النظام الدولي للوحدات

The seven SI base units and the interdependency of their definitions. Clockwise from top: kelvin (temperature), second (time), metre (length), kilogram (mass), candela (luminous intensity), mole (amount of substance) and ampere (electric current). The second of time, kelvin and kilogram are defined independently of any other base units. The metre is defined in terms of the speed of light, so depends upon the definition of the second. The definitions of the other base units are more complicated.

غلاف كتيب النظام الدولي للوحدات

النظام الدولي للوحدات يرمز له بـ (SI) (الأحرف الاولى للمصطلح الفرنسي Système International d'Unités) هونظام وحدات القياس الأوسع انتشارا في العالم، وهويستخدم في جميع بلدان العالم باستثناء الولايات الامريكية المتحدة. واشتق هذا النظام من نظام متر-كيلوغرام-ثانية للقياس باضافة بعض الوحدات، وكونه بديلا عن نظام السنتمتر-غرام-ثانية القديم يسمى هذا النظام بالنظام المتري (خاصة في الولايات الامريكية المتحدة التي لم تتبناه بشكل واسع وبربطانيا التي لا تزال في فترة التحول إلى النظام المتري)، وليست جميع وحدات القياس المترية مقبولة في هذا النظام.

الوحدات الاساسية

هناكسبعة وحدات اساسية في النظام الدولي للوحدات هي:

المتر	ويقاس بواسطته الطول ويرمز له بال "م" ويحدد المتر الطولي بالطول الموجي لإشعاع ذرة الكريبتون
الكيلوغرام	وتقاس بواسطته الكتلة ويرمز له بال "كغم"
الثانية	ويقاس بها الزمن ويرمز لها بال "ث" وتحدد بمدة اشعاع ذرة السيزيوم
الامبير	ويقاس به شدة التيار الكهربي ويحدد بالقوة الكهروديناميكية بين موصلين
الكلفن	وتقاس به درجة الحرارة ويرمز له ب "ك"
الشمعة	وتقيس شدة الضوء وليس لها إختصار (في الإنجليزيه "cd") وهي مقدار الإشعاع الناتج من ذرة البلاتين PT المتجمده
المول	وحدة لقياس كمية المادة ويستخدم عادة في الكيمياء، والمول هوعدد أفوجادرو(تقريبا 6.0221415 × 10²³) من الجزيئات الاساسية، سواء كان الحديث يدور عن ذرات اوجزيئات لمركب ما.

Metre Convention

Towards SI

World Map showing Metrication, colour-coded by year of conversion: from ca 1800 (green) to 1980 (red). Black indicates the nations that have not yet adopted the SI-system: USA, Liberia and Burma.

At the close of the 19th century three different systems of units of measure existed for electrical measurements: a CGS-based system for electrostatic units (also known as the Gaussian or ESU system), a CGS-based system for electromechanical units

SI base units^:23
Unit name	Unit symbol	name	Definition (Incomplete)	symbol
metre	m	length	Original (1793): 1/10000000 of the meridian through Paris between the North Pole and the Equator.^FG Interim (1960): 1650763.73 wavelengths in a vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom. Current (1983): The distance travelled by light in vacuum in 1/299792458 second.	L
kilogram	kg	mass	Original (1793): The grave was defined as being the weight [mass] of one cubic decimetre of pure water at its freezing point.^FG Current (1889): The mass of the International prototype kilogram.	M
second	s	time	Original (Medieval): 1/86400 of a day. Interim (1956): 1/31556925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time. Current (1967): The duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.	T
ampere	A	electric current	Original (1881): A tenth of the electromagnetic CGS unit of current. The [CGS] electromagnetic unit of current is that current, flowing in an arc 1 cm long of a circle 1 cm in radius creates a field of one oersted at the centre.^IEC Current (1946): The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 6993200000000000000♠2×10⁻⁷ newtons per metre of length.	I
kelvin	K	thermodynamic temperature	Original (1743): The centigrade scale is obtained by assigning 0 °C to the freezing point of water and 100 °C to the boiling point of water. Interim (1954): The triple point of water (0.01 °C) defined to be exactly 273.16 °K. Current (1967): The fraction 1/273.16 of the thermodynamic temperature of the triple point of water	Θ
mole	mol	amount of substance	Original (1900): The molecular weight of a substance in mass grams.^ICAW Current (1967): The amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12.	N
candela	cd	luminous intensity	Original (1946): The value of the new candle is such that the brightness of the full radiator at the temperature of solidification of platinum is 60 new candles per square centimetre. Current (1979): The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 7014540000000000000♠540×10¹² hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.	J
Note ^ Interim definitions are given only when there has been a significant difference in the definition. ^ Despite the prefix "kilo-", the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units. Nonetheless, units of mass are named as if the gram were the base unit. ^ In 1954 the unit of thermodynamic temperature was known as the "degree Kelvin" (symbol °K; "Kelvin" spelt with an upper-case "K"). It was renamed the "kelvin" (symbol "K"; "kelvin" spelt with a lower case "k") in 1967. ^ When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. The original definitions of the various base units in the above table were made by the following authorities: FG = French Government IEC = International Electrotechnical Commission ICAW = International Committee on Atomic Weights All other definitions result from resolutions by either CGPM or the CIPM and are catalogued in the SI Brochure.

