Isaac Newton formulated the law of universal gravitation and the three basic laws of motion.
Isaac Newton is considered one of the most important scientists of all time. The author of the law of universal gravitation and the laws of motion, Newton presented an entirely new way of explaining the workings of the universe. These ideas, which marked the high point of the Scientific Revolution, were presented in Newton's landmark work, Philosophiae Naturalis Principia Mathematica, in 1687. In addition to his work on gravity and motion, Newton also contributed to the study of light, developed a form of calculus, and built the first reflecting telescope.
Born on December 25, 1642, in Woolsthorpe, Lincolnshire, England, Newton was a premature baby who was not expected to live. His father had died three months previous to the birth, and his mother was remarried to the rector of a nearby parish three years later, leaving Newton in the care of his grandparents.
Failures at school and on farm
Newton did not distinguish himself in school, but he did enjoy constructing mechanical toys such as sundials and kites. At the age of 12 he was sent to King's School in the town of Grantham. He lived in the house of a local apothecary (pharmacist) while he studied there, and he developed an interest in the chemical library in the house. Newton was removed from school by his mother in the late 1650s in order to work on the family farm, which he was expected to take over someday. But Newton proved an even worse farmer than scholar. His uncle, however, saw his potential as a student and encouraged the young man to go to Cambridge University in 1660. Five years later Newton graduated, even though he had failed a scholarship exam in 1663 due to his lack of knowledge concerning geometry.
Inspired by falling apple
Newton wanted to remain at the university to earn his master's degree, but he was forced to return to the farm to escape the bubonic plague, a deadly disease that was spreading quickly through London at the time. During his time at the farm, Newton worked independently on his studies, experimenting in the areas of gravitation and optics (the study of light) and developing a form of math known as calculus. In 1666, Newton saw an apple fall to the ground, and he began to ponder the force that was responsible for the action. While this story has often been considered a legend, Newton confirmed that it did in fact happen. He first thought that the apple fell because all matter attracts other matter. He then theorized that the rate of the apple's fall was directly proportional to the attractive force Earth exerted upon it.
In addition, Newton suggested the inverse square law: force decreases according to the square of the distance from the center of Earth. Then he made a daring hypothesis (an untested idea), suggesting the force that pulled the apple was also responsible for keeping the Moon in orbit around Earth. This was an important idea because at the time most people believed in the theory of ancient Greek philosopher Aristotle (384-322 B.C.), who had said that the heavenly bodies obeyed different physical laws than objects on Earth. Newton had suggested that all bodies responded to the same physical laws, no matter where they were.
Abandons work on gravity
When Newton made calculations of what the rate of fall for the Moon should be, he came up short of what was actually observed and was quite disappointed. The problem was two-fold. First, he needed to know the radius of Earth (the distance from the surface to the center), but this was not known with precision at the time and the figure Newton used was too small. Second, he was not certain he was correct in making his calculations based on the gravitational force at the center of Earth, as opposed to the surface. Because of these issues, he set aside his work on gravity for fifteen years.
Experiments with light
During this same time (1665-66), a book about color written by English physicist and chemist Robert Boyle (1627-1691) captured Newton's interest and he began to experiment with light. Newton passed a beam of sunlight through a prism of glass and observed that the light was refracted, or split, into a spectrum, a display of colored light that contains all the colors of the rainbow. He passed the spectrum through a second prism, and the light was recombined into a white spot. In this way, Newton discovered that all of the colors of the spectrum existed in white light, a finding that earned him recognition in scientific circles. For an unexplained reason, Newton did not notice any of the visible dark lines in the spectrum of the Sun. It was not until over 150 years later that English physicist William Hyde Wollaston (1766-1828) and Bavarian physicist Joseph Fraunhofer (1787-1826) noticed the lines, and German physicist Gustav Kirchhoff (1824-1887) realized they revealed the types of elements and chemical compounds that made up heavenly bodies. Newton's experiments led him to conclude that light was comprised of a stream of particles that moved through an invisible substance, or ether. Although this theory was later disproved, it was kept alive by Newton's influence for nearly a century.
Builds reflecting telescope
Newton returned to Cambridge in 1667, where he earned his master's degree and conducted further research on the work he had begun on the farm. In 1668, he constructed a reflecting telescope, a device that used mirrors to reflect and magnify the light of distant objects. Newton's telescope was a major advance over other telescopes of the time because it created a clear, undistorted image, and it was many times more powerful than other scopes. The high-power telescopes used by modern astronomers are modeled after Newton's reflecting design. Newton presented his invention to the Royal Society(the oldest scientific organization in England); the members were so impressed that they elected him to their organization in 1672.
Becomes center of controversy
After being elected to the Royal Society, Newton appeared in front of the group to report on his experiments with light and its spectrum. While most members were impressed by his findings and his idea that light was composed of colors, physicist Robert Hooke, who had performed similar experiments and drawn different conclusions, dismissed Newton's findings as unimportant. In response, Newton sent an angry letter to Hooke, which was later published in the Royal Society's periodical. The feud between Hooke and Newton continued to grow, although Newton's increasing reputation in the British scientific community forced the two men to act more politely--at least in public.
