How many base units are in the SI system. International System of Units (SI). See what "SI Base Units" are in other dictionaries

, amount of substance and the power of light. The units of measurement for them are the basic SI units - meter, kilogram, second, ampere, kelvin, mole and candela respectively .

A complete official description of the basic SI units, as well as the SI as a whole, together with its interpretation, is contained in the current version of the SI Brochure (fr. Brochure SI, eng. The SI Brochure) and in addition to it, published by the International Bureau of Weights and Measures (BIPM) and presented on the BIPM website.

The rest of the SI units are derivatives and are formed from the basic ones with the help of equations relating the physical quantities of the International System of Quantities to each other.

The base unit can also be used for a derived quantity of the same dimension. For example, rainfall is defined as the quotient of volume divided by area, and in SI is expressed in meters. In this case, the meter is used as the coherent derived unit.

The names and symbols of the basic units, as well as all other SI units, are written in small letters (for example, meter and its designation m). This rule has an exception: the designations of units named after the names of scientists are capitalized (for example, ampere marked with A).

Basic units

The table lists all the basic SI units along with their definitions, symbols, physical quantities to which they refer, as well as a brief justification for their origin.

Improvement of the system of units

The 21st General Conference on Weights and Measures (1999) recommended in the 21st century "National Laboratories continue research to relate mass to fundamental or mass constants to determine the mass of the kilogram." Most of the expectations were associated with Planck's constant and Avogadro's number.

In an explanatory note addressed to the CIPM in October 2009, the President of the CIPM Advisory Board on Units listed the uncertainties in physical fundamental constants using the current definitions and what those uncertainties would become using the new proposed unit definitions. He recommended that the CIPM accept the proposed changes to the “definition kilograms, ampere, kelvin and pray so that they are expressed in terms of the fundamental constants h , e , k, and N A ».

XXIV General Conference on Weights and Measures

At the XXIV General Conference on Weights and Measures on October 17-21, 2011, a Resolution was adopted, according to which it is supposed in the future revision of the International System of Units to redefine the basic units so that they are based not on artifacts (standards) created by man, but on fundamental physical constants or properties of atoms, the numerical values ​​of which are fixed and assumed to be exact by definition.

Kilogram, ampere, kelvin, mole

In accordance with the decisions of XXIV CGPM, the most important changes should affect the four basic SI units: kilogram, ampere, kelvin and mole. New definitions of these units will be based on fixed numerical values ​​of the following fundamental physical constants: Planck's constant, elementary electric charge, Boltzmann's constant and Avogadro's number, respectively. All of these values ​​will be assigned exact values ​​based on the most accurate measurements recommended by the Committee on Data for Science and Technology (CODATA) .

The Resolution formulated the following provisions regarding these units:

• The kilogram will remain a unit of mass; but its value will be set by fixing the numerical value of Planck's constant to exactly 6.626 06X⋅10 −34 when it is expressed in the SI unit m 2 kg s −1, which is equivalent to J s.
• The ampere will remain the unit of electric current strength; but its magnitude will be established by fixing the numerical value of the elementary electric charge to be exactly 1.602 17X⋅10 −19 when it is expressed in the SI unit s·A, which is equivalent to Cl.
• The kelvin will remain the unit of thermodynamic temperature; but its magnitude will be set by fixing the numerical value of the Boltzmann constant to exactly 1.380 6X⋅10 −23 when it is expressed in the SI unit m −2 kg s −2 K −1 , which is equivalent to J K −1 .
• The mole will remain the unit of quantity of matter; but its magnitude will be established by fixing the numerical value of Avogadro's constant to exactly 6.022 14X⋅10 23 mol −1 when it is expressed in the SI unit mol −1 .

