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# SI base unit

The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units can be derived. 

54 relations: Absolute zero, Amount of substance, Ampere, André-Marie Ampère, Avogadro constant, Boltzmann constant, Candela, Candlepower, Celsius, Day, Dimensional analysis, Earth, Electric current, Elementary charge, General Conference on Weights and Measures, International Committee for Weights and Measures, International System of Quantities, International System of Units, Iridium, Joint Committee for Guides in Metrology, Kelvin, Kilogram, Length, Litre, Luminous intensity, Mass, Metre, Metre Convention, Metric prefix, Metrology, Molar mass constant, Mole (unit), Molecular mass, Newton (unit), Non-SI units mentioned in the SI, Paris, Physical constant, Planck constant, Platinum, Proposed redefinition of SI base units, Relative atomic mass, Second, SI derived unit, Silver nitrate, Speed of light, Steradian, Temperature, Thermodynamic temperature, Time, Triple point, ... Expand index (4 more) »

## Absolute zero

Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as 0.

## Amount of substance

Amount of substance (symbol for the quantity is 'n') is a standard-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles.

## Ampere

The ampere (symbol: A), often shortened to "amp",SI supports only the use of symbols and deprecates the use of abbreviations for units.

## André-Marie Ampère

André-Marie Ampère (20 January 177510 June 1836) was a French physicist and mathematician who was one of the founders of the science of classical electromagnetism, which he referred to as "electrodynamics".

In chemistry and physics, the Avogadro constant (named after scientist Amedeo Avogadro) is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole.

## Boltzmann constant

The Boltzmann constant, which is named after Ludwig Boltzmann, is a physical constant relating the average kinetic energy of particles in a gas with the temperature of the gas.

## Candela

The candela (or; symbol: cd) is the base unit of luminous intensity in the International System of Units (SI); that is, luminous power per unit solid angle emitted by a point light source in a particular direction.

## Candlepower

Candlepower (abbreviated as cp or CP) is an obsolete unit expressing luminous intensity, equal to 0.981 candelas.

## Celsius

The Celsius scale, previously known as the centigrade scale, is a temperature scale used by the International System of Units (SI).

## Day

A day, a unit of time, is approximately the period of time during which the Earth completes one rotation with respect to the Sun (solar day).

## Dimensional analysis

In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric charge) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms) and tracking these dimensions as calculations or comparisons are performed.

## Earth

Earth is the third planet from the Sun and the only astronomical object known to harbor life.

## Electric current

An electric current is a flow of electric charge.

## Elementary charge

The elementary charge, usually denoted as or sometimes, is the electric charge carried by a single proton, or equivalently, the magnitude of the electric charge carried by a single electron, which has charge.

## General Conference on Weights and Measures

The General Conference on Weights and Measures (Conférence générale des poids et mesures – CGPM) is the supreme authority of the International Bureau of Weights and Measures (Bureau international des poids et mesures – BIPM), the inter-governmental organization established in 1875 under the terms of the Metre Convention (Convention du Mètre) through which Member States act together on matters related to measurement science and measurement standards.

## International Committee for Weights and Measures

The International Committee for Weights and Measures (abbreviated CIPM from the French Comité international des poids et mesures) consists of eighteen persons, each of a different nationality, from Member States of the Metre Convention (Convention du Mètre) appointed by the General Conference on Weights and Measures (CGPM) whose principal task is to promote worldwide uniformity in units of measurement by taking direct action or by submitting proposals to the CGPM.

## International System of Quantities

The International System of Quantities (ISQ) is a system based on seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.

## International System of Units

The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement.

## Iridium

Iridium is a chemical element with symbol Ir and atomic number 77.

## Joint Committee for Guides in Metrology

The Joint Committee for Guides in Metrology (JCGM), is an organization in Sèvres that prepared the "Guide to the expression of uncertainty in measurement" (GUM) and the "International vocabulary of metrology – basic and general concepts and associated terms" (VIM).

## Kelvin

The Kelvin scale is an absolute thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics.

## Kilogram

The kilogram or kilogramme (symbol: kg) is the base unit of mass in the International System of Units (SI), and is defined as being equal to the mass of the International Prototype of the Kilogram (IPK, also known as "Le Grand K" or "Big K"), a cylinder of platinum-iridium alloy stored by the International Bureau of Weights and Measures at Saint-Cloud, France.

## Length

In geometric measurements, length is the most extended dimension of an object.