The two scientists' dislike for one another reached its height in 1686 when Newton published his law of universal gravitation. Hooke, who had outlined a similar theory in a letter seven years earlier, insisted that Newton had stolen his idea. It is possible that Newton was unaware of Hooke's work, which was in any event fundamentally flawed. However, modern scientists now credit Hooke with the ideas that inspired Newton to develop his own, more accurate, theory of gravitation.
Newton became involved in yet another controversy, this time with the German mathematician Gottfried Leibniz (1646-1716). Both men had independently developed a complex system of mathematical calculation called calculus, although each used different symbols and notations. Leibniz's notation, however, was considered superior and came to be preferred over that of Newton, causing a bitter controversy between the two. Their conflict quickly became a matter of national pride, and English scientists refused to accept Leibniz's version. Unfortunately this stubbornness kept the English from significantly contributing to mathematics for nearly a century.
Returns to work on gravity
Newton became very bitter about the many arguments surrounding his work, particularly his fights with Hooke. At one point he was so frustrated that he vowed not to publish any more scientific works. In the 1680s, however, Newton was drawn into publicly presenting his work again after being encouraged by his good friend, the English astronomer Edmond Halley (1656-1742). Halley told Newton that Hooke had claimed to have discovered the laws concerning the motion of celestial objects. Newton casually told Halley that he had already come up with the answer to that problem 15 years earlier in his early days of research at the family farm. Halley convinced Newton to retry the calculations that he had abandoned before. This time the calculations worked: a more accurate measurement of Earth's radius had been reported, giving Newton better data for his calculations. Also, from other work he had done, Newton also now knew that he should make the center, not the surface, the point of gravitational attraction of a sphere. With his friend's financial help, Newton published the results of his second effort in the most important work of his career, Philosophiae Naturalis Principia Mathematica ("Mathematical Principles of Natural Philosophy"), which outlined the laws of gravity and motion. This book, considered to be one of the greatest scientific works ever written, established Newton as the most important scientist in England and the world.
States law of universal gravitation
In the Principia Mathematica, which appeared in 1687, Newton took Italian scientist Galileo Galilei's findings about motion and the speed of falling objects and organized them into three basic laws of motion. The first law stated that a body at rest remains at rest, and a body in motion remains in motion. The second law declared that force is equal to mass times acceleration. The third law observed that for every action, there is an equal and opposite reaction. These three laws allowed Newton to calculate the gravitational force between Earth and the Moon. He asserted these laws acted upon any two objects in the universe, establishing the law of universal gravitation; he proceeded to estimate, quite accurately, the masses of Jupiter and Saturn. He also used his new laws to explain the motion of comets, the movement of the ocean tides, and the timing of the equinoxes (the two times each year when the Sun crosses the plane of Earth's equator; at these times, day and night are of equal length everywhere on Earth).
Contributes to Scientific Revolution
The Principia Mathematica revolutionized science by providing an explanation of the forces that controlled the regular movement of planets as described by German astronomer Johannes Kepler's (1571-1630) laws of planetary motion. It also elegantly showed how celestial bodies and earthly objects followed a single law of gravitation. This overall scheme of the workings of the universe was the crowning accomplishment of the Scientific Revolution--a trend away from the theories of ancient Greek philosophers that had been the center of scientific thought for nearly 2,000 years. From the time of Polish astronomer Nicolaus Copernicus (1473-1543), who stated that Earth and the planets revolve around the Sun, a new basis of science had been developing--a scientific method of observation and calculation that gradually disproved many of the long-accepted ideas that began in ancient Greece. Newton's laws are considered the point at which the scientific method became the most important influence in science.
Weakened by work
Principia Mathematica was written in only 18 months and apparently exerted an enormous strain on Newton. His physical exhaustion combined with the continual controversy surrounding him resulted in Newton suffering a nervous breakdown in 1692. Although he recovered and still had an extraordinary mathematical ability, he was never the same. In 1696, he secured a government post, where he made a number of important changes to the English monetary system. He was elected president of the Royal Society in 1703 and was reelected to that position every year until his death. He wrote another book, Opticks, which covered his work on light; however, to avoid antagonizing his old rival, he waited until after Hooke's death before printing it in 1704.
Remembered for landmark work
In 1705, Queen Anne knighted him; it was the first time a scientist had been so honored. Sir Isaac Newton died on March 20, 1727, at the age of 84, and was buried alongside other English heroes in Westminster Abbey. His vast influence upon science continued after his death; the only people who have since had such an important role in science and history have been English naturalist Charles Darwin (1809-1882), who popularized the idea of evolution, and German-born physicist Albert Einstein (1879-1955), who formulated the theory of relativity. But Newton was modest about his place in history. In a letter written to Hooke, Newton once stated, "if I have seen further than other men, it is because I stood on the shoulders of giants."
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