Svedberg
A svedberg unit (symbol S, sometimes Sv) is a non-metric unit for sedimentation rate. The sedimentation rate for a particle of a given size and shape measures how fast the particle 'settles', the sedimentation. It is often used to reflect the rate at which a molecule travels to the bottom of a test tube under the centrifugal force of a centrifuge. The svedberg is actually a measure of time; it is defined as exactly 10−13seconds (100 fs).
The Svedberg unit (S) offers a measure of particle size based on its rate of travel in a tube subjected to high g-force.
It should not be confused with SI unit sievert or the non-SI sverdrup, which use the same symbol.
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.
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