Viscosity measures fluid's resistance to movement through it. Low-viscosity fluids like water move easier than high-viscosity like honey. Viscosity results from molecular friction in fluids. Newton's equation for fluids expresses viscosity using force/area ratio
Dynamic viscosity describes fluid resistance to shearing flows. Viscosity is measured using viscometers and spans several orders of magnitude. Gases have lowest viscosities, thick liquids have highest
Viscosity varies significantly with temperature in gases and liquids. Gases show increasing viscosity due to molecular momentum transfer. Liquids exhibit decreasing viscosity due to molecular attraction
SAE J300 defines viscometric properties of engine oils maintained by SAE International. Standard includes 25 grades from 0W to 60, with W indicating winter grades. Used worldwide by API, ILSAC, and ACEA
Newtonian fluids exhibit linear correlation between viscous stresses and strain rate. Viscosity tensor must be constant and independent of flow state. Many common liquids and gases can be assumed Newtonian for practical calculations
Viscosity measures fluid's resistance to deformation under shear or tensile stress. Dynamic viscosity determines fluid flow type using Reynold's Number. Temperature range must be 0-370°C, 32-700°F, 273-645 K, 492-1160°R