The linear induction motor is essentially a cylindrical induction motor that has been cut and unrolled as shown below.
The field moves along the windings at a velocity v=2pf where p is the distance between the pole pieces and f is the frequency of the field. A field is induced in the rotor (above right), which is propelled along the windings. The speed of the rotor is limited only by the frequency of the field – which can be very high – and by air resistance. Very high speeds can be reached.
The induction coil has the advantage that there is no contact between rotor and motor, so friction is zero. They can be used to propel trains, to launch aircraft, propel shuttle looms, or even close curtains.