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  2. SI base unit - Wikipedia

    en.wikipedia.org/wiki/SI_base_unit

    mass "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 ...

  3. Metric system - Wikipedia

    en.wikipedia.org/wiki/Metric_system

    Length (m): The length of the equator is close to 40 000 000 m (more precisely 40 075 014.2 m). [23] In fact, the dimensions of our planet were used by the French Academy in the original definition of the metre; [24] most dining tabletops are about 0.75 metres high; [25] a very tall human (basketball forward) is about 2 metres tall. [26]

  4. List of physical constants - Wikipedia

    en.wikipedia.org/wiki/List_of_physical_constants

    The constants listed here are known values of physical constants expressed in SI units; that is, physical quantities that are generally believed to be universal in nature and thus are independent of the unit system in which they are measured. Many of these are redundant, in the sense that they obey a known relationship with other physical ...

  5. International System of Units - Wikipedia

    en.wikipedia.org/wiki/International_System_of_Units

    The definition of the kelvin measured with a relative uncertainty of the Boltzmann constant derived from two fundamentally different methods such as acoustic gas thermometry and dielectric constant gas thermometry be better than one part in 10 −6 and that these values be corroborated by other measurements.

  6. Mass - Wikipedia

    en.wikipedia.org/wiki/Mass

    If a first body of mass m A is placed at a distance r (center of mass to center of mass) from a second body of mass m B, each body is subject to an attractive force F g = Gm A m B /r 2, where G = 6.67 × 10 −11 N⋅kg −2 ⋅m 2 is the "universal gravitational constant". This is sometimes referred to as gravitational mass.

  7. Standard (metrology) - Wikipedia

    en.wikipedia.org/wiki/Standard_(metrology)

    In metrology (the science of measurement), a standard (or etalon) is an object, system, or experiment that bears a defined relationship to a unit of measurement of a physical quantity. [1] Standards are the fundamental reference for a system of weights and measures , against which all other measuring devices are compared.

  8. List of metric units - Wikipedia

    en.wikipedia.org/wiki/List_of_metric_units

    The metre (m) is the unit of length. The kilogram (kg) is the unit of mass. The ampere (A) is the unit of electric current. The kelvin (K) is the unit of thermodynamic temperature. The mole (mol) is the unit of amount of substance. The candela (cd) is the unit of luminous intensity. The SI also defines 22 derived units and associated symbols:

  9. Physical constant - Wikipedia

    en.wikipedia.org/wiki/Physical_constant

    A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that cannot be explained by a theory and therefore must be measured experimentally. It is distinct from a mathematical constant , which has a fixed numerical value, but does not directly involve any physical measurement.