Physical quantity - it's ... Measurement of physical quantities.

physics as a science that studies the phenomena of nature, using standard methodology of the study.The main stages are: observation, hypotheses, conduct experiments, study the theory.During the observation established distinctive features of the phenomenon, the course of its flow, the possible causes and consequences.The hypothesis allows to explain the course of events, to establish its laws.The experiment confirms (or not confirmed) conjecture.It allows to set the proportion values ​​during the experiment, which leads to an exact setting dependencies.Proven experience in the conjecture is the basis of scientific theory.

No theory can not claim to credibility, if not received the full and unconditional acknowledgment during the experiment.The last is associated with measuring physical quantities characterizing the process.Physical quantity - is the basis of measurement.

What is it

measurement for those values, which confirms the conjecture about the laws.Physical quantity - is a scientific description of the physical body, the ratio of quality that is common to many similar bodies.For each body of such a quantitative characteristic of a purely individual.

If we look at the literature, the reference M. Yudin et al. (1989 edition) we read that the physical quantity is "characteristic of one of the properties of the physical object (the physical system, phenomenon or process), the overall qualitative terms formany physical objects, but in quantitative terms for each individual object. "

Ozhegov (1990 edition) states that the physical quantity is - "the size, scope, length of the object."

For example, the length of - a physical quantity.Mechanics path length as the distance traveled, electrodynamics using the length of wire, in the thermodynamics of a similar value determines the thickness of the walls of blood vessels.The essence of the concept does not change: the unit value may be the same, and the value - different.

distinctive feature of a physical quantity, say, mathematical, is the availability of the units.Meter, feet, yards - examples of units of length.

Units

To measure a physical quantity, it should be compared with the value received per unit.Remember the wonderful cartoon "Forty-eight parrots."To set the length of the boa constrictor, the characters measured its length in parrots, the elephants, the monkeys.In this case, the length of boa compared with the growth of other cartoon characters.The result is quantified by reference dependent.

physical units - a measure of its measurement in certain units.Confusion in these measures arises not only because of the imperfection, diversity measures, but sometimes because of the relative units.

Russian measure of length - yards - the distance between the index finger and thumb.However, the hands of all the people are different, and yards, measured a man's hand, is different from a yard on the hand of a child or a woman.The same discrepancy between linear measures concerns fathoms (the distance between the tips of his fingers spaced apart arms) and the elbow (the distance from the middle finger to the elbow arm).

Interestingly, the shop stewards took men of small stature.Sly cloth merchants saved using several smaller Meryl: yards, elbow fathom.

System measures

This variety of measures exist not only in Russia but also in other countries.Introduction of units was often arbitrary, sometimes these units were introduced only because of the ease of measurement.For example, to measure the air pressure introduced mmHg.Renowned experience Torricelli, which used a tube, swamping mercury allowed to enter such an unusual value.

engine power compared to the horsepower (which is practiced in our time).

various physical quantities measurement of physical quantities do not only complicated and unreliable, but also complicates the development of science.

uniform system of measures

uniform system of physical quantities, convenient and optimized in every industrialized country, has become a necessity.For a basis the idea of ​​selecting the smallest possible number of units by which mathematical relationships can be expressed, and other values.These basic values ​​are not intended to be connected to each other, their value is unique and is clear in any economic system.

tried to solve this problem in different countries.Creating a unified system of measures (Metric, GHS, ISS, etc.) have been many times, but the systems were uncomfortable with either scientifically or in civil, industrial application.

targets set in the late 19th century, has turned out to solve only in 1958.At a meeting of the International Committee of Legal Metrology was presented a unified system.

Unified measures

1960 marked the historic meeting of the General Conference on Weights and Measures.The unique system, called «Systeme internationale d'unites» (abbreviated as SI) was adopted by the decision of this honorable assembly.In the Russian version of the system called the System International (SI abbreviation).

proceed on the 7 base units and 2 extra.Their numerical value is defined as the standard

Table of physical quantities SI

The system can not consist of only seven units, as a variety of physical processes in nature requires the introduction of more and more new values.The very structure provides not only the introduction of new units, and their relationship in the form of mathematical relationships (they are often called formulas of dimensions).

physical units is obtained using multiplication, exponentiation and division of the basic units in the formula dimensions.The lack of numerical coefficients in these equations makes the system not only comfortable in all respects, and coherent (coherent).

derivatives unit

Units, which are formed of seven main, are called derivatives.In addition to basic and derived units, the need for the introduction of additional (radian and steradian).Their dimensions are considered to be zero.The lack of instruments for their definition makes it impossible to measure them.Their introduction is due to the application of theoretical research.For example, the physical quantity "force" in the system is measured in Newtons.Since the force - a measure of the mutual action of bodies on each other, are the cause of varying the speed of the body of a certain mass, then define it can be the product of a unit mass per unit rate, divided by the unit of time:

F = k0M0v / T, where k - coefficient of proportionality,M - unit of mass, v - speed unit, T - unit of time.

SI dimensions gives the following formula: N = kg0m / s2, where we use three units.And kilogram and meter, and the second referred to the principal.The proportionality coefficient is equal to 1.

possible introduction of dimensionless quantities, which are defined as the ratio of homogeneous quantities.To those include the coefficient of friction, as is known, is the ratio of frictional force to the force normal pressure.

Table of physical quantities derived from basic

Common Units

Using historical values ​​of non-SI or differ only by a numericalcoefficient allowed in the measurement values.This Common Units.For example, mmHg x-ray, and others.

numerical coefficients used for the introduction of longitudinal and multiples.Attachments meet a certain number.Examples are centimeters, kilogram, deca, mega- and many others.

1 kilometer = 1000 meters,

1 centimeter = 0.01 meter.

Typology values ​​

try to indicate some basic features that allow you to set the type of value.

1. Direction.If the action of a physical quantity is directly related to the direction, it is called a vector, other - scalar.

2. Have dimension.The existence of the physical quantities of the formula makes it possible to call them dimension.If in the formula, all units have zero degree, they are called dimensionless.It would be better to call them values ​​with dimension equal to 1. Indeed, the concept of a dimensionless quantity is illogical.The main property - dimension - has not been canceled!

3. If possible addition.Additive value, which value can be added, subtracted, multiplied by the factor, and so on. D. (Eg, weight) - a physical quantity, which is integrable.

4. In relation to the physical system.Extensive - if its value can be formed from the values ​​of the subsystem.An example is the area measured in square meters.Intensive - the quantity, the value of which does not depend on the system.To those include temperature.