“A body by its weight tends to move towards its proper place.  The weight’s movement is not necessarily downwards, but to its appropriate position: fire tends to move upwards, a stone downwards.  They are acted on by their respective weights; they seek their own place.  Oil poured under water is drawn up to the surface on top of the water.  Water poured on top of oil sinks below the oil.  They are acted on by their respective densities, they seek their own place.  Things which are not in their intended position are restless.  Once they are in their ordered position, they are at rest.” -St. Augustine