![]() ![]() The two systems differ only in the scale of the three base units (centimetre versus metre and gram versus kilogram, respectively), with the third unit (second) being the same in both systems. In mechanics, the quantities in the CGS and SI systems are defined identically. The units gram and centimetre remain useful as noncoherent units within the SI system, as with any other prefixed SI units.ĭefinition of CGS units in mechanics ![]() RAM PRESSURE EQUATION CGS FREEThe continued usage of CGS units is prevalent in magnetism and related fields because the B and H fields have the same units in free space and there is a lot of potential for confusion when converting published measurements from CGS to MKS. CGS units are today no longer accepted by the house styles of most scientific journals, textbook publishers, or standards bodies, although they are commonly used in astronomical journals such as The Astrophysical Journal. SI units are predominantly used in engineering applications and physics education, while Gaussian CGS units are commonly used in theoretical physics, describing microscopic systems, relativistic electrodynamics, and astrophysics. ![]() Since the international adoption of the MKS standard in the 1940s and the SI standard in the 1960s, the technical use of CGS units has gradually declined worldwide. Starting in the 1880s, and more significantly by the mid-20th century, CGS was gradually superseded internationally for scientific purposes by the MKS (metre–kilogram–second) system, which in turn developed into the modern SI standard. Thus the CGS system never gained wide general use outside the field of science. For example, many everyday objects are hundreds or thousands of centimetres long, such as humans, rooms and buildings. ![]() The sizes of many CGS units turned out to be inconvenient for practical purposes. In 1873, a committee of the British Association for the Advancement of Science, including physicists James Clerk Maxwell and William Thomson recommended the general adoption of centimetre, gram and second as fundamental units, and to express all derived electromagnetic units in these fundamental units, using the prefix "C.G.S. Gauss chose the units of millimetre, milligram and second. The CGS system goes back to a proposal in 1832 by the German mathematician Carl Friedrich Gauss to base a system of absolute units on the three fundamental units of length, mass and time. 4 Electromagnetic units in various CGS systems.3.6 Relations between ESU and EMU units.3.3 Various extensions of the CGS system to electromagnetism.3.2 Alternative derivations of CGS units in electromagnetism.3.1 CGS approach to electromagnetic units.3 Derivation of CGS units in electromagnetism.2.1 Definitions and conversion factors of CGS units in mechanics.Among these choices, Gaussian units are the most common today, and "CGS units" is often intended to refer to CGS-Gaussian units. Furthermore, within CGS, there are several plausible ways to define electromagnetic quantities, leading to different "sub-systems", including Gaussian units, "ESU", "EMU", and Lorentz–Heaviside units. This is because the electromagnetic quantities are defined differently in SI and in CGS, whereas mechanical quantities are defined identically. Formulas for physical laws of electromagnetism (such as Maxwell's equations) take a form that depends on which system of units is being used. On the other hand, in measurements of electromagnetic phenomena (involving units of charge, electric and magnetic fields, voltage, and so on), converting between CGS and SI is more subtle. For example, the CGS unit of force is the dyne, which is defined as 1 g⋅cm/s 2, so the SI unit of force, the newton ( 1 kg⋅m/s 2), is equal to 100 000 dynes. In measurements of purely mechanical systems (involving units of length, mass, force, energy, pressure, and so on), the differences between CGS and SI are straightforward and rather trivial the unit-conversion factors are all powers of 10 as 100 cm = 1 m and 1000 g = 1 kg. In many fields of science and engineering, SI is the only system of units in use, but there remain certain subfields where CGS is prevalent. The CGS system has been largely supplanted by the MKS system based on the metre, kilogram, and second, which was in turn extended and replaced by the International System of Units (SI). All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways in which the CGS system was extended to cover electromagnetism. The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. For a topical guide, see Outline of the metric system. ![]()
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