  We study effects of pinning on the dynamics of a vortex lattice in a type II
superconductor in the strong-pinning situation and determine the
force--velocity (or current--voltage) characteristic combining analytical and
numerical methods. Our analysis deals with a small density $n_p$ of defects
that act with a large force $f_p$ on the vortices, thereby inducing bistable
configurations that are a characteristic feature of strong pinning theory. We
determine the velocity-dependent average pinning-force density $\langle
F_p(v)\rangle$ and find that it changes on the velocity scale $v_p \sim
f_p/\eta a_0^3$, where $\eta$ is the viscosity of vortex motion and $a_0$ the
distance between vortices. In the small pin-density limit, this velocity is
much larger than the typical flow velocity $v_c \sim F_c/\eta$ of the free
vortex system at drives near the critical force-density $F_c = \langle
F_p(v=0)\rangle \propto n_p f_p$. As a result, we find a generic excess-force
characteristic, a nearly linear force--velocity characteristic shifted by the
critical force-density $F_c$; the linear flux-flow regime is approached only at
large drives. Our analysis provides a derivation of Coulomb's law of dry
friction for the case of strong vortex pinning.
