Aristotelian theory of gravity
The Aristotelian theory of gravity, postulated by the ancient Greek philosopher Aristotle, was that heavier bodies fall faster than lighter ones. According to Aristotle, heavy things were attracted to the center of the Earth, which was the center of the universe. The heavier the object, the stronger the attraction (see classical element).
Aristotle's theory was superseded by the work of Galileo Galilei. According to legend, Galileo dropped balls of various densities from the tower of Pisa and found that lighter and heavier ones fell at almost the same rate.
The confusion is due to the fact that a heavier body is less affected by the resistance of air than a lighter one of the same shape.
On the surface of the moon, David Scott famously repeated Galileo's supposed experiment by dropping a feather (very light) and a hammer (somewhat heavy) from each hand at the same time. In the absence of a substantial atmosphere, the two objects fell and hit the moon's surface at the same time.
Isaac Newton was the first to mathematically codify the newer theory of gravity according to which any mass, not only the Earth, attracted other masses according to a function of their mass and the inverse square of their distance. More recently this theory was subjected to modifications by Albert Einstein. See gravity for a complete discussion.