Fluids, Thermodynamics, Waves, and Optics Overview of Course Fluids

Transcription

1 Fluids, Thermodynamics, Waves, and Optics Overview of Course Fluids Lana Sheridan De Anza College April 10, 2017

2 Overview of the Course There are 4 main sections to this course. Topics fluids thermodynamics waves light and optics

3 Overview of the Course: Textbook Topics Book Physics for Scientists and Engineers, 9th Edition, Serway & Jewett What we will cover Chapter 14, fluids Chapters 19-22, thermodynamics Chapter 15-18, waves Chapter 35-38, light and optics

4 Overview of the Course Other Books Fundamentals of Physics Extended, Halliday, Resnick, and Walker Feynman Lectures on Physics Physics for Scientists and Engineers, Knight Assignments Collected homework problems on worksheets. Uncollected homework problems from the textbook. (You still need to do them.) Read the textbook. You will need to spend time on your own thinking through concepts and reading. You will need to make time to work on problems outside of class and discuss with others.

5 Useful Survival Trick

6 Useful Survival Trick When you get stuck, use a search engine.

7 Other Resources Resources for when you have questions Me. You can me, ask me before or after class, or come to my office hours. M,W 8-8:30pm

8 Other Resources Resources for when you have questions Me. You can me, ask me before or after class, or come to my office hours. M,W 8-8:30pm Each other. Work together! It will improve your understanding.

9 Other Resources Resources for when you have questions Me. You can me, ask me before or after class, or come to my office hours. M,W 8-8:30pm Each other. Work together! It will improve your understanding. The Math & Science Tutorial Center. Where to look for course materials Course Studio. My website on the De Anza Physics page. lanasheridan/index.html

10 Overview of the Course Evaluation quizzes (10%) 3 Tests (6% + 9% + 9% = 24%) Final exam (30%) 4 collected HWs (16%) Labs (20%) Other Assignments Uncollected homework problems from the textbook. (You still need to do them.) Read the textbook.

11 Overview of the Course Evaluation Projected Grading Scheme: 95% 100% = A+ 88% 94% = A 85% 87% = A 82% 84% = B+ 73% 81% = B 70% 72% = B 65% 69% = C+ 55% 64% = C 46% 54% = D 0% 45% = F

12 Overview of the Course Note about presentation of work For each problem make sure your method is clear. Draw a diagram, define coordinates, if needed! If there is an equation or principle you are using, write it out at the start of your solution. Underline, box, highlight, or unambiguously emphasize the answer. If the reasoning is not clear, the answer is not correct. Give your answers to a reasonable number of significant figures.

13 Overview of the Course Note about collected assignments If you cannot come to class on a due date, me the assignment and bring the hard copy to the next class. If you are ill, or will have a problem handing in an assignment on time, come talk to me before the due date.

14 Fluids, Thermodynamics, and Optics Imagine yourself in the world of 1700.

15 Fluids, Thermodynamics, and Optics Imagine yourself in the world of no high speed transportation almost no mass-manufacturing no refrigeration no household appliances no airplanes or human flight

16 Fluids, Thermodynamics, and Optics Imagine yourself in the world of no high speed transportation almost no mass-manufacturing no refrigeration no household appliances no airplanes or human flight What changed?

17 Fluids, Thermodynamics, and Optics Imagine yourself in the world of no high speed transportation almost no mass-manufacturing no refrigeration no household appliances no airplanes or human flight What changed? We learned a lot about fluids and thermodynamics.

18 Fluids, Thermodynamics, and Optics Fast forward to Electromagnetic theory, thermodynamics, statistical mechanics were well-developed. This allowed the steam engine and the industrial revolution. Fluids and the effect of heating gases were well enough understood to allow manned hot air balloons by the 1780s and the Wright brothers to attempt powered fight in 1912.

19 Fluids, Thermodynamics, and Optics However, there were still a few problems for physics. Kelvin: The beauty and clearness of the dynamical theory, which asserts heat and light to be modes of motion, is at present obscured by two clouds. I. The first came into existence with the undulatory theory of light, and was dealt with by Fresnel and Dr Thomas Young; it involved the question, How could the earth move through an elastic solid, such as essentially is the luminiferous ether? II. The second is the Maxwell-Boltzmann doctrine regarding the partition of energy.

20 Fluids, Thermodynamics, and Optics As for optics, the use and manufacture of lenses has been known since 750 BCE. Many new optical devices, and a better understanding of light and waves were developed in the 1600s. 20th century progress allowed for the laser, optical drives, antireflective coatings, optical fibers, Doppler cooling, control of individual atoms, and advances in medical technology.

