Dynamic viscosity

Dynamic viscosity measures a fluid’s resistance to deformation under shear, relating shear stress to shear rate for Newtonian fluids. Its SI unit is the pascal-second.

Shear stress: The tangential force per unit area acting within a material. Dynamic viscosity relates this stress to the rate of shearing.
Pascal-second: The SI unit of dynamic viscosity, equal to one pascal multiplied by one second. It expresses stress divided by shear rate in SI units.
Viscometer: An instrument used to measure a fluid’s viscosity. Different viscometer designs infer dynamic viscosity from force, motion, or flow.
Bulk viscosity: A coefficient describing a fluid’s resistance to compression during volumetric deformation. It concerns volumetric strain rather than the shear deformation defining dynamic viscosity.
Shear rate: The rate at which adjacent layers of a material move relative to one another. For a Newtonian fluid, viscosity is shear stress divided by this rate.
Poiseuille: A non-SI unit of dynamic viscosity equal to one pascal-second. It is an alternative name for the SI unit used in some references.
Rheometer: An instrument that measures how materials deform and flow under applied forces. It can measure viscosity across changing shear rates.
Reynolds number: A dimensionless ratio of inertial forces to viscous forces in fluid flow. Dynamic viscosity sets the viscous scale in this measure of flow regime.
Newtonian fluid: A fluid whose shear stress is proportional to shear rate at fixed temperature and pressure. Its constant proportionality factor is dynamic viscosity.
Poise: A CGS unit of dynamic viscosity equal to 0.1 pascal-second. It is commonly encountered in older measurements and industrial specifications.

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