## Litre

The litre (SI spelling) or liter (American spelling) (symbols L or l, sometimes abbreviated ltr) is an SI accepted metric system unit of volume equal to 1 cubic decimetre (dm3), 1,000 cubic centimetres (cm3) or 1/1,000 cubic metre. A cubic decimetre (or litre) occupies a volume of 10 cm&times;10 cm&times;10 cm (see figure) and is thus equal to one-thousandth of a cubic metre. The original French metric system used the litre as a base unit. The word litre is derived from an older French unit, the litron, whose name came from Greek — where it was a unit of weight, not volume — via Latin, and which equalled approximately 0.831 litres. The litre was also used in several subsequent versions of the metric system and is accepted for use with the SI,, p. 124. ("Days" and "hours" are examples of other non-SI units that SI accepts.) although not an SI unit — the SI unit of volume is the cubic metre (m3). The spelling used by the International Bureau of Weights and Measures is "litre", a spelling which is shared by almost all English-speaking countries. The spelling "liter" is predominantly used in American English. One litre of liquid water has a mass of almost exactly one kilogram, because the kilogram was originally defined in 1795 as the mass of one cubic decimetre of water at the temperature of melting ice. Subsequent redefinitions of the metre and kilogram mean that this relationship is no longer exact.

## Luminous intensity

In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye.

## Mass

Mass is both a property of a physical body and a measure of its resistance to acceleration (a change in its state of motion) when a net force is applied.

## Metre

The metre (British spelling and BIPM spelling) or meter (American spelling) (from the French unit mètre, from the Greek noun μέτρον, "measure") is the base unit of length in some metric systems, including the International System of Units (SI).

## Metre Convention

The Metre Convention (Convention du Mètre), also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Brazil, Denmark, France, Germany, Italy, Peru, Portugal, Russia, Spain, Sweden and Norway, Switzerland, Turkey, United States of America, and Venezuela).

## Metric prefix

A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or fraction of the unit.

## Metrology

Metrology is the science of measurement.

## Molar mass constant

The molar mass constant, symbol Mu, is a physical constant which relates relative atomic mass and molar mass.

## Mole (unit)

The mole, symbol mol, is the SI unit of amount of substance.

## Molecular mass

Relative Molecular mass or molecular weight is the mass of a molecule.

## Newton (unit)

The newton (symbol: N) is the International System of Units (SI) derived unit of force.

## Non-SI units mentioned in the SI

This is a list of units that are not defined as part of the International System of Units (SI), but are otherwise mentioned in the SI, because either the General Conference on Weights and Measures (CGPM) accepts their use as being multiples or submultiples of SI-units, they have important contemporary application worldwide, or are otherwise commonly encountered worldwide.

## Paris

Paris is the capital and most populous city of France, with an area of and a population of 2,206,488.

## Physical constant

A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time.

## Planck constant

The Planck constant (denoted, also called Planck's constant) is a physical constant that is the quantum of action, central in quantum mechanics.

## Platinum

Platinum is a chemical element with symbol Pt and atomic number 78.

## Proposed redefinition of SI base units

The International Committee for Weights and Measures (CIPM) has proposed revised definitions of the SI base units, for consideration at the 26th General Conference on Weights and Measures (CGPM).

## Relative atomic mass

Relative atomic mass (symbol: A) or atomic weight is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a given sample to one unified atomic mass unit.

## Second

The second is the SI base unit of time, commonly understood and historically defined as 1/86,400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

## SI derived unit

SI derived units are units of measurement derived from the seven base units specified by the International System of Units (SI).

## Silver nitrate

Silver nitrate is an inorganic compound with chemical formula.

## Speed of light

The speed of light in vacuum, commonly denoted, is a universal physical constant important in many areas of physics.

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## Temperature

Temperature is a physical quantity expressing hot and cold.

## Thermodynamic temperature

Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics.

## Time

Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future.

## Triple point

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

## Vacuum permeability

The physical constant μ0, (pronounced "mu naught" or "mu zero"), commonly called the vacuum permeability, permeability of free space, permeability of vacuum, or magnetic constant, is an ideal, (baseline) physical constant, which is the value of magnetic permeability in a classical vacuum.

## Vacuum permittivity

The physical constant (pronounced as "epsilon nought"), commonly called the vacuum permittivity, permittivity of free space or electric constant, is an ideal, (baseline) physical constant, which is the value of the absolute dielectric permittivity of classical vacuum.

## Water

Water is a transparent, tasteless, odorless, and nearly colorless chemical substance that is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms.

## William Thomson, 1st Baron Kelvin

William Thomson, 1st Baron Kelvin, (26 June 1824 – 17 December 1907) was a Scots-Irish mathematical physicist and engineer who was born in Belfast in 1824.

## References

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