Meter, second, candela

The definitions of the meter and second are already associated with exact values such constants as the speed of light and the magnitude of the splitting of the ground state of the cesium atom, respectively. The current definition of the candela, while not tied to any fundamental constant, can nevertheless also be seen as tied to the exact value of an invariant of nature. Based on the foregoing, it is not supposed to change the definitions of the meter, second and candela in essence. However, in order to maintain the unity of style, it is planned to adopt new, completely equivalent to the existing, wording of the definitions in the following form:

• The meter, symbol m, is a unit of length; its value is set by fixing the numerical value of the speed of light in vacuum to exactly 299,792,458 when it is expressed in the SI unit m·s−1.
• The second, symbol c, is the unit of time; its value is set by fixing the numerical value of the frequency of the hyperfine splitting of the ground state of the cesium-133 atom at a temperature of 0 K equal to exactly 9 192 631 770, when it is expressed in the SI unit s −1, which is equivalent to Hz.
• The candela, symbol cd, is the unit of luminous intensity in a given direction; its value is set by fixing the numerical value of the luminous efficiency of monochromatic radiation with a frequency of 540 10 12 Hz equal to exactly 683, when it is expressed in the SI unit m −2 kg −1 s 3 cd sr or cd sr W −1, which equivalent to lm W −1 .

The new look of SI

In 2019, the release of the SI based on fundamental constants will come into force, in which:

see also

Notes

1. The SI Brochure Description of the SI on the website of the International Bureau of Weights and Measures (eng.)

Future changes

In the 21st century, the Conference on Weights and Measures (1999) proposed a formal effort and recommended that "National Laboratories continue research to relate mass to fundamental or mass constants to determine the mass of the kilogram." Most expectations are associated with Planck's constant and Avogadro's number.

In an explanatory note addressed to CIPM in October 2009, the President of the CIPM Units Advisory Board listed the uncertainties in physical fundamental constants using the current definitions and what those uncertainties would become using the new proposed unit definitions. He recommended that the CIPM accept the proposed changes to the "definition kilograms, ampere, kelvin and pray so that they are expressed in terms of the fundamental constants h , e , k, and N A».

see also

• Constant (physics)

Notes

Links

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See what "SI Basic Units" is in other dictionaries:

basic units- - [A.S. Goldberg. English Russian Energy Dictionary. 2006] Energy topics in general EN basic units ...

Basic units of the system

basic units of the system- Units of quantities, the dimensions and dimensions of which in this system of units are taken as initial when forming the dimensions and dimensions of derived units. Note Definitions and procedures for reproducing some basic units may be based on ... Technical Translator's Handbook

Basic units of the International System of Units (SI)- Table A.1 Name of quantity Unit of quantity Name Designation international Russian length meter m m mass kilogram kg kg time second s s electric power ... Dictionary-reference book of terms of normative and technical documentation

Basic units of the measurement system- Units of quantities, the dimensions and dimensions of which in this system of units are taken as initial when forming the dimensions and dimensions of derived units. Note. Definitions and procedures for reproducing some basic units can be based on ... ... Official terminology

basic units of speech- Elements that are distinguished in a linear speech flow and are the implementation (variants) of certain language units ... Dictionary of linguistic terms T.V. Foal

- (System International, SI) | | | Designation | | Physical quantity | Named ... ... encyclopedic Dictionary

UNITS OF PHYSICAL QUANTITIES, units of measurement used for measuring physical quantities. In the definition of the unit of a physical quantity, it is necessary to specify the standard of the physical quantity and the method of its comparison with the quantity during measurement. For example,… … Scientific and technical encyclopedic dictionary

Main- 1. Basic provisions of the rural telephone system. M., TsNIIS, 1974. 145 p. Source: Manual: Rural Telecommunication Network Design Guide 16. Basic provisions for accounting for labor and wages in ... ... Dictionary-reference book of terms of normative and technical documentation

Quantities that, by definition, are considered equal to one when measuring other quantities of the same kind. The standard unit of measurement is its physical implementation. So, the standard unit of measure meter is a rod 1 m long. In principle, one can imagine ... ... Collier Encyclopedia

Books

• Units of physical quantities in the energy sector. Accuracy of reproduction and transmission. Reference manual , LD Oleinikova , Basic metrological concepts and terms used to characterize measuring instruments and methods are given. Definitions of units of physical quantities, their ratios and designations are given ... Category: Power industry. electrical engineering Publisher:

In the 17th century, with the development of science in Europe, calls began to be heard more and more often to introduce a universal measure or Catholic meter. It would be a decimal measure, based on natural phenomena, and independent of the rulings of the person in power. Such a measure would replace the many different systems of measures that existed then.

