement sudden death (ESD) and revival of entanglement
(ROE) phenomena. Even though particles move fast, the ESD phenomenon does not
disappear if it occurs at zero velocity. However the time domain $0 \leq t \leq
t_*$ for nonvanishing entanglement becomes larger and larger with increasing
velocity. When ROE phenomenon occurs at zero velocity, even small velocity can
make this phenomenon not to occur although the oscillatory behavior of
entanglement in time is maintained. For comparatively large velocity the
amplitude of the oscillatory behavior becomes extremely small. In this way the
entanglement can be protected by particle velocity. The protection of
entanglement via velocity is compared with that via the detuning parameter.
