1 / 89

Chapter 15 Fluids and Elasticity

Chapter 15 Fluids and Elasticity. Chapter Goal: To understand macroscopic systems that flow or deform. Slide 15-2. Chapter 15 Preview. Slide 15-3. Chapter 15 Preview. Slide 15-4. Chapter 15 Preview. Slide 15-5. Chapter 15 Preview. Slide 15-6. Chapter 15 Preview. Slide 15-7.

paytah
Download Presentation

Chapter 15 Fluids and Elasticity

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 15 Fluids and Elasticity Chapter Goal: To understand macroscopic systems that flow or deform. Slide 15-2

  2. Chapter 15 Preview Slide 15-3

  3. Chapter 15 Preview Slide 15-4

  4. Chapter 15 Preview Slide 15-5

  5. Chapter 15 Preview Slide 15-6

  6. Chapter 15 Preview Slide 15-7

  7. Chapter 15 Preview Slide 15-8

  8. Gases • A gas is a system in which each molecule moves through space as a free particle until, on occasion, it collides with another molecule or with the wall of the container. • Gases are fluids; they flow, and exert pressure. • Gases are compressible; the volume of a gas is easily increased or decreased. Slide 15-19

  9. Liquids • Liquids are fluids; they flow, and exert pressure. • Liquids are incompressible; the volume of a liquid is not easily increased or decreased. Slide 15-20

  10. Volume • An important parameter of a macroscopic system is its volume V. • The S.I. unit of volume is m3. • Some unit conversions: 1 m3 = 1000 L 1L = 1000 cm3 1m3 =106 cm3 Slide 15-21

  11. Density The ratio of an object’s or material’s mass to its volume is called the mass density, or sometimes simply “the density.” The SI units of mass density are kg/m3. Slide 15-22

  12. QuickCheck 15.1 A piece of glass is broken into two pieces of different size. How do their densities compare? 1 > 3 > 2. 1 = 3 = 2. 1 < 3 < 2. Slide 15-23

  13. QuickCheck 15.1 A piece of glass is broken into two pieces of different size. How do their densities compare? 1 > 3 > 2. 1 = 3 = 2. 1 < 3 < 2. Density characterizes the substance itself, not particular pieces of the substance. Slide 15-24

  14. Densities of Various Fluids Slide 15-25

  15. Example 15.1 Weighing the Air Slide 15-26

  16. Pressure • What is “pressure”? • Consider a container of water with 3 small holes drilled in it. • Pressure pushes the water sideways, out of the holes. • In this liquid, it seems the pressure is larger at greater depths. Slide 15-27

  17. Pressure • A fluid in a container presses with an outward force against the walls of that container. • The pressure is defined as the ratio of the force to the area on which the force is exerted. The SI units of pressure are N/m2, also defined as the pascal, where 1 pascal= 1 Pa = 1 N/m2. Slide 15-28

  18. Learning About Pressure FACTS about PRESSURE Slide 15-29

  19. Pressure There are two contributions to the pressure in a container of fluid: A gravitational contribution, due to gravity pulling down on the liquid or gas. A thermal contribution, due to the collisions of freely moving gas molecules within the walls, which depends on gas temperature. Slide 15-31

  20. Atmospheric Pressure The global average sea-level pressure is 101,300 Pa. Consequently we define the standard atmosphere as Slide 15-32

  21. Pressure • If you hold out your arm, which has a surface area of about 200 cm3, the atmospheric pressure on the top of your arm is  2000 N, or about 450 pounds. • How can you even lift your arm? • The reason is that a fluid exerts pressure forces in all directions. • The air underneath your arm exerts an upward force of the same magnitude, so the net force is close to zero. Slide 15-33

  22. Example 15.2 A Suction Cup Slide 15-34

  23. Example 15.2 A Suction Cup Slide 15-35

  24. Example 15.2 A Suction Cup Slide 15-36

  25. Example 15.2 A Suction Cup Slide 15-37

  26. net= 0 Pressure in Liquids • The shaded cylinder of liquid in the figure, like the rest of the liquid, is in static equilibrium with . • Balancing the forces in the free-body diagram: • The volume of the cylinder is V = Ad and its mass is m = Ad. • Solving for pressure: Slide 15-38

