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MOST IMPORTANT SCIENTIFIC DISCOVERIES
The law of universal gravitation. History and essence of scientific discovery
Directory / The most important scientific discoveries The idea that bodies fall to the ground as a result of their attraction by the globe was far from new: the ancients, for example, Plato, knew this. But how to measure the strength of this attraction? Is it the same everywhere on the globe, and how far does it extend? Here are the questions that Newton - the author of the law of universal gravitation, confused scientists and philosophers. Discovering your third law Kepler came into such an ecstatic state that it seemed to him that he was delirious. In 1619, Kepler published the famous "Harmony of the Universe", in which he was one step away from Newton's discovery and yet did not make it. Not only did Kepler attribute the motions of the planets to some mutual attraction, he was even ready to accept the law of "square proportion" (that is, an action inversely proportional to the squares of distances). Alas, he soon abandoned it and instead assumed that attraction was inversely proportional, not to the squares of the distances, but to the distances themselves. Kepler failed to establish the mechanical principles of the laws of planetary motion discovered by him. Newton's immediate predecessors in this field were his compatriots Gilbert and especially Hooke. In 1660, Gilbert published On the Magnet, in which he compared the action of the earth on the moon with the action of a magnet on iron. In another work of Gilbert, published after his death, it is said that the Earth and the Moon influence each other like two magnets, and, moreover, in proportion to their masses. But closest to the truth came Robert Hooke, a contemporary and rival of Newton. March 21, 1666, that is, shortly before the time when Newton first delved deeply into the secrets of celestial mechanics, Hooke read at a meeting of the Royal Society of London a report on his experiments on the change in gravity depending on the distance of a falling body relative to the center of the Earth. Conscious of the unsatisfactoriness of his first experiments, Hooke came up with the idea of measuring the force of gravity by swinging a pendulum - an idea of the highest degree witty and fruitful. Two months later, Hooke reported in the same society that the force holding the planets in their orbits must be similar to that which produces the circular motion of a pendulum. Much later, when Newton was already preparing his great work for publication, Hooke, independently of Newton, came to the idea that "the force that controls the motion of the planets" should change "to some extent depending on distances", and declared that he would "build a whole system of the universe" based on this beginning. But it was here that the difference between talent and genius was revealed. Hooke's happy thoughts remained in their infancy. He did not have the strength to cope with his hypotheses, and the priority of the discovery belongs to Newton. Isaac Newton (1642–1726) was born in Woolsthorpe, Lincolnshire. His father died before the birth of his son. Newton's mother, nee Aiskof, gave birth prematurely shortly after her husband's death, and the newborn Isaac was strikingly small and frail. They thought that the baby would not survive. Newton, however, lived to a ripe old age and always, with the exception of short-term disorders and one serious illness, was distinguished by good health. In terms of property status, the Newton family belonged to the number of farmers of the middle hand. When Isaac grew up, he was placed in an elementary school. Upon reaching the age of twelve, the boy began to attend a public school in Grantham. He was placed in an apartment with the pharmacist Clark, where he lived intermittently for about six years. Life at the pharmacist first aroused in him a desire to study chemistry. On June 5, 1660, when Newton was not yet eighteen years old, he was admitted to Trinity College. The University of Cambridge was at that time one of the best in Europe: philological and mathematical sciences equally flourished here. Newton turned his main attention to mathematics. But at the same time, in 1665, he received a Bachelor of Fine Arts (verbal sciences). His first scientific experiments are related to the study of light. The scientist proved that with the help of a prism, white color can be decomposed into its constituent colors. Studying the refraction of light in thin films, Newton observed a diffraction pattern, which was called "Newton's rings". In 1666, an epidemic broke out in Cambridge, which, according to the custom of the time, was considered a plague, and Newton retired to his Woolsthorpe. Here, in the silence of the village, having no books or instruments at hand, living an almost reclusive life, the twenty-four-year-old Newton indulged in deep philosophical reflections. Their fruit was the most brilliant of his discoveries - the doctrine of universal gravitation. It was a summer day. Newton liked to meditate, sitting in the garden, in the open air. Tradition reports that Newton's thoughts were interrupted by the fall of an overflowing apple. The famous apple tree was kept for a long time as a warning to posterity. And after it dried up, it was cut down and turned into a historical monument in the form of a bench. Newton had been thinking about the laws of falling bodies for a long time, and it is quite possible that, in particular, the fall of an apple again led him to these thoughts, from which he moved on to the question: does the fall of bodies occur in the same way everywhere on the globe? So, for example, is it possible to assert that in high mountains bodies fall with the same speed as in deep mines? But how did Newton discover this law, for which the analogy with the fall of an apple could no longer have any meaning? Newton himself wrote many years later that he derived the mathematical formula expressing the law of universal gravitation from studying the famous laws of Kepler. It is possible, however, that his work in this direction was greatly accelerated by his research in the field of optics. The law that determines the "light intensity" or "degree of illumination" of a given surface is very similar to the mathematical formula for gravity. Simple geometric considerations and direct experience show that when, for example, a sheet of paper is removed from a candle at a double distance, the degree of illumination of the surface of the paper decreases, and not by half, but by four times, at a triple distance - by nine times, and so on. This is the law that in Newton's time was called briefly the law of "square proportion". More precisely, "the intensity of light is inversely proportional to the squares of distances." It was quite natural for a mind like Newton to try to apply this law to the theory of gravitation. Once having come