Viscosity of Liquids

Viscosity

• Viscosity is the property of liquids that determines their flow.
• It is compared in terms of the coefficient of viscosity.

Coefficient of Viscosity

• The coefficient of viscosity is the force per unit area required to maintain unit velocity difference between two parallel layers unit distance apart.
• It is denoted by η (eta) and its unit is g cm^-1 s^-1 or poise.
• Smaller units centipoise (10^-2 poise) and millipoise (10^-3 poise) are used.
• The SI unit is kg m^-1 s^-1.

Fluidity

• The reciprocal of the coefficient of viscosity is called fluidity.

Characteristics of Viscosity

• The coefficient of viscosity is proportional to the density of the liquid and the time of flow of the liquid.
• It is dependent on temperature.

Relationship Between Viscosity and Temperature

• The coefficient of viscosity of a liquid is proportional to the temperature and density of the liquid.
• η = Constant T d, where η is the coefficient of viscosity, T is the temperature, and d is the density of the liquid.

Comparison of Viscosity of Two Liquids

• The ratio of the coefficients of viscosity of two liquids is equal to the ratio of their temperatures and densities.
• η_l / η_w = T_1 / T × d_1 / d_w, where η_l and η_w are the coefficients of viscosity of the two liquids, and T_1, d_1, T, and d_w are their respective temperatures and densities.