Stuff You Should Know How Kilogram Works

Metric unit of mass

"kg" redirects here. For other uses, meet KG.

Kilogram
Kilogram maintained by the General Conference on Weights and Measures
General information
Unit system	SI base unit
Unit of	mass
Symbol	kg
Conversions
1 kg in ...	... is equal to ...
Avoirdupois	≈ two.204623 pounds[Notation 1]
British Gravitational	≈ 0.0685 slugs

The kilogram (besides kilogramme ^[one]) is the base of operations unit of mass in the International Organization of Units (SI), the metric system, having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. Information technology means 'm grams'.

The kilogram was originally defined in 1795 as the mass of ane litre of h2o. Modernistic superseding definitions of a kilogram agree with this original definition to within thirty parts per million. In 1799, the platinum Kilogramme des Athenaeum replaced it as the standard of mass. In 1889, a cylinder of platinum-iridium, the International Prototype of the Kilogram (IPK), became the standard of the unit of measurement of mass for the metric system and remained so until 2019.^[2] The kilogram was the terminal of the SI units to exist defined by a physical artefact.

The kilogram is at present divers in terms of the second and the metre, based on fixed primal constants of nature.^{[3] [4]} This allows a properly-equipped metrology laboratory to calibrate a mass measurement musical instrument such as a Kibble residue equally the primary standard to determine an exact kilogram mass, although precision kilogram masses remain in employ as secondary standards for ordinary purposes.

Definition [edit]

The kilogram is defined in terms of 3 fundamental physical constants: The speed of calorie-free c, a specific diminutive transition frequency Δν _Cs , and the Planck constant h.

According to the Full general Briefing on Weights and Measures (CGPM)

The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be half-dozen.626070 15 ×10⁻³⁴ when expressed in the unit J⋅s, which is equal to kg⋅g^two⋅s⁻¹, where the metre and the second are defined in terms of c and Δν _Cs .

—CGPM ^{[5] [vi]}

A Kibble remainder is used to mensurate a kilogram with electricity and magnetism.

This definition is generally consistent with previous definitions: the mass remains inside thirty ppm of the mass of one litre of water.^[7]

Timeline of previous definitions [edit]

• 1793: The grave (the forerunner of the kilogram) was defined as the mass of one litre (dm³) of water, which was determined to be 18841 grains.^[viii]
• 1795: the gram (¹/₁₀₀₀ of a kilogram) was provisionally defined every bit the mass of one cubic centimetre of h2o at the melting signal of ice.^[nine]
• 1799: The Kilogramme des Athenaeum was manufactured every bit a prototype. Information technology had a mass equal to the mass of 1 dm³ of h2o at the temperature of its maximum density, which is approximately 4 °C.
• 1875–1889: The Metre Convention was signed in 1875, leading to the production of the International Paradigm of the Kilogram (IPK) in 1879 and its adoption in 1889.
• 2019: The kilogram was divers in terms of the Planck constant equally approved by the General Conference on Weights and Measures (CGPM) on sixteen Nov 2018.

Proper name and terminology [edit]

The kilogram is the only base SI unit with an SI prefix (kilo) as part of its proper name. The word kilogramme or kilogram is derived from the French kilogramme ,^[10] which itself was a learned coinage, prefixing the Greek stem of χίλιοι khilioi "a thousand" to gramma , a Late Latin term for "a small weight", itself from Greek γράμμα .^[11] The word kilogramme was written into French law in 1795, in the Decree of eighteen Germinal,^[12] which revised the provisional system of units introduced by the French National Convention ii years earlier, where the gravet had been defined equally weight ( poids ) of a cubic centimetre of water, equal to 1/1000 of a grave .^[13] In the decree of 1795, the term gramme thus replaced gravet , and kilogramme replaced grave .