The British philosopher John Wilkins proposed to take as a unit of length the length of a pendulum, the half-period of which would be equal to one second. However, depending on the place of measurements, the value was not the same. French astronomer Jean Richet established this fact during a trip to South America (1671 - 1673).

In 1790, Minister Talleyrand proposed to measure the reference length by placing the pendulum at a strictly established latitude between Bordeaux and Grenoble - 45 ° north latitude. As a result, on May 8, 1790, the French National Assembly decided that the meter is the length of a pendulum with a half-period of oscillation at a latitude of 45 °, equal to 1 s. In accordance with today's SI, that meter would be equal to 0.994 m. This definition, however, did not suit the scientific community.

On March 30, 1791, the French Academy of Sciences accepted a proposal to set the standard meter as part of the Paris meridian. The new unit was to be one ten-millionth of the distance from the equator to the North Pole, that is, one ten-millionth of a quarter of the circumference of the Earth, measured along the Paris meridian. This became known as "Meter authentic and final."

On April 7, 1795, the National Convention adopted a law on the introduction of the metric system in France and instructed the commissioners, who included C. O. Coulomb, J. L. Lagrange, P.-S. Laplace and other scientists, experimentally determine the units of length and mass.

In the period from 1792 to 1797, by decision of the revolutionary Convention, the French scientists Delambre (1749-1822) and Mechain (1744-1804) measured the arc of the Parisian meridian, 9 ° 40 "long, from Dunkirk to Barcelona in 6 years , laying a chain of 115 triangles through all of France and part of Spain.

Subsequently, however, it turned out that due to incorrect consideration of the pole compression of the Earth, the standard turned out to be shorter by 0.2 mm. Thus, the meridian length of 40,000 km is only approximate. The first prototype of the standard meter made of brass, however, was made in 1795. It should be noted that the unit of mass (the kilogram, whose definition was based on the mass of one cubic decimeter of water) was also tied to the definition of the meter.

The history of the formation of the SI system

On June 22, 1799, two platinum standards were made in France - the standard meter and the standard kilogram. This date can rightly be considered the day the development of the current SI system began.

In 1832, Gauss created the so-called absolute system of units, taking for the main three units: a unit of time - a second, a unit of length - a millimeter, and a unit of mass - a gram, because using these units the scientist managed to measure the absolute value of the Earth's magnetic field (this system called CGS Gauss).

In the 1860s, under the influence of Maxwell and Thomson, the requirement was formulated that the base and derived units must be consistent with each other. As a result, the CGS system was introduced in 1874, and prefixes were also allocated to denote submultiples and multiples from micro to mega.

In 1875, representatives of 17 states, including Russia, the USA, France, Germany, Italy, signed the Meter Convention, according to which the International Bureau of Measures, the International Committee of Measures were established, and the regular convocation of the General Conference on Weights and Measures (CGPM) began to operate. . At the same time, work began on the development of the international standard of the kilogram and the standard of the meter.

In 1889, at the first conference of the CGPM, the ISS system was adopted, based on the meter, kilogram and second, similar to the GHS, but the ISS units were seen as more acceptable due to convenience from practical use. Units for optics and electricity will be introduced later.

In 1948, by order of the French government and the International Union of Theoretical and Applied Physics, the ninth General Conference on Weights and Measures instructed the International Committee on Weights and Measures to propose, in order to unify the system of units of measurement, their ideas for creating a unified system of units of measurement, which could be accepted by all states parties to the Meter Convention.

