The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. It was assigned to the United States in 1889 and is periodically recertified and traceable to the primary international standard, "The Kilogram", held at the Bureau International des Poids et Mesures (BIPM) near Paris.

The kilogram or kilogramme (symbol: kg) is the SI base unit of mass. It is defined as being equal to the mass of the international prototype of the kilogram. Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ...

The kilogram is the only SI base unit that employs a prefix,^[1] and the only SI unit that is still defined in relation to an artifact rather than to a fundamental physical property. It has been suggested that this article or section be merged with prototyping. ...

The pound, being defined as exactly 453.59237 grams, results in the kilogram being approximately equivalent to 2.205 avoirdupois pounds^[2] in the Imperial system and the customary system of weights and measures used in the United States. The avoirdupois system is a system of weights defining terms such as pound and ounce. ... The pound (abbreviations: lb or, sometimes in the United States, #) is a unit of mass in a number of different systems, including various systems of units of mass that formed part of English units, Imperial units, and United States customary units. ... This article is about post-1824 Imperial units, please see also English unit, U.S. customary unit or Avoirdupois. ...

History

The kilogram was originally defined as one thousand times "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a meter, and at the temperature of melting ice",^[3] and later as the mass of one litre of pure water at standard atmospheric pressure and at the temperature at which water has its maximum density (277.13 K, 3.98 °C).^{[citation needed]} This definition was hard to realize accurately, partially because the density of water depends slightly on the pressure, and pressure units include mass as a factor, introducing a circular dependency in the definition. The litre or liter (U.S. spelling, see spelling differences) is a unit of volume. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Atmospheric pressure is the pressure caused by the weight of air above any area in the Earths atmosphere. ... Fig. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... A circular definition is one that assumes a prior understanding of the term being defined. ...

To avoid these problems, the kilogram was redefined as precisely the mass of a particular standard mass created to approximate the original definition. Since 1889, the SI system defines the unit to be equal to the mass of the international prototype of the kilogram, which is made from an alloy of 90% platinum and 10% iridium (by weight) and machined into a right-circular cylinder (height = diameter) of 39 mm. The international prototype is kept at the Bureau International des Poids et Mesures (International Bureau of Weights and Measures) in Sèvres on the outskirts of Paris. Official copies of the prototype kilogram are made available as national prototypes, which are compared to the Paris prototype ("Le Grand Kilo") roughly every 40 years. The international prototype is one of three cylinders made in 1879. In 1883, it was found to be indistinguishable from the mass of the kilogram standard at the time, and formally ratified as the kilogram by the 1st CGPM in 1889.^[4] Standardization, in the context related to technologies and industries, is the process of establishing a technical standard among competing entities in a market, where this will bring benefits without hurting competition. ... Year 1889 (MDCCCLXXXIX) was a common year starting on Tuesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Thursday of the 12-day slower Julian calendar). ... Look up si, Si, SI in Wiktionary, the free dictionary. ... An alloy is a homogeneous mixture of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. ... General Name, Symbol, Number platinum, Pt, 77 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... General Name, Symbol, Number iridium, Ir, 77 Chemical series transition metals Group, Period, Block 9, 6, d Appearance silvery white Atomic mass 192. ... To help compare different orders of magnitude this page lists lengths between 10-2 m and 10-1 m (1 cm and 10 cm). ... The Bureau International des Poids et Mesures (International Bureau of Weights and Measures, or BIPM) is a standards organization, one of the three organizations established to maintain the SI system under the terms of the Metre Convention. ... Road to Sèvres, Jean-Baptiste Camille Corot, 1855-1865. ... City flag City coat of arms Motto: Fluctuat nec mergitur (Latin: Tossed by the waves, she does not sink) Paris Eiffel tower as seen from the esplanade du Trocadéro. ... To help compare orders of magnitude of different times this page lists times between 3. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, never GCWM). ...

By definition, the error in the repeatability of the current definition is exactly zero; however, any changes in the standard over time can be found by comparing the official standard to its official copies. Because the official copies and the official standard are made of roughly the same materials and kept under the same conditions, comparing the relative masses between standards over time estimates the stability of the standard. The international prototype of the kilogram seems to have lost about 50 micrograms in the last 100 years and the reason for the loss is still unknown.^[5] The observed variation in the prototype has intensified the search for a new definition of the kilogram.

