9. VISCOUSITY

1.8  Viscosity

Viscosity is the property of liquid due to which it opposes the relative motion between the layers of fluid. It is also known as liquid friction.

SI unit of viscosity is Pascal-second (Pa.s) and CGS unit is Poise.

1.8.1  Effect of heat on viscosity

In liquids the source for Viscosity is considered to be atomic bonding. As we understand that, with the increase of temperature, the bonds break and make the molecule free to move. So, we can conclude that the viscosity decreases as the temperature increases and vice versa.

In gases, due to the lack of cohesion, the source of viscosity is the collision of molecules. Here, as the temperature increases the viscosity increases and vice versa. This is because the gas molecules utilize the given thermal energy in increasing its kinetic energy that makes them random and therefore resulting in more the number of collisions.