Svedberg
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A Svedberg (symbol S, sometimes Sv) is a non-SI physical unit used in ultracentrifugation. It is named after the Swedish physicist and chemist Theodor Svedberg (1884-1971), winner of the Nobel prize in chemistry in 1926 for his work in the chemistry of colloids and his invention of the ultracentrifuge.
The sedimentation rate or co-efficient of a particle or macromolecule is computed by dividing the constant speed of sedimentation (in m/s) into the acceleration applied (in m/s2). The speed is constant because the acceleration applied by the ultracentrifuge (measuring typically in the millions of gravities) is cancelled by the viscous resistance of the medium (normally water) through which the particle is moving. The result has the dimensions of a unit of time and is expressed in svedbergs. One svedberg is defined as exactly 10-13s.
The svedberg is not additive: a particle formed of two 5 S particles will not have a sedimentation co-efficient of 10 S.