The French spelling was adopted in Great britain when the word was used for the first time in English language in 1795,^{[14] [10]} with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with "kilogram" having become past far the more common.^[1] UK police regulating the units to be used when trading by weight or measure does not forbid the utilize of either spelling.^[xv]

In the 19th century the French word kilo , a shortening of kilogramme , was imported into the English linguistic communication where it has been used to mean both kilogram^[xvi] and kilometre.^[17] While kilo as an alternative is acceptable, to The Economist for example,^[18] the Canadian authorities'due south Termium Plus arrangement states that "SI (International Organization of Units) usage, followed in scientific and technical writing" does non allow its usage and it is described equally "a common informal proper name" on Russ Rowlett's Dictionary of Units of Measurement.^{[19] [20]} When the United states of america Congress gave the metric organisation legal condition in 1866, it permitted the utilise of the give-and-take kilo as an alternative to the give-and-take kilogram,^[21] just in 1990 revoked the status of the give-and-take kilo.^[22]

The SI system was introduced in 1960 and in 1970 the BIPM started publishing the SI Brochure, which contains all relevant decisions and recommendations by the CGPM concerning units. The SI Brochure states that "Information technology is not permissible to apply abbreviations for unit symbols or unit names ...".^{[23] [Annotation two]}

Kilogram condign a base unit: the part of units for electromagnetism [edit]

It is primarily because of units for electromagnetism that the kilogram rather than the gram was eventually adopted as the base of operations unit of measurement of mass in the SI. The relevant series of discussions and decisions started roughly in the 1850s and effectively concluded in 1946. By the end of the 19th century, the 'practical units' for electrical and magnetic quantities such equally the ampere and the volt were well established in practical employ (e.yard. for telegraphy). Unfortunately, they were not coherent with the and so-prevailing base units for length and mass, the centimeter, and the gram. Still, the 'practical units' besides included some purely mechanical units. In detail, the product of the ampere and the volt gives a purely mechanical unit of measurement of power, the watt. Information technology was noticed that the purely mechanical practical units such as the watt would be coherent in a system in which the base unit of length was the meter and the base unit of measurement of mass was the kilogram. Because no one wanted to supervene upon the second as the base unit of time, the metre and the kilogram are the just pair of base units of length and mass such that (one) the watt is a coherent unit of power, (2) the base units of length and time are integer-ability-of-ten ratios to the metre and the gram (so that the organization remains 'metric'), and (3) the sizes of the base units of length and mass are convenient for practical use.^{[Note 3]} This would still leave out the purely electrical and magnetic units: while the purely mechanical practical units such as the watt are coherent in the metre-kilogram-2nd organisation, the explicitly electrical and magnetic units such as the volt, the ampere, etc. are non.^{[Annotation v]} The but fashion to also make those units coherent with the metre-kilogram-2d system is to modify that system in a different fashion: the number of fundamental dimensions must be increased from iii (length, mass, and fourth dimension) to four (the previous three, plus one purely electric one).^{[Note six]}

The country of units for electromagnetism at the end of the 19th century [edit]

During the second half of the 19th century, the centimetre–gram–second organization of units was becoming widely accepted for scientific piece of work, treating the gram every bit the fundamental unit of measurement of mass and the kilogram equally a decimal multiple of the base unit formed by using a metric prefix. However, every bit the century drew to a shut, at that place was widespread dissatisfaction with the units for electricity and magnetism in the CGS organization. There were two obvious choices for absolute units.^{[Note seven]} of electromagnetism: the 'electrostatic' (CGS-ESU) system and the 'electromagnetic' (CGS-EMU) organisation. But the sizes of coherent electric and magnetic units were not convenient in either of these systems; for instance, the ESU unit of measurement of electrical resistance, which was later named the statohm, corresponds to near nine×x¹¹ ohm, while the EMU unit, which was later named the abohm, corresponds to 10⁻⁹ ohm.^{[Note viii]}

To circumvent this difficulty, a third prepare of units was introduced: the and then-called practical units. The practical units were obtained as decimal multiples of coherent CGS-EMU units, chosen so that the resulting magnitudes were convenient for practical utilise and so that the practical units were, as far every bit possible, coherent with each other.^[26] The practical units included such units as the volt, the ampere, the ohm, etc.,^{[27] [28]} which were later incorporated in the SI system and which are used to this day.^{[Note 9]} The reason the meter and the kilogram were later called to be the base of operations units of length and mass was that they are the only combination of reasonably sized decimal multiples or submultiples of the meter and the gram that tin be fabricated coherent with the volt, the ampere, etc.

