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 international prototype, made of platinum-iridium, is kept at the BIPM under conditions specified by the 1st CGPM in 1889.

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? Mass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. ...

It 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. A cultural artifact is an man-made object which gives information about the culture of its creator and users. ...

A kilogram is approximately equivalent to 2.205 avoirdupois pounds 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 is the name of a number of units of mass, all in the range of 300 to 600 grams. ... 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 the mass of one litre of pure water at standard atmospheric pressure and at the temperature at which water has its maximum density (3.98 degrees Celsius). 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 (see spelling differences) is a unit of volume. ... Water is a tasteless, odorless substance that is essential to all known forms of life and is known as the universal solvent. ... Atmospheric pressure is the pressure caused by the weight of air above any area in the Earths atmosphere. ... In thermodynamics, temperature is the physical property of a system that underlies the common notions of hot and cold —something that is hotter has the greater temperature. ... The Celsius scale is a temperature scale named after the Swedish astronomer Anders Celsius (1701 â€“ 1744), who first proposed a similar system two years before his death. ... 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 platinum and iridium of 39 mm height and diameter and is kept at the Bureau International des Poids et Mesures (International Bureau of Weights and Measures), near 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 10 years. The international prototype kilogram was made in the 1880s. 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. ... 1889 (MDCCCLXXXIX) was a common year starting on Tuesday (see link for calendar). ... Cover of brochure The International System of Units. ... An alloy is a combination, either in solution or compound, 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, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 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. ...   City flag City coat of arms Motto: Fluctuat nec mergitur (Latin: Tossed by the waves, she does not sink) Coordinates Time Zone CET (GMT +1) Administration Country France Région ÃŽle-de-France Département Paris (75) Subdivisions 20 arrondissements Mayor Bertrand Delanoë  (PS) (since 2001) City Statistics Land area... To help compare orders of magnitude of different times this page lists times between 3. ... // Development and commercial production of electric lighting Development and commercial production of gasoline-powered automobile by Karl Benz, Gottlieb Daimler and Maybach First commercial production and sales of phonographs and phonograph recordings. ...

By definition, the error in the repeatability of the current definition is exactly zero; however, in the usual sense of the word, it can be regarded as of the order of 2 micrograms. This is found by comparing the official standard with its official copies, which are made of roughly the same materials and kept under the same conditions. There is no reason to believe that the official standard is any more or less stable than its official copies, thus giving a way to estimate its stability. This procedure is performed roughly once every forty years.

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 (reported in Der Spiegel, 2003 #26). The observed variation in the prototype has intensified the search for a new definition of the kilogram. It is accurate to state that any object in the universe that had a mass of 1 kilogram 100 years ago, and has not changed since then, now has a mass of 1.000 000 050 kg. This perspective is paradoxical and defeats the purpose of a standard unit of mass, since the standard should not change arbitrarily over time. The philosopher Saul Kripke elaborated on the philosophical implications of this kind of problem, referring, however, to the then-current definition of the metre in terms of an artifact, a choice which was later dropped. Photo of the cover of the first issue of Der Spiegel (1/1947) Der Spiegel (German for The Mirror) is Europes biggest and Germanys most influential weekly magazine, published in Hamburg, with a circulation of around one million per week. ... This article or section does not cite its references or sources. ... The metre, or meter (US), is a measure of length. ...

The gram

The gram or gramme is the term to which SI prefixes are applied. BIC pen cap, about 1 gram. ... An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple (supramultiple 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 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 "markgrave" and the German "Graf"), and nobility titles were not considered compatible with the notion of égalité. now. ... now. ... now. ... The French Revolution (1789–1799) was a pivotal period in the history of French, European and Western civilization. ... now. ... Look up Count in Wiktionary, the free dictionary Countess redirects here. ... 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. As a practical realization, a sphere would be used and its size would be measured by interferometry. Another specific proposed definition for the kilogram that fixes the Avogadro constant is below.
• The ion accumulation approach involves accumulation of gold atoms and measuring the electrical current required to neutralise them.