The gram

The gram or gramme is the term to which SI prefixes are applied. BIC pen cap, about 1 gram. ... An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ...

The reason the base unit of mass has a prefix is historic. Originally, the decimal system of units was commissioned by Louis XVI of France and in the original plans, the kilogram was supposed to be called the grave. A gramme was simply an alternative name for a thousandth of a grave, properly named milligrave, and a tonne was an alternative name for 1000 graves, properly named kilograve. However, the metric system didn't come in effect until after the French Revolution. At that time, the name "grave" had become politically incorrect, since it is an alternative word for the title "count" (cognate with the British margrave and the German Graf), and nobility titles were not considered compatible with the notion of égalité. Louis XVI, born Louis-Auguste de France (23 August 1754 – 21 January 1793) ruled as King of France and Navarre from 1774 until 1791, and then as King of the French from 1791 to 1792. ... now. ... now. ... now. ... The French Revolution (1789–1815) was a period of political and social upheaval in the political history of France and Europe as a whole, during which the French governmental structure, previously an absolute monarchy with feudal privileges for the aristocracy and Catholic clergy, underwent radical change to forms based on... A count is a nobleman in most European countries, equivalent in rank to a British earl, whose wife is also still a countess (for lack of an Anglo-Saxon term). ... Margrave is the English and French form (recorded since 1551) of the German title Markgraf (from Mark march and Graf count) and certain equivalent nobiliary (princely) titles in other languages. ... Graf is a German noble title equal in rank to a count (derived from the Latin Comes, with a history of its own) or a British earl (an Anglo-Saxon title derived from the Viking title Jarl). ... Tympanum of a church Liberté, égalité, fraternité, French for Liberty, equality, fraternity (brotherhood), is the motto of the French Republic. ...

The gram was also the base unit of the older CGS system of measurement, a system which is no longer widely used. This article or section is in need of attention from an expert on the subject. ...

Proposed future definitions

There is an ongoing effort to introduce a new definition for the kilogram by way of fundamental or atomic constants. The proposals being worked on are:

Atom-counting approaches

• One Avogadro approach attempts to define the kilogram as a fixed number of silicon atoms of the same isotope. Silicon is the element of choice because the process of creating monocrystalline silica is well-known. As a practical realization the monocrystaline rod would be cut and polished into a sphere, the weight of which would be measured using three different approaches in development by several different institutes. The sizes of the best spheres would be measured by interferometry. As the crystaline structure of the monocrystal is known, the number of atoms in this one kilogram could be estimated.
• The ion accumulation approach involves accumulation of gold atoms and measuring the electrical current required to neutralise them.

Avogadros number, also called Avogadros constant (NA), named after Amedeo Avogadro, is formally defined to be the number of carbon-12 atoms in 12 grams (0. ... It has been suggested that Silicons ranking be merged into this article or section. ... A sphere is a perfectly symmetrical geometrical object. ... It has been suggested that Optical interferometry be merged into this article or section. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow robert ford An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ...

Fundamental-constant approaches

In a similar manner that the metre was redefined to fix the speed of light to an exact value of 299,792,458 m/s, there are proposals to redefine the kilogram in such a way to fix other physical constants of nature to exact values. The or meter (see spelling differences) is a measure of length. ... A line showing the speed of light on a scale model of Earth and the Moon The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation... // ...

• Planck's constant: The Watt balance uses the current balance that was formerly used to define the ampere to relate the kilogram to a value for Planck's constant, based on the definitions of the volt and the ohm. Using the Watt balance, a possible definition for the kilogram would be: The kilogram is the mass of a body at rest whose equivalent energy corresponds to a frequency of exactly (299792458²/66260693)×10⁴¹ Hz.

This would have the effect of defining Planck's constant to be h = 6.6260693×10^-34 J s. This is consistent with the current 2002 CODATA value for Planck's constant which is 6.6260693×10^-34 ± 0.0000011×10^-34 J s.

• Avogadro constant: The kilogram is the mass of exactly (6.0221415×10²³/0.012) unbound carbon-12 atoms at rest and in their ground state.

This would have the effect of defining Avogadro's number to be N_A = 6.0221415×10²³ elementary entities per mole and, consequently, a simpler and concise definition for the mole. This is consistent with the current 2002 CODATA value for the Avogadro constant which is 6.0221415×10²³ ± 0.0000010×10²³ mol^-1.

