  We show by numerical simulations that the presence of nonlinear
velocity-dependent friction forces can induce a finite net drift in the
stochastic motion of a particle in contact with an equilibrium thermal bath and
in an asymmetric periodic spatial potential. In particular, we study the
Kramers equation for a particle subjected to Coulomb friction, namely a
constant force acting in the direction opposite to the particle's velocity. We
characterize the nonequilibrium irreversible dynamics by studying the
generalized fluctuation-dissipation relation for this ratchet model driven by
Coulomb friction.
