Gyroscope in Gimbals:
A spinning object, e.g. a coin on edge, is more stable against falling over than when it isn't spinning. This concept is used in mechanical inertial guidance systems, where a spinning wheel is mounted in gimbals to prevent torques to the axis of the wheel. Professor Lewin walks through the lecture hall with such a 3-axis gimballed gyroscope. The direction of the axis of rotation of the spinning flywheel does not change as he moves around.