3.3.4.1 Discussion—Kinematic viscosity is the ratio between
momentum transport and momentum storage. Such
ratios are called diffusivities with dimensions of length squared
divided by time and the SI unit is metre squared divided by
second (m2
/s). Among the transport properties for heat, mass,
and momentum transfer, kinematic viscosity is the momentum
diffusivity.
3.3.4.2 Discussion—Formerly, kinematic viscosity was de-
fined specifically for viscometers covered by this test method
as the resistance to flow under gravity. More generally, it is the
ratio between momentum transport and momentum storage.
3.3.4.3 Discussion—For gravity-driven flow under a given
hydrostatic head, the pressure head of a liquid is proportional
to its density, ρ, if the density of air is negligible compared to
that of the liquid. For any particular viscometer covered by this
test method, the time of flow of a fixed volume of liquid is
directly proportional to its kinematic viscosity, ν, where
ν = η ⁄ρ, and η is the dynamic viscosity