Physical Quantities and Units | Physical Quantity Definition

Physical Quantity Definition

A physical quantity is characterized by defining how it is measured or by expressing how it is computed from other measurements. For instance, distance and time are expressed by defining methods for evaluating them, while we express average speed by stating that it is computed as distance traveled divided up by time covered.

Four fundamental physical quantities (length, time, mass, and electric current) are utilized in order to express almost all physical quantities.

Physical quantities are expressed in terms of units, which are standard values. For instance, the length of a race (a physical quantity) can be defined in units of meters. Without standard units, it would be highly challenging to define and equate measured values in a purposeful way. 

There are two leading units systems practiced globally: SI units (i.e. metric system) and English units (i.e. imperial system). English units were historically used by the British Empire and are still extensively utilized in the United States. Almost every other country on the planet practices SI units. The acronym “SI” is inferred from the French word Système International.