viskozitesi

Viskozitesi, or viscosity, is a measure of a fluid’s resistance to gradual deformation by shear or tensile stresses. It quantifies how easily a liquid flows under an applied force and reflects internal friction between its molecules. Dynamic viscosity is denoted by μ and measured in pascal-seconds (Pa·s). Kinematic viscosity, denoted by ν, divides μ by the fluid density (ν = μ/ρ) and is expressed in square meters per second (m^2/s). Common units used in industry include Pa·s for dynamic viscosity and stokes or centistokes for kinematic viscosity.

Fluids are broadly categorized as Newtonian or non-Newtonian. Newtonian fluids have a constant viscosity independent of shear rate, such as water or mineral oil at a given temperature. Non-Newtonian fluids show a viscosity that changes with shear rate; examples include shear-thinning liquids (ketchup), shear-thickening suspensions (paint suspensions), and viscoelastic materials (polymers).

Viscosity is strongly temperature-dependent: most liquids become less viscous as temperature increases. This behavior is often described by Arrhenius-type or other empirical relations. Pressure can also influence viscosity, particularly at high pressures, in dense liquids and polymers.

Measurement methods include capillary viscometers (for lower viscosities), falling-ball viscometers, rotational viscometers, and rheometers, which characterize viscosity across different shear rates and temperatures. Viscosity is a critical parameter in lubrication, fuel and ink formulation, polymer processing, and many food and pharmaceutical applications. In lubricants, viscosity indices describe how viscosity changes with temperature, while kinematic viscosity is used to rate fluids in hydraulic and bearing systems.