  27. Example 15.3 The Pressure on a Submarine Slide 15-39

  28. Liquids in Hydrostatic Equilibrium • No! • A connected liquid in hydrostatic equilibrium rises to the same height in all open regions of the container. Slide 15-40

  29. QuickCheck 15.2 What can you say about the pressures at points 1 and 2? p1 > p2. p1 = p2. p1 < p2. Slide 15-41

  30. QuickCheck 15.2 What can you say about the pressures at points 1 and 2? p1 > p2. p1 = p2. p1 < p2. Hydrostatic pressure is the same at all points on a horizontal line through a connected fluid. Slide 15-42

  31. Liquids in Hydrostatic Equilibrium • No! • The pressure is the same at all points on a horizontal line through a connected liquid in hydrostatic equilibrium. Slide 15-43

  32. QuickCheck 15.3 An iceberg floats in a shallow sea. What can you say about the pressures at points 1 and 2? p1 > p2. p1 = p2. p1 < p2. Slide 15-44

  33. QuickCheck 15.3 An iceberg floats in a shallow sea. What can you say about the pressures at points 1 and 2? p1 > p2. p1 = p2. p1 < p2. Hydrostatic pressure is the same at all points on a horizontal line through a connected fluid. Slide 15-45

  34. Example 15.4 Pressure in a Closed Tube Slide 15-46

  35. Example 15.4 Pressure in a Closed Tube Slide 15-47

  36. Example 15.4 Pressure in a Closed Tube Slide 15-48

  37. Example 15.4 Pressure in a Closed Tube Slide 15-49

  38. QuickCheck 15.4 What can you say about the pressures at points 1, 2, and 3? p1 = p2 = p3. p1 = p2 > p3. p3 > p1 = p2. p3 > p1 > p2. p1 = p3 > p2. Slide 15-50

  39. QuickCheck 15.4 What can you say about the pressures at points 1, 2, and 3? p1 = p2 = p3. p1 = p2 > p3. p3 > p1 = p2. p3 > p1 > p2. p1 = p3 > p2. Hydrostatic pressure is the same at all points on a horizontal line through a connected fluid. Slide 15-51

  40. Gauge Pressure where 1 atm = 101.3 kPa. Many pressure gauges, such as tire gauges and the gauges on air tanks, measure not the actual or absolute pressure p but what is called gauge pressure pg. A tire-pressure gauge reads the gauge pressure pg, not the absolute pressure p. Slide 15-52

  41. Example 15.5 An Underwater Pressure Gauge Slide 15-54

  42. Barometers • Figure (a) shows a glass tube, sealed at the bottom and filled with liquid. • We seal the top end, invert the tube, place it in an open container of the same liquid, and remove the seal. • This device, shown in figure (b), is a barometer. • We measure the height h of the liquid in the tube. • Since p1 = p2: Slide 15-57

  43. Pressure Units Slide 15-58

  44. The Hydraulic Lift • Consider a hydraulic lift, such as the one that lifts your car at the repair shop. • The system is in static equilibrium if: Force-multiplying factor If h is small, negligible Slide 15-60

  45. The Hydraulic Lift • Suppose we need to lift the car higher. • If piston 1 is pushed down a distance d1, the car is lifted higher by a distance d2: Work is done on the liquid by the small force; work is done by the liquid when it lifts the heavy weight. What about PE grav of the liquid!!! Slide 15-61

  46. Example 15.7 Lifting a Car Slide 15-62

  47. Example 15.7 Lifting a Car Slide 15-63

  48. Buoyancy • Consider a cylinder submerged in a liquid. • The pressure in the liquid increases with depth. • Both cylinder ends have equal area, so Fup > Fdown. • The pressure in the liquid exerts a net upward force on the cylinder: • Fnet = Fup – Fdown. • This is the buoyant force. Slide 15-64

  49. Buoyancy The buoyant force on an object is the same as the buoyant force on the fluid it displaces. Slide 15-65

  50. Buoyancy • When an object (or portion of an object) is immersed in a fluid, it displaces fluid. • The displaced fluid’s volume equals the volume of the portion of the object that is immersed in the fluid. • Suppose the fluid has density f and the object displaces volume Vfof fluid. • Archimedes’ principle in equation form is: Slide 15-66

More Related