Kilogram

History

The Gram was introduced during the unification of the regional measures decided during the French revolution by the law of the 18 germinal year III (April 7th, 1795), Article VI ds Bulletin of the laws, 1st series, No 135. It is one of the elements of the triad " length-weight-volume" : déci Meter - (kilo) gram Liter of this unification.

The gram was initially defined as the mass of one cubic centimeter Eau to the Température of 4°C, which corresponds to a maximum of Density.

June 22nd, 1799, a standard in Platinum of one kilogram (original name, the serious ), is the mass of one decimetre cubic of water, was deposited (as well as a standard of the meter) with the Files of France, thanks to preceding work of various scientists, in particular Lavoisier (guillotine in 1794).

This standard became by definition the representation of the kilogram (thousand grams) by the law of December 10th, 1799.

It is only in 1875, however, that the unit of mass was redefined like “kilogram”, which became thus the only unit of IF including a multiplying prefix.

A new platino-iridium standard of mass practically identical to the Kilogram of the Files was to be carried out since 1875, but casting was rejected because the proportion of Iridium, 11,1%, was apart from the 9 - 11% specified. It is only into 1889 that the Kilogram of the Files was replaced by the international prototype of the kilogram, preserved since this date at the Pavillon of Breteuil.

Definitions

Current definition

The kilogram is currently defined as the mass of a Cylindre in iridic Platine (90% Platine and 10% Iridium) of 39 mm of Diamètre and 39 mm top declared unit IF of Masse since 1889 by the International office of the weights and measures (BIPM).

This measuring unit is the last of the IF to being defined by means of a material standard manufactured by the man, i.e. a Artifact. This one is preserved under three sealed cloches from which it is extracted only to carry out calibrations (operation which took place only three times since its creation).

In spite of these precautions, the mass of the prototype already varied few micrograms.

According to James Clerk Maxwell (1831 - 1879):

Even though the kilogram cylinder is housed in has special vault under controlled conditions At the BIPM, its farmhouse edge drift transistor slightly over the years and it is subject to exchanges in farmhouse because off contamination, material loss from surface cleaning, but other effects. With property off natural is, by definition, always the same and edge in theory Be measured anywhere, whereas the kilogram is accessible only At BIPM and could Be damaged gold destroyed .

Proposals for future definitions

Since the IF defined the values of the constants of Josephson (CIPM (1988) Recommendation 1, statement 56; 19) and von Klitzing (CIPM (1988), Recommendation 2, statement 56; 20), it is possible to combine these values (K_J ≡ 4,835 979 X 10⁺¹⁴ Hz/V and R_K ≡ 2,581 280 7 X 10⁺⁴ Ω) with the definition of the amp in order to define the kilogram as this:

The kilogram is the mass which would undergo a Accélération precisely 2 X 10^-7 m S ² when it is subjected to the force per meter between two parallel drivers, rectilinear, infinite length, of negligible circular section, placed at a distance of one meter one of the other in the Vide, and through which passes a constant Electric current of exactly 6,241 509 629.152 65 X 10¹⁸ elementary charges a second.

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

It is probable that, with the next convention of the BIPM, in October 2007, in Paris, the gram will be defined like derived unit, and the value of the Constante of Planck (H) will be fixed with: 6,626 069 01 X 10^-34 J.s

That will depend on the precision improved of the Balance of Watt and its agreement with the precision improved of measurement of the mass of a mole of very pure Silicium, which depends on the precision of the meter “x-rays”, which will be able to improve via work of the physicist Theodor W. Hänsch.

Another approach would be to base itself on the weight of a definite number of atoms. This calculation is not simple and could be simplified in the case of a pure crystal thus making it possible to know the number of atoms per unit of volume. Attempts in this direction were made thanks to the manufacture of a sphere (relatively easy to machine) Silicium, by taking account of the proportion of the various isotopes. The precision thus obtained is of 3 out of 10 million. A silicon 28 ball could reach an accuracy of 2 per 100 million by 2010.

Multiples, submultiples and other units

As the basic unit “kilogram” comprises already a prefix, prefixes IF are added by exception to the word “gram” or its symbol G, although the Gram is only one submultiple of the kilogram (1 G = 10^-3 kg).

For example:

1 mégagramme (Mg) = 1 000 kg;
1 milligram (Mg) = 0,000 001 kg.

In the old books, only the multiples and submultiples of the kilogram are used:

myriagramme (mag): 1 mag = 10 kg;
myriogramme (mog): 1 mog = 0,000 000 1 kg (= 100 µg).

In practice, only the multiples of the kilogram are used:

kilogram (kg): 1 kg = 1 kg;
mégagramme (Mg) : 1 Mg = 1 000 kg;
gigagramme (Gg): 1 Gg = 1 000 000 kg = 10⁶ kg;
téragramme (Tg): 1 Tg = 1 000 000 000 kg = 10⁹ kg;
pétagramme (Pg): 1 Pg = 10¹² kg;
exagramme (Eg): 1 Eg = 10¹⁵ kg;
zettagramme (Zg): 1 Zg = 10¹⁸ kg;
yottagramme (Yg): 1 Yg = 10²¹ kg.

In practice, only the submultiples of the kilogram are used (the units in italics are not very used):

kilogram (kg): 1 kg = 1 kg;
hectogram (hg) 1 Hg = 0,1 kg;
decagram (dag) : 1 dag = 0,01 kg;
gram (G): 1 G = 0,001 kg;
decigram (dg) : 1 dg = 0,000 1 kg;
centigram (cg) 1 cg = 0,000 01 kg;
milligram (mg): 1 Mg = 0,000 001 kg = 10^-6 kg;
microgram (µg): 1 µg = 0,000 000 001 kg = 10^-9 kg;
nanogramme (ng): 1 ng = 10^-12 kg;
picogramme (pg): 1 pg = 10^-15 kg;
femtogramme (fg): 1 fg = 10^-18 kg;
attogramme (ag): 1 Ag = 10^-21 kg;
zeptogramme (zg): 1 zg = 10^-24 kg;
yoctogramme (yg): 1 yg = 10^-27 kg.

See also: Prefix of the international system

One also usually uses names of old units, but round to “exact” values

the delivers: 1 lb = 0,5 kg, 1 kg = 2 lb;
the serious : 1 G = 1 kg, 1 kg = 1 G;
the quintal: 1 Q = 100 kg, 1 kg = 0,01 Q;
the ton: 1 T = 1 000 kg, 1 kg = 0,001 T.

The Anglo-Saxon Unités are rather largely used all over the world. One usually uses the units of the system avoirdupois (front), and, in certain specific cases, the units of the system troy (T): Drug S and noble metals.

Système avoirdupois

delivers (front lb): 1 front lb = 0,453 592 37,1 kg = 2,204 622 6 lb front
ounce (front OZ): 1 front OZ = 0,028 349.523.125 kg, 1 kg = 35,273 961.950 front OZ

Système troy

delivers (lb T): 1 lb T = 0,373 241.721 6 kg, 1 kg = 2,679 228.881 lb T
ounce (OZ T): 1 front OZ = 0,031 103.476 8 kg, 1 kg = 32,150 747 OZ T

The table below indicates the correspondences between the units; the values in italics indicate the crossings between the Anglo-Saxon systems.

See too

kilogram|kilogram

international System of Constant units
Balance of Watt
fundamental

External bonds

the name “kilogram”: does an imagination of the history
Combien weigh exactly a liter of fresh water in kilogram? Contains information on the genesis of the word kilogram.

Random links: