Gravity is the force of attraction between any two objects in the universe with mass. Although it is much weaker than any of the other fundamental forces (electromagnetism, the weak force, and the strong force) and is neglected in the interactions of elementary particles, which occur at short distances, the effects of gravity manifest themselves at larger length scales, most notably at astronomical distances.

Historically, gravity is the first of the fundamental forces of nature whose behavior was extensively studied and elucidated. Aristotle maintained the rate at which objects fell depended upon their masses. If two objects are dropped, the heavier one falls faster. Galileo showed that Aristotle's conclusion was false. Any two objects fall towards the center of Earth with the same rate of acceleration. This observation is an empirical one. It does not provide an explanation for why gravity acts as it does.

Isaac Newton offered...