Accompanied by the sound of music, Prof. Lieberman enters the stage carrying a large aluminium suitcase. He presents its strange behaviour. It is apparently very difficult to get the suitcase to move the way he wants it to. Finally he manages to put the suitcase on its edge onto a stool. He lets go and the suitcase remains standing, tipped at an angle, and it even starts to rotate slowly.
How does this work?
The trick is a spinning gyroscope that is hidden in the suitcase.
To explain what is going on we can have a look at an ordinary toy top. If it is set in rotation, it spins very fast around its own axis. If the axis is slanted, the top’s axis itself starts to rotate around a virtual vertical axis that meets the tip of the top. This movement is called precession.
The suitcase behaves similarly. The gyroscope inside the suitcase spins around its own axis at great speed. Since the suitcase is tilted, precession takes place, which makes the whole suitcase and the stool rotate.
