| Most car speedometers
use this same type of mechanism. The design is simple and there
are very few parts to wear out. The spinning magnet produces an
electric current in the aluminum wheel. Those induced currents,
in turn, produce a magnetic force, which causes the aluminum wheel
to rotate until a spring balances the magnetic force. The faster
the spinning, the stronger the currents, the greater the magnetic
force...the more the wheel turns.