Isaac Newton published a comprehensive theory of gravity in 1687. Though others had thought about it before him, Newton was the first to create a theory that applied to all objects, large and small, using mathematics that was ahead of its time. Newton’s theory was successful for hundreds of years - until Einstein came along and turned it on its head.
Sir Isaac Newton
Isaac Newton was born in England in 1643. As a young man he went to Trinity College in Cambridge, enrolling first as a student and eventually staying on as a fellow. During this period he developed the first versions of his three laws of motion, including the law of gravity. During his career, he also made significant advances in the field of optics and the understanding of centrifugal force. He eventually became the first English scientist to be knighted for his work.
The Discovery of Gravity
A popular story says that Newton came up with the theory of gravity instantly, when an apple fell from a tree and hit him on the head. Actually, Newton saw an apple falling from a tree, and it got him to thinking about the mysterious force that pulls objects to the ground. He compared the straight path of the apple to the curved path of a fired cannonball. He wondered what would happen if the cannonball went faster and faster, and realized it would eventually “fall” around the curve of the Earth forever, and never hit the ground. This “forever falling” motion describes the movement of the Moon around the Earth, and the Earth around the Sun.
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The Importance of Gravity
Gravity pulls falling objects to the ground, but people already knew intuitively that something like that was going on. The really groundbreaking thing about the law of gravity was that it applied to objects of all sizes, stating that the more mass an object had, the more it attracted other objects. At the time of Newton's discovery, people didn't have much of an idea of how the orbits of moons and planets worked. The new discovery explained a lot about that, in particular why orbiting objects don't just fly off into space.
Before and After Newton
In 1589, Galileo conducted experiments with gravity, such as dropping balls from the Leaning Tower of Pisa; he discovered that they hit the ground at the same time despite having different weights. Newton’s work, 100 years later, put together a picture of gravity good enough to last another two centuries. However, although Newton’s theory described how objects attracted each other, it didn’t explain why. In 1915, Einstein's Theory of Relativity described gravity as mass warping time and space. It also describes the way that even light bends when passing near stars and other extremely massive objects. Still, despite this more recent tweaking, Newton's original theory explains a great deal of the behavior of objects throughout the universe.