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Mystaraspace: Gravityby Bruce Heard
Objects of ten tons or more, like a ship for example, exert their own gravity. Gravity is comparable to normal Mystaran gravity, except it extends to a much shorter range (no more than 100ft from edges of the hull). The ship's gravity centres on its heaviest, single part, which has prompted some space explorers to fit a mast underneath their ship, ending with a very dense, heavy object. This gives the illusion of vertical gravity that is roughly perpendicular to the ship's decks. Naturally, this counterweight is removed or jettisoned before crossing into a planet's Skyshield.
Should a larger object, like a planet for example, be close enough, it would affect the smaller object as a whole, single object. The latter means that a ship's own gravity does not change when cruising near a planet, causing passengers to suddenly lose their footing and fall off their ship. The rule of thumb is that a ship and its passengers would be attracted by a planet as if they were one single object until they crossed its Skyshield, at which point normal laws of physic apply.
Small addendum (there I go, nitpicking again!):
Objects of immense size -- say a million tons or more; i.e. suns, planets, moons, and very large asteroids -- interact with each others' gravity in a different manner. Their gravity's range extends much, much farther when similarly-large objects are concerned, decreasing with distance in exactly the same manner as IRL gravity does. For interactions between objects of a million-plus tonnage, the strength of gravity varies in proportion to their mass; it's only when smaller objects are involved, that the force of gravity remains constant.
Just making sure Mystara's entire solar system doesn't fall apart, due to short-range gravity! ;-)