Viscosity

• Viscosity refers to the resistance to the flow of liquid arising as a result of the internal friction within the layers as they pass over other layer.
• Viscosity arises due to the strong intermolecular forces between the molecules that holds them together and resist the passing of layers over other.
• The layers of molecules of the flowing liquid that are in contact with the surface are stationary.
• Increase in the distance between the two layers increases the velocity of the upper layer.
• Flow of liquid with regular gradation of velocity while passing over other layer is termed as laminar flow.

• It is equal to the force when the velocity gradient and area of contact is unity. Therefore, η can be called the measure of viscosity.
• It is measured in unit called Nsm^-2.

Problem:

A liquid is streaming between two layers. Figure the shearing power if the shear speed is 0.25 m/s and has length 2 m and element thickness is 2Ns/m2.

Solution:

d u = 0.25 m/s,

d z = 0.125/s

η = 2 Ns/m^2

F = η A du/dz

F = 2 Ns/m² × 0.125 /s

F = 0.5 N/m²