set up: ================ () (wheel) || (pivot) * take +ve y axis directed to the right * take +ve x axis directed out of this screen * take +ve z axis directed upwards we know that weight of the wheel(-z-axis) about the pivot will produce a torque in the direction given by the right hand rule(into the screen). if the wheel is spinning anti-clockwise, an angular momentum will direct to the +y-axis given by right hand rule. so the torque will cause angular momentum to shift in the direction of "into the screen" . so why does angular momentum follow the direction of the torque? also, if right hand rule is just a convention, why does the angular momentum always seem to follow the direction of the torque in 1 way( into the screen) , instead of "out of the screen" since torque is just defined to be perpendicular to the force-radius plane? i realise that the wheel always seem to precess in 1 direction about the pivot as a result... anyone can solve my doubts? thanks a lot!