The international system of units (SI), physical quantities, and their dimensions

Abstract

In this chapter, we introduce the International System of Units (SIInternationalSystem of Units (SI)unitsThe International System ofphysical quantitybasephysical quantityderivednon-SI unit) on the basis of the SI brochure Le Système International d'unités (SI) [2.1], supplemented by [2.2]. We give a short review of how the SI was worked out and who is responsible for the further development of the system. Following the above-mentioned publications, we explain the concepts of base physical quantities and derived physical quantities on which the SI is founded, and present a detailed description of the SI base units and of a large selection of SI derived units. The base units comprise the meter, the kilogram, the second, the ampere, the kelvin, the mole, and the candela. For derived units, we describe how they are defined by equations in terms of the base physical quantities as products or ratios of the units for the base quantities. We also discuss a number of non-SI units which still are in use, especially in some specialized fields. A table (Table 2.17) presenting the values of various energy equivalents closes the chapter.