Definition of energy
Ability of a physical system to produce a job.
This definition, although it is the most widespread, can be misleading because of the vagueness of the term "capacity", and therefore, it is better to define the energy as what, when a work occurs, decreases in an amount equal to the work produced. Energy, then, is measured in the same units as labor.
History of the study of energy
The notion of energy appears for the first time from the investigations of Joule and Carnot on the conversion of heat in mechanical work and thanks to the theory of Helmholtz in which it connects the work done by an isothermal system with the internal energy and the Entropy of this system. In this way energy is not only linked to the concept of mechanical work, but also to electrical, chemical or calorific work. This is why we can talk about electrical energy, chemical energy and heat energy.
Parallelly, it can be said that if a certain amount of work disappears in an isolated physical system, or an equivalent part of this work, forming part of various forms of energy, the same amount of work must appear under other forms of energy according to the definition Law of conservation of energy.
As a result of investigations by William Thomson and RJE Clausius in the mid- XIX, it was put in evidence the process of energy degradation, that is, that useful work that can be obtained in an isolated system not all energy is conserved but there is a part of this energy that degrades (entropy, second Principle of thermodynamics). Later on, and following A. Einstein's theory on the equivalence between mass and energy (1905), the principle of conservation was extended, and at the moment it is not differentiated between the conservation of the mass and the conservation of the energy giving rise to The theory of relativity, law of conservation.
In 1900, Max Planck gave the explanation of many hitherto unexplained phenomena through the quantum theory of energy (quantum mechanics), which assumed the contribution a fundamental concept for the knowledge of energy.
Definition of different types of energy
Energy can be presented in various forms, which, by the principle of conservation of energy, can be transformed into one another. Therefore, we can speak of different types of energy more in terms of its effects than of its natural origin. In this sense, energy can be classified in mechanics, thermodynamics, electromagnetic and nuclear.
Definition of mechanical energy
The mechanical energy is due to the geometric and dynamic variables of the system, from a macroscopic point of view, and is the one that responds to the simplest mathematical scheme.
The definition of mechanical energy in a material body of constant mass (m) is the sum of its kinetic energy and its potential energy. The kinetic energy is proportional to the speed of the body while the potential energy depends on the position of the body in the field of forces that surrounds it. Thus in the case of free fall the position would be determined by the height and field of forces by the force of gravity. Also the potential energy of deformation due to the elastic properties of a deformed body could be considered, such as a compressed spring.
Definition of thermodynamic energy
The definition of thermodynamic energy makes sense from a molecular point of view. Taking into account thermodynamic variables, we can define the internal energy U of a system as the sum of the kinetic energies of the molecules that compose it and the potential energy of the forces between them. Each of the atoms or molecules of a body or of a substance are in continuous movement, whether of rotation, translation or vibration, with respect to the position of equilibrium, more or less intense according to the temperature. From this point of view we can say that thermal energy is equivalent to the kinetic energy of molecules, as formulated by L. Boltzmann in his kinetic theory of gases.
The internal energy is not a measurable quantity of an absolute form, but only the variations of energy between two states of the system (first principle of thermodynamics) are measured.
The name given to it depends on the manifestation of this energy or the nature of the phenomenon that generates it. We define
(Binding energy or formation energy the difference between the energy of a molecule and that of the atoms that form it (bond),
- Energy of dissociation the energy released in the dissociation of a compound,
- Activation energy the increase of energy necessary for a chemical reaction (activation energy) and
- Resonance energy the difference between the theoretical formation energy and the actual formation energy of a resonant compound.
Free energy relates the variation of internal energy (U) or enthalpy (H) with the variation of the entropy (S) of a system and serves to indicate in which direction the system (affinity) will evolve spontaneously.
Definition of electromagnetic energy
The definition of electromagnetic energy is energy derived from the electromagnetic nature of matter.
Electromagnetic energy manifests itself basically in two ways: by transforming itself into kinetic energy of the electric charges that are in its zone of influence - which can be converted into heat (Joule effect) or mechanical energy (electric motors) - or propagating as radiant energy outside Of the medium where it has been generated in the form of electromagnetic waves - which can then be converted into light energy, etc. - or also, at atomic scale, emitting particles carrying a certain amount of energy determined by the Planck equation (photoelectric effect).
Definition of nuclear energy
The ultimate definition of energy is nuclear energy. This type of energy keeps the components of the atomic nucleus close together. The mass of an atomic nucleus is less than the sum of the masses of the elementary particles that form it (mass defect). This mass defect is due to the appearance of a cohesive energy absorbed by the nuclear structure and which can be calculated by Einstein's theory of relativity.
This energy can be released in the form of radiant energy and kinetic energy from the particles that are expelled from the nucleus.
Use of energy
The use of energy as a source of labor has always been an essential necessity for man and one of the fundamental factors of modern economic development and technical progress.
Until the beginning of the industrial revolution, apart from isolated experiments, man used muscle power, hydraulic energy and wind power for the production of mechanical work, as well as vegetable fuels for the production of heat. These were until then the only resources used to obtain energy, although in time these systems were perfected to achieve higher yields (more rational use of animals, improvement of sailing techniques, invention of the hydraulic wheel, etc.).
The development principle for energy exploitation techniques was in the emergence of the steam engine and the transformation of the hydraulic wheel into a turbine. Later, the construction of the first combustion engines gave the definitive push in the obtaining of mechanical energy from the heat.
Today, the most commonly used sources of energy are waterfalls, fuels and nuclear fission, and, less importantly, solar, wind, geothermal and tidal power.
The exploitation of hydroelectric power requires appropriate topographic and hydrographic conditions and the construction of reservoir and large-scale machinery in order to achieve acceptable energy yields (which can reach up to 80% or more of the potential energy of the water). Generally always for the production of electric energy.
The most important source of energy is fuels that have experienced exponential growth in recent years. The maximum yield is much lower than that obtained by hydraulic energy but its high concentration of energy explains the considerable development suffered. The heat obtained from the fuels is used directly or converted into mechanical energy (engines, turbines ...) and also in obtaining electrochemical electricity (fuel cell).
The third type of energy most commonly used is nuclear energy, which is usually obtained by fission of the nuclei of substances such as uranium, plutonium, thorium, etc. & hellip; The technology of nuclear fusion reactions is not yet sufficiently developed to permit industrial exploitation and is used only in experimental laboratories and war applications. The energy obtained in nuclear fission manifests itself in the form of heat, and reaches temperatures much higher than those obtained with conventional fuels, however, the yields that can be obtained are still very low (of the order of 30% ). Nuclear energy is basically applied in the production of electric power and in the propulsion of ships. The electrical energy obtained with this system (nuclear power station) has a reasonable cost only in the case of large reactors, which provide very high powers.
Last review: November 25, 2016