• Electron mass: The kilogram is the base unit of mass, equal to 1 097 769 238 499 215 084 016 780 676 223 electron mass units.

This would have the effect of defining the electron mass to be m_e = 9.1093826×10^-31 kg. This is consistent with the current 2002 CODATA value for the electron mass which is 9.1093826×10^-31 ± 0.0000016×10^-31 kg.

• Elementary charge: The kilogram is the mass which would be accelerated at precisely 2×10^-7 m/s² if subjected to the per metre force between two straight parallel conductors of infinite length, of negligible circular cross section, placed 1 metre apart in vacuum, through which flow a constant current of exactly 6 241 509 479 607 717 888 elementary charges per second.

This redefinition of the kilogram has the effect of fixing the elementary charge to be e = 1.60217653×10^-19 C and would result in a functionally equivalent definition for the coulomb as being the sum of exactly 6 241 509 479 607 717 888 elementary charges and the ampere as being the electrical current of exactly 6 241 509 479 607 717 888 elementary charges per second. This is consistent the current 2002 CODATA value for the elementary charge which is 1.60217653×10^-19 ± 0.00000014×10^-19 C.

A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ... The watt balance is an electromechanical apparatus used for the precise measurement of the SI unit of electric current, the ampere. ... The ampere balance (also current balance or Kelvin balance) is an electromechanical apparatus used for the precise measurement of the SI unit of electric current, the ampere. ... Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ... Josephson junction array chip developed by NIST as a standard volt. ... The ohm (symbol: Ω) is the SI unit of electric resistance. ... The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ... Look up second in Wiktionary, the free dictionary. ... The Avogadro constant (symbols: L, NA), also called the Avogadro number and, in German scientific literature, sometimes also known as the Loschmidt constant/number, is formally defined to be the number of entities in one mole,[1][2] that is the number of carbon-12 atoms in 12 grams (0. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... CODATA (Committee on Data for Science and Technology) was established in 1966 as an interdisciplinary committee of the International Council of Science (ICSU), formerly the International Council of Scientific Unions. ... Properties The electron is a fundamental subatomic particle which carries a negative electric charge. ... CODATA (Committee on Data for Science and Technology) was established in 1966 as an interdisciplinary committee of the International Council of Science (ICSU), formerly the International Council of Scientific Unions. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... The coulomb (symbol: C) is the SI unit of electric charge. ... The coulomb (symbol: C) is the SI unit of electric charge. ... Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ...

CIPM RECOMMENDATION 1 (CI-2005)

CIPM RECOMMENDATION 1 (CI-2005):^[6] Preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole in terms of fundamental constants Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...

The International Committee for Weights and Measures (CIPM),

• Approve in principle the preparation of new definitions and mises en pratique of the kilogram, the ampere and the kelvin so that if the results of experimental measurements over the next few years are indeed acceptable, all having been agreed with the various Consultative Committees and other relevant bodies, the CIPM can prepare proposals to be put to Member States of the Metre Convention in time for possible adoption by the 24th CGPM in 2011;
• Give consideration to the possibility of redefining, at the same time, the mole in terms of a fixed value of the Avogadro constant;
• Prepare a Draft Resolution that may be put to the 23rd CGPM in 2007 to alert Member States to these activities;

The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, never GCWM). ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, never GCWM). ...

Link with weight

When the weight of an object is given in kilograms, the property intended is almost always mass. Occasionally the gravitational force on an object is given in "kilograms", but the unit used is not a true kilogram: it is the deprecated kilogram-force (kgf), also known as the kilopond (kp). An object of mass 1 kg at the surface of the Earth will be subjected to a gravitational force of approximately 9.8 newtons (the SI unit of force). A value of 9.80665 m/s² (980.665 cm/s² as the CGPM defined it, when cgs systems were the primary systems used) is only an agreed-upon conventional value (3rd CGPM (1901), CR 70) whose purpose is to define grams force. The local gravitational acceleration g varies with latitude and altitude and location on the Earth, so before this conventional value was agreed upon, the gram-force was only an ill-defined unit. (See also g, a standard measure of gravitational acceleration.) A spring scale measures the weight of an object In the physical sciences, weight is a measurement of the gravitational force acting on an object. ... The deprecated unit kilogram-force (kgf) or kilopond (kp) is the force exerted by one kilogram of mass in standard Earth gravity (defined as exactly 9. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... The newton (symbol: N) is the SI unit of force. ... g (also gee, g-force or g-load) is a non-SI unit of acceleration defined as exactly 9. ...

