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EXAMPLE If a certain value of Power is written as : P = 42.3 x 103 W = 42.3 kW, then : ''P'' represents the physical quantity of power : ''42.3 x 103'' is the numerical value : ''k'' is the SI Prefix '' Kilo '', representing 103 : ''W'' is the symbol for the Unit of power, the Watt SYMBOLS FOR PHYSICAL QUANTITIES Usually, the Symbol s for physical quantities are chosen to be a single lower case or capital letter of the Latin or Greek Alphabet . Often, the symbols are modified by Subscript s and Superscript s, in order to specify what they pertain to - for instance ''Ep'' is usually used to denote Potential Energy and ''cp'' Heat Capacity at constant Pressure . EXTENSIVE AND INTENSIVE QUANTITIES A quantity is called:
Some extensive physical quantities may be prefixed in order to further qualify their meaning:
There are also physical quantities that can be classified as neither extensive nor intensive, for example Angular Momentum , Area , Force , Length , and Time . PHYSICAL QUANTITIES AS ''COORDINATES'' OVER SPACES OF PHYSICAL ''QUALITIES'' The meaning of the term physical ''quantity'' is generally well understood (everyone understands what it is meant by ''the frequency of a periodic phenomenon'', or ''the resistance of an electric wire''). It is clear that behind a set of quantities like temperature − inverse temperature − logarithmic temperature, there is a qualitative notion: the ''cold−hot'' quality. Over this one-dimensional quality space, we may choose different ''coordinates'': the temperature, the inverse temperature, etc. Other quality spaces are multidimensional. For instance, to represent the properties of an ideal elastic medium we need 21 coefficients, that can be the 21 components of the elastic stiffness tensor , or the 21 components of the elastic compliance tensor (inverse of the stiffness tensor), or the proper elements (six eigenvalues and 15 angles) of any of the two tensors, etc. Again, we are selecting coordinates over a 21-dimensional quality space. On this space, each point represents a particular elastic medium. It is always possible to define the distance between two points of any quality space, and this distance is —inside a given theoretical context— uniquely defined. For instance, two periodic phenomena can be characterized by their periods, and , or by their frequencies, and |
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