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In 1799, the platinum Kilogramme des Archives replaced it as the standard of mass. In 1889, a cylinder composed of platinum–iridium, the International Prototype of the Kilogram (IPK), became the standard of the unit of mass for the metric system and remained so for 130 years, before the current standard was adopted in 2019. [6]
The undecimogramme is a unit of mass equal to ten picograms (10 pg). The gamma (γ) is a unit of mass equal to one microgram (1 μg). The gravet is a unit of mass equal to one gram (1 g). The grave is a unit of mass equal to one kilogram (1 kg). The bar is a unit of mass equal to one megagram (1 Mg).
A derived unit is used for expressing any other quantity, and is a product of powers of base units. For example, in the modern metric system, length has the unit metre and time has the unit second, and speed has the derived unit metre per second. [5]: 15 Density, or mass per unit volume, has the unit kilogram per cubic metre. [5]: 434
The International System of Units, internationally known by the abbreviation SI (from French Système international d'unités), is the modern form of the metric system and the world's most widely used system of measurement.
Non-SI units accepted for use with SI units include: the tonne (t) (or "metric ton"), equal to 1000 kg; the electronvolt (eV), a unit of energy, used to express mass in units of eV/c 2 through mass–energy equivalence; the dalton (Da), equal to 1/12 of the mass of a free carbon-12 atom, approximately 1.66 × 10 −27 kg. [note 2]
The kilogram is the only standard unit to include an SI prefix (kilo-) as part of its name. The gram (10 −3 kg) is an SI derived unit of mass. However, the names of all SI mass units are based on gram, rather than on kilogram; thus 10 3 kg is a megagram (10 6 g), not a *kilokilogram.
"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 6.626 070 15 × 10 −34 when expressed in the unit J s, which is equal to kg m 2 s −1, where the metre and the second are defined in terms of c and ∆ν Cs." [1] The mass of one litre of water at the temperature ...
The Metre Convention was signed on 20 May 1875 and further formalised the metric system (a predecessor to the SI), quickly leading to the production of the IPK.The IPK is one of three cylinders made in London in 1879 by Johnson Matthey, which continued to manufacture nearly all of the national prototypes as needed until the new definition of the kilogram came into effect in 2019.