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The kilogram ( symbol kg) is the unit of mass in the International System of Units (SI) History

The program was introduced during the unification of regional measures decided during the French Revolution by the law of 18 Germinal Year III ( 7 April 1795 ), art. VI ds Bulletin of Acts, 1st Series, No. 135. This is one element of the triad "length-mass-volume": Decision meter - (kilo) gram- liter of this unification.

Gram was originally defined as the mass of a cubic centimeter of water at the temperature of 4 C, which corresponds to a maximum density.

On 22 June 1799 , in a standard deck of a kilogram (original name, the grave ), or the mass of a cubic foot of water, was tabled (and a standard of a meter) in the Archives of France, thanks the previous work of various scholars, particularly Lavoisier (guillotined in 1794 ).

This became the standard by defining the representation of a kilogram (one thousand grams) by the law of 10 December 1799.

It was not until 1875 , however, that the mass unit was redefined as "kilogram", which thus became the only unit of the SI prefix multiplier including a .

A new standard platinum-iridium mass virtually identical to the kilogram of the Archives was to be achieved soon in 1875 , but the casting was rejected because the proportion of iridium , 11.1% were outside of 9 to 11% specified. It was not until 1889 that the kilogram of the Archives was replaced by the International Prototype Kilogram, kept since that date to lodge Breteuil , sometimes called the large K.

Definitions

Current definition

Artist's impression of the standard kilogram platinum-iridium.

The kilogram is now defined as the mass of the prototype at the Pavillon de Breteuil, a cylinder of platinum -iridium (90% platinum and 10% iridium ) to 39.17 mm in diameter and 39.17 mm high reported unit SI of mass since 1889 by the International Bureau of Weights and Measures (BIPM)

In fact, we only know that the masses of copies have increased over the prototype. In addition, it is likely that the mass of the prototype has also increased, but less than copies. It is also possible that the masses and copies of the prototype and have decreased but the mass of the prototype has declined more rapidly than the masses of copies. Proposed future definitions
Sphere of one kilogram of monocrystalline silicon Avogadro Project at the Australian Centre for Precision Optics .

To ensure the long-term stability of the international system of units, the 21st General Conference of Weights and Measures in 2000 , recommended that "national laboratories continue their efforts to refine experiments that link the unit of mass to fundamental or atomic constants and could in future serve as a basis for a new definition of the kilogram. "

Since the SI defined the constants of the Josephson (CIPM ( 1988 ) Recommendation 1, PV 56, 19) and von Klitzing (CIPM ( 1988 ), Recommendation 2, PV 56, 20), it is possible to combine these values (K J4.835 979 10 14Hz / V and R K2.581 280 7 10 4 ) with the definition of the amp to define the kilogram as follows:

"The kilogram is the mass that suffer acceleration of precisely 2 10 -7 m / s 2 when subjected to the force per meter between two straight parallel conductors of infinite length, of negligible circular cross section, placed at a distance of one meter apart in vacuum , and through which passes an electric current constant exactly 6.24150962915265 10 18elementary charges per second. "

These units are also used in physics relativistic as units of energy (via the relationship E = mc 2 ).

It is possible that at the next convention of the BIPM, the gram is defined as a derived unit, and the value of the Planck constant (h) is fixed at: 6.62606901 10 -34 J s.

This will depend on the improved accuracy of the watt balance and its correlation with the improved accuracy of measuring the mass of one mole of silicon very pure, which depends on the accuracy of the meter "X-rays, which can s improve through the work of physicist Theodor W. Hnsch , .

Another approach would be based on the weight of a defined number of atoms. This statement is not simple and could be simplified in the case of a pure crystal thus know the number of atoms per unit volume. Attempts in this direction have been made through the manufacture of a sphere (relatively easy to machine) of silicon , taking into account the proportion of different isotopes. The accuracy thus obtained is 3 out of 10 million. A silicon ball 28 could achieve an accuracy of 2 to 100 million by 2010 .

Multiple, multiple sub-units

As the base unit "kilogram" already has a prefix, the SI prefixes are added as an exception to the word "gram" or its symbol g, while the program is a submultiple of a kilogram (1 g = 10 -3 kg).

For example:

  • 1 megagram ( Mg ) = 1000 kg;
  • 1 milligram ( mg ) = 0.000 001 kg.

In older books, only the multiples and sub-multiples of kilogram are used:

  • myriagramme (mag): 1 mag = 10 kg;
  • myriogramme (mog): 1 mog = 0.000 000 (1 kg = 100 mcg).

In practice, only multiples of the kilogram are used:

  • kilogram (kg): 1 kg = 1 kg;
  • megagram (Mg): 1 Mg = 1 000 kg;
  • gigagram (Gg): 1 Gg = 1,000,000 kg = 10 6 kg;
  • teragram (Tg): 1 Tg = 1 billion kg = 10 9 kg;
  • petagrams (Pg): 1 Pg = 10 12 kg;
  • exagramme (Eg): 1 Eg = 10 15 kg;
  • zettagramme (Zg) Zg 1 = 10 18 kg;
  • yottagramme ( Yg ): 1 Yg = 10 21 kg.
Correspondence between multiple kilogram in the international system of units
kg Mg Gg Tg Pg Eg Zg Yg
kg 1 0,001 10 -6 10 -9 10 -12 10 -15 10 -18 10 -21
Mg 1 000 1 0,001 10 -6 10 -9 10 -12 10 -15 10 -18
Gg June 10 1 000 1 0,001 10 -6 10 -9 10 -12 10 -15
Tg September 10 June 10 1 000 1 0,001 10 -6 10 -9 10 -12
Pg October 12 September 10 June 10 1 000 1 0,001 10 -6 10 -9
Eg October 15 October 12 September 10 June 10 1 000 1 0,001 10 -6
Zg October 18 October 15 October 12 September 10 June 10 1 000 1 0,001
Yg October 21 October 18 October 15 October 12 September 10 June 10 1 000 1

In practice, only sub-multiples of kilogram are used (units in italics are little used):

  • kilogram (kg): 1 kg = 1 kg;
  • HG (hg) 1 hg = 0.1 kg;
  • dcagramme (dag): 1 dag = 0.01 kg;
  • gram (g) 1 g = 0.001 kg;
  • decigramme (dg): 1 dg = 0, 0001 kg;
  • centigram (cg) 1 cg = 0, 00 001 kg;
  • milligram (mg): 1 mg = 0, 000 001 kg = 10 -6 kg;
  • microgram (mcg): 1 g = 0, 000 000 001 kg = 10 -9 kg;
  • nanogram (ng): 1 ng = 10 -12 kg;
  • picogram (pg): 1 pg = 10 -15 kg;
  • femtogram (fg): 1 fg = 10 -18 kg;
  • attogramme (ag) 1 ag = 10 -21 kg;
  • zeptogramme (zg): 1 zg = 10 -24 kg;
  • yoctogramme ( ug ): 1 ug = 10 -27 kg.
Correspondence between sub-multiples of the kilogram in the international system of units
yg zg ag fg pg ng g mg cg dg g dag hg kg
yg 1 0,001 10 -6 10 -9 10 -12 10 -15 10 -18 10 -21 10 -22 10 -23 10 -24 10 -25 10 -26 10 -27
zg 1 000 1 0,001 10 -6 10 -9 10 -12 10 -15 10 -18 10 -19 10 -20 10 -21 10 -22 10 -23 10 -24
ag June 10 1 000 1 0,001 10 -6 10 -9 10 -12 10 -15 10 -16 10 -17 10 -18 10 -19 10 -20 10 -21
fg September 10 June 10 1 000 1 0,001 10 -6 10 -9 10 -12 10 -13 10 -14 10 -15 10 -16 10 -17 10 -18
pg October 12 September 10 June 10 1 000 1 0,001 10 -6 10 -9 10 -10 10 -11 10 -12 10 -13 10 -14 10 -15
ng October 15 October 12 September 10 June 10 1 000 1 0,001 10 -6 10 -7 10 -8 10 -9 10 -10 10 -11 10 -12
g October 18 October 15 October 12 September 10 June 10 1 000 1 0,001 10 -4 10 -5 10 -6 10 -7 10 -8 10 -9
mg October 21 October 18 October 15 October 12 September 10 June 10 1 000 1 0,1 0,01 0,001 10 -4 10 -5 10 -6
cg October 22 October 19 October 16 October 13 October 10 July 10 April 10 10 1 0,1 0,01 0,001 10 -4 10 -5
dg October 23 October 20 October 17 October 14 October 11 August 10 May 10 100 10 1 0,1 0,01 0,001 10 -4
g October 24 October 21 October 18 October 15 October 12 September 10 June 10 1 000 100 10 1 0,1 0,01 0,001
dag October 25 October 22 October 19 October 16 October 13 October 10 July 10 April 10 1 000 100 10 1 0,1 0,01
hg October 26 October 23 October 20 October 17 October 14 October 11 August 10 May 10 April 10 1 000 100 10 1 0,1
kg October 27 October 24 October 21 October 18 October 15 October 12 September 10 June 10 May 10 April 10 1 000 100 10 1

It also uses the names of old units, but rounded to values "exact"

  • the book : 1 lbs ~ 0.5 kg, 1 kg ~ 2 lbs;
  • the grave : 1 G = 1 kg 1 kg = 1 G;
  • the hundredweight Metric: 1 q = 100 kg 1 kg = 0.01 q;

Not to be confused with

the quintal former French: 48.951 kg or about

the hundredweight short of North America: 45.359 kg or about

the quintal along the imperial English: about 50.802 kg.

  • the ton : 1 ton = 1000 kg 1 kg = 0.001 t.
Correspondence between the kilogram and the old units "mtrises"
book kilogram kgs ton
book 1 0,453 592 37 0,005 5 10 -4
serious 2 1 0,01 0,001
kilogram 2 1 0,01 0,001
kgs 200 100 1 0,1
ton 2 000 1 000 10 1

The English units are fairly widely used around the world. Commonly used system of units avoirdupois (av), and in some specific cases, the units of the system troy (t): drugs and precious metals.

  • Avoirdupois system
    • pound (lb. av): 1 lb av = 0.453 592 37 kg 1 kg = 2.204 622 6 lb av
    • ounces (oz av): 1 oz av = 0.028 349 523 125 kg 1 kg = 35.273 961 950 oz av
  • Troy system
    • pound (lb t): t = 0.373 lb 1 241 721 6 kg, 1 kg = 2.679 228 881 lb t
    • ounce (oz t): 1 oz t = 0.031 103 476 8 kg, 1 kg = 32.150 747 oz t

The table below shows the connections between units, and values in italics indicate interbreeding between the Anglo-Saxon.

Correspondence with English units (rounded)
g oz av oz t lb t lb av kg
g 1 0,035 3 0,032 2 0,002 68 0,002 20 0,001
oz av 28,3 1 0,911 0,076 0 0.062 5 (1/ 16) 0,0283
oz t 31,1 1,097 1 0.083 3 (1/ 12) 0,068 6 0,031 1
lb t 373 13,2 12 1 0,823 0,373
lb av 454 16 14,6 1,22 1 0,454
kg 1 000 35,3 32,2 2,68 2,20 1

The carat is another unit of mass.

References


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