who came up with the idea of gravity
History of gravitational theory In the 4th century BC, the Greek philosopher Aristotle believed that there is no effect or motion without a cause. The cause of the downward motion of heavy bodies, such as the element earth, was related to their nature, which caused them to move downward toward the center of the universe, which was their natural place. Conversely, light bodies such as the element fire, move by their nature upward toward the inner surface of the sphere of the Moon. Thus in Aristotle's system heavy bodies are not attracted to the earth by an external force of gravity, but tend toward the center of the universe because of an inner gravitas or heaviness.[1][2]
Conservation of mass By the 18th century the principle of conservation of mass during chemical reactions was widely used and was an important assumption during experiments, even before a definition was formally established[9], as can be seen in the works of Joseph Black, Henry Cavendish, and Jean Rey.[10]. The first to outline the principle was given by Mikhail Lomonosov in 1756. He demonstrated it by experiments and had discussed the principle before in 1774 in correspondence with Leonhard Euler, though his claim on the subject is sometimes challenged.[11] A more refined series of experiments were later carried out by Antoine Lavoisier who expressed his conclusion in 1773 and popularized the principle of conservation of mass. The demonstrations of the principle led alternatives theories obsolete, like the phlogiston theory that claimed that mass could be gained or lost in combustion and heat processes.