Physics as a science that studies natural phenomena,uses standard research methodology. The main stages can be called: observation, hypothesis, experiment, substantiation of the theory. During the observation, the distinctive features of the phenomenon, its course, possible causes and consequences are established. The hypothesis allows us to explain the course of the phenomenon, to establish its laws. The experiment confirms (or does not confirm) the validity of the hypothesis. Allows you to establish a quantitative ratio of the values during the experiment, which leads to an exact establishment of dependencies. The hypothesis confirmed in the course of the experiment forms the basis of a scientific theory.
No theory can claimaccuracy, if not received complete and unconditional confirmation during the experiment. Conducting the latter is associated with measurements of physical quantities characterizing the process. Physical quantity is the basis of measurement.
What it is
Measurement refers to those quantities thatconfirm the validity of the hypothesis of patterns. Physical quantity is a scientific characteristic of the physical body, the qualitative relation of which is common to many similar bodies. For each body, such a quantitative characteristic is purely individual.
If we turn to the special literature, thenthe reference book of M. Yudin et al. (1989 edition) reads that a physical quantity is: “a characteristic of one of the properties of a physical object (physical system, phenomenon or process), common in many respects for many physical objects, but quantitatively individual for each object. "
Ozhegov's Dictionary (1990 edition) states that a physical quantity is “the size, volume, length of a subject”.
For example, length is a physical quantity.Mechanics treats length as the distance traveled, electrodynamics use the length of the wire, in thermodynamics, a similar value determines the thickness of the walls of the vessels. The essence of the concept does not change: the units of values may be the same, and the value - different.
A distinctive feature of a physical quantity, say, from a mathematical one, is the presence of a unit of measure. Meter, foot, arshin - examples of units of length.
Units
To measure a physical quantity, it shouldcompare with the value adopted for the unit. Remember the wonderful cartoon "Forty-eight parrots." To establish the length of the boa, the heroes measured its length either in parrots, in elephants, or in monkeys. In this case, the length of the boa constrictor was compared with the growth of other cartoon characters. The result was quantitatively dependent on the standard.
A unit of physical quantity is a measure of its measurement ina specific system of units. Confusion in these measures arises not only because of imperfections, heterogeneity of measures, but sometimes also because of the relativity of units.
Russian measure of length - arshin - the distance betweenforefinger and thumb. However, the hands of all people are different, and the yardstick, measured by the hand of an adult man, differs from the yardstick on the arm of a child or woman. The same discrepancy between the length measures applies to the fathoms (the distance between the fingertips of the hands apart) and the elbow (the distance from the middle finger to the elbow of the hand).
Interestingly, the shop clerks took men of small stature. Cunning merchants saved fabric with the help of several smaller measures: arshin, elbow, sazhen.
Measuring Systems
Такое разнообразие мер существовало не только в Russia, but also in other countries. The introduction of units of measure was often arbitrary; sometimes these units were introduced only because of the convenience of measuring them. For example, to measure the atmospheric pressure, mm Hg was entered. Torricelli's well-known experience in which a tube filled with mercury was used made it possible to introduce such an unusual value.
Various physical quantities measurement of physical quantities made not only complex and unreliable, but also complicating the development of science.
Unified system of measures
Unified system of physical quantities, convenient andoptimized in every industrialized country has become a must. The idea of choosing the smallest possible number of units, with the help of which other quantities could be expressed in mathematical relationships, was taken as a basis. Such basic values should not be related to each other, their value is determined unambiguously and clearly in any economic system.
Эту проблему решить пытались в различных странах.The creation of a unified system of measures (Metric, GHS, ISS, and others) was undertaken repeatedly, but these systems were inconvenient either from a scientific point of view or in domestic, industrial applications.
The task, set at the end of the 19th century, was solved only in 1958. A unified system was presented at the meeting of the International Committee of Legal Metrology.
Unified system of measures
1960 was marked by a historic meeting.General Conference on Weights and Measures. The unique system called “Systeme internationale d" unites "(abbreviated as SI) was adopted by the decision of this honorary assembly. In the Russian version, this system is called the International System (abbreviation SI).
The basis taken 7 basic units and 2 additional. Their numerical value is determined as a reference.
