Why Induction Machine always runs below synchronous speed?

Induction motor works on the principle of induction. When both rotating magnetic field of stator and rotor of induction motor rotates with same speed no emf is induced in the rotor conductors resulting no torque is produced in the rotor of induction machine and motor will stop. Therefore in order to have torque for rotating the rotor induced emf is required. Hence Induction motor rotates with speeds less than synchronous speed.