The Gravity Time Line
About 365 BC, Aristotle discovered that free fall is an form of accelerated motion, but made an incorrect assumption that heavier objects fall faster than light ones.
About 325 BC, Pytheas, Greek observed the strong Atlantic tides on a trip to Norway and theorized that they were caused by the moon.
About 250 BC, Archimedes discovers the principle of specific gravity of objects based on the displacement of water.
1100 AD, Book written containing table of specific densities and a general formulation of the law of gravity �Abu �l Fath Al-Chuzini�
Gutenberg printing press 1454 AD
1632 AD, Galileo�s explains the relationship of relativity to physics using the closed cabin of a ship.
1665 AD, Newton develops the first version of the law of gravity. Newton left London during a Plague, and while in the country observed a falling apple which made him realize that the moon must be falling, too.
1687 AD, Newton publishes the law of universal gravitation and three laws of motion.
1673 AD, Huygen develops equations for pendulum and develops the laws of centripetal force
1674 AD, Hook attempt to develop theory of planetary motion based on a balance between centrifugal force and gravity attraction.
1679 AD, Hook proposes that gravity is inversely proportionally to distance.
1679 AD, Richer observes that the period of a pendulum is different at different location, indicating that gravity varies with position.
1680 AD, Newton proves that the attraction of gravity has to be an inverse square of the distance to generate the elliptical orbits that Kepler discovered.
1687 AD, Newton publishes Principia describing the three laws of motion and the law of gravitation.