A molecular kinetic model is developed for the gas-dynamic flow around a flat plate moving through the air at positive and negative angles of attack. It is shown that, at low velocities of the plate motion, the lift and the drag are determined by the gas-dynamics of the air flow in the rear region while at high velocities close to the speed of sound velocity the impact interaction between the plate and the molecules of the surrounding medium in the front region is of critical importance. No separated flow occurs behind the plate at low velocities. The conditions under which the drag and the lift of the plate reverse their directions are determined.

 

Key words: gas-dynamic process, flow, plate, air resistance, molecular kinetic theory, lift force, drag force.