Magic wheel
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The magic wheel, or magnetic wheel is a wheel that continues to spin for a time, after being started, as if by magic. This device was invented in medieval Bavaria. It looked like a wagon wheel spinning on an axle, affixed to a base. The superstitious people of the time believed it spun by the power of magic.
The secret of the magic wheel was magnets (lodestones), not magic. Several large magnets were affixed to the wheel's outside rim, like the seats of a Ferris wheel. Each magnet was backed by a lead plate 'seat'. An extra stationary magnet was affixed to the base. Each magnet on the wheel's rim was attracted to the magnet in the base. The attraction (between the wheel and base) causes the wheel to turn on its own. Each magnet was attracted in turn to the magnet in the base, as it passed over it. The magnets were not allowed to touch one another.
Incorrectly deemed by some to be a perpetual motion machine, the magic wheel eventually comes to a stop because of frictional losses at the central bearing. Proponents of "free energy" devices have advanced the theory that the lead plating interrupts the magnetic attraction between the rim magnets and the stationary magnet in sequence, thus permitting the wheel to continue turning and bring the next rim magnet into position. This reasoning is nonsensical for two reasons. Lead does not block magnetic fields, and even if it did, considerations of symmetry quite straightforwardly imply that no interaction between rim magnets and the stationary magnets could generate the net increase in energy necessary to keep the wheel rotating.
The magic wheel was an impressive invention for the Dark Ages, a time when even some European kings were illiterate. An early German woodcut depicts a magic wheel.
