[size=150][b]Isaac Newton (1643–1727)[/b], English physicists and mathematician, in 1687 in[i] Philosophicae Naturalis PrincipiaMathematica[/i] formulated laws of motion and the law of gravity (an inverse–square law of gravity) and developed a mathematical method that enabled him to derive Kepler’s laws as consequences of his (Newton’s) laws (What is interesting is that despite this he provide geometric proof of Kepler’s laws in [i]Principia[/i]). [br][br][/size][size=150]From [url=https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion]Newton's laws of motion[/url] and [url=https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation]gravity[/url] we are particularly interested in the following three assertions:[br][br][/size][list][*][size=150]An object keeps its state of motion (rest or a motion at a constant speed in the same direction) unless an external force is impressed on it (1[sup]st[/sup] law, the law of inertia).[/size][/*][/list][list][*][size=150]The change in motion is proportional to the motive force impressed; it is made in the direction of the straight line in which that force is impressed (2[sup]nd[/sup] law).[/size][/*][/list][list][*][size=150]The force of gravity diminishes as R[sup]-2[/sup], where R is the distance from a planet to the Sun (the inverse square of the distance nature of gravity).[br][/size][/*][/list][size=150][br][/size]