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. The forces required to disturb the surface of soil have been an important concern of humankind since the invention of the plow, the principal animal-powered tool for this task, about 6 000 y ago [1]. In this paper we consider the forces on the simplest possible plow, a flat blade inclined in the direction of motion, interacting with the simplest possible soil, a non-cohesive granular material. Remarkably, this ancient problem has recently received significant attention [2,3] because of renewed interest in the complex and poorly understood rheology of dry granular materials [4].A simple inclined blade has also been studied as a surrogate for the more complicated situation of a rolling wheel moving over a granular roadbed [5][6][7][8][9][10][11][12]. Both plows and rolling wheels exhibit an oscillatory instability which produces a spontaneous rippling of the roadbed, leading to a condition known as washboard or corrugated road. Washboard ripples bedevil drivers on unpaved roads worldwide and their mitigation is a serious engineering challenge [13][14][15]. The modern framework of nonlinear pattern formation [16] gives new insight into the formation of washboard ripples [10][11][12]. A key feature of the washboard instability is the existence of a critical speed v c below which the flat roadbed is stable. It has been shown that neither a spring and dashpot suspension, nor compaction of the roadbed are essential to the existence of the instability [10]. For a wide plow, the problem can be reasonably studied in a 2D vertical plane. Dimensional analysis arguments suggest [10,11] that the critical speed for the instability scales as v c ∼ (mg 2 /ρw) 1/4 , where g is the acceleration due to gravity, m is the mass of the plow, w is its width and ρ is the density of the granular material [11].In this paper, we examine the case of a fixed plow using a combination of experiment and molecular dynamics simulation. An understanding of this basic state is a pre-requisite to the elucidation of its subsequent instability to form a washboard pattern. To do this, we must account for the lift and drag force...