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Natural Science - Year I

Unit 30: Newton and Mechanics

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History Weblecture for Unit 30

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History Lecture for Unit 30: Newton's Laws of Motion

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Lecture outline:

The Mechanical Universe

Isaac Newton

Read a short biography of Newton's life at the University of St. Andrews' mathematics website.

  • Where and how was Newton educated? Where did he teach?
  • What were the three important discoveries Newton made in his "miracle years"?
  • What was the method of fluxions?
  • How did Newton's theory of optics differ from Aristotle's?
  • What started the controversy between Newton and Robert Hooke?
  • What was the Principia Mathematica?

Isaac Newton was born the year Galileo died, and he brought together many of the missing pieces of the support required to show that Galileo's understanding of mechanics and the Copernican system had been correct.

Newton attended Cambridge University for awhile, but was sent back to his home on the farm when bubonic plague broke out in London and Cambridge in 1665. Isolated and not liking to farm, he spent his time researching many things that interested him—the behavior of light when it breaks into a spectrum and the motion of different kinds of moving bodies. When the plague was over, his mathematical publications were enough to secure him the chair of Lucasian Professor of Mathematics at Cambridge (a position now held by Stephen Hawking).

Newton continued his researches after his appointment. The idea of a force proportional to the inverse of the square of the distance between two bodies (F ~ 1/r2 had already occurred to him, as it had to the English scientist Robert Hooke (whom we've already met as the first man to identify cells in cork under the microscope), to the Royal Astronomer Edmund Halley, and to the Dutch scientist Christiaan Huygens. Newton realized that a simple application of a force law might explain the motion of the moon around the earth, and the planets around the sun, but he knew that such a law would required the planets to move in circular orbits, rather than Kepler's ellipses. He set about to determine a way to derive elliptical motion from a central attractive force, and invented calculus to handle the math. He performed all the calculations, and checked all the laws to make sure they were internally consistent. There was only one problem: based on the accepted distance between the earth and the moon, the predicted rate of motion for the moon from his calculations was wrong. So he didn't publish his theories.

He did write some letters to the newly formed Royal Academy of Science on various scientific subjects, which gained him a reputation throughout Europe as an extraordinary mathematician, and the lasting enmity of Robert Hooke, who felt that Newton had plagiarized his works. The works also gained him the attention of Halley, who had some new figures on lunar distance for Newton. Newton recalculated his predictions for the motion of the moon, found they now matched observation, and wrote the Mathematical Principles of Natural Philosophy, or the Principia Mathematica. This book portrayed the world as a mechanical device, with all motion the result of existing forces. Three laws of motion (which we discuss in the science section) account for all movement. The universal law of gravitation claims that every mass in the universe attracted every other mass in the universe according to an unchanging relationship. With these claims (and their mathematical proofs and examples), Newton finally dispensed with Aristotelian concepts of motion and the division of the earth and the rest of the celestial universe into different kinds of matter.

Read an excerpt from the Principia Mathematica at the Fordham University website.

  • What does Newton consider the basis for knowledge about matter and objects?
  • What kinds of qualities does Newton ascribe to all bodies?
  • How does Newton's view of matter compare to that of the ancient Greek monists?
  • How does Newton use the principle of induction to create hypotheses?

Newton's publication put him into greater controversy with Hooke and started a controversy with Leibniz over which of them had invented calculus first. In 1704 he published a work on light, called the Optics, in which he described the behavior of light as small particles of some substance, and attacked the wave theory of light proposed by Christiaan Huygens and Robert Hooke. The debate over calculus and the publication of the Optics in English rather than Latin reveal a new nationalistic and competitive attitude toward scientific research. Much of the controversy was supported by letters between Newton's friends (who wanted the English to be able to claim to have invented calculus) and Leibniz's friends (who wanted the German people to get the credit).

The publication of works in the vernacular also shows a changing relationship between academic science and the rest of the people. By publishing the Optics in English rather than in Latin, Newton made it more difficult for the international community of scholars (who would know Latin but not English) to have access to his work, but much easier for the non-university trained English public to learn his ideas.

Study/Discussion Questions:

Further Study/On Your Own