Svedberg

A svedberg unit (symbol S, sometimes Sv) is a non-SI unit for sedimentation rate. The sedimentation rate is the rate at which particles of a given size and shape travel to the bottom of the tube under centrifugal force. This reflects the rate at which a molecule sediments under the centrifugal force of a centrifuge. The svedberg is technically a measure of time, and is defined as exactly 10−13 seconds (100 fs).