Viskoosit

Viskoosit is the Finnish term for viscosities, describing the property of a fluid that resists gradual deformation by shear or tensile stresses. In English, viscosity refers to two related concepts: dynamic (absolute) viscosity, symbolized by η, and kinematic viscosity, symbolized by ν. Dynamic viscosity measures a liquid’s internal friction as it flows; the SI unit is the pascal-second (Pa·s). The centipoise (cP) is a common subunit, where 1 cP equals 0.001 Pa·s. Kinematic viscosity is the ratio of dynamic viscosity to density (ν = η/ρ) and is measured in units such as m²/s or centistokes (cSt), where 1 cSt equals 1 mm²/s.

Fluids can be Newtonian, with viscosity independent of shear rate, or non-Newtonian, where viscosity changes with shear rate or time. Temperature strongly influences viscosity: for most liquids, viscosity decreases as temperature rises. Molecular structure, phase, and impurities also affect viscosity. Measurement of viscosity, or viscometry, uses devices such as capillary viscometers (for example Ubbelohde) that measure flow time under gravity, and rotational viscometers (cone-plate, parallel-plate) that measure torque at controlled shear rates. Rheometers assess viscosity across a range of shear rates and temperatures.

Viscosity is critical in lubrication, food and beverage processing, polymer extrusion, paint and coating properties, and medical and geological contexts. The term viskoosit is used in Finnish science and industry to refer to these viscous properties.