In a moving linear induction motor, each magnetic-field pole travelling in the gap between stator and track, grows from zero at the stator's stem and decays astern. It follows that, if compared with an induction motor having the same pole size and number, and working at the same crest-gap density, tractive capability is less because of the transient nature of working fields. A linear stator with four fully excited pole pitches has the equivalent of one tractively effective field pole when slip is 10%. To assess the separate influence of stern drag, changes in field-pole energy are examined as stern fields emerge. The paper derives 11 expressions for operating power, some in terms of the stator, others of the track, and these are collectively consistent with power received from the stator at the gap. Results are applied to predict power-slip characteristics for three linear motors.