21 This Course Questions we want to answer: How does an airplane wing create an upward lifting force? Why does hot metal start to glow read when heated?

22 This Course Questions we want to answer: How does an airplane wing create an upward lifting force? Why does hot metal start to glow read when heated? When a block of ice is left out at room temperature and pressure it will melt. Why does this happen?

23 This Course Questions we want to answer: How does an airplane wing create an upward lifting force? Why does hot metal start to glow read when heated? When a block of ice is left out at room temperature and pressure it will melt. Why does this happen? Why is it not uncommon to see a glass cup fall and shatter, but we never see a pile of broken glass reassemble itself into a cup?

24 This Course Questions we want to answer: How does an airplane wing create an upward lifting force? Why does hot metal start to glow read when heated? When a block of ice is left out at room temperature and pressure it will melt. Why does this happen? Why is it not uncommon to see a glass cup fall and shatter, but we never see a pile of broken glass reassemble itself into a cup? Why can you hear someone s voice when they are still around a corner from you, but you can t see them?

25 This Course Questions we want to answer: How does an airplane wing create an upward lifting force? Why does hot metal start to glow read when heated? When a block of ice is left out at room temperature and pressure it will melt. Why does this happen? Why is it not uncommon to see a glass cup fall and shatter, but we never see a pile of broken glass reassemble itself into a cup? Why can you hear someone s voice when they are still around a corner from you, but you can t see them? Why is the sky bright during the day? Why is the daytime sky blue?

26 This Course Goals: be able to answer those types of conceptual questions know how to use theory to solve problems understanding principles and how they apply to technology

27 Quick Reminder: What is Physics? Physics is the science of fundamental interactions of matter and energy.

28 Quick Reminder: What is Physics? Physics is the science of fundamental interactions of matter and energy. How is it done? Make a simplified model of the system of interest, then apply a principle to make a quantitative prediction.

29 Quick Reminder: What is Physics? Physics is the science of fundamental interactions of matter and energy. How is it done? Make a simplified model of the system of interest, then apply a principle to make a quantitative prediction. System Any physical object or group of objects about which we would like to make quantitative predictions.

30 Quick Reminder: What is Physics? Physics is the science of fundamental interactions of matter and energy. How is it done? Make a simplified model of the system of interest, then apply a principle to make a quantitative prediction. System Any physical object or group of objects about which we would like to make quantitative predictions. Model A simplified description of a system and its interactions that includes only what is necessary to make predictions.

31 Fluids In 4A we talked about the motion of rigid objects. They could translate or rotate. Fluids, on the other hand, deform. The methods we looked at for describing forces and motion of rigid objects need to be extended to deal with fluids.

32 Fluids Matter can be in one of four states: solid liquid gas plasma

33 Fluids Solids have definite shape and volume. Liquids have definite volume, but can flow and change shape. Gases have neither definite volume or definite shape. In fact, whether we treat a particular substance as a solid or a liquid can depend on the time scale of interest.

34 Fluids The term fluid encompasses both liquids and gases. It is a collection of molecules that are only weakly influenced by intermolecular forces and thus can flow over each other. 1 Figure from Wikipedia, user Duk.

35 Fluids The term fluid encompasses both liquids and gases. It is a collection of molecules that are only weakly influenced by intermolecular forces and thus can flow over each other. Formally, Fluids deform continuously under shearing stress. 1 Figure from Wikipedia, user Duk.

36 r substance to change t the substance as a Fluid Statics held together We firstby consider fluid statics: fluids at rest in a container. r. Both liquids and ples and analysis ics of a fluid at rest, mics. At any point on the surface of the object, the force exerted by the fluid is perpendicular to the surface of the object. s those discussed in object submerged in ides. In other words, Figure 14.1 The forces exerted cular Fluids to the surfaces will exert pressure by a fluid on on objects the surfaces submerged of a sub-imerged them and also in Section the12.4. walls of the container. object. 417

37 held together by r. Both Pressure liquids and the object, the force exerted by the fluid is perpendicular to the surface of the object. ples and analysis ics of a fluid at rest, mics. s those discussed in object submerged in ides. In other words, Figure 14.1 The forces exerted cular to the surfaces by a fluid on the surfaces of a submerged object. in Section Pressure is the normal force per unit area on a surface: P = F A 417

38 Pressure It is possible that the pressure on a surface varies over the surface. Then we will need to extend our definition: δf = P δa δf is the force on a tiny area δa. As δa 0, the pressure can be a continuous function of the position on the surface.

