Isaac Newton

Early Years

The great English scientist Isaac Newton was born in the little village ofWoolthorpe, not far from the old university town of Cambridge, on December25, 1642. His father, a farmer, died before his son’s birth. Little Isaacwas left to the care of his mother, uncle and grandmother who sent him toschool. In his early years young Isaac shone more as one who could make thingswith his hands than a scholar. His neighbors watched him making variousthings and thought ho would probably become a well-known clock maker. Therewas ground for thinking thus became he had already made a clock of a kindwhich his neighbors had never heard of before. It worked by water. Besidesthe water-clock, Isaac also made a sundial. His grandmother was never at aloss to know the hour; for the water-clock could tell it in the house, andthe sundial outside. It is said that the sundial is still at Woolthorpe, ona wall of the house where Newton lived. When he grew older, however, he took a considerable interest inmathematics. Though Isaac Newton never lost his manual skill his ability as amathematician and a physicist was the most important in his life. Accordingto Newton himself, his first physical experiment was carried out in 1658,when he was sixteen years old. Wishing to find out the strength of the windduring a storm, he jumped against and before the wind and by the length ofhis jump he could judge the strength of the wind. Thus, even in his boyishsports, he was searching out the secrets of nature and could find outdifficult things in simple ways. His brain was always busy observingdifferent phenomena of nature.

[pic] Earth mass

Not far from his grandmother’s home there was a windmill. When the

windmill was not working he examined the mechanism and when the windmillworked he watched the process of its work. Then he made a model of thewindmill; every part of the mill and its machinery was complete. If Isaac was left to himself, he was either making something’s or studyingsome book. At night he looked up at the stars, and wondered if they wereworlds like our own, and how great their distance from the earth was. Therewere a lot of questions in his mind but nobody was able to answer them. When Isaac was fourteen years old, his mother took her son from school tohelp her on the farm at Woolthorpe, where she lived with three otherchildren – Isaac’s brother and two sisters. For more than two years heworked on the farm and then his mother sent him back again to school toprepare for the University. On June 5, 1551, Newton entered the University of Cambridge where hestudied mathematics. Soon he became famous having made a number ofimportant contributions to mathematics by the time he was twenty-one. When Newton was twenty-two years old he began studying the theory ofgravitation. In 1665, while on a visit in his negative village, he saw anapple fall from a tree and began wondering what force made the apple fall.Probably this was influenced by his knowledge of Galileo’s experiment fromthe Tower of Pisa. [pic] Moon

The Problem of Gravitation

We know that the moon makes a circle round the earth in about every twenty-eight days. We know also that our earth and other planets move around thesun. Does it not seem probable that the earth pulls the moon, and it movesin its orbit under the influence of the earth’s gravitation? Perhaps also

the sun pulls the earth and the other planets. It was over such possibilities that young Isaac Newton was thinking in thesolitude of his Lincolnshire home when the Great Plague raged in London andhe, along with other students, was sent home from Cambridge because of thisplague. In that quiet period of almost two years he finished consideringhis discoveries which had perhaps the most far-reaching effect in the wholehistory of science: the method of fluxions, decomposition of light and thelaw of gravitation. As a young man at Cambridge Newton had read with great interest thewritings of Galileo, he knew the geometry of Descartes, and he had alreadypartly worked out the methods of calculus, which he called the method offluxions. So when he began to think “of gravity extending to the orb of themoon”, as he wrote, he immediately put this idea to the test ofcalculation. When Newton first began his calculations the available information of theearth’s radius and of the moon’s distance were not accurate. The relativedistance between the various planets was not accurately known at the time.Newton did not know whether he could treat the sun and the planets asthough they were points, concentrated at their respective centres throughwhich he could assume the forces acted so he put his calculations aside andlet the problem wait. For some years he studied light, in which subject alone his work wasenough to place him in the first ranks among men of science. Newton performed many experiments with light and found that white lightwas made up of rays of different colors. He invented the reflectingtelescope, that was very small in diameter, but magnified objects to fortydiameters. Newton developed a mathematical method which is now known as the

Binomial Theorem and also differential and integral calculus. In 1669 he was appointed professor and began lectures on mathematics andoptics at Cambridge.

Newton’s Theory of gravitation

Some years after Newton had begun to work on the problem of gravitation aFrench observer made a new estimate of the earth’s radius, and reported hisresults at meeting of the Royal Society. Newton then reviewed his old notesand examined the information he had. He found that now he was nearer to thesolution of the problem than before, but he did not publish his results, hewas still not satisfied, because his theory was not completely worked out. However, the time had come to publish his results on gravitation becausethe problem was being discussed on all sides. An important work oncentrifugal force by a Dutch scientist Christian Huygens appeared in 1673.The mathematical difficulties seemed insurmountable, so Huygens, togetherwith some Fellows of the royal Society approached Newton on the subject. Hewas asked what path a body would take if it were attracted by a mass with aforce acting inversely as the square of the distance. And Newton’simmediate answer was, “an ellipse.” Newton gathered together all his earlier calculations, and succeeded incompleting his whole theory. First he examined the general problem of theattraction of one mass by another. He showed that a massive sphere attractsanother as if the whole mass were concentrated at the centre. This was aresult of great importance. It enabled Newton to treat the problems of thesun, moon and earth like problems of geometry, for the masses of thesebodies could he treated as if concentrated at points. Thus he at lastjustified the method of treatment which he had first adopted for theproblem of the earth and moon. The proof of his inverse square law was now

complete. He had demonstrated that the gravitational pull of the earthextends as far as the moon and keeps it in its orbit. He demonstrated thatthis pull is in accordance with the same law as that by which a stone fallsto the ground, namely gravity.

[pic] Newton

Newton then showed that the inverse square law represents not onlyKepler’s third law, but his first two laws as well. Thus he not onlycombined the three results of Kepler, but the extended his own theory ofgravitation to the movements of the planets round the sun. the wholemachinery of the solar system was thus brought under the sway of one law,which states that every particle attracts very other particle with a forcewhich changes inversely as the square of the distance between them. Thisstatement is part of Newton’s law of gravitation, which, together with allhis other theories, was given to the world in his great work Elements ofNatural Philosophy published in 1687. It is interesting to mote that Newton did not want to publish his book. Helocked it in his desk and decided to keep it there forever. However, other scientists began to take interest in the subject ofgravitation. Astronomers, physicists and others talked about it atconferences in London. Wren, the famous architect, offered a prize to anyscientists who could prove why the path of a planet must be an ellipse. Butnobody could solve the problem. Newton said he had already got the answer,and promised to send his manuscript some time later. Halley received themanuscript in the autumn of the same year but Newton’s great work, Elementsof Natural Philosophy, was published only in the middle of 1687. With thisbook, a new period in the development of science began.

Newton’s law of inverse squares thus joined in one simple mathematicalstatement the behavior of the planets as well as of bodies on this earth.It was the first synthesis of physical knowledge. As such his contributionto science is unique.