Svedberg

A Svedberg unit (symbol S, sometimes Sv) is a non-metric unit for sedimentation coefficient. The Svedberg unit (S) offers a measure of a particle's size based on its sedimentation rate, i.e. how fast a particle of given size and shape 'settles' to the bottom of a solution. The Svedberg is a measure of time, defined as exactly 10−13 seconds (100 fs). A Svedberg unit (symbol S, sometimes Sv) is a non-metric unit for sedimentation coefficient. The Svedberg unit (S) offers a measure of a particle's size based on its sedimentation rate, i.e. how fast a particle of given size and shape 'settles' to the bottom of a solution. The Svedberg is a measure of time, defined as exactly 10−13 seconds (100 fs). For biological molecules, sedimentation rate is typically measured as the rate of travel in a centrifuge tube subjected to high g-force. The Svedberg (S) is distinct from the SI unit sievert or the non-SI unit sverdrup, which also use the symbol Sv. The unit is named after the Swedish chemist Theodor Svedberg (1884–1971), winner of the 1926 Nobel Prize in chemistry for his work on disperse systems, colloids and his invention of the ultracentrifuge. The Svedberg coefficient is a nonlinear function. A particle's mass, density, and shape will determine its S value. It depends on the frictional forces retarding its movement, which, in turn, are related to the average cross-sectional area of the particle. The sedimentation coefficient is the ratio of the speed of a substance in a centrifuge to its acceleration in comparable units. A substance with a sedimentation coefficient of 26S (26×10−13 s) will travel at 26 micrometers per second (26×10−6 m/s) under the influence of an acceleration of a million gravities (107 m/s2). Centrifugal acceleration is given as rω2; where r is the radial distance from the rotation axis and ω is the angular velocity in radians per second.