Gyroscopic Motion - I

(2) If a body which is spinning is precessed about the perpendicular axis, the gyroscopic couple has to be applied on the body. The body in turn will apply a reaction on the members which apply gyroscopic couple on the body, as per Newton's third law.

If the axes of spinning and precession are perpendicular to each other, the gyroscopic couple is

This shows that if is high, a huge amount of torque is needed to precess it. This fact about the gyroscope is exploited by using it to provide stability to vehicles.

A bicycle remains stable at high speed because of gyroscopic motion. If you want to turn the bicycle towards left, lean your body towards left. By leaning the bicycle towards left, you shift the center of mass towards left. This produces, a torque pointing from front wheels towards rear wheel. Hence, the angular momentum vector rotates about a vertical axis and the bicycle precesses towards left.