The Gyroscope

French physicist J. B. Foucault used gyroscope to prove that the Earth is revolving around its axis. Foucault's gyroscope was mounted on a Cardan joint (see the picture) and that is why it could spin at three joint angles to three axes, each at the right angle to the two others.

A spinning bicycle wheel is also a gyroscope. When you try to turn it to the left, the whole bike leans to this side. Similarly, if you hit a spinning-top while it is spinning from one direction, it starts performing precession motion, i.e. its axis circles round slowly. The Earth axis follows the precession cycle every 25000 years. Until recently gyroscopes driven by a stream of air under low pressure and spinning with the speed of 15000-20000 revolutions per minute, helped aircraft crew navigate.

Even in a levitron, the gyroscope motion is essential to stabilise its suspension in the magnetic field.

Once we turn the spinning wheel upside down, the whole chair starts to turn around. The law of conservation of angular momentum is at work.