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Energodynamic system of physical quantities and concepts
To not mix with SI, unifying UNITS (explanation).
Physical quantities reflect the properties of physical systems. Therefore, in order to understand what is called a physical quantity, it is useful previously acquainted with the article devoted to explaining the concepts "physical system".
In International vocabulary of metrology JCGM 200:2012 given a definition: "property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference".
In the note indicated that the concept of "quantity" in a general sense can be divided, for example, to the concepts of "physical quantity", "chemical quantity" and "biological quantity" or base quantity and the derived quantity.
In the dictionary-reference of M.Yudin and others (1989), this definition is slightly different: "physical quantity (quantity) is the characteristic of one of the properties of a physical object (a physical system, a phenomenon or process), the overall qualitatively many physical objects, but in terms of quantity individual for each object". In this definition, there is change: physical quantity is not a property, and characteristic of one of the properties. However, no significant difference between the concepts of "property" and "characteristic".
Take, for example, such a property as the length. It really is used to describe a completely different objects. In mechanics it is the length of the path, for electricity it is the length of the conductor, in hydraulics it is tube length, in the heat transfer it is the wall thickness of the radiator, etc. But the numerical value of the length of each of these objects are different. Length of automobile is several meters, the length of the track or high-voltage - many kilometers, and the wall thickness of the radiator easier to evaluate in millimeters. Although the nature of the length of all of these examples is the same.
We also call attention to the fact that in the above definitions of the term "physical quantity" is not directly linked to the process of measurement. After all, there are physical quantities that are not measured but calculated. K.Gomoyunov (1983) writes: "... physical quantity can be regarded as a mental model of the property. More specifically - as a quantitative expression of the property or as a quantitative knowledge of the property ". With this approach, the inclusion of the concept of "physical quantity" mention of the measurement process is not required.
Physical quantity necessarily has a dimension and unit, this is different from the mathematical number. Although there are numbers that reflect the properties of physical phenomena, but are not physical quantities. These are called ordinal quantities, defined in the International Vocabulary of Metrology JCGM 200:2012 so: "quantity, defined by a conventional measurement procedure, for which a total ordering relation can be established, according to magnitude, with other quantities of the same kind, but for which no algebraic operations among those quantities exist". This, for example, the earthquake strength on the Richter scale, octane number for petroleum fuel. Such quantities have neither dimensions or units, for them have its own scales of values.
Physical quantities are classified according to several criteria:
1. In direction. The physical quantity that reflects the direction of motion, called vector quantity, otherwise scalar quantity.
2. By the character of dimension. The physical quantity which has dimension formula, in which at least one dimension of a non-zero exponent, called dimensional quantity. If all dimensions have a zero exponent, then this quantity called dimensionless quantity. International Vocabulary of Metrology JCGM 200:2012 allows the use by the term "dimensionless quantity" only for historical reasons, but recommended to prefer the term "quantity of dimension one".
3. If possible summation. The physical quantity is called the additive quantity, if its values can be summarized, multiplied by a numerical factor, divided against each other, as, for example, that can be done with the force or moment of force, and non-additive quantity, if the mathematical operations have no physical meaning, such as a thermodynamic temperature whose value does not make sense to add or subtract.
4. With respect to the of a physical quantity physical system. The physical quantity is called extensive quantity, if its value is the sum of the values of the same physical quantities for subsystems of which comprises a system such as that of volume and intensive quantity, if its value does not depend on the size of the system, such as in thermodynamic temperature.
Principles of Building of physical quantities systems are explained in an article devoted base physical quantities. According to the International Vocabulary of Metrology JCGM 200:2012 the system of quantities is"set of quantities together with a set of noncontradictory equations relating those quantities".
Judging by the history of the problem of generalization and systematization of physical quantities, for a couple of centuries have created many different systems of quantities and appear proposals to create new systems of quantities. Currently physics uses the International System of quantities ISQ, on which is based the system of units SI.
However, in the definition of the system of quantities there is no indication of its relationship with the system of units, from which we can conclude that such a relationship is not surely. In an article on differences between quantities systems and systems of units this assertion in detail argued.
In the analysis of each of the physical system can be viewed as many forms of motion within the system Every form of motion has its own properties, each of which is a physical quantity. Even if these properties would be a little, but by multiplying the number of properties on the number of forms of motion, and then by the number of physical systems, we get a huge amount of physical quantities. However, the number may be lower than in the reference books. Many physical quantities as to resemble each other in different areas of physics, but in a new capacity. The reason is that the methodology of modern physics and technology there are, in our opinion, three serious drawbacks (J.Kogan, 1998, 2006).
First drawback is that the physical quantities on the same physical content in different areas of physics called differently and represent by different symbols. And because of this one stringent specialist is not always possible to understand the other stringent specialist, although they can talk about one and the same Output is seen as follows: if it is difficult to change the names and symbols should be clearly indicated which quantities in a single areas of physics correspond to similar quantities in the other area.
The second drawback is that the laws are the same in their physical content, in different areas of physics and engineering are written in different ways, and it is misleading stringent specialists. For example, in the equations of vibration coefficient of proportionality in the first term (design parameter of the system) is called in the mechanics of rigidity but is used in electrodynamics the reciprocal quantity, called the capacitance. Here is seen a way out: it is necessary to find a generalized form of writhing of patterns in different areas of physics and engineering. This, in turn, could help to find new patterns still unknown to science in new and emerging areas of physics and engineering.
Great success in this direction has made the theory of physical analogies. But simple analogies it's a coincidence that may be, and sometimes are random. A new direction in physics - energodynamics - provide a rigorous theoretical basis under theory of physical analogies, arguing that the physical analogies derived from the laws of nature, based on generalized patterns, and showing which form of physical analogies conforms to the laws of nature.
A third disadvantage is that when you look at the lists of physical quantities in various directories is not clear what guided the authors of directories, having the physical quantities in varying sequence. At the same time in different directories sequence of quantities are also different. Usually, it is not clear for what reason one quantity is listed among before the other quantities? Perhaps the authors of the directories are available at this is some justification, but they are usually not explained.
1. Гомоюнов К.К., 1983, Совершенствование преподавания технических дисциплин. – Л.: Изд. Ленинградского ун-та, 206 с. (Gomoyunov K.K., 1983, Improving teaching of technical disciplines. Leningrad: Leningrad University Press, 206 p.)
2. Коган И.Ш., 1998, О возможном принципе систематизации физических величин. – “Законодательная и прикладная метрология”, 5, с.с. 30-43. (J.Sh. Kogan, 1998, Possible principle of systematization of physical quantities. "Legal and Applied Metrology", 5, p.p. 30-43)
3. Коган И.Ш., 2006, Обобщение и систематизация физических величин и понятий. – Хайфа, 207 с. (Kogan J.Sh., 2006, A generalization and systematization of physical quantities and concepts. - Haifa, 207 pp.)
4. Юдин М.Ф., Селиванов М.Н, Тищенко О.Ф., Скороходов А.И., 1989, Основные термины в области метрологии. – М.: Изд. Стандартов. (M.F. Yudin, M.N. Selivanov, O.F. Tishchenko, A.I. Skorohodov, 1989, Basic Terms in Metrology M. Ed. Standards)
5. JCGM 200:2012 International vocabulary of metrology – Basic and general concepts and associated terms (VIM). 3rd ed. 2008 version with minor corrections. URL: http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2012.pdf,
© J. Kogan Date of the first publication 01.04.2008
Date of last updating 21.01.2014