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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Law of energy conservation. History and essence of scientific discovery
Directory / The most important scientific discoveries The most important achievement of natural science is the establishment of the law of conservation of energy. The meaning of this law goes far beyond the limits of a particular physical law. Instead of the law of conservation of masses, this law forms the cornerstone of the scientific materialistic worldview, expressing the fact of the indestructibility of matter and motion. Actually, the philosophical prerequisites for such a statement were already there. They were also among the ancient philosophers, especially the atomists, and Descartes, and were especially concretely and distinctly seen in Lomonosov. In 1807, a member of the Paris Academy of Sciences, French physicist and chemist Joseph Louis Gay-Lussac, studying the properties of gases, set up an experiment. Before that, it was already known that the compressed gas, expanding, cools. The scientist suggested that this may be because the heat capacity of the gas depends on its volume. He decided to check it out. Gay-Lussac caused the gas to expand from a vessel into a void, that is, another vessel from which the air had been previously evacuated. To the surprise of all the scientists who observed the experiment, no decrease in temperature occurred, the temperature of the entire gas did not change. The result obtained did not justify the assumptions of the scientist, and he did not understand the meaning of the experiment. Gay-Lussac made a major discovery and failed to notice it. A very important role in the development of the doctrine of the transmutability of the forces of nature was played by the research of the Russian scientist Emil Khristianovich Lenz, adjoining in this respect to research Faraday. His remarkable works on electricity have a clear energy orientation and have significantly contributed to the strengthening of the law. Therefore, Lenz rightfully occupies one of the first places in the galaxy of creators and strengtheners of the law of conservation of energy. The first to accurately formulate this great law of natural science was the German physician Robert Mayer. Robert Julius Mayer (1814–1878) was born in Heilbronn to a druggist's family. After graduating from high school, Mayer entered the Faculty of Medicine at the University of Tübingen. Here he did not attend mathematical and physical courses, but he thoroughly studied chemistry with Gmelin. He failed to finish the university in Tübingen without a break. He was arrested for participating in a banned gathering. In prison, Mayer went on a hunger strike and on the sixth day after his arrest was released under house arrest. From Tübingen, Mayer went to Munich, then to Vienna. Finally, in January 1838, he was allowed to return to his homeland. Here he passed the exams and defended his dissertation. Mayer soon made the decision to join a Dutch ship bound for Indonesia as a ship's doctor. This journey played an important role in its discovery. Working in the tropics, he noticed that the color of the venous blood of the inhabitants of a hot climate is brighter and scarlet than the dark color of the blood of the inhabitants of cold Europe. Mayer correctly explained the brightness of the blood in the inhabitants of the tropics: due to the high temperature, the body has to produce less heat. After all, in a hot climate, people never freeze. Therefore, in hot countries, arterial blood is less oxidized and remains almost the same red when it passes into the veins. Mayer came up with an assumption: would the amount of heat released by the body change when the same amount of food is oxidized, if the body, in addition to releasing heat, still does work? If the amount of heat does not change, then more or less heat can be obtained from the same amount of food, since work can be converted into heat, for example, by friction. If the amount of heat changes, then work and heat owe their origin to the same source - food oxidized in the body. After all, work and heat can be transformed into one another. This idea immediately made it possible for Mayer to clarify and enigmatic Gay-Lussac's experiment. If heat and work are mutually converted, then when gases expand into a vacuum, when it does not produce any work, since there is no pressure force opposing the increase in its volume, the gas should not be cooled. If, when the gas expands, it has to do work against external pressure, then its temperature should decrease. But if heat and work can turn into each other, if these physical quantities are similar, then the question arises about the relationship between them. Mayer tried to find out: how much work is required to release a certain amount of heat and vice versa? By that time, it was known that to heat a gas at constant pressure, when the gas expands, more heat is needed than to heat the gas in a closed vessel. That is, the heat capacity of a gas at constant pressure is greater than at constant volume. These quantities were already well known. But it has been established that both of them depend on the nature of the gas: the difference between them is almost the same for all gases. Mayer realized that this difference in heat is due to the fact that the gas, when expanding, does work. The work done by one mole of an expanding gas when heated by one degree is easy to determine. Any gas at low density can be considered ideal - its equation of state was known. If you heat a gas by one degree, then at constant pressure its volume will increase by a