Short answers, pulled from the story.
Isaac Newton published his work Philosophiæ Naturalis Principia Mathematica on the 5th of July 1687. This text combined his laws of motion with new mathematical analysis to explain Kepler's empirical results.
The equation for universal gravitation takes the form F equals G times m1 times m2 divided by r squared. Here F is the gravitational force acting between two objects, m1 and m2 represent the masses of those objects, r denotes the distance between the centers of mass, and G stands for the gravitational constant.
Henry Cavendish conducted his famous experiment in 1798 within a laboratory setting to measure the gravitational constant G for the first time. His work proved that gravity acts between masses in a controlled environment and provided a concrete number for the constant G.
Newton felt deep discomfort with the notion of action at a distance because he stated that one body acting upon another through a vacuum without mediation was an absurdity. He refused to explain how gravity traveled across empty space and described only the mathematical relationship while rejecting speculative causes hitherto unknown.
Albert Einstein's theory of general relativity superseded Newton's law of gravitation when deviations from Newtonian predictions became apparent as dimensionless parameters grew large. Einstein proposed that gravitation results from curved spacetime instead of force propagation, which explained motions of light and mass consistent with all available data.