Coupling field is link between electrical and mechanical energies in electromechanical energy conversions. If the output is mechanical (motor), coupling field reacts with input electrical energy in terms of Back EMF which opposes the input. Coupling field absorbs energy from electrical system, converts and delivers mechanical energy. If output is electrical (generator), coupling field reacts with input mechanical energy in terms of Magnetic Drag which opposes the input. Coupling field absorbs energy from mechanical system converts and delivers electrical energy.