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an attribute that, in a qualitative respect, is a universal characteristic of many physical objects—that is, of physical systems, states of such systems, and processes occurring in such systems—but, in a quantitative respect, is independent for every object. Length, mass, and electrical resistance are examples of physical quantities that characterize the properties of objects; pressure, temperature, and magnetic induction are some of the physical quantities that characterize the state of a system; velocity and power are two of the physical quantities that characterize processes.
Various measurement methods are used for the quantitative evaluation of a physical quantity, that is, for determining the value of a physical quantity as a certain number of the units adopted for the quantity. Letter symbols are assigned to the physical quantities used in the equations of physics that express the relationships between the quantities in physical objects.
The term “physical quantity” is used not only in physics but also in other sciences, such as chemistry and biology, when a quantitative comparison of the properties of objects under study is performed by physical methods (seeMETROLOGY and DIMENSIONS).