electric motor
A motor turns electricity into motion. Feed current into a coil sitting in a magnetic field and the coil twists — spinning fans, drills, pumps, cars, and hard drives. It answers the everyday question: how does electricity actually make something turn?
Precisely, a current-carrying loop in a magnetic field feels a turning force (a torque) tau = N B I A sin(theta), where N turns carry current I in a loop of area A tilted at angle theta to the field B. This torque spins the coil. A clever switch called a commutator (or its electronic equivalent) flips the current's direction every half-turn, so the torque keeps pushing the same way and the coil keeps rotating instead of just wobbling to a stop.
Motors are everywhere, and they are simply generators run in reverse. The honest and important subtlety is that while the coil spins it is also generating — it produces a back-EMF that opposes the supply (Lenz's law). This back-EMF limits the current, which is why a motor draws a large surge of current at the instant of start-up, before it has picked up speed.
In a cordless drill, pressing the trigger sends current into the armature coil and the magnetic torque spins the bit. Jam the bit so it stops turning and the back-EMF vanishes, the current spikes, and the motor quickly overheats.
Current in the coil makes torque; the commutator keeps it turning one way.
The very same device is a motor when driven by current and a generator when driven by motion. Regenerative braking in electric cars uses exactly this reversal to charge the battery.