Electric motor. Close up of part of the electric motor of a hand drill, showing the rotor (gold, centre), carbon brushes (small grey blocks left and right of the rotor), commutator (within the rotor), and rotating coil (copper wire, top). The rotor and rotating coil make up part of the armature. The armature is the part that rotates under the influence of a magnetic field, as electrical energy is converted into motion.