The contact force formula_13 is formula_14 where formula_15 is the gravitational acceleration and formula_16 is the vertical axis pointing upwards. The torque about the center of mass is formula_17 which we can rewrite as formula_18 where formula_19. We can conclude that both the angular momentum formula_20, and the disk are precessing about the vertical axis formula_16 at rate At the same time formula_22 is the angular velocity of the point of contact with the plane. Let's define axis formula_23 to lie along the symmetry axis of the disk and pointing downwards. Then it holds that formula_24, where formula_25 is the inclination angle of the disc with respect to the horizontal plane. The angular velocity can be thought of as composed of two parts formula_26, where formula_27 is the angular velocity of the disk along its symmetry axis. From the geometry we easily conclude that: