English to Italian Tech/Engineering Electronics / Elect Eng

An AC (Alternating Current) induction motor consists of two assemblies - a stator and a rotor. The interaction of currents flowing in the rotor bars and the stators' rotating magnetic field generates a torque. In an actual operation, the rotor speed always lags the magnetic field's speed, allowing the rotor bars to cut magnetic lines of force and produce useful torque.
The difference between the synchronous speed of the magnetic field, and the shaft rotating speed is slip - and would be some number of RPM or frequency.
The slip increases with an increasing load, thus providing a greater torque.
electric motor current torque curves
It is common to express the slip as a ratio between shaft rotation speed and synchronous magnetic field speed. The Slip is often expressed as
S = (ns - na) 100% / ns (1)
where
S = slip
ns = synchronous speed of magnetic field (rev/min, rpm)
na = shaft rotating speed (rev/min, rpm)
When the rotor is not turning the slip is 100 %.
Full-load slip varies from less than 1 % in high hp motors to more than 5-6 % in minor hp motors.