  The Fokker-Planck equation for a heavy particle in a granular fluid is
derived from the Liouville equation. The host fluid is assumed to be in its
homogeneous cooling state and all interactions are idealized as smooth,
inelastic hard spheres. The similarities and differences between the
Fokker-Planck equation for elastic and inelastic collisions are discussed in
detail. Although the fluctuation-dissipation relation is violated and the
reference fluid is time dependent, it is shown that diffusion occurs at long
times for a wide class of initial conditions. The results presented here
generalize previous results based on the Boltzmann-Lorentz equation to higher
densities.
