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VISCOSITY

VISCOSITY. Department of Physics The Open University of Sri Lanka. Content. Learning Outcomes Defining vis cosity Newton’s formula Variation of viscosity with temperature Poiseuille's formula. Learning Outcomes. After completing this session you should be able to

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VISCOSITY

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  1. VISCOSITY • Department of Physics • The Open University of Sri Lanka

  2. Content • Learning Outcomes • Defining viscosity • Newton’s formula • Variation of viscosity with temperature • Poiseuille's formula

  3. Learning Outcomes After completing this session you should be able to • explain what is viscosity • explain the differences between fluid flow, steady (laminar flow) and turbulent flow • explain Newton’s formula • explain the variation of viscosity with temperature

  4. Defining viscosityViscosity is a measure of a fluid's resistance to flow. Low viscosity Flow easily High viscosity Does not flow easily Milk Ketchup

  5. Steady flow When a fluid moves slowly, its flow is orderly. If every fluid passing through a given point follows the same line of the flow it is named as Laminar flow or Steady flow. Slow Fast Slow

  6. Turbulent flow The motion of a fluid in which the elements move irregularly and in a much more complex manner is said to be a turbulent flow.

  7. Water flowing from a tap is also another good example for both Steady flow and Turbulent flow Steady flow Turbulent flow

  8. Newton’s formula for Coefficient of Viscosity () Newton’s law of viscosity states that “Shear stress (Tangential pressure) is directly proportional to Velocity gradient”  Boundary plate (2D, moving) Velocity, U Shear stress (T) Gradient fluid Boundary plate (2D, stationary)

  9. Units and dimensions of viscosity- Units Dimensions

  10. Variation of viscosity with temperature in a gas The viscosity in a gas will increase with temperature

  11. Variation of viscosity with temperature in liquids Liquids show a reduction in viscosity with increasing temperature Viscosity Temperature 0C

  12. Poiseuille's formula Volume flow rate Q=dV/dt Parabolic velocity profile 2R P 2 P1 L Volume flow rate of liquid = Q Radius of the tube = R viscosity =  Pressure gradient =

  13. Author : D. L. N. Jayathilaka Web Content Developer : B. KrishniPerera Produced by The Open University of Sri Lanka 2014

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