Table of physical quantities SI
Name of the main unit | Measured value | Notation | |
International | Russian | ||
Basic units | |||
kilogram | Weight | kg | kg |
meter | Length | m | m |
second | Time | from | from |
ampere | Current strength | A | A |
kelvin | Temperature | TO | TO |
mole | Amount of substance | supposedly | mole |
candela | The power of light | sd | cd |
Additional units | |||
Radian | Flat angle | rad | glad |
Steradian | Solid angle | wed | wed |
The system itself cannot consist of only sevenunits, since the diversity of physical processes in nature requires the introduction of new and new quantities. The structure itself provides not only the introduction of new units, but also their interconnection in the form of mathematical relationships (they are often referred to as dimensional formulas).
The unit of physical quantity is obtained withusing multiplication, exponentiation and division of the basic units in the formula of dimensions. The absence of numerical coefficients in such equations makes the system not only convenient in all respects, but also coherent (consistent).
Derivative units
Единицы измерения, которые формируются из семи main, called derivatives. In addition to the basic and derived units, it became necessary to introduce additional ones (radians and steradians). Their dimension is considered to be zero. The absence of measuring instruments for their determination makes it impossible to measure them. Their introduction is due to the application in theoretical studies. For example, the physical quantity “force” in this system is measured in newtons. Since force is a measure of the mutual action of bodies on each other, which is the reason for varying the speed of a body of a certain mass, it can be defined as the product of a unit of mass per unit of speed divided by a unit of time:
F = k٠M٠v / T, where k is a proportionality coefficient, M is a unit of mass, v is a unit of speed, T is a unit of time.
SI gives the following formula dimensions: N = kg٠m / s2where three units are used. Both kilogram, and meter, and second are related to the main ones. The proportionality coefficient is 1.
Возможно введение безразмерных величин, которые are defined as the ratio of homogeneous quantities. These include the coefficient of friction, as is well known, equal to the ratio of the force of friction to the force of normal pressure.
The table of physical quantities derived from the main
Unit name | Measured value | Dimensional formula |
Joule | energy | kgm2٠c-2 |
Pascal | pressure | kg٠ m-1 ٠c-2 |
Tesla | magnetic induction | kg A-1 ٠c-2 |
Volt | voltage | kg ٠m2 ٠c-3٠A-1 |
Ohm | Electrical resistance | kg ٠m2 ٠c-3٠A-2 |
pendant | Electric charge | And with |
Watt | power | kg ٠m2 ٠c-3 |
Farad | Electric capacity | m-2٠kg-1 ٠c4٠A2 |
Joule on kelvin | Heat capacity | kg ٠m2٠c-2 ٠К-1 |
Becquerel | Radioactive substance activity | FROM-1 |
Weber | Magnetic flow | m2 ٠kg ٠s-2٠A-1 |
Henry | Inductance | m2 ٠kg ٠s-2 ٠A-2 |
Hertz | Frequency | from-1 |
Gray | Absorbed Dose | m2 ٠c-1 |
Sievert | Equivalent radiation dose | m2 ٠c-2 |
Suite | Illumination | m-2 ٠kd ٠sr-2 |
Lumen | Light flow | cd ٠sr |
Newton | Strength weight | m ٠kg ٠s-2 |
Siemens | Electrical conductivity | m-2 ٠kg-1 ٠c3 ٠A2 |
Farad | Electric capacity | m-2 ٠kg-1 ٠c4 ٠A2 |
Off-system units
Use of historically established values notincluded in the SI or differing only by a numerical factor, is allowed when measuring values. These are non-system units. For example, mm Hg, x-rays and others.
Numerical coefficients are used to enter partial and multiple values. Prefixes correspond to a certain number. An example would be centi-, kilo-, deca-, mega- and many others.
1 kilometer = 1000 meters,
1 centimeter = 0.01 meter.
Typology of values
Let us try to indicate a few basic features that allow us to establish the type of quantity.
1. Direction. If the action of a physical quantity is directly related to the direction, it is called vectorial, others are scalar.
2. The presence of dimension.The existence of a formula for physical quantities makes it possible to call them dimensional. If in the formula all units have zero degree, then they are called dimensionless. It would be more correct to call them quantities with a dimension equal to 1. After all, the concept of a dimensionless quantity is illogical. The main property - the dimension - has not been canceled!
3. If possible addition. An additive quantity whose value can be added, subtracted, multiplied by a factor, etc. (for example, mass) is a physical quantity that is summable.
4. In relation to the physical system.Extensive - if its value can be compiled from the values of the subsystem. An example is the area measured in square meters. Intensive - a value whose value does not depend on the system. These include temperature.
