  We investigate the relativistic corrections to the static potential, i.e. the
O(1/m) potential and the O(1/m^2) velocity-dependent potentials, in SU(3)
lattice gauge theory. They are important ingredients of potential
nonrelativistic QCD for heavy quarkonium. Utilizing the multi-level algorithm,
we obtain remarkably clean signals of these potentials up to r=0.9 fm. We
observe long range nonperturbative contributions to these corrections.
