  Vortex dynamics in superfluids is investigated in the framework of the
nonlinear Schr\"{o}dinger equation. The natural motion of the vortex is of
cyclotron type, whose frequency is found to be on the order of phonon velocity
divided by the coherence length, and may be heavily damped due to phonon
radiation. Trapping foreign particles into the vortex core can reduce the
cyclotron frequency and make the cyclotron motion underdamped. The density
fluctuations can follow the vortex motion adiabatically within the phonon wave
length at the cyclotron frequency, which results in a further downward
renormalization of the cyclotron frequency. We have also discussed applications
on the dynamics of vortices in superconducting films.
