Centimetre gram second system of units CGS is an acronym for centimetre-gram-second. This is a system of physical units which preceded, and has largely been replaced by, the standard SI system (SI was based on the metre-kilogram-second system of units, hence the unofficial but occasionally used name mks). The cgs system is still in use; this is largely because many electromagnetic formulas are simpler in cgs units, but also because much of the older physics literature uses these units, and in some cases because they are more convenient in a particular context. Additionally, cgs units are still widely used in astronomy. Electromagnetic Units While for most units the difference between cgs and SI is a mere power of 10, the differences in electromagnetic units are considerable; so much so that formulas for physical laws need to be changed depending on what system of units one uses. In SI, electric current is defined via the magnetic force it exerts and charge is then defined as current multiplied with time. In one variant of the cgs system, esu, or electrostatic units, charge is defined via the force it exerts on other charges, and current is then defined as charge per time. One consequence of this approach is that Coulomb's law does not contain a constant of proportionality. There are actually about half a dozen systems of electromagnetic units in use, most based on the cgs system. These include emu, or electromagnetic units (chosen such that the Biot-Savart Law has no constant of proportionality), Gaussian, and Heaviside-Lorentz units. Further complicating matters is the fact that some physicists and engineers use hybrid units, such as volts per centimetre for electric field. Units The units of cgs (specifically esu) are as follows: length: centimetre 1 cm = 0.01 m mass: gram 1 g = 0.001 kg time: second force: dyne = g·cm/s² = 10-5 N energy: erg = g·cm²/s² = 10-7 J power: g·cm²/s³ = 10-7 W pressure: barye = g/cm·s² = 0.1 Pa viscosity: poise = g/cm·s = 0.1 Pa·s charge: esu, franklin or statcoulomb = √ (g·cm³/s²) = 3.336 × 10-10 C electric potential: statvolt = erg/esu = 299.8 V electric field: statvolt/cm = dyne/esu magnetic field: 1 gauss = 1 oersted = 1 statvolt/cm = 1 dyn/esu = 10-4 T magnetic flux: 1 maxwell = 1 gauss·cm² = 10-8 Wb magnetic induction: 1 gauss = 1 maxwell/cm² resistance: s/cm resistivity: s capacitance: cm = 1.113 × 10-12 F inductance: s²/cm = 8.988 × 1011 H The mantissas 2998, 3336, 1113, and 8988 are derived from the speed of light and are more precisely 299792458, 333564095198152, 1112650056, and 89875517873681764. A centimetre of capacitance is the capacitance between a sphere of radius 1 cm in vacuum and infinity. The capacitance between two spheres of radii R and r is $\backslash frac-\backslash frac\}$ See Also Scientific units named after people FAVORITE ARTICLES: History of the World    History of the United States    History of Europe    Ancient History    History    Military History    World War I    Bombing of Dresden    California    US Constitution    Frank Sinatra    Boston    Marbury v. Madison This article is licensed under the GNU Free Documentation License at http://www.gnu.org/copyleft/fdl.html You may copy and modify it as long as the entire work (including additions) remains under this license. You must provide a link to http://www.gnu.org/copyleft/fdl.html To view or edit this article at Wikipedia go to http://www.wikipedia.org/wiki/Centimetre_gram_second_system_of_units