A
svedberg unit (symbol
S, sometimes
Sv) is a non-
SI unit for sedimentation rate. The sedimentation rate for a particle of a given size and shape measures how fast the particle 'settles', or
sediments. 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 technically a measure of time, and is defined as exactly 10
-13 seconds (100
fs).