certain amount. Thus, Mayer found that for any gas, the difference between the heat capacity of the gas at constant pressure and the heat capacity of the gas at constant volume is a quantity called the gas constant. It depends on the molar mass and temperature. This equation now bears his name. Simultaneously with Mayer and independently of him, the law of conservation and transformation of energy was developed Joule и Helmholtz. Helmholtz's mechanical approach, which he himself was forced to recognize as narrow, made it possible to establish an absolute measure for "living force" and to consider all possible forms of energy either in the form of kinetic ("living forces") or potential ("tension forces"). The quantity of the transformed form of motion can be measured by the magnitude of that mechanical work, for example, in lifting a load, which could be obtained if the entire motion that has disappeared is spent on this lifting. The experimental substantiation of the principle consists, first of all, in the proof of the quantitative certainty of this work. Joule's classical experiments were devoted to this problem. James Prescott Joule (1818-1889) - Manchester brewer - began with the invention of electromagnetic apparatus. These devices and the phenomena associated with them have become a concrete vivid manifestation of the transmutability of physical forces. First of all, Joule investigated the laws of heat generation by electric current. Since experiments with galvanic sources (1841) did not make it possible to establish whether the heat developed by the current in the conductor was only the transferred heat of chemical reactions in the battery, Joule decided to experiment with induction current. He placed a coil with an iron core in a closed vessel with water, the ends of the coil winding were connected to a sensitive galvanometer. The coil was set in rotation between the poles of a strong electromagnet, through the winding of which current was passed from the battery. The number of revolutions of the coil reached 600 per minute, while alternately a quarter of an hour the winding of the electromagnet was closed, a quarter was open. The heat that was released due to friction in the second case was subtracted from the heat released in the first case. Joule found that the amount of heat generated by inductive currents is proportional to the square of the current strength. Since in this case the currents arose due to mechanical movement, Joule came to the conclusion that heat can be created using mechanical forces. Further, Joule, replacing the rotation of the hand with the rotation produced by a falling weight, established that "the amount of heat that is able to heat 1 pound of water by 1 degree, is equal and can be converted into mechanical force, which is able to raise 838 pounds to a vertical height of 1 foot". These results were summarized by him in the work "On the Thermal Effect of Magnetoelectricity and the Mechanical Significance of Heat", reported at the Physical and Mathematical Section of the British Association on August 21, 1843. Finally, in the works of 1847-1850, Joule develops his main method, which was included in physics textbooks. It gives the most perfect definition of the mechanical equivalent of heat. The metal calorimeter was mounted on a wooden bench. An axis passes inside the calorimeter, carrying blades or wings. These wings are located in vertical planes forming an angle of 45 degrees with each other (eight rows). Four rows of plates are attached to the side walls in the radial direction, which do not prevent the rotation of the blades, but prevent the movement of the entire mass of water. For thermal insulation purposes, the metal axle is divided into two parts by a wooden cylinder. At the outer end of the axle there is a wooden cylinder, on which two ropes are wound in the same direction, leaving the surface of the cylinder at opposite points. The ends of the ropes are attached to fixed blocks, the axes of which lie on light wheels. On the axis are wound ropes that carry loads. The height of the fall of goods is measured by rails. Next, the Joule determined the equivalent by measuring the heat generated by the friction of cast iron on cast iron. A cast-iron plate rotated on an axis in the calorimeter. Rings slide freely along the axis, carrying a frame, a tube and a disk, fitted in shape to a cast-iron plate. With the help of a rod and a lever, you can apply pressure and press the disc against the record. Joule made the last measurements of the mechanical equivalent in 1878. Mayer's calculations and Joule's experiments completed the bicentennial dispute about the nature of heat. The principle of equivalence between heat and work proved by experience can be formulated as follows: in all cases when work appears from heat, an amount of heat equal to the work received is spent, and vice versa, when work is spent, the same amount of heat is obtained. This conclusion has been called the First Law of Thermodynamics. According to this law, work can be converted into heat and vice versa - heat into work. Moreover, both of these values are equal to each other. This conclusion is valid for the thermodynamic cycle, in which the system must be reduced to the initial conditions. Thus, for any circular process, the work done by the system is equal to the heat received by the system. The discovery of the First Law of Thermodynamics proved the impossibility of inventing a perpetual motion machine. At first, the law of conservation of energy was called so - "perpetual motion machine is impossible." Author: Samin D.K.
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