  We study the dynamics of an intruder moving through a fluidized granular
medium in three dimensions ($d=3$). The intruder and grains have both
translational and rotational degrees of freedom. The energy-dissipation
mechanism is solid friction between all pairs of particles. We keep the
granular system fluidized even at rather high densities by randomly perturbing
the linear and angular velocities of the grains. We apply a constant external
force of magnitude $F$ to the intruder, and obtain its steady state velocity
$V_s$ in the center-of-mass frame of the grains. The $F$-$V_s$ relation is of
great interest in the industrial processing of granular matter, and has been
the subject of most experiments on this problem. We also obtain the mobility,
which is proportional to the inverse viscosity, as a function of the volume
fraction $\phi$. This is shown to diverge at the jamming volume fraction. For
$\phi$ below the jamming fraction, we find that $V_s \sim F$ for small $F$ and
$V_s \sim F^{1/2}$ for large $F$. The intruder shows diffusive motion in the
plane perpendicular to the direction of the external force.