Count Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e Cerreto, (Turin August 9, 1776 - July 9, 1856) was a great Italian scientist. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... A sphere (< Greek σφαίρα) is a perfectly symmetrical geometrical object. ... This article or section is in need of attention from an expert on the subject. ... An ion is an atom or group of atoms that normally are electrically neutral and achieve their status as an ion by loss (or addition) of an electron. ... General Name, Symbol, Number gold, Au, 79 Chemical series transition metals Group, Period, Block 11, 6, d Appearance metallic yellow Atomic mass 196. ...

Fundamental-constant approaches

In a similar manner that the metre was redefined to fix the speed of light to an exact value of 299792458 m/s, there are proposals to redefine the kilogram in such a way to fix other physical constants of nature to exact values. The metre, or meter (US), is a measure of length. ... 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. In metric units, c is exactly 299,792,458 metres per second (1,079,252,848. ... In science, a physical constant is a physical quantity whose numerical value does not change. ...

• 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 (299792458²/66260693×10⁴³) 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. ... A multimeter can be used to measure current The ampere (symbol: A) is the SI base unit of electric 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 (symbol: J) is the SI unit of energy, which is defined as the potential to do work. ... Look up second in Wiktionary, the free dictionary. ... Avogadros number (NA) is a large number used in chemistry, formally defined as the number of carbon-12 atoms in 0. ... The mole and its simple conversions into different units of measurements. ... 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. ... A multimeter can be used to measure current The ampere (symbol: A) is the SI base unit of electric current. ...

CIPM RECOMMENDATION 1 (CI-2005)

CIPM RECOMMENDATION 1 (CI-2005) ^[2]: Preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole in terms of fundamental constants The International Committee for Weights and Measures is the English name of the Comité international des poids et mesures (CIPM, sometimes written in English Comité International des Poids et Mesures). ... A multimeter can be used to measure current The ampere (symbol: A) is the SI base unit of electric current. ... The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero—the lowest possible temperature where nothing could be colder and no heat energy remains in a substance—is defined as zero kelvin (0 K). ... The mole and its simple conversions into different units of measurements. ...

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 9.80665 newtons (the SI unit of force). Note that the factor of 980.765 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.) 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. ... Earth (IPA: , often referred to as the Earth, Terra, or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... The newton (symbol: N) is the SI unit of force. ... For other uses, see g force. ...

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.
  • The coefficient is close to the reciprocal of Avogadro's number: 1 unified atomic mass unit = 1.66054 yg
  • Although the unified atomic mass unit is often convenient as a unit, one may sometimes want to use yoctograms to relate easily to other SI values.
  • Mass of a free electron: 0.00091 yg
  • Mass of a free proton : 1.6726 yg
  • Mass of a free neutron: 1.6749 yg

Cornell redirects here. ... NEMS or nanoelectromechanical systems are similar to MEMS but smaller. ... The cantilevered beam (green) projects out into space from its supports (blue). ... In physics a nucleon is a collective name for the two baryons: the neutron and the proton. ... Properties For other articles with similar names, see Atom (disambiguation). ... In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ... Avogadros number, also called Avogadros constant (NA) is a large constant used in chemistry and physics. ... 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. ... The electron is a fundamental subatomic particle that carries an electric charge. ... Properties [1][2] 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 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'. Micro is a SI prefix in the SI system of units denoting a factor of 10−6 (one millionth). ...

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 (symbol t), sometimes referred to as a metric tonne, is a measurement of weight. ... 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. ... Cover of brochure The International System of Units. ...

References

1. ^ http://www.bipm.org/en/si/history-si/name_kg.html
2. ^ http://www.bipm.fr/utils/common/pdf/CIPM2005.zip

External links

• National Physical Laboratory FAQ on kilogram definition, the need for a new definition, and some alternatives
• Conversion Calculator for Units of MASS (& Weight)
• More on the NIST Watt Balance
• Redefinition of the kilogram: a decision whose time has come
• More on the Avogadro project
• Conversion: Units of Weight
• 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