When most people think of Gravity they think of the line, “what comes up, must come down”—as anyone who’s ever been hit by a ball at gym class has learned the hard way. However, gravity has a much greater impact than that (pun not intended).
Gravity is the force of attraction between objects. Without it, the solar system would not have been formed, as it is what pulled the planets into revolution around the sun, and keeps the moon from spinning off into the other end of the universe.
Humans have always had an instinctive awareness of gravity, but it took many centuries for it to be correctly explained. Much of the early misconceptions were rooted in a false belief that the earth was the center of the universe. Galileo was the first to observe that even objects of different weights fell at the same rate toward the Earth. Sir Isaac Newton also put forward the law of universal gravitation, which computed the force of gravity as F=G(m1m2/d2), where G is a constant. In the case of objects with different weights, he also saw that force was affected by mass and acceleration (F=M multiplied by A). This meant that while force was the same, the acceleration varied according to size.
Newton’s theories, however, were not able to explain some phenomena observed by astronomers by the end of the 19th century. Albert Einstein was able to address some issues (like Mercury’s orbit), but his theory of relativity still could not explain quantum gravity. String theory has since emerged.