As a result, in 1954, the tenth CGPM proposed and adopted the following six units: meter, kilogram, second, ampere, degree Kelvin and candela. In 1956, the system was called "Système International d'Unitйs" - the international system of units. In 1960, a standard was adopted, which was first called the "International System of Units", and the abbreviation "SI" was assigned. The basic units remained the same six units: meter, kilogram, second, ampere, degree Kelvin and candela. (The Russian-language abbreviation "SI" can be deciphered as "International System").

In 1963, in the USSR, according to GOST 9867-61 "International System of Units", SI was adopted as the preferred one for the areas of the national economy, in science and technology, as well as for teaching in educational institutions.

In 1968, at the thirteenth CGPM, the unit "degree Kelvin" was replaced by "kelvin", and the designation "K" was also adopted. In addition, a new definition of the second was adopted: a second is a time interval equal to 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground quantum state of the cesium-133 atom. In 1997, a refinement will be adopted according to which this time interval refers to a cesium-133 atom at rest at 0 K.

In 1971, at 14 CGPM, another basic unit "mol" was added - a unit of the amount of a substance. A mole is the amount of substance in a system containing as many structural elements as there are atoms in carbon-12 with a mass of 0.012 kg. When using a mole, the structural elements must be specified and may be atoms, molecules, ions, electrons and other particles, or specified groups of particles.

In 1979, the 16th CGPM adopted a new definition for the candela. Candela - luminous intensity in a given direction of a source emitting monochromatic radiation with a frequency of 540 1012 Hz, the luminous energy intensity of which in this direction is 1/683 W/sr (watt per steradian).

In 1983, at the 17th CGPM, a new definition of the meter was given. A meter is the length of the path traveled by light in a vacuum in (1/299,792,458) seconds.

In 2009, the Government of the Russian Federation approved the “Regulations on Units of Values ​​Allowed for Use in the Russian Federation”, and in 2015 it was amended to exclude the “validity period” of some non-systemic units.

Purpose of the SI system and its role in physics

To date, the international system of physical quantities SI has been adopted throughout the world, and is used more than other systems both in science and technology, and in everyday life of people - it is a modern version of the metric system.

Most countries use the units of the SI system in technology, even if in everyday life they use units traditional for these territories. In the US, for example, customary units are defined in terms of SI units using fixed coefficients.

An exhaustive detailed description of the SI system in official form is set out in the SI Brochure published since 1970 and in an addendum to it; these documents are published on the official website of the International Bureau of Weights and Measures. Since 1985, these documents have been issued in English and French, and are always translated into a number of world languages, although the official language of the document is French.

The exact official definition of the SI system is formulated as follows: “The International System of Units (SI) is a system of units based on the International System of Units, together with names and symbols, as well as a set of prefixes and their names and symbols, together with the rules for their use, adopted by the General Conference Weights and Measures (CGPM).

The SI system defines seven basic units of physical quantities and their derivatives, as well as prefixes to them. Standard abbreviations for unit designations and rules for writing derivatives are regulated. There are seven basic units, as before: kilogram, meter, second, ampere, kelvin, mole, candela. Basic units differ in independent dimensions, and cannot be derived from other units.

As for derived units, they can be obtained on the basis of basic ones by performing mathematical operations such as division or multiplication. Some of the derived units, such as "radian", "lumen", "pendant", have their own names.

Before the name of the unit, you can use a prefix, such as a millimeter - a thousandth of a meter, and a kilometer - a thousand meters. The prefix means that the unit must be divided or multiplied by an integer that is a specific power of ten.

Physical quantity called the physical property of a material object, process, physical phenomenon, characterized quantitatively.

The value of a physical quantity expressed by one or more numbers characterizing this physical quantity, indicating the unit of measurement.

The size of a physical quantity are the values ​​of the numbers appearing in the meaning of the physical quantity.

Units of measurement of physical quantities.

The unit of measurement of a physical quantity is a fixed size value that is assigned a numeric value equal to one. It is used for the quantitative expression of physical quantities homogeneous with it. A system of units of physical quantities is a set of basic and derived units based on a certain system of quantities.

Only a few systems of units have become widespread. In most cases, many countries use the metric system.

Basic units.

