360Newton publishes the Principia
In July 1687, Isaac Newton published the Principia, setting out his three laws of motion and the law of universal gravitation. He showed that the same force pulls an apple to the ground and holds the planets in their orbits. The book became the foundation of physics for more than two centuries.
Isaac Newton's Philosophiae Naturalis Principia Mathematica, or Mathematical Principles of Natural Philosophy, was published in London on 5 July 1687.
In it, Newton set out three laws of motion. An object stays at rest or moves steadily unless a force acts on it. Force equals mass times acceleration. And for every action there is an equal and opposite reaction.
He also described universal gravitation: every mass attracts every other mass with a force that weakens with the square of the distance. With this law, he explained the orbits of the planets, the motion of the Moon, the tides and the paths of comets.
The astronomer Edmond Halley encouraged Newton to write the book and paid for its printing.
Newton's laws remain the basis of engineering, from bridges to spacecraft. Only in the 20th century did Einstein's relativity refine them for very high speeds and strong gravity.
- 1665–66
- Newton's early work on gravity
- 5 July 1687
- Principia published
- 1713
- Second edition
- 1758
- Halley's Comet returns as predicted
Sources: Britannica · Royal Society · Cambridge University Library.