## Units and dimensions::Physical quantity

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Units and dimensions Units

Most physical quantities include a unit, but not all – some are dimensionless. Neither the name of a physical quantity, nor the symbol used to denote it, implies a particular choice of unit, though SI units are usually preferred and assumed today due to their ease of use and all-round applicability. For example, a quantity of mass might be represented by the symbol m, and could be expressed in the units kilograms (kg), pounds (lb), or daltons (Da).

Dimensions

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The notion of physical dimension of a physical quantity was introduced by Joseph Fourier in 1822.<ref>Fourier, Joseph. Théorie analytique de la chaleur, Firmin Didot, Paris, 1822. (In this book, Fourier introduces the concept of physical dimensions for the physical quantities.)</ref> By convention, physical quantities are organized in a dimensional system built upon base quantities, each of which is regarded as having its own dimension.

Physical quantity sections
Intro  Symbols, nomenclature  Units and dimensions  Base quantities  General derived quantities  See also  References  Sources

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