39 Pressure It is possible that the pressure on a surface varies over the surface. Then we will need to extend our definition: δf = P δa δf is the force on a tiny area δa. As δa 0, the pressure can be a continuous function of the position on the surface. Units: the Pascal (after Blaise Pascal), symbol Pa 1 Pa = 1 N/m 2

40 Pressure Pressure is a scalar quantity. We relate it to force, a vector, by: δf = P δa ˆn where ˆn is a unit vector perpendicular to the small area δa. In a gas or liquid, its underlying cause is molecular collisions: 1 Diagram by Brant Carlson, on Wikipedia.

41 Question Quick Quiz Suppose you are standing directly behind someone who steps back and accidentally stomps on your foot with the heel of one shoe. Would you be better off if that person were A a large, male professional basketball player wearing sneakers or B a petite woman wearing spike-heeled shoes? 1 Page 418, Serway & Jewett

42 Question Quick Quiz Suppose you are standing directly behind someone who steps back and accidentally stomps on your foot with the heel of one shoe. Would you be better off if that person were A a large, male professional basketball player wearing sneakers or B a petite woman wearing spike-heeled shoes? 1 Page 418, Serway & Jewett

43 Ambient Atmospheric Pressure The air around us exerts force on us, the walls of the room, the floor, etc. Is it a large pressure?

44 Ambient Atmospheric Pressure The air around us exerts force on us, the walls of the room, the floor, etc. Is it a large pressure? In a sense, yes! P 0 = P atm = Pa

45 Pressure in a Liquid in a Gravitational Field In a uniform gravitational field, liquid pressure depends on depth. P liq = ρgh where ρ = m/v is the mass density of the liquid and h is the depth. It does not depend on the total amount of water involved, just the depth of water.

46 Liquid Pressure A slice of liquid of cross section A at a depth h must support all the water in a column directly above it. The force exerted downward by the column of water is F = mg = ρvg.

47 Liquid Pressure F = mg = ρvg = ρahg 1 Figure from HyperPhysics.

48 Liquid Pressure F = mg = ρvg = ρahg Pressure, P liq = F A = ρahg A = ρgh. 1 Figure from HyperPhysics.

49 Total Pressure The liquid pressure only expresses the pressure due to the weight of the fluid above. However, this is not the total pressure in most circumstances, eg. diving on earth.

50 Total Pressure The liquid pressure only expresses the pressure due to the weight of the fluid above. However, this is not the total pressure in most circumstances, eg. diving on earth. The total pressure or absolute pressure is the sum of the pressure due to the liquid and the pressure due to the atmosphere. P total = P 0 + ρgh where P 0 = P atm = Pa.

51 Pressure varies with Depth

52 Pascal s Barrel

53 Density of Water For water: ρ w = kg/m 3 That is ρ w = 1 g/cm 3.

54 Density of Water For water: ρ w = kg/m 3 That is ρ w = 1 g/cm 3. Originally, the gram was defined to be the mass of one cubic centimeter of water at the melting point of water.

55 Questions Calculate the water pressure at the base of the Hoover Dam. The depth of water behind the dam is 220 m. 2 2 Question from Hewitt, Conceptual Physics, 11th ed. 3 See example 14.4, page 422, Serway & Jewett, 9th ed.

56 Questions Calculate the water pressure at the base of the Hoover Dam. The depth of water behind the dam is 220 m. 2 Density of water: ρ w = 1000 kg/m 3 2 Question from Hewitt, Conceptual Physics, 11th ed. 3 See example 14.4, page 422, Serway & Jewett, 9th ed.

57 Questions Calculate the water pressure at the base of the Hoover Dam. The depth of water behind the dam is 220 m. 2 Density of water: ρ w = 1000 kg/m 3 P liq = Pa P total Pa 2 Question from Hewitt, Conceptual Physics, 11th ed. 3 See example 14.4, page 422, Serway & Jewett, 9th ed.

58 Questions Calculate the water pressure at the base of the Hoover Dam. The depth of water behind the dam is 220 m. 2 Density of water: ρ w = 1000 kg/m 3 P liq = Pa P total Pa Now consider, if the dam is 380 m long, what is the total force exerted by the water on the dam? 3 2 Question from Hewitt, Conceptual Physics, 11th ed. 3 See example 14.4, page 422, Serway & Jewett, 9th ed.

59 Questions Calculate the water pressure at the base of the Hoover Dam. The depth of water behind the dam is 220 m. 2 Density of water: ρ w = 1000 kg/m 3 P liq = Pa P total Pa Now consider, if the dam is 380 m long, what is the total force exerted by the water on the dam? 3 F = N 2 Question from Hewitt, Conceptual Physics, 11th ed. 3 See example 14.4, page 422, Serway & Jewett, 9th ed.

