1. College Physics, 7th Edition
Lecture Outline
Chapter 9
College Physics, 7th Edition
Wilson / Buffa / Lou
© 2010 Pearson Education, Inc.

2. Chapter 9 Solids and Fluids
© 2010 Pearson Education, Inc.

3. Units of Chapter 9 Solids and Elastic Moduli
Fluids: Pressure and Pascal’s Principle
Buoyancy and Archimedes’ Principle
Fluid Dynamics and Bernoulli’s Equation
Surface Tension, Viscosity, and Poiseuille’s Law
© 2010 Pearson Education, Inc.

4. 9.1 Solids and Elastic Moduli
All solids are elastic to some degree, due to the spring-like structure of the intermolecular bonds holding them together.
© 2010 Pearson Education, Inc.

5. 9.1 Solids and Elastic Moduli
Stress is defined as the force per unit area:
© 2010 Pearson Education, Inc.

6. 9.1 Solids and Elastic Moduli
The stress results in a change in the shape of the solid, called the strain:
The strain is related to the stress; how much strain a particular stress causes depends on the material.
© 2010 Pearson Education, Inc.

7. 9.1 Solids and Elastic Moduli
Changes in length, shape, and volume are described by Young’s modulus, the shear modulus, and the bulk modulus, respectively.
Young’s modulus:
© 2010 Pearson Education, Inc.

8. 9.1 Solids and Elastic Moduli
Stress is proportional to strain until the strain gets too large. Then a material becomes permanently deformed, and finally breaks.
© 2010 Pearson Education, Inc.

9. 9.1 Solids and Elastic Moduli
© 2010 Pearson Education, Inc.

10. 9.1 Solids and Elastic Moduli
Shear modulus:
© 2010 Pearson Education, Inc.

11. 9.1 Solids and Elastic Moduli
Bulk modulus (the only one relevant for fluids—why?)
© 2010 Pearson Education, Inc.

12. 9.2 Fluids: Pressure and Pascal’s Principle
Pressure is defined as the force per unit area:
If the force is at an angle to the surface, the more general form (blue box) is used.
© 2010 Pearson Education, Inc.

13. 9.2 Fluids: Pressure and Pascal’s Principle
Unit of pressure: the Pascal (Pa)
Density is defined as mass per unit volume:
© 2010 Pearson Education, Inc.

14. 9.2 Fluids: Pressure and Pascal’s Principle
© 2010 Pearson Education, Inc.

15. 9.2 Fluids: Pressure and Pascal’s Principle
The pressure in a fluid increases with depth, due to the weight of fluid above it.
© 2010 Pearson Education, Inc.

16. 9.2 Fluids: Pressure and Pascal’s Principle
Pressure applied to an enclosed fluid is transmitted undiminished to every point in the fluid and to the walls of the container.
© 2010 Pearson Education, Inc.

17. 9.2 Fluids: Pressure and Pascal’s Principle
Hydraulic lifts and shock absorbers take advantage of Pascal’s principle.
© 2010 Pearson Education, Inc.

18. 9.2 Fluids: Pressure and Pascal’s Principle
Since the pressure is constant, a small force acting over a small area can become a large force acting over a large area.
© 2010 Pearson Education, Inc.

19. 9.2 Fluids: Pressure and Pascal’s Principle
There are a number of methods used to measure pressure.
© 2010 Pearson Education, Inc.

20. 9.2 Fluids: Pressure and Pascal’s Principle
Absolute pressure is the total force per unit area. We often measure the gauge pressure, which is the excess over atmospheric pressure.
Atmospheric pressure historically was measured using a mercury barometer.
© 2010 Pearson Education, Inc.

21. 9.2 Fluids: Pressure and Pascal’s Principle
The pressure corresponding to 1 mm of mercury is called the torr (in honor of Torricelli).
© 2010 Pearson Education, Inc.

22. 9.3 Buoyancy and Archimedes’ Principle
A body immersed wholly or partially in a fluid experiences a buoyant force equal in magnitude to the weight of the volume of fluid that is displaced:
An object’s density will tell you whether it will sink or float in a particular fluid.
© 2010 Pearson Education, Inc.

