884. Can you explain gyroscopic precession? — BW, Newport, RI
When a gyroscope is spinning rapidly, it has a large amount of a conserved physical quantity called angular momentum. Angular momentum is a special measure of rotational motion that can't be created or destroyed—it can only be transferred between objects. As long as nothing tries to transfer angular momentum to or from the spinning gyroscope, it will continue to spin at a steady pace about a fixed axis in space. But when an external torque (a twist) is exerted on the gyroscope, a transfer of angular momentum takes place. The gyroscope's rate of rotation or its axis of rotation begins to change so that its angular momentum changes. If you apply a twist to the gyroscope around its axis of rotation, it will either spin faster or slower, depending on which way you twist it. But if you twist the gyroscope about a different axis, its axis of rotation will shift—the gyroscope will undergo precession. The direction of this precession depends on how you apply the twist and tends to be very non-intuitive.