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Kilogram
Description
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 meter and the second are defined in terms of c and Δν_{Cs}.
Abbreviation: kg
Reference: Bureau International des Poids et Mesures 2019 The International System of Units (SI), Gnaiger MitoFit Preprint Arch 2020.4
Quantity Symbol for quantity Q Symbol for dimension Name of abstract unit u_{Q} Symbol for unit u_{Q} [*] elementary entity ^{*,$} U_{X} U elementary unit x count ^{*,$} N_{X} = N·U_{X} X elementary unit x amount of substance ^{*,§} n_{X} = N_{X}·N_{A}^{-1} N mole mol charge ^{*,€} Q_{el} = z_{X}·e·N_{X} I·T coulomb C = A·s length l L meter m mass m M kilogram kg time t T second s electric current I I ampere A thermodynamic temperature T Θ kelvin K luminous intensity I_{v} J candela cd
- [*] SI units, except for the canonical 'elementary unit' [x]. The following footnotes are canonical comments.
- ^{*} For the elementary quantities N_{X}, n_{X}, and Q_{el}, the entity-type X of the elementary entity U_{X} has to be specified in the text and indicated by a subscript: n_{O2}; N_{ce}; Q_{el}.
- ^{$} Count N_{X} equals the number of elementary entities U_{X}. In the SI, the quantity 'count' is explicitly considered as an exception: "Each of the seven base quantities used in the SI is regarded as having its own dimension. .. All other quantities, with the exception of counts, are derived quantities" (Bureau International des Poids et Mesures 2019 The International System of Units (SI)). An elementary entity U_{X} is a material unit, it is not a count (U_{X} is not a number of U_{X}). N_{X} has the dimension X of a count and U_{X} has the dimension U of an elementary entity; both quantities have the same abstract unit, the 'elementary unit' [x].
- ^{§} Amount n_{X} is an elementary quantity, converting the elementary unit [x] into the SI base unit mole [mol] using the Avogadro constant N_{A}.
- ^{€} Charge is a derived SI quantity. Charge is an elementary quantity, converting the elementary unit [x] into coulombs [C] using the elementary charge e, or converting moles [mol] into coulombs [C] using the Faraday constant F. z_{X} is the charge number per elementary entity U_{X}, which is a constant for any defined elementary entity U_{X}. Q_{el} = z_{X}·F·n_{X}
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- Entity, count, and number, and SI base quantities / SI base units
Quantity name Symbol Unit name Symbol Comment elementary U_{X} elementary unit [x] U_{X}, U_{B}; [x] not in SI count N_{X} elementary unit [x] N_{X}, N_{B}; [x] not in SI number N - dimensionless = N_{X}·U_{X}^{-1} amount of substance n_{B} mole [mol] n_{X}, n_{B} electric current I ampere [A] A = C·s^{-1} time t second [s] length l meter [m] SI: metre mass m kilogram [kg] thermodynamic temperature T kelvin [K] luminous intensity I_{V} candela [cd]
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