Examples

• Attogram: a research team at Cornell University made a detector using NEMS cantilevers with sub-attogram sensitivity.
• Yoctogram: can be used for masses of nucleons, atoms and molecules. It is a little large for light particles, but yocto- is the last official prefix in the sequence.
• Although the unified atomic mass unit (1 / Avogadro's number g ) is often convenient as a unit, one may sometimes want to use yoctograms to relate easily to other SI values:
  • Unified atomic mass unit = 1.6605 × 10⁻²⁷ kg or 0.0016605 yg
  • Mass of a free electron = 9.1094 × 10^-31 kg or 0.0000009 yg
  • Mass of a free proton = 1.6726 × 10⁻²⁷ kg or 0.0016726 yg
  • Mass of a free neutron = 1.6749 × 10⁻²⁷ kg or 0.0016749 yg

Cornell University is a private university located in Ithaca, New York, USA. Its two medical campuses are in New York City and Education City, Qatar. ... NEMS or nanoelectromechanical systems are similar to MEMS but smaller. ... The cantilevered beam (green) projects from its supports (blue), balanced by the structure (red block), which supports the load (red arrow). ... In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle still characterizing a chemical element. ... In science, a molecule is a group of atoms in a definite arrangement held together by chemical bonds. ... Avogadros number, also called Avogadros constant (NA), named after Amedeo Avogadro, is formally defined to be the number of carbon-12 atoms in 12 grams (0. ... The atomic mass unit (amu), unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic masses and molecular masses. ... e- redirects here. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... This article or section does not adequately cite its references or sources. ...

SI multiples

When the Greek small letter mu ('µ') in the symbol of microgram is technically unavailable it should be replaced by Latin small letter 'u'^{[citation needed]}, but other informal abbreviations like 'mcg' (confusingly also used to designate the obsolete term "millicentigram", equal to 10 µg) can also be encountered in practice. In the pharmaceutical industry, 'mcg' is used in the place of 'µg' to designate "microgram." The decagram is alternatively spelled 'dekagram'. Look up micro- in Wiktionary, the free dictionary. ...

The megagram (1000 kg) is also more commonly known as the (metric) tonne (t), also spelled ton (the long ton is a measure of 2240 lb, whereas the short ton is 2000 lb). The unit tonne is accepted to be used with the SI and may take the same prefixes, see also metre-tonne-second system of units. A tonne or metric ton (symbol t), sometimes referred to as a metric tonne, is a measurement of mass equal to 1,000 kilograms. ... A long ton is the name used in the US for the unit called the ton in the avoirdupois or Imperial system of measurements, as used (alongside the metric system) in the United Kingdom and to some extent in other Commonwealth countries. ... The short ton is a unit of mass equal to 907. ... The metre-tonne-second or mts system of units is a system of physical units introduced in the Soviet Union in 1933, but abolished in 1955. ...

See also

• Orders of magnitude (mass) for comparisons with other masses
• Metric system
• SI

Category: ... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... Look up si, Si, SI in Wiktionary, the free dictionary. ...

References

1. ^ http://www.bipm.org/en/si/history-si/name_kg.html
2. ^ One pound avoirdupois is defined as precisely 0.453 592 37 kg. Thus, one kilogram is aproximately equal to 2.204 622 6218 lbs.
3. ^ http://smdsi.quartier-rural.org/histoire/18germ_3.htm
4. ^ New Techniques in the Manufacture of Platinum-Iridium Mass Standards, T. J. Quinn, Platinum Metals Rev., 1986, 30, (2), Pg. 74 – 79
5. ^ Reported in Der Spiegel, 2003 #26
6. ^ http://www.bipm.fr/utils/common/pdf/CIPM2005.zip

This article or section does not cite its references or sources. ...

External links

• National Physical Laboratory FAQ on kilogram definition, the need for a new definition, and some alternatives
• More on the NIST Watt Balance
• Redefinition of the kilogram: a decision whose time has come
• More on the Avogadro project
• International Bureau of Weights and Measures (BIPM)
• Attogram Detection
• World's most sensitive scales weigh a zeptogram, by New Scientist.com
• Scales tip with tiniest mass yet, by BBC News Online
• Robert Matthews: What a kilogram really weighs. Article about the current problem of defining the kilogram.