This accounts for sparks from a fire going upward attempting to return to the appropriate sphere. Even Aristotle knew of a mysterious force called gravity which drew unsupported objects towards the Earth. The genius of Newton's Theory of Universal Gravitation lay in recognizing that not only the Earth but any object with mass exerted such a force, which was inversely proportional to the square of its distance from another object. Hence the motions of heavenly bodies were shown to obey the same laws as everyday objects, as opposed to the explanation given by 14th century philosophers who said that angels pushed them. David McConnell, Calgary Canada Heavy objects have gravity, so they go down.
Light objects have levity so they float up.
It's as simple as that. The first three answers are on the right lines. Aristotle did say matter wished to return to its rightful place. But Newton didn't formulate a theory of gravity, he applied mathematics to the problem. Gailileo's experiments were concerned with this force, and he realised it was universal.