The reason is that electric quantities cannot be isolated from mechanical and thermal ones: they are connected past relations such every bit current × electrical potential deviation = ability. For this reason, the applied system also included coherent units for sure mechanical quantities. For example, the previous equation implies that ampere × volt is a coherent derived practical unit of ability;^{[Notation 10]} this unit was named the watt. The coherent unit of free energy is then the watt times the 2d, which was named the joule. The joule and the watt also have user-friendly magnitudes and are decimal multiples of CGS coherent units for energy (the erg) and ability (the erg per second). The watt is not coherent in the centimeter-gram-second arrangement, simply it is coherent in the meter-kilogram-second system—and in no other arrangement whose base of operations units of length and mass are reasonably sized decimal multiples or submultiples of the meter and the gram.

However, unlike the watt and the joule, the explicitly electrical and magnetic units (the volt, the ampere...) are not coherent even in the (accented iii-dimensional) meter-kilogram-second arrangement. Indeed, one can work out what the base units of length and mass have to be in order for all the practical units to be coherent (the watt and the joule as well as the volt, the ampere, etc.). The values are 10^seven metres (one one-half of a meridian of the Globe, called a quadrant) and 10⁻¹¹ grams (called an eleventh-gram ^{[Note 11]}).^{[Annotation thirteen]}

Therefore, the total absolute system of units in which the applied electric units are coherent is the quadrant–eleventh-gram–second (QES) system. However, the extremely inconvenient magnitudes of the base of operations units for length and mass made it so that no one seriously considered adopting the QES organisation. Thus, people working on practical applications of electricity had to use units for electrical quantities and for free energy and power that were not coherent with the units they were using for e.grand. length, mass, and strength.

Meanwhile, scientists developed yet another fully coherent absolute system, which came to exist called the Gaussian organisation, in which the units for purely electrical quantities are taken from CGE-ESU, while the units for magnetic quantities are taken from the CGS-EMU. This system proved very user-friendly for scientific work and is still widely used. All the same, the sizes of its units remained either too large or too pocket-sized—by many orders of magnitude—for practical applications.

Finally, in both CGS-ESU and CGS-EMU as well as in the Gaussian system, Maxwell'due south equations are 'unrationalized', meaning that they contain various factors of 4π that many workers plant awkward. So yet another system was developed to rectify that: the 'rationalized' Gaussian arrangement, usually chosen the Lorentz–Heaviside system. This system is still used in some subfields of physics. Notwithstanding, the units in that organization are related to Gaussian units by factors of √4π ≈ 3.5 , which means that their magnitudes remained, like those of the Gaussian units, either far as well large or far too small for applied applications.

The Giorgi proposal [edit]

In 1901, Giovanni Giorgi proposed a new system of units that would remedy this situation.^[29] He noted that the mechanical applied units such as the joule and the watt are coherent not simply in the QES system, just likewise in the meter-kilogram-second (MKS) system.^{[thirty] [Note 14]} It was of course known that adopting the meter and the kilogram equally base units—obtaining the three dimensional MKS organization—would not solve the problem: while the watt and the joule would exist coherent, this would non be and then for the volt, the ampere, the ohm, and the rest of the practical units for electrical and magnetic quantities (the only iii-dimensional absolute system in which all practical units are coherent is the QES system).

But Giorgi pointed out that the volt and the rest could be fabricated coherent if the idea that all physical quantities must exist expressible in terms of dimensions of length, mass, and time, is relinquished and a fourth base dimension is added for electric quantities. Any practical electrical unit could exist chosen as the new cardinal unit, contained from the meter, kilogram, and second. Likely candidates for the fourth independent unit included the coulomb, the ampere, the volt, and the ohm, merely somewhen, the ampere proved to be the well-nigh convenient for metrology. Moreover, the liberty gained by making an electric unit independent from the mechanical units could be used to rationalize Maxwell's equations.

