Viscosity is a measure of resistance to flow which arises due to the internal friction between layers of fluid as they slip past one another while liquid flows.

Liquid flows over a fixed surface, the layer of molecules in the immediate contact of surface is stationary.

The velocity of upper layers increases as the distance of layers from the fixed layer increases.

The type of flow in which there is a regular gradation of velocity in passing from one layer to the next is called laminar flow.

The velocity of the layer at a distance dz is changed by a value du then velocity gradient is given by the amount du/dz

AViscosity coefficient is the force when velocity gradient is unity and the area of contact is unit area.

‘ η’ is measure of viscosity.

SI unit of viscosity coefficient is 1 newton second per square metre

Greater the viscosity, the more slowly the liquid flows.

Hydrogen bonding and van der Waals forces are strong enough to cause high viscosity.

Glass is an extremely viscous liquid.

Glass is so viscous that many of its properties resemble solids.

Viscosity of liquids decreases as the temperature rises because at high temperature molecules have high kinetic energy and can overcome the intermolecular forces to slip past one another between the layers.