The ghastly pseudo-scientific form of physics that plagued Western Civilization up until the Reineissance. The theories put forth by Aristotle are very much descriptive of Aristotelian philosophy, whose credo is basically "seeing is believing". Under his system, an object at rest, if acted upon by a force, would take to motion and gradually return to rest by its own means. It also stipulated that heavier objects will fall at a faster rate than lighter objects (which Galileo easily disproved with his infinitely simple and amazingly famous cannonball experiment).
I would like to add extra emphasis to the 'seeing' part of the aforementioned credo; Aristotle didn't seem to investigate his theories very intensly. Even an ancient Greek, without the assistance of modern technology (or the scientific basis Newton built upon), could conclude that, for instance, the terrain a ball rolled on and the amount of wind present had something to do with the rate at which it rolled. Something as simple as rope-burn would easily explain the presence of something resembling friction. Well, that's enough of my anti-Aristotelian drivel. Just remember that he might have written some very inspiring words, but he's also written some very misguided ones...
I'd also like to point out that I pronounce it 'Air-ist-oh-teel-yan'.