# Isaac Newton

#### 1642 - 1727

Issac Newton is possibly the most influential scientist of all time. In the second half of the 17th century, he produced a breathtaking number of physics and mathematical laws and methods, explaining forces and physical phenomena, and deriving mathematical explanations still in use today.

• Nationality
• English

• Subject
• Physics, Mathematics

• Fields
• Mechanics, Optics, Calculus, Philosophy

• Posts
• Lucasian Professor of Mathematics, 1669

President of the Royal Society

Warden of the Royal Mint

• Publications
• Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), 1687, probably the most influential scientific book ever published, and laid the foundations of classical mechanics, calculus, and optics.

Hypothesis of Light, 1675, in which the ether is evoked as the medium through which light may propagate.

• Laws
• 3 Laws of Motion: these laws are still used, and were the only interpretation of the relationships of matter, time and space, until Einstein's Relativity.

Law of Universal Gravity: which established that gravity was the same for all matter, was a force which acted at a distance, and reduced by the square of the distance separating two masses.

Law of Optics

• Theories
• Newton's mathematical descriptions of the physical universe were applied to orbits and motions of all planets, comets and moons, and thereby proved beyond doubt the Copernican/Keplerian/Galilean model of the heoliocentric system (Sun at centre of solar system instead of the Earth).

Optics: light spectra and theory of colour. White light divides into the rainbow of colours through a prism. Newton proposed that light is composed of particles.

Differential calculus: long-running dispute with supporters of Gottfried Leibniz about who invented calculus. Today, it is considered the invention was independent, with Newton probably having precedence, but did not publish until after Leibniz had revealed his differential calculus method, using a different technique and different notation.

Newton also made significant contributions to other mathematical fields, including power series, binomial theorem, roots of a function and cubic plane curves.

• Equations
• Second Law of Motion: \$F = ma\$

Universal Gravity: The force of attraction between two masses is proportion to the inverse square of their separating distance, r: \$F_g = G⋅{M⋅m}/{r^2}\$, where \$G\$ is the universal gravitational constant.

• Experiments/Discoveries
• Thought experiments, including Newton's Cannon

Division of light to composite colours (using prisms)

First practical refracting telescope, which improved astronomical observation potential

Determination of the speed of sound.

Newtonian fluids.

Newton published his Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), in 1687. This single book is probably the most influential scientific book ever published, and laid the foundations of classical mechanics, calculus, and optics.

The argument over who had precedence in the invention of calculus, between Newton and Gottfried Leibniz, raged for centuries. However, Newton's applications of techniques to optics, mechanics and astronomical phenomena were unequalled by any scientist in history. It was not until Einstein that a more complete explanation of physical phenomena was on offer, but Newton's laws and mathematics are still used by engineers and scientists today.

#### Sir Isaac Newton, 1642 - 1727, English Scientist

Sir Isaac Newton was a professor of physics and mathematics at Cambridge University, and is generally considered the most influential scientist who has ever lived. He wrote an important book, Principia Mathematica, in 1687. In this book he describes his laws of motion, gravity, calculus, and optics. Newton's laws of mechanics and optics, as well as his invention of calculus, and many other revolutionary ideas, are still used today in all physics and engineering.

Isaac Newton, English physicist and mathematician, 1642-1727

Isaac Newton’s contributions to physics and mathematics literally changed the world, and made the Industrial Revolution possible. Amongst the things he discovered and invented were: gravitational force, the three laws of motion, calculus, optics and a new type of telescope. Despite all these amazing discoveries, his personal passion was for other things, primarily alchemy. He was a professor at Cambridge University for many years before publishing his groundbreaking book ‘Principia Mathematica’, which set out the laws which were not challenged till Albert Einstein’s Relativity theory in 1905.

Newton was also the inventor of the Newtonian telescope, the reflecting telescope utilising a concave mirror in place of the objective lens as in the Galilean refracting telescope.

Newton did not ‘invent’ gravity. Instead, he posed the question: why does an apple fall to the ground, and yet the Moon does not?

His answer was in the form of a thought experiment, one of the tools of empirical science, in which he asked what would happen to the trajectory of a cannonball fired horizontally from cannons of ever increasing strength. The realisation that there would be a velocity at which, in the absence of air resistance, the ball would fly around the Earth forever, led to his explanation of orbits. Through this Newton realised that the Moon was subject to the same gravity as objects near the Earth. The conclusion was that gravity was a universal force, acting at a distance, which diminishes with the inverse square of the distance.

A brilliant man, his ideas went unchallenged, though not without controversy, till Albert Einstein proposed a more complete explanation of space, energy, matter and time.

#### Controversies around Newton:

• Gottfried Leibniz claimed prior invention of the calculus Newton describes in his 1687 book. The controversy over who invented this most important mathematical tool raged across Europe for two hundred years, at times isolating English scientists and mathematicians. Today, scholars generally hold that Newton had delayed publication of his work, for reasons of fear of its being stolen, for more than 20 years. He may have invented differential calculus (which he called fluxions) before Leibniz invented integral calculus independently, but they are quite rightly jointly accredited for calculus’s development and adoptation.
• Thomas Young, an English physicist in the early 1800s, proposed a wave model for light. Since Newton had proposed light to be a particle, Young’s work was suppressed. Newton would have been horrified to find that the excessive veneration of his name and presumed infallibility would lead to the suffocation of the scientific method. It was the Scot, James Clerk Maxwell, 1831 - 1879, who eventually gave us a description of light as an electromagnetic wave. This work opened the way for Einstein to challenge Newton for the complete description of the nature of the universe in his revolutionary Relativity Theory, in 1905.
• Newton was a very difficult character. He made enemies as easily as he solved mathematical equations. Among these was Robert Hooke (1635 - 1703), another great scientist, and pioneer of the use of the microscope, and leading member of the newly created Royal Society. Newton’s antagonism for Hooke led to his refusing to participate in this society until after Hooke’s death, in 1703, when he became its president. Newton was not above chronyism in his conduct as president.
• Although heralded as a founder of modern physics and the scientific method, Newton was more interested in alchemy. He held strong religious beliefs, as an Arian, and rejected the christian version of the scriptures. For this reason, he was secretive and reclusive all his life. Since his death, many have accused him of being a heretic, and even a sorcerer.
• The famous anecdote of the falling apple in his family’s home orchard in Lincolnshire is an icon of popular science. It stands with Archimedes’ leaping from his bath, and running naked down the road calling ‘Eureka’, as a great moment of discovery, and symbolic of a chance event triggering a tremendous insight. The truth is that there is only one mention of the supposed apple event in Newton’s copious journals, made 50 years later, and this does not specifically state that it was a falling apple that triggered his thought pattern. Although a pleasant story, it is most certainly a myth, like the incorrect story that Einstein did poorly at school. Still, a good story is hard to kill, and why should we anyway?