rotor
A rotating part of a mechanical device; for example, in an electric motor, generator, alternator, or pump.
rotor: the spinning part that makes the machine work
A rotor is the component inside a rotating machine that actually spins. In an electric motor, it is the part that turns when current flows through it in a magnetic field. In a generator or alternator, it is what you turn (or what wind or water turns) to produce electricity. In a pump or compressor, it moves fluid or gas. The rotor sits inside a fixed outer shell called a stator, and the magnetic or mechanical interaction between them creates the useful work.
Rotors vary widely by application. In a small AC induction motor, the rotor is often a cast aluminum cage embedded in laminated steel, with no electrical connections needed. In a DC motor, the rotor is wound with copper coil and must be connected to power through a commutator and brushes. In a turbine or centrifugal pump, the rotor might be a single impeller blade assembly. In a rotary compressor, it can be a pair of interlocking lobes or screws. The material, shape, and construction depend entirely on the speed, torque, and medium involved.
Mechanical challenges and failure modes
Rotors must balance precisely. Even small imbalances cause vibration that wears bearings and generates noise. Dynamic balancing is typically done after assembly, often on a balance machine that spins the rotor and identifies where weight must be added or removed. Rotors also face thermal stress: as they spin, friction and electrical resistance generate heat, and uneven heating can warp the shaft or crack laminations. In corrosive environments, rotor surfaces rust or pit, weakening the material and accelerating wear.
The term rotor comes from the Latin rotare, meaning to turn, and has been standard engineering vocabulary for over a century. It appears alongside stator (the stationary part) in nearly every rotating electrical machine specification. In trade catalogs and drawings, rotors are often specified by shaft diameter, bore diameter, stack length, rated speed in revolutions per minute, and material composition. Understanding the rotor is essential for anyone selecting, maintaining, or troubleshooting motors, generators, pumps, and compressors.