Bob, a budding physicist, is sitting on a swivel chair at rest, holding out a large motorized flywheel in front of him. The wheel is oriented parallel to the ground.
Bob's swivel chair is a magical, 100% completely frictionless swivel chair, and Bob's weight is entirely supported by it (i.e. his feet aren't touching the ground). When Bob turns on the motorized flywheel, the wheel starts to spin counterclockwise. Naturally, as a physicist would expect, Bob in his chair immediately begins to rotate clockwise, since total angular momentum must be conserved.
After a fun bout of spinning, Bob deactivates the motor and the flywheel abruptly stops turning. Naturally, because angular momentum is conserved, Bob's chair also abruptly stops spinning so that Bob is once again at rest.
Sandra, another physicist, sees the fun Bob is having and decides to try the same thing with her own swivel chair. However, Sandra's chair isn't a magic frictionless chair like Bob's. It is very well oiled and has a low coefficient of friction, but the coefficient isn't exactly zero.
Undeterred, Sandra starts up her counterclockwise-spinning flywheel in the same way as Bob did, and rejoices as she begins to spin clockwise in her chair. But then, when she kills the motor and the flywheel abruptly stops spinning, she discovers to her surprise that she is not at rest. Instead, something very peculiar—some might even say "remarkable"—happens.
She repeats the experiment several times and notes with amazement that the peculiar phenomenon is reproducible no matter what the starting orientation of her chair and no matter how long she runs the flywheel before stopping it.
What is the phenomenon? What happens when Sandra stops the flywheel?