  We express dynamics of domain walls in ferromagnetic nanowires in terms of
collective coordinates generalizing Thiele's steady-state results. For weak
external perturbations the dynamics is dominated by a few soft modes. The
general approach is illustrated on the example of a vortex wall relevant to
recent experiments with flat nanowires. A two-mode approximation gives a
quantitatively accurate description of both the steady viscous motion of the
wall in weak magnetic fields and its oscillatory behavior in moderately high
fields above the Walker breakdown.