The thought that one should give up on having a purely 'absolute' arrangement (i.eastward. one where merely length, mass, and time are the base dimensions) was a departure from a viewpoint that seemed to underlie the early breakthroughs by Gauss and Weber (especially their famous 'accented measurements' of Globe'due south magnetic field^{[31] : 54–56} ), and information technology took some time for the scientific customs to accept it—non least because many scientists clung to the notion that the dimensions of a quantity in terms of length, mass, and time somehow specify its 'fundamental physical nature'.^{[32] :24, 26 [thirty]}

Acceptance of the Giorgi system, leading to the MKSA system and the SI [edit]

By the 1920s, dimensional analysis had become much meliorate understood^[30] and it was becoming widely accustomed that the choice of both the number and of the identities of the "central" dimensions should be dictated by convenience only and that in that location is aught really fundamental about the dimensions of a quantity.^[32] In 1935, Giorgi'due south proposal was adopted by the IEC as the Giorgi system. It is this system that has since then been called the MKS organization,^[33] although 'MKSA' appears in conscientious usage. In 1946 the CIPM approved a proposal to adopt the ampere as the electromagnetic unit of the "MKSA system".^{[34] : 109, 110} In 1948 the CGPM commissioned the CIPM "to make recommendations for a single practical system of units of measurement, suitable for adoption by all countries adhering to the Metre Convention".^[35] This led to the launch of SI in 1960.

To summarize, the ultimate reason that the kilogram was chosen over the gram as the base unit of mass was, in i give-and-take, the volt-ampere. Namely, the combination of the meter and the kilogram was the just choice of base of operations units of length and mass such that one. the volt-ampere—which is also chosen the watt and which is the unit of power in the practical system of electric units—is coherent, 2. the base units of length and mass are decimal multiples or submultiples of the meter and the gram, and 3. the base units of length and mass take user-friendly sizes.

The CGS and MKS systems co-existed during much of the early on-to-mid 20th century, just as a event of the decision to adopt the "Giorgi organisation" equally the international system of units in 1960, the kilogram is now the SI base unit for mass, while the definition of the gram is derived.

Redefinition based on fundamental constants [edit]

A Kibble residuum, which was originally used to measure the Planck constant in terms of the IPK, can now be used to calibrate secondary standard weights for practical utilize.

The replacement of the International Prototype of the Kilogram equally the primary standard was motivated past evidence accumulated over a long menstruum of fourth dimension that the mass of the IPK and its replicas had been changing; the IPK had diverged from its replicas past approximately 50 micrograms since their manufacture late in the 19th century. This led to several competing efforts to develop measurement engineering precise plenty to warrant replacing the kilogram artefact with a definition based directly on physical fundamental constants.^[2] Physical standard masses such as the IPK and its replicas still serve as secondary standards.

The International Commission for Weights and Measures (CIPM) approved a redefinition of the SI base units in November 2018 that defines the kilogram past defining the Planck constant to exist exactly six.626070 15 ×x⁻³⁴ kg⋅chiliad^two⋅southward^−ane , finer defining the kilogram in terms of the second and the metre. The new definition took event on 20 May 2019.^{[2] [5] [36]}

Prior to the redefinition, the kilogram and several other SI units based on the kilogram were divers by a man-made metallic artefact: the Kilogramme des Archives from 1799 to 1889, and the International Image of the Kilogram from 1889 to 2019.^[two]

In 1960, the metre, previously similarly having been divers with reference to a single platinum-iridium bar with two marks on information technology, was redefined in terms of an invariant physical abiding (the wavelength of a particular emission of light emitted by krypton,^[37] and later the speed of light) so that the standard can be independently reproduced in different laboratories by post-obit a written specification.

At the 94th Meeting of the International Committee for Weights and Measures (CIPM) in 2005, it was recommended that the same be done with the kilogram.^[38]

In October 2010, the CIPM voted to submit a resolution for consideration at the Full general Conference on Weights and Measures (CGPM), to "take note of an intention" that the kilogram exist divers in terms of the Planck abiding, h (which has dimensions of energy times time, thus mass × length^two / time) together with other physical constants.^{[39] [forty]} This resolution was accepted by the 24th briefing of the CGPM^[41] in October 2011 and farther discussed at the 25th conference in 2014.^{[42] [43]} Although the Committee recognised that significant progress had been made, they concluded that the data did non yet appear sufficiently robust to adopt the revised definition, and that work should continue to enable the adoption at the 26th meeting, scheduled for 2018.^[42] Such a definition would theoretically let any apparatus that was capable of delineating the kilogram in terms of the Planck constant to exist used every bit long as it possessed sufficient precision, accuracy and stability. The Kibble balance is one way to practice this.

