Isaac Newton was a famous scientist and mathematician from England who lived long ago. He was born in the manor house at Woolsthorpe, in England. His family were farmers. Newton went to Trinity College, part of Cambridge University. In 1669 he became the Lucasian Professor at Cambridge. At Cambridge, Newton showed little interest in teaching. His lectures were sparsely attended, and sometimes no one showed up at all. Newton wrote a famous book about how things move. It is called the Principia. A mathematician at the Open University wrote that the Principia made Newton famous even though few people read it and even fewer understood it.

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. 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. He called this pull gravity. If two objects are twice as far apart, the pull of gravity 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 that pull keeps the Moon going around the Earth.

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. Halley also paid to have the Principia printed. Newton had written a famous book about how things move.

In the Principia, Newton's 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. Newton wrote that a change of motion is proportional to the force pressing on an object and happens in the direction of that force. People write this second law as F=ma: force equals mass times acceleration. His third law says that when one object pushes on another, the second pushes back just as hard in the opposite direction.

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. White light is made of all the colors of the rainbow, and Newton showed this. 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 of motion and gravity became the base of classical mechanics, the study of how large things move.

Newton's laws helped scientists understand how the planets move around the Sun and how the Moon moves around the Earth. Newton's laws are still used to reach the Moon, Mars and other places beyond Earth. Newton lived to be 84 years old. He is buried in Westminster Abbey in London. 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.

Words to know

• plague: a bad sickness
• orbit: path around something
• inertia: keeps moving, stays
• prism: light-splitting glass
• ellipse: stretched circle