Conservation of Momentum
Source GM Core pg. 87
When a creature Pushes Off a floating creature or object in a zero-gravity environment, they also Push the creature or object, but each of them move at half Speed. If they use Push Off as a free action after a melee Strike that deals bludgeoning damage or a successful Shove, they both move at full Speed instead. A creature Pushed Off this way becomes untethered and can Grab an Edge if they float past something that can stop their movement and lose the untethered condition.
If an untethered creature or object was already moving in one direction and is Pushed Off in the same direction, add Speed to the distance they float at the end of their turns equal to the amount they moved Pushing Off. If the untethered creature was already moving toward a different but not opposite cardinal direction, add Speed equal to half the distance, and if the untethered creature was already moving in the opposite cardinal direction, instead reduce the amount of distance they float by the distance they moved Pushing Off.
If an untethered creature or object was already moving in one direction and is Pushed Off in the same direction, add Speed to the distance they float at the end of their turns equal to the amount they moved Pushing Off. If the untethered creature was already moving toward a different but not opposite cardinal direction, add Speed equal to half the distance, and if the untethered creature was already moving in the opposite cardinal direction, instead reduce the amount of distance they float by the distance they moved Pushing Off.