There is still debate on how much Newton owes his idea to Hooke. But it may be that Newton was also inspired by the earlier work of Hooke. In the story, Newton arrives at the idea of universal gravity from his own insight, inspired by the drop of an apple. This gets us back to the story of Newton’s apple. Robert Hooke went so far as to accuse Newton of plagiarism for the idea. The inverse square relation had been demonstrated for gravity in the mid-1600s by Ismael Ballialdus, and Huygens proposed a similar idea for the circular planetary orbits.

Newton’s idea of an inverse square force for gravity wasn’t entirely original either. In contrast, Descartes thought that a lighter object could never move a heavier object. So if a light object and a heavy object were to collide, for example, both would move in proportion to their mass. Newton expressed his third law not as an equality of forces, but rather that due to the forces between two objects their motion was in proportion to each other. His third law was unique, and actually contradicted earlier works, such as that of Descartes. In fact in the Principia he states that they are “accepted by mathematicians and confirmed by experiments of many kinds.” Newton himself doesn’t present his first two laws as new ideas. Descartes also predates Newton’s second law by noting that an object will only change its state when a force is applied to it, though Newton’s version is more refined, and presents a geometric description of an object’s change of motion under force. Rene Descartes proposed a similar idea, stating that bodies have a natural state of rest or motion, and that their tendency is to stay in that state. Newton’s first law is also known as the law of inertia, and it parallels the idea proposed earlier by Galileo Galilei and Christiaan Huygens. Jean Leon Huens, in Our Universe Newton contemplates the universe. Newton didn’t quite express them in this way, but the modern versions encompass his versions. These rules were presented in his Principia (or Mathematical Principles of Natural Philosophy) in 1687. The fourth is his law of universal gravity, that there is a gravitational force between any two objects with a strength that decreases proportional to the square of their distance of separation. The first three are known as Newton’s laws of motion: a moving object will continue at the same speed and direction unless a force (push or pull) acts on it, a force applied to an object will cause the object to accelerate (change speed) in the direction of that force, and forces happen between two objects. What we now call Newtonian dynamics can be summarized in four simple rules. The genius of Newton’s work was not the originality of the ideas, but that these ideas were integrated into a cohesive theoretical framework. But ideas in Newton’s theory were not entirely unique to him, and the true power of Newton’s theory wasn’t realized until after his death. In many ways one can divide our scientific understanding of the world into pre-Newton and post-Newton. It portrays Newton as a genius with a revolutionary insight. Whether true or not, it is a story we love to tell. Earlier mentions appear in works of Voltaire and Robert Greene. The story comes most famously from Memoirs of Sir Isaac Newton’s Life by William Stukeley in 1752. There’s long been some debate as to the truth behind this tale. This inspired his idea of universal gravity. He was sitting under an apple tree when he saw an apple fall to the ground. You probably know the story of Isaac Newton.

Apple newton theory