Motor Slip & Synchronous Speed

Why an induction motor's rotor never quite catches up to its own rotating magnetic field — and why "catching up" would mean the motor stops making torque entirely.

It sounds like a defect: put a load on a perfectly healthy induction motor and its shaft speed drops a little below the speed of the magnetic field spinning inside it. It never fully recovers, no matter how well the motor is built. But that small, permanent lag — called slip — isn't a symptom of anything wrong. It is the entire mechanism by which the motor produces torque in the first place. A motor with zero slip would be a motor producing zero torque.