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Who said: “I seem to have been only like a boy playing on the seashore, ... finding a smoother pebble or a prettier shell ... whilst the great ocean of truth lay all undiscovered before me.”
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Sir Isaac Newton
(25 Dec 1642 - 20 Mar 1727)

English physicist and mathematician who made seminal discoveries in several areas of science, and was the leading scientist of his era.


Isaac Newton
“A change in motion”

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“A change in motion is proportional to the motive force impressed and takes place along the straight line in which that force is impressed.”
— Isaac Newton
2nd Law of Motion, from The Principia.

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Newton wrote his famous three laws of motion in his magnum opus on mechanics, Philosophiæ Naturalis Principia Mathematica. Translated into English, the title is The Principia: Mathematical Principles of Natural Philosophy, familiarly known as simply the Principia. It was first published on 5 Jul 1687, and as the title suggests, it was written in Latin, the language then commonly used by scientists. As it was originally written, the second law of motion appeared in print as:

“Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam quâ vis illa imprimitur.”

Newton did not publish a version in English, though various translations have been made since then. The quote as given above is as translated by I. B. Cohen and Anne Whitman (1999). It is very faithful to the original Latin, as seen by comparing with a direct version from Google Translate:

“Law II: The alteration of motion is ever proportional to the motive force impressed; and is made in the right line in which that force is impressed.”

The sense in which Newton meant “change in motion” is what we now call “change in momentum with respect to time.” In a physics class, it is quickly shown how the statement reduces to the familiar equation: F=ma. Because the force, F and the acceleration a are vector quantities, the direction of the resulting acceleration will be the along same straight line as the direction of the impressed force.

After stating his second law, Newton gives further explanation (as translated by Cohen and Whitman):

“If some force generates any motion, twice the force will generate twice the motion, and three times the force will generate three times the motion, whether the force is impressed all at once or successively by degrees. And if the body was previously moving, the new motion (since motion is always in the same direction as the generative force) is added to the original motion if that motion was in the same direction or is subtracted from the original motion if it was in the opposite direction or, if it was in an oblique direction, is combined obliquely and compounded with it according to the directions of both motions.”

Text by Webmaster, with quote from The Principia: Mathematical Principles of Natural Philosophy (1687), 3rd edition (1726), as translated by I.B. Cohen and Anne Whitman The Principia: Mathematical Principles of Natural Philosophy: A New Translation (1999), Axioms, or Laws of Motion, Law 2, 416-417. (source)


See also:
  • Science Quotes by Sir Isaac Newton.
  • 25 Dec - short biography, births, deaths and events on date of Newton's birth.
  • Isaac Newton - biography from Famous Men of Science (1889)
  • Isaac Newton - Comments on his “Playing on the Seashore” Quote
  • Isaac Newton - “Playing on the Seashore” illustrated quote - Medium 500px.
  • Isaac Newton - “Playing on the Seashore” illustrated quote - Large 800px.
  • Isaac Newton - context of quote “A change in motion” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “In experimental philosophy” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “In experimental philosophy” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “Standing on the shoulders of giants” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “Standing on the shoulders of giants” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “Impressed force is the action” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “Impressed force is the action” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “Inherent force of matter is the power of resisting…” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “Inherent force of matter is the power of resisting…” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “Plato is my friend” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “Plato is my friend” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “Colours which appear through the Prism ” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “Colours which appear through the Prism ” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “Nature does nothing in vain” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “Nature does nothing in vain” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “No more causes of natural things should be admitted” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “No more causes of natural things should be admitted” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “Truth is ever to be found in simplicity” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “Truth is ever to be found in simplicity” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “Every body perseveres in its state of being at rest” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “Every body perseveres in its state of being at rest” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “God, in the beginning, formed matter” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “God, in the beginning, formed matter” - Large image (800 x 400 px)
  • Isaac Newton - context of quote “The cause of gravity is what I do not pretend to know” - Medium image (500 x 250 px)
  • Isaac Newton - context of quote “The cause of gravity is what I do not pretend to know” - Large image (800 x 400 px)
  • Sir Isaac Newton’s Apple-Tree - debunking the myth, from Historic Ninepins: A Book of Curiosities by John Timbs (1869)
  • Newton and the Dog - debunking the myth about Newton’s dog Diamond.
  • Booklist for Isaac Newton.

Nature bears long with those who wrong her. She is patient under abuse. But when abuse has gone too far, when the time of reckoning finally comes, she is equally slow to be appeased and to turn away her wrath. (1882) -- Nathaniel Egleston, who was writing then about deforestation, but speaks equally well about the danger of climate change today.
Carl Sagan Thumbnail Carl Sagan: In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. (1987) ...(more by Sagan)

Albert Einstein: I used to wonder how it comes about that the electron is negative. Negative-positive—these are perfectly symmetric in physics. There is no reason whatever to prefer one to the other. Then why is the electron negative? I thought about this for a long time and at last all I could think was “It won the fight!” ...(more by Einstein)

Richard Feynman: It is the facts that matter, not the proofs. Physics can progress without the proofs, but we can't go on without the facts ... if the facts are right, then the proofs are a matter of playing around with the algebra correctly. ...(more by Feynman)
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Isaac Newton



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