[ceptimus]

In old-fashioned cars with speedometers and tachometers with real mechanical hands (pointers) the dials worked by this effect. There was a spinning cable connected to the wheels or engine that spun a magnet around inside the instrument. There was an aluminium cup around the magnet - and that cup was connected to the indicator hand/pointer with a spring pulling it back towards zero. The faster you drove, the faster the magnet spun, and that dragged the cup with it against the force of the spring, so indicating your speed.

This was the standard way of doing it up till about 30 years ago. Most modern vehicles have electrically driven instruments, even if they still have mechanical hands.