Dimensional Analysis and Similarity in Fluid Mechanics

1Homogeneity of Relationships and Conversion of Units

1.1 Introduction

The creation of a system of units requires the definition of basic units, their values, and the units derived from them. In mechanics, the units used are length, mass and time, but other options are possible as well, such as length and time, force and time, or mass, speed and time.

The first general conference on weights and measures was held in 1889 at the headquarters of the BPIM (Bureau international des poids et mesures or International Office of Weights and Measures), at the Breteuil pavilion in Sevres (in the suburbs of Paris). In this conference, new international prototypes of the meter and kilogram were officially adopted and filed with the Office.

In 1960, the 11th General Conference of Weights and Measures established the International System (SI), in which the rules for prefixes, derived units and other indications were established. The SI is based on a choice of seven well-defined base units that the convention considered dimensionally independent: the meter, the kilogram, the second, the ampere, the kelvin, the mole and the candela. Derived units are formed by combining the base units according to the algebraic relationships connecting the corresponding quantities. The names and symbols of some of these units may be replaced by special names and symbols, which may be used to express the names and symbols of other derived units.

In November 2018, the International System of units later underwent ...