23. 9.3 Buoyancy and Archimedes’ Principle
The buoyant force on an object that is completely submerged:
© 2010 Pearson Education, Inc.

24. 9.3 Buoyancy and Archimedes’ Principle
It is the average density that matters; a boat made of steel can float because its interior is mostly air.
An object’s density may be changed; submarines fill tanks with water to submerge, and with air to rise.
© 2010 Pearson Education, Inc.

25. 9.3 Buoyancy and Archimedes’ Principle
Specific gravity is the ratio of an object’s density to that of water at 4°C.
© 2010 Pearson Education, Inc.

26. 9.4 Fluid Dynamics and Bernoulli’s Equation
In an ideal fluid, flow is steady, irrotational, nonviscous, and incompressible.
Steady flow means that all the particles of a fluid have the same velocity as they pass a given point.
Steady flow can be described by streamlines.
© 2010 Pearson Education, Inc.

27. 9.4 Fluid Dynamics and Bernoulli’s Equation
Irrotational flow means that a fluid element (a small volume of the fluid) has no net angular velocity. This condition eliminates the possibility of whirlpools and eddy currents. (The flow is nonturbulent.)
In the previous figure, the paddle wheel does not turn, showing that the flow at that point is irrotational.
© 2010 Pearson Education, Inc.

28. 9.4 Fluid Dynamics and Bernoulli’s Equation
Nonviscous flow means that viscosity is negligible. Viscosity produces drag, and retards fluid flow.
Incompressible flow means that the fluid’s density is constant. This is generally true for liquids, but not for gases.
© 2010 Pearson Education, Inc.

29. 9.4 Fluid Dynamics and Bernoulli’s Equation
Equation of continuity:
© 2010 Pearson Education, Inc.

30. 9.4 Fluid Dynamics and Bernoulli’s Equation
If the density is constant,
© 2010 Pearson Education, Inc.

31. 9.4 Fluid Dynamics and Bernoulli’s Equation
Bernoulli’s equation is a consequence of the conservation of energy.
© 2010 Pearson Education, Inc.

32. 9.4 Fluid Dynamics and Bernoulli’s Equation
One consequence of Bernoulli’s equation, that the pressure is lower where the speed is higher, can be counterintuitive.
© 2010 Pearson Education, Inc.

33. 9.4 Fluid Dynamics and Bernoulli’s Equation
The flow rate from a tank with a hole is given by Bernoulli’s equation; the pressure at open areas is atmospheric pressure.
© 2010 Pearson Education, Inc.

34. 9.5 Surface Tension, Viscosity, and Poiseuille’s Law
Surface tension is due to the forces that molecules in a liquid exert on each other. There is a net inward force at the surface.
© 2010 Pearson Education, Inc.

35. 9.5 Surface Tension, Viscosity, and Poiseuille’s Law
All real fluids have some viscosity, which causes drag.
© 2010 Pearson Education, Inc.

36. 9.5 Surface Tension, Viscosity, and Poiseuille’s Law
The higher a fluid’s viscosity, the more it resists flow.
© 2010 Pearson Education, Inc.

37. 9.5 Surface Tension, Viscosity, and Poiseuille’s Law
Poiseuille’s law describes viscous flow in a tube or pipe of length L and radius r.
© 2010 Pearson Education, Inc.

38. Review of Chapter 9
Stress is a measure of the force causing a deformation; strain is a measure of the deformation itself.
Elastic modulus is the ratio of stress to strain.
Pressure is defined as force per unit area.
Pressure varies with depth in a fluid:
© 2010 Pearson Education, Inc.

39. Review of Chapter 9
Pressure in an enclosed fluid is transmitted unchanged to every part of the fluid.
The buoyant force is equal to the weight of displaced fluid.
An object will float if its average density is less than that of the fluid; if it is greater, the object will sink.
© 2010 Pearson Education, Inc.

40. Review of Chapter 9 Equation of continuity: Flow rate equation:
Bernoulli’s law:
© 2010 Pearson Education, Inc.

41. Review of Chapter 9 Surface tension is due to intermolecular forces.
Viscosity is a fluid’s internal resistance to flow.
Poiseuille’s law:
© 2010 Pearson Education, Inc.