to the conclusion that the attraction of the Moon by the Earth determines the motion of the earth's satellite, Newton inevitably came to a similar hypothesis regarding the motion of the planets around the Sun. But his mind was not content with untested hypotheses. He began to calculate, and it took decades for his assumptions to turn into the grandest system of the universe. At the same time, Newton could never have developed and proved his brilliant idea if he had not mastered the powerful mathematical method known today under the name of differential and integral calculus. Justice requires to note the contribution of Robert Hooke. Thus, the astute Hooke corrected Newton's conclusion and wrote to the latter that falling bodies should not deviate exactly to the east, but to the southeast. He agreed with the arguments of Hooke, and the experiments carried out by the latter fully confirmed the theory. Hooke corrected another Newton's mistake. Isaac believed that a falling body, due to the connection of its movement with the movement of the Earth, would describe a helical line. Hooke showed that a helical line is obtained only if air resistance is taken into account and that in vacuum the movement must be elliptical - we are talking about true movement, that is, one that we could observe if we ourselves did not participate in the movement. the globe. After checking Hooke's conclusions, Newton became convinced that a body thrown at a sufficient speed, being at the same time under the influence of the earth's gravity, can indeed describe an elliptical path. Reflecting on this subject, Newton discovered the famous theorem, according to which a body under the influence of an attractive force, similar to the force of gravity, always describes a conic section, that is, one of the curves obtained when a cone is intersected by a plane (ellipse, hyperbola, parabola and in special cases a circle and a straight line). In addition, Newton determined that the center of attraction, that is, the point at which the action of all attractive forces acting on a moving point is concentrated, is at the focus of the described curve. Thus, the center of the Sun is (approximately) in the general focus of the ellipses described by the planets. Having achieved such results. Newton immediately saw that he had deduced theoretically, that is, based on the principles of rational mechanics, one of Kepler's laws, which states that the centers of the planets describe ellipses and that the center of the Sun is at the focus of their orbits. But Newton was not satisfied with this basic agreement between theory and observation. He wanted to see if it was possible, with the help of theory, to actually calculate the elements of planetary orbits, that is, to predict all the details of planetary motions? At first he was not lucky. John Conduitt writes of it this way: "In 1666 he again left Cambridge ... to go to his mother in Lincolnshire, and while he was meditating in the garden, it occurred to him that the force of gravity (which causes an apple to fall on earth) is not limited to a certain distance from the earth, but that the force must extend much farther than is usually thought. Why not to the moon, he said to himself, and if so, this should influence its movement and perhaps keep it in orbit , whereupon he determined to calculate what the effect of such an assumption might be; but as he had no books at that time, he used the commonly used proposition, common among geographers and our sailors before Norwood measured the earth, which is that in one degree of latitude on the surface of the Earth contains 60 English miles.The calculation did not coincide with his theory and forced him to be content with the assumption that, along with the force of gravity, there must also be an admixture of the force to which and the Moon, if she were transported in her motion by a whirlwind ... " The study of the laws of elliptical motion significantly advanced Newton's research. But as long as the calculations did not agree with the observation, Newton must have suspected the existence of some source of error or incompleteness of the theory, still eluding him. It was not until 1682 that Newton was able to use the more accurate meridian data obtained by the French scientist Picard. Knowing the length of the meridian, Newton calculated the diameter of the globe and immediately entered the new data into his previous calculations. To his greatest joy, the scientist was convinced that his old views were completely confirmed. The force that causes bodies to fall to the Earth turned out to be exactly equal to that which controls the movement of the Moon. This conclusion was for Newton the highest triumph of his scientific genius. Now his words were fully justified: "Genius is the patience of thought concentrated in a certain direction." All his deep hypotheses, long-term calculations turned out to be correct. Now he was completely and finally convinced of the possibility of creating an entire system of the universe based on one simple and great principle. All the most complex movements of the moon, planets and even comets wandering through the sky became quite clear to him. It became possible to scientifically predict the movements of all the bodies of the solar system, and perhaps the sun itself, and even stars and star systems. At the end of 1683, Newton finally communicated to the Royal Society the main principles of his system in the form of a series of theorems on the motion of the planets. However, the theory was too brilliant for there to be envious people who tried to ascribe at least part of the glory of this discovery to themselves. No doubt, some of the British scientists of that time came quite close to Newton's discoveries, but to understand the difficulty of the question does not mean to solve it. The famous architect and mathematician Christopher Wren tried to explain the motion of the planets by "the fall of bodies on the Sun, connected with the original motion." The astronomer Halley assumed that Kepler's laws could be explained by the action of a force inversely proportional to the squares of distances, but he could not prove this. Hooke assured the members of the Royal Society that all the ideas contained in the Elements had already been proposed to them a hundred times; those that were not expounded by him before are erroneous. Huygens completely and categorically rejected the idea of mutual gravitation of particles, allowing the presence of gravitation only inside bodies. Leibniz continued to insist that the motion of the planets could only be explained by means of some ethereal swirling fluid, knocking the planets off the rectilinear path Bernoulli and Cassini also stubbornly talked about vortices. However, the noise gradually subsided, and the glory of the discovery of universal gravitation rightfully went to Isaac Newton. Author: Samin D.K.
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