  We studied the drag and lift forces acting on an inclined plate while it is
dragged on the surface of a granular media, both in experiment and numerical
simulation. In particular, we investigated the influence of the horizontal
velocity of the plate and its angle of attack. We show that a steady wedge of
grains is moved in front of the plow and that the lift and drag forces are
proportional to the weight of this wedge. These constants of proportionality
vary with the angle of attack but not (or only weakly) on the velocity. We
found a universal effective friction law which accounts for the dependence on
all the above-mentioned parameters. The stress and velocity fields are
calculated from the numerical simulations and show the existence of a shear
band under the wedge and that the pressure is non-hydrostatic. The strongest
gradients in stress and shear occur at the base of the plow where the
dissipation rate is therefore highest.