60 Questions Now consider, if the dam is 380 m long, what is the total force exerted by the water on the dam? 3 See example 14.4, page 422, Serway & Jewett, 9th ed.

61 he middle ear. Using this technique equalizes the pressure. Questions Now consider, if the dam is 380 m long, what is the total force exerted by the water on the dam? 14.5). Determine the h y cannot calculate the pressure in the water e dam also increases., we must use integraproblem. H ttom of the dam. We x a distance y above the O on each such strip is Figure (Example 14.4) Water See example 14.4, page 422, Serway & Jewett, 9th ed. w dy y

62 Pressure in a liquid We have this expression for total pressure: P total = P 0 + ρgh What if the pressure at the surface of the liquid, P 0, was increased to P 1. How would we expect this relation to change?

63 Pressure in a liquid We have this expression for total pressure: P total = P 0 + ρgh What if the pressure at the surface of the liquid, P 0, was increased to P 1. How would we expect this relation to change? P total = P 1 + ρgh The differences in pressure between the different layers of liquid remain the same, but the pressure at each depth h increases.

64 Pascal s Law This simple idea is captured by Pascal s Law. Pascal s law applied to confined, incompressible fluids. Pascal s Law A change in pressure applied to one part of an (incompressible) fluid is transmitted undiminished to every point of the fluid.

65 Pascal s Law This simple idea is captured by Pascal s Law. Pascal s law applied to confined, incompressible fluids. Pascal s Law A change in pressure applied to one part of an (incompressible) fluid is transmitted undiminished to every point of the fluid. This does not mean that the pressure is the same at every point in the fluid. It means that if the pressure is increased at one point in the fluid, it increases by the same amount at all other points.

66 Pascal s Principle Since the changes in pressures at the left end and the right end are the same: Since A 2 > A 1, F 2 > F 1. P 1 = P 2 F 1 = F 2 A 1 A 2

67 Hydraulic Lift This has applications: 1 Figure from hyperphysics.phy-astr.gsu.edu.

68 Question If a pair of pistons are connected on either end of a hydraulic tube. The first has area 0.2 m 2 and the second has an area of 4 m 2. A force of 30 N is applied the first piston. What is the force exerted by the second piston on a mass that rests on it?

69 Question If a pair of pistons are connected on either end of a hydraulic tube. The first has area 0.2 m 2 and the second has an area of 4 m 2. A force of 30 N is applied the first piston. What is the force exerted by the second piston on a mass that rests on it? If the first piston is depressed a distance of 1 m by the 30 N force, how far does the second piston rise?

70 Measuring Pressure 418 Chapter 14 Fluid Mechanics Pressure in a fluid could be measured using a device like this: Vacuum A S F Figure 14.2 A simple device for The pressure is measuring proportional the topressure the compression exerted of the spring. by a fluid. 1 Diagram from Serway & Jewett, 9th ed. The pre The device to a spring the piston is balanced measured d force exert the fluid at of the force

71 Barometers Barometers are devices for measuring local atmospheric pressure. Typically, simple barometers are filled with mercury, which is very dense. The weight of the mercury in the tube exerts the same pressure as the surrounding atmosphere. On low pressure days, the level of the mercury drops. On high pressure days it rises.

72 Mercury Barometer The pressure at points A and B is the same. The pressure at B is P 0. h P 0 Above the mercury in the tube is a vacuum, so pressure at A is ρ Hg gh. (ρ Hg = 13.6 kg/m 3 ) A P 0 B Therefore, P 0 = ρ Hg gh. h P 0 Pressure is sometimes quoted in inches of mercury. a 1 Diagrams from Serway & Jewett, 9th ed.

73 mon baromd Manometer at one end. 14.6a). The of the merpoint A, due to the atmold move mererefore, P 0 5 the mercury lumn varies, us determine atm 5 be the pres- The pressure being measured, P, can be compared to atmospheric pressure P 0 by measuring the height of the incompressible fluid in the U-shaped tube. a P A h P 0 B b If h is positive, P > P 0, if negative, P < P m Figure 14.6 Two devices for P P 0 is calledmeasuring the gauge pressure: pressure. (a) a mercury barometer and (b) an open-tube

74 Summary content of the course static fluids pressure Pascal s law buoyancy Quiz Wednesday, April 12, in class. Test Wednesday, April 19, in class. Collected Homework due Wednesday, April 19. (Uncollected) Homework Get the textbook: Physics for Scientists and Engineers, 9th Edition, Serway & Jewett Read Ch 14. Ch 14, onward from page 435, OQs: 1; CQs: 1, 3, 7; Probs: 1, 3, 7, 9, 11, 15, 19, 21