As part of this projection, a variety of very different technologies and approaches were considered and explored over many years. Some of these approaches were based on equipment and procedures that would enable the reproducible production of new, kilogram-mass prototypes on demand (albeit with boggling effort) using measurement techniques and cloth properties that are ultimately based on, or traceable to, concrete constants. Others were based on devices that measured either the acceleration or weight of paw-tuned kilogram exam masses and which expressed their magnitudes in electrical terms via special components that permit traceability to physical constants. All approaches depend on converting a weight measurement to a mass and therefore require the precise measurement of the force of gravity in laboratories. All approaches would accept precisely fixed one or more than constants of nature at a divers value.

SI multiples [edit]

Because an SI unit of measurement may non accept multiple prefixes (see SI prefix), prefixes are added to gram, rather than the base unit of measurement kilogram, which already has a prefix as role of its name.^[44] For instance, ane-millionth of a kilogram is 1mg (i milligram), not 1μkg (1 microkilogram).

SI multiples of gram (g)

Submultiples				Multiples
Value	SI symbol	Proper noun		Value	SI symbol	Name
10−1 k	dg	decigram		101 g	dag	decagram
10−ii g	cg	centigram		102 g	hg	hectogram
x−iii grand	mg	milligram		103 thou	kg	kilogram
ten−six g	µg	microgram		106 one thousand	Mg	megagram (tonne)
10−ix g	ng	nanogram		ten9 1000	Gg	gigagram
10−12 one thousand	pg	picogram		1012 g	Tg	teragram
10−15 m	fg	femtogram		ten15 g	Pg	petagram
10−18 g	ag	attogram		1018 one thousand	Eg	exagram
10−21 chiliad	zg	zeptogram		1021 g	Zg	zettagram
10−24 g	yg	yoctogram		1024 g	Yg	yottagram
Mutual prefixed units are in bold face up.[Note 15]

• The microgram is typically abbreviated "mcg" in pharmaceutical and nutritional supplement labelling, to avoid defoliation, since the "μ" prefix is not always well recognised outside of technical disciplines.^{[Annotation sixteen]} (The expression "mcg" is as well the symbol for an obsolete CGS unit of measurement of measure known every bit the "millicentigram", which is equal to 10μg.)
• In the United Kingdom, considering serious medication errors have been made from the confusion betwixt milligrams and micrograms when micrograms has been abbreviated, the recommendation given in the Scottish Palliative Intendance Guidelines is that doses of less than i milligram must be expressed in micrograms and that the word microgram must be written in full, and that information technology is never acceptable to use "mcg" or "μg".^[45]
• The hectogram (100 g) is a very ordinarily used unit in the retail food trade in Italy, commonly called an etto, short for ettogrammo, the Italian for hectogram.^{[46] [47] [48]}
• The erstwhile standard spelling and abbreviation "deka-" and "dk" produced abbreviations such as "dkm" (dekametre) and "dkg" (dekagram).^[49] As of 2020,^[update] the abbreviation "dkg" (x one thousand) is even so used in parts of cardinal Europe in retail for some foods such equally cheese and meat, e.grand. here:.^{[50] [51] [52] [54]}
• The unit proper name megagram is rarely used, and even then typically only in technical fields in contexts where especially rigorous consistency with the SI standard is desired. For most purposes, the name tonne is instead used. The tonne and its symbol, "t", were adopted by the CIPM in 1879. It is a not-SI unit accepted past the BIPM for use with the SI. According to the BIPM, "This unit is sometimes referred to as 'metric ton' in some English-speaking countries."^[55] The unit proper noun megatonne or megaton (Mt) is oft used in general-interest literature on greenhouse gas emissions, whereas the equivalent unit in scientific papers on the subject is often the teragram (Tg).

Run across also [edit]

• 1795 in science
• 1799 in scientific discipline
• General Conference on Weights and Measures (CGPM)
• Gram
• Grave (original name of the kilogram, its history)
• Gravimetry
• Inertia
• International Agency of Weights and Measures (BIPM)
• International Committee for Weights and Measures (CIPM)
• International System of Units (SI)
• Kibble remainder
• Kilogram-force
• Litre
• Mass
• Mass versus weight
• Metric system
• Metric ton
• Milligram per cent
• National Institute of Standards and Technology (NIST)
• Newton
• SI base units
• Standard gravity
• Weight

Notes [edit]

1. ^ The avoirdupois pound is role of both Us customary system of units and the Imperial organisation of units. It is defined as exactly 0.453592 37 kilograms.
2. ^ The French text (which is the administrative text) states " Il n'est pas autorisé d'utiliser des abréviations cascade les symboles et noms d'unités ... "
3. ^ If information technology is known that the metre and the kilogram satisfy all 3 conditions, and so no other choice does: The coherent unit of power, when written out in terms of the base units of length, mass, and time, is (base of operations unit of mass) × (base unit of length)²/(base unit of time)ⁱⁱⁱ. It is stated that the watt is coherent in the metre-kilogram-second organization; thus, 1 watt = ( 1 kg) × ( ane m)²/( one s)³. The second is left as it is and it is noted that if the base unit of length is changed to L m and the base unit of mass to M kg , then the coherent unit of measurement of ability is ( M kg ) × ( L thousand )^two/( one s)³ = M L ² × ( i kg) × ( 1 grand)²/( 1 s)³ = 1000 L ² watt. Since base of operations units of length and mass are such that the coherent unit of power is the watt, information technology must be that M 50 ² = one. It follows that if the base unit of measurement of length is changed by a factor of L , and then the base unit of measurement of mass must change by a factor of 1/Fifty ⁱⁱ if the watt is to remain a coherent unit. Information technology would be impractical to make the base unit of length a decimal multiple of a metre ( x m, 100 m, or more). Therefore the merely option is to make the base unit of measurement of length a decimal submultiple of the metre. This would hateful decreasing the meter by a factor of ten to obtain the decimetre ( 0.one thousand), or past a cistron of 100 to get the centimetre, or by a factor of 1000 to get the millimetre. Making the base unit of measurement of length even smaller would not be applied (for case, the next decimal factor, 10000 , would produce the base unit of measurement of length of one-tenth of a millimetre), and then these 3 factors (10, 100, and 1000) are the only acceptable options equally far as the base of operations unit of length. But and so the base unit of mass would have to be larger than a kilogram, past the following respective factors: 10² = 100, 100² = 10000 , and grand² = x^{half dozen} . In other words, the watt is a coherent unit of measurement for the following pairs of base of operations units of length and mass: 0.1 m and 100 kg, 1 cm and 10000 kg, and 1 mm and 1000 000 kg. Even in the first pair, the base of operations unit of mass is impractically large, 100 kg, and as the base unit of length is decreased, the base unit of measurement of mass gets even larger. Thus, bold that the second remains the base of operations unit of time, the metre-kilogram combination is the merely ane that has base units for both length and mass that are neither also large nor too small-scale, and that are decimal multiples or divisions of the metre and gram, and has the watt as a coherent unit.
4. ^ A system in which the base quantities are length, mass, and time, and but those three.
5. ^ There is merely ane three-dimensional 'absolute' arrangement^{[Note 4]} in which all practical units are coherent, including the volt, the ampere, etc.: ane in which the base of operations unit of length is x⁷ yard and the base unit of mass is 10⁻¹¹ k. Clearly, these magnitudes are not practical.
6. ^ Meanwhile, there were parallel developments that, for contained reasons, eventually resulted in three boosted fundamental dimensions, for a total of seven: those for temperature, luminous intensity, and the amount of substance.
7. ^ That is, units which accept length, mass, and fourth dimension every bit base dimensions and that are coherent in the CGS organization.
8. ^ For quite a long fourth dimension, the ESU and EMU units did not accept special names; one would only say, eastward.one thousand. the ESU unit of measurement of resistance. It was manifestly merely in 1903 that A. Due east. Kennelly suggested that the names of the EMU units exist obtained by prefixing the proper noun of the corresponding 'practical unit' by 'ab-' (short for 'absolute', giving the 'abohm', 'abvolt', the 'abampere', etc.), and that the names of the ESU units exist analogously obtained past using the prefix 'abstat-', which was later shortened to 'stat-' (giving the 'statohm', 'statvolt', 'statampere', etc.).^{[24] : 534–v} This naming system was widely used in the U.South., but, manifestly, not in Europe.^[25]
9. ^ The utilize of SI electric units is substantially universal worldwide (besides the clearly electrical units similar the ohm, the volt, and the ampere, it is likewise nearly universal to use the watt when quantifying specifically electrical power). Resistance to the adoption of SI units by and large concerns mechanical units (lengths, mass, force, torque, pressure), thermal units (temperature, heat), and units for describing ionizing radiation (activity referred to a radionuclide, captivated dose, dose equivalent); it does not concern electrical units.