Measure physical quantity - means to compare it with another similar physical quantity, taken as a unit.

The length of an object is compared with a unit of length, body weight - with a unit of weight, etc. But if one researcher measures the length in sazhens, and another in feet, it will be difficult for them to compare these two values. Therefore, all physical quantities around the world are usually measured in the same units. In 1963, the International System of Units SI (System international - SI) was adopted.

For each physical quantity in the system of units, an appropriate unit of measurement must be provided. Standard units is its physical realization.

The length standard is meter- the distance between two strokes applied on a specially shaped rod made of an alloy of platinum and iridium.

Standard time is the duration of any correctly repeating process, which is chosen as the movement of the Earth around the Sun: the Earth makes one revolution per year. But the unit of time is not a year, but give me a sec.

For a unit speed take the speed of such uniform rectilinear motion, at which the body makes a movement of 1 m in 1 s.

A separate unit of measurement is used for area, volume, length, etc. Each unit is determined when choosing one or another standard. But the system of units is much more convenient if only a few units are chosen as the main ones, and the rest are determined through the main ones. For example, if the unit of length is a meter, then the unit of area is a square meter, volume is a cubic meter, speed is a meter per second, and so on.

Basic units The physical quantities in the International System of Units (SI) are: meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), candela (cd) and mole (mol).

There are also derived SI units, which have their own names:

Andmeasurements. To obtain an accurate, objective and easily reproducible description of a physical quantity, measurements are used. Without measurements, a physical quantity cannot be quantified. Definitions such as "low" or "high" pressure, "low" or "high" temperature reflect only subjective opinions and do not contain comparison with reference values. When measuring a physical quantity, it is assigned a certain numerical value.

Measurements are made using measuring devices. There is a fairly large number of measuring instruments and fixtures, from the simplest to the most complex. For example, length is measured with a ruler or tape measure, temperature with a thermometer, width with calipers.

Measuring instruments are classified: according to the method of presenting information (indicating or recording), according to the method of measurement (direct action and comparison), according to the form of presentation of indications (analog and digital), etc.

The measuring instruments are characterized by the following parameters:

Measuring range- the range of values ​​of the measured quantity, on which the device is designed during its normal operation (with a given measurement accuracy).

Sensitivity threshold- the minimum (threshold) value of the measured value, distinguished by the device.

Sensitivity- relates the value of the measured parameter and the corresponding change in instrument readings.

Accuracy- the ability of the device to indicate the true value of the measured indicator.

Stability- the ability of the device to maintain a given measurement accuracy for a certain time after calibration.

General information

Prefixes can be used before unit names; they mean that the unit must be multiplied or divided by a certain integer, a power of 10. For example, the prefix "kilo" means multiplying by 1000 (kilometer = 1000 meters). SI prefixes are also called decimal prefixes.

International and Russian designations

Subsequently, basic units were introduced for physical quantities in the field of electricity and optics.

SI units

The names of SI units are written with a lowercase letter, after the designations of SI units, a period is not put, unlike the usual abbreviations.

Basic units

Derived units

Derived units can be expressed in terms of basic units using mathematical operations: multiplication and division. Some of the derived units, for convenience, have been given their own names, such units can also be used in mathematical expressions to form other derived units.

The mathematical expression for a derived unit of measure follows from the physical law by which this unit of measure is determined or the definition of the physical quantity for which it is introduced. For example, speed is the distance a body travels per unit time; accordingly, the unit of speed is m/s (meter per second).

Often the same unit can be written in different ways, using a different set of basic and derived units (see, for example, the last column in the table ). However, in practice, established (or simply generally accepted) expressions are used that best reflect the physical meaning of the quantity. For example, to write the value of the moment of force, N m should be used, and m N or J should not be used.

The Kelvin and Celsius scales are related as follows: °C = K − 273.15

Non-SI units

Some non-SI units are "acceptable for use in conjunction with the SI" by decision of the General Conference on Weights and Measures.

Other units are not allowed.

However, other units are sometimes used in various fields.

• System units