centimetergramsecond

Centimeter-gram-second (CGS) is a traditional system of physical units that uses the centimeter for length, the gram for mass, and the second for time as base units. It was developed in the 19th century and was widely used in physics before the International System of Units (SI) became dominant in the mid-20th century. In CGS, many common derived units are defined in terms of these base units, such as the dyne for force and the erg for energy.

In CGS, the derived units include the dyne (1 dyne = 1 g·cm/s^2) and the erg (1 erg = 1 g·cm^2/s^2). Other CGS-derived quantities, such as viscosity in the poise, are defined using the same base units. The system provides a coherent framework for mechanics and some areas of electromagnetism, but electromagnetic units can vary significantly across different CGS sub-systems.

There are several electromagnetism-focused variants of CGS, the most notable being CGS electrostatic (CGS-ES) and CGS electromagnetic (CGS-EMU). These differ in how electric charges, electric fields, and magnetic fields are treated, which leads to different numerical values for constants in Coulomb’s and Ampère’s laws compared to SI. Relatedly, Gaussian and Heaviside-Lorentz are names used for particular rationalized or non-rationalized forms of CGS electromagnetism.

Today, CGS has largely been supplanted by SI, but it remains part of the historical record and persists in some specialized areas and older scientific literature, where CGS units may still be encountered in discussions of theory and in archival data.