«(...) a torque τ applied perpendicular to the axis of rotation, and therefore perpendicular to L, results in a motion perpendicular to both τ and L. This motion is called precession.»(http://en.wikipedia.org/wiki/Gyroscope) Why does this happen? Assumpting this makes all further calculus very easy and we can calculate the angular speed of the precession motion without difficulty (see http://physics.nad.ru/Physics/English/gyro_txt.htm). But WHY do we assumpt this? What's the reason why the gyroscope does not rotate over the "expected" axle, as it does when the rotor is stopped? (I do not want you to tell me about experimental facts... I think it is pretty obvious that I am seeking for a theorical explanation) Please answer me as soon as possible. Thanks in advance. Stay cool!