The law of conservation and conversion of energy is one of the most important postulates of physics. Consider the history of its appearance, as well as the main areas of application.
Pages of history
First, find out who discovered the law of conservation and conversion of energy. In 1841, experiments were conducted by the British physicist Joule and the Russian scientist Lenz, as a result of which scientists were able to find out in practice the relationship between mechanical work and heat.
Numerous studies conducted by physicists in different corners of our planet have predetermined the discovery of the law of conservation and conversion of energy. In the mid-nineteenth century, the German scientist Meyer was given its wording. The scientist tried to summarize all the information about electricity, mechanical motion, magnetism, human physiology that existed at that time.
Around the same period, similar thoughts were expressed by scientists in Denmark, England, Germany.
Experiments with warmth
Despite the variety of ideas regarding heat, a complete picture of it was given only by the Russian scientist Mikhail Vasilievich Lomonosov. Contemporaries did not support his ideas, they believed that heat was not connected with the movement of the smallest particles of which the substance consists.
The law of conservation and transformation of mechanical energy, proposed by Lomonosov, was supported only after Rumford was able to prove the presence of particle motion inside the substance during the experiments.
To obtain heat, physicist Davy tried to melt ice, rubbing two pieces of ice against each other. He put forward a hypothesis according to which heat was considered as the oscillatory motion of particles of matter.
The law of conservation and the transformation of energy according to Mayer implied the immutability of the forces that cause the appearance of heat. A similar idea was criticized by other scientists who reminded that the force is related to speed and mass, therefore, its value could not remain unchanged.
At the end of the nineteenth century, Mayer summarized his ideas in a pamphlet and tried to solve the urgent problem of heat. How was the law of conservation and transformation of energy used at that time? In mechanics, there was no consensus on the methods of obtaining, converting energy, so until the end of the nineteenth century this question remained open.
Feature of the law
The law of conservation and conversion of energy is one of the fundamental ones, which allows, under certain conditions, to measure physical quantities. It is called the first law of thermodynamics, the main object of which is the conservation of this value in an isolated system.
The law of conservation and conversion of energy establishes the dependence of the amount of heat on various factors. In the course of experimental studies conducted by Maier, Helmholtz, and Joule, various types of energy were isolated: potential, kinetic. The combination of these species was called mechanical, chemical, electrical, thermal.
The law of conservation and transformation of energy had the following formulation: "A change in kinetic energy is equal to a change in potential energy."
Meyer concluded that all varieties of this magnitude are capable of transforming into each other if the total amount of heat remains unchanged.
Mathematical expression
For example, the energy balance acts as a quantitative expression of the law in the chemical industry .
The law of conservation and conversion of energy establishes a relationship between the magnitude of thermal energy, which falls into the interaction zone of various substances, with that amount that leaves this zone.
The transition of one type of energy to another does not mean that it disappears. No, only its transformation into a different form is observed.
In this case, there is a relationship: work - energy. The law of conservation and transformation of energy implies the constancy of this quantity (its total amount) during any processes taking place in an isolated system. This indicates that in the process of transition of one species to another, quantitative equivalence is observed. In order to give a quantitative characteristic of different types of motion, nuclear, chemical, electromagnetic, and thermal energy are introduced in physics.
Modern wording
How is the law of conservation and transformation of energy in our days read? Classical physics offers a mathematical record of this postulate in the form of a generalized equation of state for a thermodynamic closed system:
W = Wk + Wp + U
This equation shows that the total mechanical energy of a closed system is determined as the sum of the kinetic, potential, internal energies.
The law of conservation and transformation of energy, the formula of which was presented above, explains the invariability of this physical quantity in a closed system.
The main disadvantage of mathematical notation is its relevance only for a closed thermodynamic system.
Open systems
Given the principle of increments, it is quite possible to extend the law of conservation of energy to open physical systems. This principle recommends writing mathematical equations related to the description of the state of the system, not in absolute terms, but in their numerical increments.
In order to fully take into account all forms of energy, it was proposed to add to the classical equation of an ideal system the sum of the increments of energies that are caused by changes in the state of the analyzed system under the influence of various forms of the field.
In a generalized version, the equation of state has the following form:
dW = Σi Ui dqi + Σj Uj dqj
It is this equation that is considered the most complete in modern physics. It was it that became the basis of the law of conservation and transformation of energy.
Value
There are no exceptions to this law in science; it governs all natural phenomena. It is on the basis of this postulate that hypotheses about various engines can be put forward, including the refutation of the reality of developing an eternal mechanism. It can be used in all cases when it is necessary to explain the transitions of one type of energy to another.
Application in mechanics
How is the law of conservation and transformation of energy currently read? Its essence lies in the transition of one type of this quantity to another, but at the same time its general value remains unchanged. Those systems in which mechanical processes are carried out, called conservative. Such systems are idealized, that is, they do not take into account friction forces, other types of resistances that cause the dispersion of mechanical energy.
In a conservative system, only mutual transitions of potential energy into kinetic occur.
The work of the forces that act in a similar system on the body is not related to the shape of the path. Its value depends on the final and initial position of the body. As an example of such forces in physics, gravity is considered. In a conservative system, the magnitude of the work of force in a closed area is zero, and the law of conservation of energy will be valid in the following form: "In a conservative closed system, the sum of the potential and kinetic energy of the bodies that make up the system remains unchanged."
For example, in the case of a free fall of the body, the transition of potential energy to the kinetic form occurs, while the total value of these species does not change.
Finally
Mechanical work can be considered as the only way for the mutual transition of mechanical motion into other forms of matter.
This law has found application in technology. After turning off the car engine, there is a gradual loss of kinetic energy, the subsequent stop of the vehicle. Studies have shown that in this case a certain amount of heat is released, therefore, the rubbing bodies heat up, increasing their internal energy. In the case of friction or any resistance to movement, a transition of mechanical energy into an internal quantity is observed, which indicates the correctness of the law.
Its modern formulation is: “The energy of an isolated system does not disappear into nowhere, does not appear from nowhere. In any phenomena existing within the system, there is a transition of one type of energy to another, transfer from one body to another, without a quantitative change. ”
After the discovery of this law, physicists do not abandon the idea of creating a perpetual motion machine, in which, in a closed cycle, there would be no change in the amount of heat transferred by the system to the outside world, in comparison with the heat received from the outside. Such a machine could become an inexhaustible source of heat, a way to solve the energy problem of mankind.