Named units derived from SI base units^:3
Name	Symbol	Quantity	Expressed in terms of other SI units	Expressed in terms of SI base units
radian	rad	angle	1	m/m
steradian	sr	solid angle	1	m²/m²
hertz	Hz	frequency		s⁻¹
newton	N	force, weight		kg⋅m⋅s⁻²
pascal	Pa	pressure, stress	N/m²	kg⋅m⁻¹⋅s⁻²
joule	J	energy, work, heat	N⋅m	kg⋅m²⋅s⁻²
watt	W	power, radiant flux	J/s	kg⋅m²⋅s⁻³
coulomb	C	electric charge or quantity of electricity		s⋅A
volt	V	voltage (electrical potential difference), electromotive force	W/A	kg⋅m²⋅s⁻³⋅A⁻¹
farad	F	electric capacitance	C/V	kg⁻¹⋅m⁻²⋅s⁴⋅A²
ohm	Ω	electric resistance, impedance, reactance	V/A	kg⋅m²⋅s⁻³⋅A⁻²
siemens	S	electrical conductance	A/V	kg⁻¹⋅m⁻²⋅s³⋅A²
weber	Wb	magnetic flux	V⋅s	kg⋅m²⋅s⁻²⋅A⁻¹
tesla	T	magnetic field strength	Wb/m²	kg⋅s⁻²⋅A⁻¹
henry	H	inductance	Wb/A	kg⋅m²⋅s⁻²⋅A⁻²
degree Celsius	°C	temperature relative to 273.15 K		K
lumen	lm	luminous flux	cd⋅sr	cd
lux	lx	illuminance	lm/m²	m⁻²⋅cd
becquerel	Bq	radioactivity (decays per unit time)		s⁻¹
gray	Gy	absorbed dose (of ionizing radiation)	J/kg	m²⋅s⁻²
sievert	Sv	equivalent dose (of ionizing radiation)	J/kg	m²⋅s⁻²
katal	kat	catalytic activity		s⁻¹⋅mol
Notes 1. The radian and steradian, once given special status, are now considered dimensionless derived units.^:3 2. The ordering of this table is such that any derived unit is based only on base units or derived units that precede it in the table.

Prefixes

نطقب:SI-Prefixes

Non-SI units accepted for use with SI

The litre is classed as a non-SI unit accepted for use with the SI.
Being one thousandth of a cubic metre, the litre is not a coherent unit of measure with respect to SI.

Unit names as adjectives

In English, a space is recommended between the number and the unit symbol when used as an adjective, e.g. "a 25 kg sphere".

The normal rules of English apply to unit names, where a hyphen is incorporated into the adjectival sense, e.g. "a 25-kilogram sphere".

Chinese and Japanese

Chinese expressway distances road sign in eastern Beijing. Although the primary text is in Chinese, the distances use the internationally recognised numerals and symbols.

Printing SI symbols

Further rules are specified in respect of production of text using printing presses, word processors, typewriters and the like.

Realisation of units

Silicon sphere for the Avogadro project used for measuring the Avogadro constant to a relative uncertainty of 2×10⁻⁸ or less.

United Kingdom and the former Empire

Metrication logo of the Board of Trade

United States

Logo of the American National Metrication Council, an organization set up by American National Standards Institute (ANSI) to coordinate the country's transition to the metric system.

Even though Congress set up a framework for the use of the metric system in the nineteenth century, the United States continues to use customary units for most purposes apart from science and medicine, though as a result of their Spanish heritage, metric units are used widely in Puerto Rico.

A 2010 Cadillac SRX. All General Motors products are designed using metric units.

الاتحاد الاوروبي

"New SI"

Relations between proposed SI units definitions (in colour) and seven physical constants (in grey) with fixed numerical values in the proposed system. Unlike the current (2013) definition, the base units are derived from one or more constants of nature.

انظر أيضاً

History of measurement
List of international common standards
List of scientific units named after people
Metre–tonne–second system of units
Names of large numbers
Names of small numbers
Order of magnitude

المنظمات

Institute for Reference Materials and Measurements (IRMM)

Standards and conventions

Coordinated Universal Time (UTC)
Unified Code for Units of Measure

الهامش

^ International Bureau of Weights and Measures (2006). (PDF) (8th ed.). ISBN
^ خطأ استشهاد: وسم <ref> غير سليم؛ لا نص تم توفيره للمراجع المسماة NIST330
^ Quantities Units and Symbols in Physical Chemistry, IUPAC
^ Page, Chester H; Vigoureux, Paul, eds. (20 May 1975). . Washington, D.C.: National Bureau of Standards. pp. 238–244.
^ McKenzie, A.E.E (1961). . Cambridge University Press. p. 322.
^ "USMA FAQ on hyphenation for adjective forms". Retrieved 2 April 2014.
^ "Avogadro Project". National Physical Laboratory. Retrieved 2010-08-19.
^ Barbrow, Louis E.; Judson, Lewis V. (March 1976) [First published October 1963]. "Weights and Measures Standards of the United States – A brief history, Special Publication 447". National Bureau of Standards. pp. 10–20. LCCN 76-600055.
^ "Appendix G : Weights and Measures". The World Factbook. Central Intelligence Agency. Retrieved 2011-09-03.
^ Porter, Darwin; Prince, Danforth (2006). Frommer's Puerto Rico (8th ed.). Wiley Publishing. p. 58. ISBN .

وصلات خارجية

رسمية

BIPM Bureau International des Poids et Mesures (SI maintenance agency) (home page)
- BIPM brochure (SI reference)
NIST Official Publications
- NIST Special Publication 330, 2008 Edition: The International System of Units (SI)
- NIST Special Publication 811, 2008 Edition: Guide for the Use of the International System of Units
- NIST Special Pub 814: Interpretation of the SI for the United States and Federal Government Metric Conversion Policy
Rules for SAE Use of SI (Metric) Units
النظام الدولي للوحدات at the Open Directory Project
EngNet Metric Conversion Chart Online Categorised Metric Conversion Calculator
U.S. Metric Association. 2008. A Practical Guide to the International System of Units