Isaac Newton was born in the manor house at Woolsthorpe, in England. His family were farmers, and his father died before Newton was born. At school, Newton's reports called him idle and inattentive. His mother took him out of school to run the family farm, but he returned to school and went on to university. Newton went to Trinity College, part of Cambridge University.
As a student Newton wrote in a notebook, in Latin, 'Plato is my friend, Aristotle is my friend, but my best friend is truth.' According to de Moivre, Newton's interest in mathematics began in 1663. He bought an astrology book at a fair in Cambridge and could not understand its mathematics. In 1669 Newton became the Lucasian Professor at Cambridge, a professor's chair that Isaac Barrow had held. Yet he showed little interest in teaching. His lectures were sparsely attended, and sometimes no one showed up at all.
A sickness called the plague closed Cambridge University, so Newton went home to Woolsthorpe. While away from Cambridge because of the plague, Newton began important work in mathematics, light, physics and astronomy in less than two years. Newton had early versions of his three laws of motion by 1666. He began working on them in a notebook at the family farm in Woolsthorpe. Kepler's third law links a planet's distance from the Sun to the time its orbit takes. It inspired Newton to come up with three laws of his own to explain how planets move.
Newton said that everything pulls on everything else, and he called this pull gravity. His law of universal gravitation says all matter attracts all other matter. The pull is proportional to the product of the masses and inversely proportional to the square of the distance between them. If two objects are twice as far apart, the pull between them is only one fourth as strong. Newton showed that if gravity gets weaker with the square of the distance, then gravity on Earth's surface correctly predicts how long the Moon takes to orbit. The Earth pulls on the Moon with gravity, and the Sun's gravity pulls on the planets and holds them in their paths around the Sun.
Before Newton, thinkers assigned different causes to different types of motion, according to physicist Stephen Hawking. By unifying all motion, Newton shifted science toward a search for large, unifying patterns in nature. In the Principia, Newton applied his laws to orbiting bodies, projectiles, pendulums and free-fall near the Earth. His first law says a moving object keeps its speed and direction, and a still object stays still, unless an outside force acts on it. The law is often called inertia. His third law says that when one object pushes on another, the second pushes back just as hard in the opposite direction.
In 1684 Edmond Halley asked Newton what orbit a body follows under an inverse-square force. Newton replied at once that it would be an ellipse. Halley persuaded Newton to write out his new physics in full. The result, the Principia, was published in 1687. Newton's friend Edmond Halley paid to have the Principia printed. A mathematician at the Open University wrote that the Principia made Newton famous even though few people read it and even fewer understood it.
Newton shone sunlight through a glass prism and saw a band of colors. He split white light into colors with one prism. Then he used a second prism to join the colors back into white light. In a key experiment, Newton passed one color from the spectrum through a hole and a second prism. The second prism bent it by the same amount without changing its color, showing that each color is a pure part of white light. White light is made of all the colors of the rainbow, and Newton showed this. Newton explained the color of an object as the colors it reflects after it absorbs all the others. Newton named seven colors in the spectrum: red, orange, yellow, green, blue, indigo and violet. He admitted that choosing seven was rather arbitrary.
Telescopes with glass lenses showed blurry colors. A mirror reflects all colors of light by the same amount, so a mirror telescope fixes this. Newton made a telescope that uses a mirror. As of November 2026, reflecting telescopes, which use mirrors as Newton's did, are mainstays of astronomy, including the Hubble Space Telescope. Newton became Warden of the Royal Mint in 1696 and Master of the Mint in 1699, a post he kept until his death in 1727. At the Royal Mint, Newton helped take old coins out of use and replace them with more reliable ones. In 1703 he was elected President of the Royal Society, a group of scientists.
Queen Anne made Newton a knight in 1705, so he was called Sir Isaac Newton. Newton's laws are still used to reach the Moon, Mars and other places beyond Earth. Near the end of his life Newton said he felt like a boy on the seashore, finding a smoother pebble or prettier shell while the great ocean of truth lay undiscovered. Newton lived to be 84 years old. He is buried in Westminster Abbey in London. His monument there was finished in August 1730 and unveiled the following year. The carved scene on Newton's monument shows figures with a telescope, a prism, and a balance weighing the Sun and planets.
Words to know
- plague: a bad sickness
- orbit: path around something
- spectrum: band of colors
- inertia: keeps moving, stays
- ellipse: stretched circle
