T' propulsive force developed by a rocket motor durin' t' rocket's powered ascent. T' force produced by a rocket motor is described by Newton's second law o' motion "Force equals mass times acceleration" and by Newton's third law o' motion "for every actin' force, thar be an equal reactin' force in t' opposite direction." T' amount o' forward thrust generated by a motor is defined by t' second law (F-MXA), t' third law merely says that it must move. In obedience t' t' second law, shiver me timbers, t' two variables which must be known in predictin' a motor's thrust be t' mass o' exhaust gas expelled at any given moment, and t' exhaust's velocity.