hydrodynamically equivalent sphere

in polymers
https://doi.org/10.1351/goldbook.H02896
A hypothetical sphere, impenetrable to the surrounding medium, displaying in a hydrodynamic field the same frictional effect as an actual @M03667@. The size of a hydrodynamically equivalent sphere may be different for different types of motion of the macromolecule, e.g. for @D01716@ and for viscous flow.
Source:
Purple Book, 1st ed., p. 60 [Terms]