Sir Isaac Newton contributed significantly to the field of science over his lifetime. He invented calculus and provided a clear understanding of optics. But his most significant work had to do with forces, and specifically with the development of a universal law of gravity. [See also our overview of **Famous Astronomers** and great scientists from many fields who have contributed to the rich history of discoveries in astronomy.]

**Newton's life**

Born to a poor family in Woolsthorpe, England, in 1642, Isaac Newton attended Trinity College in Cambridge, England only after it became apparent that he would never be a successful farmer. While there, he took interest in mathematics, optics, physics, and astronomy. After his graduation, he began to teach at the college, and was appointed as the second Lucasian Chair there. Today, the chair is considered the most renowned academic chair in the world.

In 1689, Newton was elected as a member of parliament for the university. In 1703, he was elected as president of the Royal Society, a fellowship of scientists that still exists today. He was knighted by Queen Anne in 1705. He never married.

Newton died in 1727, at the age of 84. After his death, his body was moved to a more prominent place in Westminster Abbey. During the exhumation, large amounts of mercury were found in the scientist's system, likely due to his work with alchemy.

**Motion in the universe**

The popular myth tells of an apple falling from a tree in his garden, which brought Newton to an understanding of forces, particularly gravity. Whether the incident actually happened is unknown, but historians doubt the event — if it ocurred — was the driving force in Newton’s thought process. His most famous work came with the publication of his "Philosophiae Naturalis Principia Mathematica" ("Mathematical Principles of Natural Philosophy"), generally called Principia. In it, he determined the three laws of motion for the universe.

The first describes how objects move at the same velocity unless an outside force acts upon it. (A force is something that causes or changes motion.) Thus, an object sitting on a table remains on the table until a force – the push of a hand, or gravity – acts upon it. Similarly, an object travels at the same speed unless it interacts with another force, such as friction.

His second law of motion provided a calculation for how forces interact. The force acting on an object is equal to the object's mass times the acceleration it undegoes.

Newton's third law states that for every action in nature, there is an equal and opposite reaction. If one body applies a force on a second, then the second body exerts a force of the same strength on the first, in the opposite direction. [VIDEO: Final Nail in Newton's Theory]

From all of this, Newton calculated the universal law of gravity. He found that as two bodies move farther away from one another, the gravitational attraction between them decreases by the inverse of the square of the distance. Thus, if the objects are twice as far apart, the gravitational force is only a fourth as strong; if they are three times as far apart, it is only a ninth of its previous power.

These laws helped scientists understand more about the motions of planets in the solar system, and of the moon around Earth.

**A scientist across disciplines**

While a student, Newton was forced to take a two year hiatus when plague closed Trinity college. At home, he continued to work with optics, using a prism to separate white light, and became the first person to argue that white light was a mixture of many types of rays, rather than a single entity. He continued working with light and color over the next few years, and published his findings in “Opticks” in 1704.

Disturbed by the problems with telescopes at the time, he invented the reflecting telescope, grinding the mirror and building the tube himself. Relying on a mirror rather than lenses, the telescope presented a sharper image than refracting telescopes at the time. Modern techniques have reduced the problems caused by lenses, but large telescopes such as the James Webb Space Telescope use mirrors. [Stacking Up the 10 Biggest Telescopes on Earth]

As a student, Newton studied the most advanced mathematical texts of his time. While on hiatus, he continued to study mathematics, laying the ground for differential and integral calculus. He united many techniques that had previously been considered seperately, such as finding areas, tangents, and the lengths of curves. He wrote De Methodis Serierum et Fluxionum in 1671, but was unable to find a publisher.

Newton also established a cohesive scientific method, to be used across disciplines. Previous explorations of science varied depending on the field. Newton established a set format for experimentation still used today.

**Isaac Newton quotes**

"Amicus Plato amicus Aristoteles magis amica verita."

(Plato is my friend, Aristotle is my friend, but my greatest friend is truth.)

—Written in the margin of a notebook while a student at Cambridge. In Richard S. Westfall, *Never at Rest* (1980), 89.

"Genius is patience."

—*The Homiletic Review, Vol. 83-84* (1922), Vol. 84, 290.

"If I have seen further it is by standing on the shoulders of giants."

—Letter to Robert Hooke (5 Feb 1675-6).In H. W. Turnbull (ed.), *The Correspondence of Isaac Newton*, 1, 1661-1675 (1959), Vol. 1, 416.

"I see I have made my self a slave to Philosophy."

—Letter to Henry Oldenburg (18 Nov 1676). In H. W. Turnbull (ed.), *The Correspondence of Isaac Newton, 1676-1687* (1960), Vol. 2, 182.

"I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."

—First reported in Joseph Spence, *Anecdotes, Observations and Characters, of Books and Men* (1820), Vol. 1 of 1966 edn, sect. 1259, p. 462

"To any action there is always an opposite and equal reaction; in other words, the actions of two bodies upon each other are always equal and always opposite in direction."

— *The Principia: Mathematical Principles of Natural Philosophy* (1687)

"Truth is ever to be found in simplicity, and not in the multiplicity and confusion of things."

—'Fragments from a Treatise on Revelation". In Frank E. Manuel, *The Religion of Isaac Newton* (1974), 120.

*—Nola Taylor Redd*

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