Al-Baghdadi's theory of motion distinguished between velocity and acceleration and showed that force is proportional to acceleration rather than velocity. The 14th-century philosophers Jean Buridan and Albert of Saxony later refer to Abu'l-Barakat in explaining that the acceleration of a falling body is a result of its increasing impetus. Abu'l-Barakat also developed Philoponus' theory of impetus, stating that the mover imparts a violent inclination ("mayl qasri") on the moved and that this diminishes as the moving object distances itself from the mover.