In general, in any flow, layers move at different velocities and the fluid's viscosity arises from the shear stress between the layers that ultimately opposes any applied force. Volume viscosity is essential for Acoustics in fluids, see Stokes' law (sound attenuation) Newton's theory Extensional viscosity is widely used for characterizing polymers. For example, at 'room temperature', water has a nominal viscosity of 1.0 Г— 10 -3 Paв€™s and motor oil has a nominal apparent viscosity of 250 Г— 10 -3 Paв€™s. Simply put, this quantity is the ratio between the pressure exerted on the surface of a fluid, in the lateral or horizontal direction, to the change in velocity of the fluid as you move down in the fluid (this is what is referred to as a velocity gradient). That is why they are often referred to as simply viscosity. Shear viscosity and dynamic viscosity are much better known than the others.

Extensional viscosity is the viscosity coefficient when applied stress is extensional stress valid for non-Newtonian fluids.

Shear viscosity is the viscosity coefficient when applied stress is a shear stress, valid for non-Newtonian fluids.

Bulk viscosity is the same as volume viscosity.

Volume viscosity is the viscosity coefficient that determines the dynamics of compressible Newtonian fluid.

Kinematic viscosity is the dynamic viscosity divided by the density for Newtonian fluid.

Dynamic viscosity is the viscosity coefficient that determines the dynamics of incompressible Newtonian fluid.

They are introduced in the main books on hydrodynamics and rheology. There are several different viscosity coefficients depending on the nature of applied stress and nature of the fluid. When looking at a value for viscosity, the number that one most often sees is the coefficient of viscosity. A viscous glue was made from mistletoe berries and used for lime-twigs to catch birds. The word 'viscosity' derives from the Latin word ' viscum' for mistletoe.

5.1.1 Effect of temperature on the viscosity of a gas.

4.1.3 Dynamic versus kinematic viscosity.

4.1.1 Viscosity (dynamic/absolute viscosity).

In turbulent flow the imaginary layers of liquid do not flow parallel to each other. At high rates of flow or flow in tubes of large diameter the flow type changes to what is known as turbulent flow. The kind of flow consistent with this equation is called laminar or streamlines flow. This equation has been verified quite accurately for flow of liquids through tubes. If the volume of liquid flowing in t seconds is V, then according to Poiseille This thin film is assumed to be stationary and the rate of flow increases to a maximum at the centre of the tube.

The viscous drag results from the thin film of liquid that adheres to the wall of the tube. The velocity of flow becomes uniform when the pressure drop, P = P 1вЂ“ P 2, along the length, l, balances the viscous drag of the liquid. Consider a liquid flowing through a tube of length, l, and of circular cross-section with radius, R. Although the correct version of the formula, which is widely used in measurement of viscosity, was deried Hagenbach the formula is known as Poiseuille equation. Poiseuille studied the flow of liquids through capillaries and deried an expression for the co-efficient of viscosity.

The Poiseuille Equation in Viscosity of Liquids

Viscosity formular