3. Objectives  Be flexible because objectives in this section are somewhat fluid at this juncture.

4. Reading Activity Questions?

5. Viscosity  A friction force between adjacent layers of fluid as the layers move past one another  In liquids, it is mainly due to the cohesive forces between molecules  In gases, it is caused by collisions between molecules.  Coefficient of viscosity, η (lowercase eta) (Pa-s)

6. Viscosity  Determined by measuring the force required to move a plate over a stationary one with a given amount of liquid between them

7. Viscosity  Determined by measuring the force required to move a plate over a stationary one with a given amount of liquid between them

8. Viscosity  Units for η (eta) are N·s/m 2 or Pa·s  CGS is dyne·s/cm 2 which is called a poise (P)  100 centipoise (cP) = 1P

9. Coefficients of Viscosity

10.  Temperatures are specified because it has a strong effect on viscosity  Viscosity for most fluids decreases rapidly with increase in temperature

11. Flow In Tubes: Poiseuille’s Equation  Without viscosity, fluids could flow freely without an applied force  Because of viscosity, a pressure difference between the ends of the tube are necessary to cause the fluid to flow

12. Flow In Tubes: Poiseuille’s Equation  Rate of flow of a fluid depends on:  Viscosity  Pressure difference  Dimensions of the tube  Poiseuille’s Equation assumes  Fluid is incompressible  Laminar flow

13. Flow In Tubes: Poiseuille’s Equation  Q is the volume rate of flow in m 3 /s  r is the inside radius of the tube  L is the length of the tube  P 1 -P 2 is the pressure difference between the ends  η is the coefficient of viscosity

14. Flow In Tubes: Poiseuille’s Equation  Q, the volume rate of flow is  Directly proportional to the pressure difference  Inversely proportional to the viscosity and length of the tube  Directly proportional to the fourth power of the radius

15. Flow In Tubes: Poiseuille’s Equation  Q, the volume rate of flow is  Directly proportional to the fourth power of the radius  Do blood vessels have constant diameter?

16. Flow In Tubes: Poiseuille’s Equation  Q, the volume rate of flow is  Directly proportional to the fourth power of the radius  Do blood vessels have constant diameter?  Blood vessel diameter decreases as they branch out  The body controls blood vessel diameter by bands of muscles surrounding the arteries  Arteriosclerosis and cholesterol buildup decrease diameter forcing a higher pressure gradient for same blood flow

17. Surface Tension  Because of the cohesion of liquid molecules, the surface of a liquid acts like a stretched membrane under tension  Drip of a faucet  Water beading on a surface  Meniscus in a test tube

18. Surface Tension  Surface tension, γ, is defined as the force, F, per unit length, L that, across any line in a surface, tends to pull the surface closed

19. Surface Tension  Because of surface tension, insects can walk on water and objects more dense than water can ‘float’

20. Surface Tension  Soaps and detergents contain substances called surfactants that decrease the surface tension of water  Allows the water to penetrate crevices and between fibers

21. Capillarity  Water in a glass will tend to ‘stick’ to the glass and slope upward at the edges toward the glass  Mercury, on the other hand, tends to ‘stick’ more to itself and slopes downward toward the glass  Sloping upward or downward is a function of the liquid’s cohesion and adhesion properties and the surface it is in contact with

22. Capillarity  Cohesion refers to the attractive force between molecules of the same type (the liquid)  Adhesion refers to the attractive force between molecules of different types (the liquid and the glass)

23. Capillarity  In tubes of relatively small diameter, liquids will either rise or fall relative to surrounding fluid based on its adhesive and cohesive properties  Fluids with strong adhesive properties will rise  Fluids with strong cohesive properties will fall  The amount of rise or fall depends on the surface tension  Capillarity Demonstration

24. Important News  Because of time constraints, battle fatigue and PTSD, there are no homework problems for 10-12 and 10-13  Concepts from 10-12 and 10-13 (i.e. Reading Activity) are testable  Read through section 10-13 on your own and pay special attention to the Reading Activity!

26. Lsn 10-11, #46-52 Homework