Momentum

From Traxus

Marathon (in all three engines) stores player momentum in what are referred to as "body coordinates". This means that, when you're falling, you will continue to fall in the same direction relative to yourself. For example, if you're falling forward, by turning to your left, you will begin to move in that direction (what was once your left but is now your front). This quirk in the game's physics (obviously true physics do not behave in this manner) allows you to reach places you would not normally be able to reach, if the player is properly rotated as he is flung through the air.