10. ^ In alternating current (AC) circuits one can introduce three kinds of power: active, reactive, and apparent. Though the 3 take the same dimensions and thus the same units when those are expressed in terms of base units (i.due east. kg⋅m²⋅s^-3), it is customary to use dissimilar names for each: respectively, the watt, the volt-ampere reactive, and the volt-ampere.
11. ^ At the fourth dimension, information technology was popular to denote decimal multiples and submultiples of quantities by using a system suggested past G. J. Stoney. The arrangement is easiest to explain through examples. For decimal multiples: 10^ix grams would be denoted as gram-nine, x¹³ 1000 would be a meter-thirteen, etc. For submultiples: 10⁻⁹ grams would exist denoted equally a ninth-gram, 10⁻¹³ grand would exist a thirteenth-meter, etc. The system also worked with units that used metric prefixes, so due east.thou. ten¹⁵ centimeter would be centimeter-xv. The dominion, when spelled out, is this: we denote 'the exponent of the power of ten, which serves as multiplier, by an appended cardinal number, if the exponent be positive, and by a prefixed ordinal number, if the exponent be negative.'^[27]
12. ^ This is also obvious from the fact that in both absolute and applied units, electric current is charge per unit time, and so that the unit of time is the unit of measurement of accuse divided by the unit of measurement of electric current. In the practical organization, we know that the base of operations unit of measurement of fourth dimension is the second, and so the coulomb per ampere gives the 2d. The base unit of time in CGS-EMU is then the abcoulomb per abampere, but that ratio is the same as the coulomb per ampere, since the units of current and charge both utilize the same conversion gene, 0.ane, to become between the EMU and practical units (coulomb/ampere = ( 0.1 abcoulomb)/( 0.1 abampere) = abcoulomb/abampere). So the base unit of time in EMU is also the 2nd.
13. ^ This tin be shown from the definitions of, say, the volt, the ampere, and the coulomb in terms of the EMU units. The volt was chosen as 10⁸ EMU units (abvolts), the ampere as 0.1 EMU units (abamperes), and the coulomb every bit 0.1 EMU units (abcoulombs). Now nosotros use the fact that, when expressed in the base of operations CGS units, the abvolt is k^i/2·cm^3/two/s², the abampere is g^1/ii·cm^1/2/due south, and the abcoulomb is g^1/ii·cm^1/2. Suppose we choose new base of operations units of length, mass, and time, equal to L centimeters, M grams, and T seconds. Then instead of the abvolt, the unit of measurement of electric potential will exist ( Grand × chiliad)^ane/ii·( L × cm)^3/2/( T × southward)² = M ^i/two 50 ^iii/2/ T ⁱⁱ × thousand^1/2·cm^3/2/south^two = Thousand ^ane/2 50 ^3/2/ T ² abvolts. We want this new unit to be the volt, so we must have M ^ane/2 Fifty ^iii/ii/ T ² = 10⁸ . Similarly, if we want the new unit for current to be the ampere, we obtain that One thousand ^1/2 50 ^1/2/ T = 0.1 , and if we want the new unit of charge to exist the coulomb, we become that 1000 ^1/two L ^1/2 = 0.1 . This is a organization of three equations with three unknowns. By dividing the middle equation past the last one, we get that T = one, and then the 2nd should remain the base unit of time.^{[Note 12]} If we so divide the commencement equation by the middle one (and use the fact that T = ane), we get that Fifty = x⁸ / 0.1 = 10^ix , so the base unit of length should be 10⁹ cm = 10⁷ chiliad. Finally, we square the final equation and obtain that M = 0.ane ²/L = 10⁻¹¹ , so the base unit of mass should be x⁻¹¹ grams.
14. ^ The dimensions of energy are M L ^two/ T ² and of power, One thousand Fifty ²/ T ³. One meaning of these dimensional formulas is that if the unit of mass is changed past a cistron of Grand , the unit of measurement of length by a factor of Fifty , and the unit of fourth dimension by a gene of T , then the unit of energy will change by a factor of M L ⁱⁱ/ T ² and the unit of ability by a factor of 1000 Fifty ²/ T ⁱⁱⁱ. This ways that if the unit of measurement of length is decreased while at the same fourth dimension increasing the unit of mass in such a manner that the product Thousand L ² remains constant, the units of energy and power would not change. Clearly, this happens if M = 1/Fifty ² . Now, the watt and joule are coherent in a organisation in which the base of operations unit of length is ten⁷ one thousand while the base unit of mass is 10⁻¹¹ grams. They will then as well be coherent in any system in which the base unit of length is Fifty × 10⁷ m and the base unit of measurement of mass is i/50 ² × 10⁻¹¹ g , where 50 is whatsoever positive existent number. If we gear up L = x^−seven , we obtain the meter as the base unit of length. Then the respective base of operations unit of mass is 1/( 10^−vii )² × ten⁻¹¹ 1000 = 10¹⁴ × 10⁻¹¹ g = 10³ g = 1 kg.
15. ^ Benchmark: A combined total of at least 5 occurrences on the British National Corpus and the Corpus of Contemporary American English language, including both the singular and the plural for both the -gram and the -gramme spelling.
16. ^ The practice of using the abbreviation "mcg" rather than the SI symbol "μg" was formally mandated in the Usa for medical practitioners in 2004 by the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) in their "Do Not Use" List: Abbreviations, Acronyms, and Symbols because "μg" and "mg" when handwritten can exist confused with one another, resulting in a m-fold overdosing (or underdosing). The mandate was also adopted by the Institute for Safe Medication Practices.

