- Published: Friday, 08 October 2021 15:00
Welcome back! This week we're visiting that ever-popular demonstration of conservation of angular momentum: the rotating chair and the bicycle wheel gyroscope, demo D3-05. You can see it in action in the video below, with physics student Dan Horstman.
When the user sits in the (stationary) chair with the wheel spinning and its axis oriented vertically, the wheel has an initial angular momentum. When they change the orientation of the wheel, this changes the direction of the wheel’s angular momentum; the human and chair now gain angular momentum opposite to the change in the wheel’s, so that the total angular momentum of the system stays constant.
Because the friction in the bearing of the rotating chair is very low, several cycles of this procedure can usually be completed before the system loses its energy and stops.
This is the same underlying physics that lets gyroscopes be used to orient spacecraft, or to stabilize ships at sea. It can also be entertaining to watch someone try to carry a suitcase with a spinning gyroscope hidden in it, and watch it pull them sideways whenever they turn a corner!