Knowra Viscosity Viscosity Viscosity measures a fluid’s resistance to flow or deformation under shear. It relates the shear stress applied to a fluid to the resulting rate of deformation.
Newtonian fluid : A fluid whose shear stress is proportional to its rate of deformation, with constant viscosity at fixed conditions. Viscosity is constant for these fluids at fixed temperature and pressure.
Dynamic viscosity : A fluid property relating shear stress to shear rate, measured in pascal-seconds in SI. This is the direct measure of shear resistance described by viscosity.
Viscometer : An instrument that measures a fluid’s viscosity under specified conditions. Different viscometers measure viscosity through flow, rotation, or related responses.
Elasticity : A material’s ability to return toward its original shape after deformation. Viscosity describes rate-dependent flow, while elasticity describes recoverable deformation.
Non-Newtonian fluid : A fluid whose viscosity changes with shear rate, time, or applied stress. Its flow shows why viscosity need not be a single constant.
Kinematic viscosity : Dynamic viscosity divided by density, measured in square metres per second in SI. It expresses viscous diffusion while accounting for fluid density.
Rheology : The study of how materials flow and deform under applied forces. Viscosity is one of rheology’s central ways to describe material response.
Surface tension : The energy cost per unit area of a liquid interface, arising from intermolecular forces. Surface tension governs interfaces; viscosity governs resistance to shear flow.
Shear stress : Force per unit area acting parallel to a surface or material layer. Shear stress is the applied force that viscosity relates to deformation rate.
Fluid : A substance that continuously deforms under applied shear stress, including liquids and gases. Viscosity characterizes resistance to deformation in fluids.
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