References [edit]

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External links [edit]

Wikimedia Commons has media related to Kilogram.

External images
BIPM: The IPK in iii nested bell jars
NIST: K20, the US National Image Kilogram resting on an egg crate fluorescent light panel
BIPM: Steam cleaning a 1 kg prototype before a mass comparison
BIPM: The IPK and its six sister copies in their vault
The Age: Silicon sphere for the Avogadro Project
NPL: The NPL's Watt Remainder project
NIST: This particular Rueprecht Residual, an Austrian-made precision remainder, was used by the NIST from 1945 until 1960
BIPM: The FB‑2 flexure-strip balance, the BIPM's modern precision balance featuring a standard deviation of one ten-billionth of a kilogram (0.1μg)
BIPM: Mettler HK1000 balance, featuring oneμg resolution and a 4kg maximum mass. Also used by NIST and Sandia National Laboratories' Main Standards Laboratory
Micro-g LaCoste: FG‑5 accented gravimeter, (diagram), used in national laboratories to measure gravity to iiμGal accuracy

• NIST Improves Accurateness of 'Watt Residuum' Method for Defining the Kilogram
• The UK'south National Concrete Laboratory (NPL): Are whatever bug caused by having the kilogram defined in terms of a physical artefact? (FAQ - Mass & Density)
• NPL: NPL Kibble balance
• Metrology in France: Watt balance
• Australian National Measurement Institute: Redefining the kilogram through the Avogadro constant
• International Bureau of Weights and Measures (BIPM): Home page
• NZZ Folio: What a kilogram really weighs
• NPL: What are the differences between mass, weight, strength and load?
• BBC: Getting the measure of a kilogram
• NPR: This Kilogram Has A Weight-Loss Problem, an interview with National Establish of Standards and Technology physicist Richard Steiner
• Avogadro and tooth Planck constants for the redefinition of the kilogram
• Realization of the awaited definition of the kilogram
• Sample, Ian (November 9, 2018). "In the balance: scientists vote on first change to kilogram in a century". The Guardian . Retrieved November 9, 2018.

Videos [edit]

• The BIPM YouTube aqueduct
• "The part of the Planck constant in physics" - presentation at 26th CGPM coming together at Versailles, France, November 2018 when voting on superseding the IPK took place.

tennysonwilich.blogspot.com

Source: https://en.wikipedia.org/wiki/Kilogram

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