HARSHA K

VISCOSITY
Viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the informal concept of "thickness", for example honey as a much higher viscosity than water.

 Viscosity is a property arising from  collision between neighboring particles in a fluid that are moving different velocities.

When a fluid is forced through a tube, the particles which compose the fluid generally move more quickly near the tubes axis and more slowly near its walls therefore some stress is needed to overcome the friction between particle layers to keep the fluid moving

For a given velocity pattern, the stress required is proportional to the fluids viscosity

A fluid that has no resistance to shear stress is know as an ideal or inviscid fluid. Zero viscosity is observed only at very low temperatures in superfluids. otherwise, all fluids have positive viscosity, and are technically said to be viscous or viscid. in common parlance however a liquid is said to be viscous if its viscosity is substantially greater than that of water

A fluid with a relatively high viscosity such as pitch may appear to be a solid.

Viscosity describes a fluid's resistance to flow. Liquids such as water that flow easily, have a lower viscosity than do liquids such as ketchup. Viscosity has little effect on the ability of a penetrant material to enter a defect but it does have an effect on the speed at which the penetrant fills a defect.