Newton Publishes the Principia and the Laws of Motion and Gravity
Three laws and one inverse-square force explain a falling apple and the Moon's orbit with the same mathematics
Quick facts
- Published
- 1687, Philosophiae Naturalis Principia Mathematica
- Three laws of motion
- Inertia; F = ma; action and reaction
- Law of gravitation
- Force proportional to mass product, inverse to distance squared
- Unified
- Falling bodies, lunar orbit, and planetary orbits under one force
What happened
In July 1687 Isaac Newton published Philosophiae Naturalis Principia Mathematica, a work MacTutor calls the greatest scientific book ever written. In it Newton set out three laws of motion, that a body stays at rest or in uniform motion unless acted on by a force, that force equals mass times acceleration, and that every action has an equal and opposite reaction, versions of which he already had in early form by 1666. He then proposed universal gravitation: every two masses in the universe attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. From this single law Newton deduced Kepler's three empirical laws of planetary motion and showed that a stone falling to Earth was subject to precisely the same force which kept the Moon in its orbit about the Earth and the planets in their orbits around the Sun, unifying terrestrial and celestial mechanics under one mathematical framework for the first time.
Why it matters
The Principia gave physics its first complete, predictive mathematical system, one that would govern engineering, astronomy, and physical prediction for over two centuries until relativity and quantum mechanics revealed its limits. Newton was candid about what his theory did not explain: MacTutor notes that when critics pressed him on how gravity could act across empty space, he said only that he was explaining how things worked but not attempting to explain why they worked that way, a distinction that still runs through physics today.
How we know
The Principia survives as a printed text in multiple contemporary editions and Newton's own manuscripts and correspondence, including his 1687 exchanges with Edmond Halley, who financed and organized its publication; MacTutor's biography draws on this documentary record.
Sources
- MacTutor History of Mathematics, University of St Andrews. Isaac Newton (1643 - 1727) · Primary source (author-declared)mathshistory.st-andrews.ac.uk · Cited as a "primary" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- MacTutor History of Mathematics, University of St Andrews. Gravitation · Primary source (author-declared)mathshistory.st-andrews.ac.uk · Cited as a "primary" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
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Related timelines
- The Scientific Revolution → · The Principia is often treated as the capstone of the Scientific Revolution; see that timeline for how Newton's work built on Copernicus, Kepler, and Galileo.