Svedberg unit is a non-system international unit for sedimentation rate of a particle when centrifuged. The shape, density, and mass of a particle will be calculated by its Svedberg value. This value is dependent on the frictional forces that slow down its movement. More specifically, the Svedberg unit is a measure of time, and equal to 100 femtoseconds (10^-13 seconds). Sedimentation rate specifies the size of the molecule, with larger molecules having a higher sedimentation coefficient. For macromolecules and organelles like ribosomes, the sedimentation rate is usually measured as the rate of travel in a centrifuge tube under high g-force conditions.  As an example, a 70S ribosome stands for 70 svedberg.