The scientists of the Renaissance had accomplished a great deal. They had put to rest the teachings of Aristotle/Ptolemy (teachings that had thrived for nearly 2,000 years) and replaced them with a much more accurate idea of what our solar system looks like. With this key information, the stage was now set for the human understanding of gravity to take a giant leap forward.As the story goes, the young English physicist and mathematician Sir Isaac Newton (1643 AD-1727 AD) first became interested in the force of gravity one day as he sat in contemplation under an apple tree and was suddenly struck on the head by a falling piece of fruit. The incident left Newton with a sore skull and a remarkable idea: what if gravity, the force that pulled apples out of trees, actually reached as high as the moon? From here, it was a short leap to the concept that the Earth’s gravity was responsible for keeping the moon in orbit and that the Sun’s gravity was responsible for keeping the planets in orbit.
But if such a force did exist, Newton realized, it must be governed by certain rules to define how it should effect matter. Making use of Kepler’s laws of planetary motion, Newton set out to discover these rules. He worked on the problem for a time and came up with a partial answer. Yet his full solution was not made public until 1687 when he published his three book volume Philosophiae Naturalis Principia Mathematica ,or simply Principia for short. In this publication, which many consider to be the greatest single piece of scientific literature ever written and which also contained his laws of motion, Newton finally disclosed to the public his law of universal gravitation.Newton’s law, which said that all matter in the universe attracts all other matter in the universe, was a major step forward for scientific thought. For the first time in history, people finally had an understanding of gravitation that went well beyond just the force that keeps our feet on the ground. We now realized that gravity was a universal force.
For more on Newton's law of universal gravitation see What is Gravity? Page 4.
