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The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science and technology. [citation needed] The names and symbols of SI base units are written in lowercase, except the symbols of those named after a person, which are written with an initial capital letter.
The SI comprises a coherent system of units of measurement starting with seven base units, which are the second (symbol s, the unit of time ), metre (m, length ), kilogram (kg, mass ), ampere (A, electric current ), kelvin (K, thermodynamic temperature ), mole (mol, amount of substance ), and candela (cd, luminous intensity ).
2019 definition: 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 ΔνCs.
The metric system is a decimal -based system of measurement. The current international standard for the metric system is the International System of Units (Système international d'unités or SI), in which all units can be expressed in terms of seven base units: the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and ...
International System of Units. In the International System of Units (SI), there are seven base units: kilogram, metre, candela, second, ampere, kelvin, and mole . Several derived units have been defined, many with special names and symbols. In 2019 the seven SI base units were redefined in terms of seven defining constants.
There are seven ISQ base quantities. The symbols for them, as for other quantities, are written in italics. [1] The dimension of a physical quantity does not include magnitude or units. The conventional symbolic representation of the dimension of a base quantity is a single upper-case letter in roman (upright) sans-serif [c] type.
The kilogram (also kilogramme[ 1]) is the base unit of mass in the International System of Units (SI), having the unit symbol kg[ 1]. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. [ 2] It means 'one thousand grams '.
Unit system Domain Derivation Unit name Unit symbol Dimension symbol Quantity name Definition In SI base units In other SI units SI: Physics: Basic: second [n 1] s: T: time: The duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. s: SI ...