Coefficient of Viscosity

The Viscosity of a fluid described as the resistance of liquid. For example liquids like water, alcohol, petrol and more flow freely and faster than glycerin, honey, and oil. This is because of its physical property and is called viscosity. In simple words, it explains the fluid’s flow resistance.

The viscosity is calculated in terms of coefficient of viscosity. It is constant for a liquid and depends on its liquid’s nature. The Poiseuille’s method is formally used to estimate the coefficient of viscosity, in which the liquid flows through a tube at the different level of pressures. It is defined as the degree up to which a fluid resists the flow under an applied force; it is measured by the tangential friction force acting per unit area divided by the velocity gradient under conditions of streamline flow.

Coefficient of Viscosity

The coefficient of viscosity of fluids will be decreased as the temperature increases, while it is inverse in the case of gases. While the coefficient of viscosity of gases will increase with the increase in temperature. The increase in temperature for the fluid deliberate the bonds between molecules. These bonds are directly associated with the viscosity and finally, the coefficient is decreased. An important question most people do not ask is, why even measure Viscosity? The main reason behind this being, that viscosity data on a material gives manufacturers a chance to predict how the material will react and behave when consumers interact with it. The most simplistic formula for measuring viscosity is:

viscosity = shear stress / shear rate

The coefficient of Viscosity Formula

The force of friction between two layers of fluid having the area in square centimeter and separated by distance will have a velocity is given by:

\(f\mu A \frac{dV}{dx}\)


\(f = \eta \; A \; \frac{dV}{dx}\)


\(\small \eta\) is coefficient of viscosity

\(\small \frac{dV}{dx}\) is velocity gradient

For example: If \(\small dx\) is \(\small 1 \; cm \), \(\small A \) is \(\small 1\; cm^{2}\) and \(\small dv\) is \(\small 1\; cm / s\)

Then, \(\small f = \eta\)

The coefficient of viscosity is defined as the force of friction that is required to maintain a difference of velocity of 1cm/s between parallel layers of fluid. The unit is usually expressed in poise or centipoise. As we all know that viscosity is nothing but the measure of a substance’s resistance to the motion under an applied force The resulting unit is measured in centipoise which is the equivalent of 1 mPa (MilliPascal second)

The major industries where Viscosity measurements are used are in the food industry to improve the overall cost-effectiveness and maximizing production efficiency. Besides, the food industry Viscosity is also primarily used in other industries such as Adhesives, Petroleum, Concrete, and Cosmetics industry.

For more information related to Viscosity, you can also check out the Dynamic Viscosity Formula, used for calculating internal resistance for fluids.

Practise This Question

The quantity of solute present in a given amount of solution represents: