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Mechanical Properties of Fluids

Mechanical Properties of Fluids. Viscosity. Mechanical Properties of Fluids. Viscosity. Internal friction present between two layers of a liquid which resists the flow of liquid is viscosity. · A liquid with high viscosity is thick and flows slowly.

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Mechanical Properties of Fluids

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  1. Mechanical Properties of Fluids Viscosity

  2. Mechanical Properties of Fluids Viscosity Internal friction present between two layers of a liquid which resists the flow of liquid is viscosity. · A liquid with high viscosity is thick and flows slowly. · A liquid with low viscosity is thin and flows quickly. · Different liquids have different viscosities.

  3. Mechanical Properties of Fluids Viscosity Factors Affecting Viscosity Size of molecules : Viscosity of a liquid having large molecules is high whereas the viscosity of those liquids that have small molecules is low. Shape of molecules : Spherical molecules provide resistance but oval shaped or disc like molecules provide greater resistance in the flow of liquid. That’s why viscosity of liquids having spherical molecules is low.

  4. Mechanical Properties of Fluids Viscosity Factors Affecting Viscosity Inter molecular forces : Liquids having large inter molecular forces have greater viscosity. Temperature : Viscosity of liquid decreases with increase in temperature. Because an increase in temperature, reduces the forces of attraction between molecules.

  5. Mechanical Properties of Fluids Viscosity Laminar Flow The velocities of layers increase uniformly from bottom (zero velocity) to the top layer (velocity v). For any layer of liquid, its upper layer pulls it forward while lower layer pulls it backward. This results in force between the layers. This type of flow is known as laminar.

  6. Mechanical Properties of Fluids Viscosity A portion of liquid, which at some instant has the shape ABCD, take the shape of AEFD after short interval of time (Δt). During this time interval the liquid has undergone a shear strain of Δx/l. Strain in a flowing fluid increases with time continuously. Stress is depend on ‘rate of change of strain’ i.e. Δx/(l Δt) or v/l .

  7. Mechanical Properties of Fluids Viscosity The coefficient of viscosity () for a fluid is defined as the ratio of shearing stress to the strain rate. The SI unit of viscosity is poiseiulle (Pl). Its other units are N.S/m2 or Pa s. The dimensions of viscosity are [ML-1T-1].

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