Question

Explain the term viscosity.what is the cause of viscosity of liquids and gases. {Oct/Nov}​

Answer 1

Answer:

Viscosity can be conceptualized as quantifying the internal frictional force that arises between adjacent layers of fluid that are in relative motion. For instance, when a fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. In such a case, experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow through the tube. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion: the strength of this force is proportional to the viscosity.

A fluid that has no resistance to shear stress is known as an ideal or inviscid fluid. Zero viscosity is observed only at very low temperatures in superfluids. Otherwise, the second law of thermodynamics requires all fluids to have positive viscosity;[2][3] such fluids are technically said to be viscous or viscid. A fluid with a high viscosity, such as pitch, may appear to be a solid.

Answer 2

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Viscosity:-

The viscosity of a fluid is a measure of its resistance to deformation at a given rate.

• A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion.

Cause of Viscosity of liquid and gas :-

• Viscosity increases with temperature for a gas. More collisions per unit time mean more momentum transport to viscous losses per unit time.

• Viscosity decreases with temperature for a liquid. The intermolecular forces weaken with temperature so the viscosity goes down. This effect exceeds the collision argument for gases even though both are fluids.

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Additional information:-

Types of Viscosity

As we know, the viscosity is the measure of the friction of fluids. There are two ways to measure a fluid’s viscosity as follows:

1. Dynamic Viscosity (Absolute Viscosity)
2. Kinematic Viscosity

Many are confused between the two viscosity measures and consider them to be one and the same. In reality, they have significant differences between them. For a few applications, kinematic viscosity is more useful than absolute or dynamic viscosity.

Unit:

• The unit of kinematic viscosity is Stokes, named after the British physicist, Sir George Gabriel Stokes.

• A stoke is defined as one centimeter squared per second.