Fluid Mechanics with teacher's notes

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$Holt Math Minnesota Test Prep Workbook for Grade 9$

$Math Skills: More Practice$

TEMPERATURE IN A GAS Density and pressure are not the only two quantities useful in describing a fluid. The temperature of a fluid is also important. We often associate the concept of temperature with how hot or cold an object feels when we touch it. Thus, our senses provide us with qualitative indications of temperature. But to understand what the temperature of a gas really measures, we must turn again to the kinetic theory of gases. Like pressure, temperature in a gas can be understood on the basis of what is happening on the atomic scale. Kinetic theory predicts that temperature is proportional to the average kinetic energy of the particles in the gas. The higher the temperature of the gas, the faster the particles move. As the speed of the particles increases, the rate of collisions against the walls of the container increases. More momentum is transferred to the container walls in a given time interval, resulting in an increase in pressure. Thus, kinetic theory predicts that the pressure and temperature of a gas are related. As we will see later in this chapter, this is indeed the case. The SI units for temperature are kelvins and degrees Celsius (written K and °C). To quickly convert from the Celsius scale to the Kelvin scale, add 273. Room temperature is about 293 K (20°C). Section Review Copyright © by Holt, Rinehart and Winston. All rights reserved. temperature 1. Which of the following exerts the most pressure while resting on a floor? a. a 25 N box with 1.5 m sides b. a 15 N cylinder with a base radius of 1.0 m c. a 25 N box with 2.0 m sides d. a 25 N cylinder with a base radius of 1.0 m 2. Water is to be pumped to the top of the Empire State Building, which is 366 m high. What gauge pressure is needed in the water line at the base of the building to raise the water to this height? (Hint: See Table 9-1 for the density of water.) 3. A room on the first floor of a hospital has a temperature of 20°C. A room on the top floor has a temperature of 22°C. In which of these two rooms is the average kinetic energy of the air particles greater? 4. The temperature of the air outside on a cool morning is 11°C. What is this temperature on the Kelvin scale? a measure of the average kinetic energy of the particles in a substance CONCEPT PREVIEW Temperature and temperature scales will be discussed further in Chapter 10. 5. When a submarine dives to a depth of 5.0 × 10 2 m, how much pressure, in Pa, must its hull be able to withstand? How many times larger is this pressure than the pressure at the surface? (Hint: See Table 9-1 for the density of sea water.) Fluid Mechanics 331 SECTION 9-2 Section Review ANSWERS 1. a 2. 3.59 × 10 6 Pa 3. room on the top floor 4. 284 K 5. 5.0 × 10 6 Pa; 5.0 × 10 1 331
Section 9-3 Demonstration 7 Fluid flow around a table-tennis ball Purpose Introduce students to some of the interesting effects of fluid flow. Materials table-tennis ball glued to the end of a piece of light string, water faucet Procedure Tell the class that this section covers the surprising phenomena of fluids in motion “sucking in” things around them. Hold the end of the string so that the ball is a few centimeters below the faucet but away from the stream path. When you turn on the faucet, the ball is attracted to the water. Demonstration 8 Fluid flow through two cans Purpose Further introduce the effects of fluid flow. Materials two soda cans, flat surface Procedure Lay the soda cans on their sides approximately 2 cm apart on a table or other flat surface. Ask students what would happen if you were to blow air between the two cans. Ask a student volunteer to blow between the cans. The cans will move toward each other. Explain that the air moves faster between the cans, lowering the pressure between them and drawing them together. 332 9-3 SECTION OBJECTIVES • Examine the motion of a fluid using the continuity equation. • Apply Bernoulli’s equation to solve fluid-flow problems. • Recognize the effects of Bernoulli’s principle on fluid motion. 332 Chapter 9 9-3 Fluids in motion FLUID FLOW Figure 9-10 The water flowing around this cylinder exhibits laminar flow and turbulent flow. ideal fluid a fluid that has no internal friction or viscosity and is incompressible Have you ever gone canoeing or rafting down a river? If so, you may have noticed that part of the river flowed smoothly, allowing you to float calmly or to simply paddle along. At other places in the river, there may have been rocks or dramatic bends that created foamy whitewater rapids. When a fluid, such as river water, is in motion, the flow can be characterized in one of two ways. The flow is said to be laminar if every particle that passes a particular point moves along the same smooth path traveled by the particles that passed that point earlier. This path is called a streamline. Different streamlines cannot cross each other, and the streamline at any point coincides with the direction of fluid velocity at that point. The smooth stretches of a river are regions of laminar flow. In contrast, the flow of a fluid becomes irregular, or turbulent, above a certain velocity or under conditions that can cause abrupt changes in velocity, such as where there are obstacles or sharp turns in a river. Irregular motions of the fluid, called eddy currents, are characteristic of turbulent flow. Examples of turbulent flow are found in water in the wake of a ship or in the air currents of a severe thunderstorm. Figure 9-10 shows a photograph of water flowing past a cylinder. Hydrogen bubbles were added to the water to make the streamlines and the eddy currents visible. Notice the dramatic difference in flow patterns between the laminar flow and the turbulent flow. Laminar flow is much easier to model because it is predictable. Turbulent flow is extremely chaotic and unpredictable. The ideal fluid model simplifies fluid-flow analysis Many features of fluid motion can be understood by considering the behavior of an ideal fluid. While discussing density and buoyancy, we assumed all of the fluids used in problems were practically incompressible. A fluid is incompressible if the density of the fluid always remains constant. Incompressibility is one of the characteristics of an ideal fluid. The term viscosity refers to the amount of internal friction within a fluid. Internal friction can occur when one layer of fluid slides past another layer. A fluid with a high viscosity flows more slowly through a pipe than does a fluid with a low viscosity. As a viscous fluid flows, part of the kinetic energy of the fluid is Copyright © by Holt, Rinehart and Winston. All rights reserved.
Page 1 and 2: Chapter 9 Overview Section 9-1 defi
Page 3 and 4: Section 9-1 Demonstration 1 Volume
Page 5 and 6: SECTION 9-1 The Language of Physics
Page 7 and 8: SECTION 9-1 Demonstration 4 Lifting
Page 9 and 10: SECTION 9-1 PRACTICE GUIDE 9A Solvi
Page 11 and 12: SECTION 9-2 STOP 326 Misconception
Page 13 and 14: SECTION 9-2 Visual Strategy Figure
Page 15: SECTION 9-2 Classroom Practice The
Page 19 and 20: SECTION 9-3 Misconception STOP Aler
Page 21 and 22: SECTION 9-3 Classroom Practice The
Page 23 and 24: Section 9-4 Demonstration 10 Temper
Page 25 and 26: SECTION 9-4 Classroom Practice The
Page 27 and 28: Chapter 9 Summary Teaching Tip Ask
Page 29 and 30: 9 REVIEW & ASSESS 12. because the p
Page 31 and 32: 9 REVIEW & ASSESS 42. 7.1 m 43. 17
Page 33 and 34: 9 REVIEW & ASSESS 63. 60.9 m/s 2 64
Page 35 and 36: Chapter 9 Laboratory Exercise NOTE
Page 37 and 38: CHAPTER 9 LAB Boyle’s Law Apparat

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