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Aristotle's Gravitational Theory
Had the idea the the four elements of the earth had their proper places and the heavier elements return towards the center of the universe; heavier objects fell faster as it contained the heavier objects -
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Ptolemy's Gravitational Theory
Geocentric Theory; the earth was the center of the universe, it stays at rest so everything revolves around it; Ptolemy made a system of circles and epicycles that show the motion of the planets and stars revolving around the earth and everytime an observation didn't agree to the theory, he added another epicycle so the motion stays perfected -
Newton's Gravitational Theory
Upon being hit on the head with an apple from a tree he was sitting under, he thought of its acceleration as a cause of gravity. Newton's orbital cannon proved that if cannon was fired horizontally from mountain, it would either fall or orbit, depending on velocity, and he also made a point that the moon has neither acceleration or gravity, since it hasn't fallen onto the earth -
Cavendish's Gravitational Theory
measures the value of G (gravity), leading to the first accurate value for the gravitational constant; used to measure the mass of the sun and the weight of earth -
Einstein's Gravitational Theory
gravity was part of relativity; gravity was not a force, but a curve in space-time; based on an idea that because of gravity, objects moving in straight parallel lines will intersect because there paths become spherical; states law of mass-energy conservation: e=mc2