Electric motor

An electric motor is a magnet being pushed by electricity, over and over. Ørsted had shown in 1820 that a wire carrying current is wrapped in a circular magnetic field; set that field near a permanent magnet and the two shove each other sideways. The trick of a motor is to arrange the geometry so the shove always turns the shaft the same way — and to reverse the current at the instant the coil passes the magnet, so the next half-turn pushes instead of pulls. Do that and rotation never stops.

Faraday's first version in 1821 needed no switching at all: a single wire hung to swing freely around a magnet standing in a cup of conductive mercury circled endlessly as long as the current ran. It was a toy — it could turn nothing useful — but it proved the principle: electricity could be spent as motion.

Before the motor, every machine drew its power from where the power was: a mill sat on a river, a workshop ran off a steam engine's shafts and belts, a hand tool ran off a hand. The motor cut that cord. Power could now travel down a wire as electricity and become motion at the far end, in any size, anywhere a wire reached — a factory of independent machines, a fan, a tram, a pump in a basement, a drill you hold. It is the mirror image of the generator: the generator turns motion into current, the motor turns current back into motion, and between them electricity became the universal go-between for moving things.

The leap from Faraday's spinning wire to a machine that could do work came in 1834. In Potsdam, Moritz Hermann Jacobi built the first genuinely practical motor — a rotating armature switched by a commutator — that could lift about eleven pounds a foot every second, roughly fifteen watts of real mechanical power. The same year, in a Vermont smithy, the blacksmith Thomas Davenport and his wife Emily Davenport built the first American motor; Davenport's US patent of 1837 (number 132) was the world's first patent on an electric motor. All of them work the same way the coil in the recipe does: a coil in a magnetic field, and a switch — the commutator — that flips the current each half-turn so the push keeps coming.

The recipe above is the whole idea reduced to a battery, a magnet, and a bent loop of wire. Half-stripping one end of the coil is a crude commutator: it lets current through for the useful half of each rotation and cuts it for the other, so the coil is shoved forward and then coasts, forward and coasts, into a steady spin.

Jacobi's and Davenport's early motors ran on batteries, and battery current was far too costly to compete with steam — the motor waited on a cheap source of electricity. That arrived with Faraday's generator scaled up into the dynamo and, after 1886, the alternating-current grid. Once current was cheap, the motor swallowed the mechanical world: electric trams and subways, elevators that made the skyscraper possible, factory machines each with their own motor instead of belts off a single steam shaft, and eventually the small motors hidden in every fan, pump, drill, disc drive, and appliance. Most of the electricity generated on Earth is spent turning motor shafts.