Impossible wheel
The
impossible wheel, also known as the
BC wheel (after the comic strip B.C), represents the most basic type of
unicycle, consisting of a single spoked
wheel with pegs extending from the
axle. The rider mounts the wheel by jumping onto it while in motion. This contraption has no pedals, so when the wheel's
inertia runs out due to
gravity and
friction, the ride ends.
The impossible wheel has of course no practical place in general transportation. In practice, the pegs would rotate with the wheel, making it, as the name implies, impossible to stand on.