Lesson Plans

Physics: Principles with Applications 5th Revised Edition ©2002

by Douglas Giancoli

Week 12

Chapter 10: Fluids

College Board Performance Objectives:

• Define the properties of fluids.
• In terms of structure, distinguish the differences between solids, liquids, gases, and plasma.
• Distinguish between mass density, weight density, and specific gravity.
• Define the concept of pressure and that of absolute pressure.
• State and apply Pascal's Principle.
• State Archimedes' Principle and its relationship to buoyancy.
• Understand Bernoulli's Equation and its application to ideal fluids.
• Demonstrate an understanding of the workings of an airfoil.
• Discuss surface tension and viscosity.
• Write Poiseuille's equation and give several examples.
• Understand the effect of friction on fluid flow through a horizontal pipe of circular cross section.

College Board Lab Objectives:

• Determine the specific gravity of several solid objects whose density is greater than water.
• Determine the specific gravity of a solid material whose density is less than water.
• Determine the specific gravity of several liquids.
• Design an experiment to measure buoyant effects in fluids.
• Design and conduct an experiment to study and measure liquid viscosity.

Suggested Labs:

• Measurement of Density and Specific Gravity
• Archimedes' Principle
• Bernoulli's Principle
• Viscosity

Resources:

• Chapter 10: Fluids — pp. 275–302
• Student Study Guide — pp. 10-1–10-16
• Instructor's Solution Manual — pp. 150–176
• Test Items File — pp. 161–176

Pacing Guide:

• Density and Specific Gravity—day 1
• Pressure in Fluids—day 1
• Atmospheric Pressure and Gauge Pressure—day 1
• Pascal's Principle—day 2
• Measurement of Pressure; Gauges and Barometer—day 2
• Buoyancy and Archimedes' Principle—day 3
• Fluid in Motion—days 3 and 4
• Bernoulli's Equation—days 3 and 4
• Viscosity—day 4
• Surface Tension and Capillarity—day 4
• Lab—day 5
• Block Scheduling
  Density, specific gravity, pressure in fluids, atmospheric pressure, Pascal's principle, and measurement of pressure require a block. Archimedes' principle, buoyancy, and fluids in motion require a second block. The equation of continuity, the flow rate equation, Bernoulli's equation, surface tension, and viscosity require another block. Stress problem solving with Bernoulli's equation and the equation of continuity.

Key Words:

Critical Thinking Questions:

1. Neglecting temperature variations, determine the ratio of the density of saltwater at a depth of 500 m to the density of saltwater at the surface.
2. An irregularly-shaped metal sample has a weight of 93.0 N in air and 80.3 N when immersed in water.
   1. Calculate the volume of the sample.
   2. What is its density?
   3. The same sample is submerged in an organic liquid where its apparent weight is 84.6 N. What is the density of the liquid?
3. A 55 gallon drum contains water. Water squirts out of a circular hole in the side of the drum. The depth of the water in the drum is H and the vertical distance from the water level to the hole is Y. Show that the horizontal distance, the range R, the water strikes the ground is given byR = 2.
4. Water flows smoothly at a speed v through a cylindrical tube of radius R. What is the speed of the fluid at the point where the tube is enlarged to a radius 8R?
5. Water enters a building through a 6.00 cm diameter pipe with a velocity of 1.20 m/s. The water exits 15.0 m above street level through a 2.00 cm pipe with a velocity of 0.400 m/s. What is the pressure difference between the two levels expressed in Pa and in atm.

Troubleshooting Tips/Error Traps:

• Expressing pressure is complicated. Students are often confused when subjected to pressure units: pascal, atmosphere, in. of Hg, mm of Hg, torr, bar, psi, and other ways of expressing pressure. Explain proper use. Usually a historical background can be given to show why all these different units exist. Applying dimensional analysis will help show the relationships.
• Students usually will be confused when calculating the pressure due to a static column of fluid. The stumbling block is whether or not to include atmospheric pressure. Show examples that atmospheric pressure must be added to the calculations.
• When making calculations with buoyancy, students often tend to use the weight of the body instead of the weight of an equivalent volume of the fluid being displaced.
• Use of Bernoulli's Equation requires consistency in using units and proper identification of terms.

End of Chapter Activity:

1. A coin has a mass of 3.0 g, a radius of 9.5 mm, and a thickness of 1.5 mm. What is the specific gravity of the coin?
   1. 1.8
   2. 3.4
   3. 3.5
   4. 4.5
   5. 7.1
2. If the atmosphere were compressed so it had the density of water, it would cover the earth to a depth of approximately
   1. 0.76 m
   2. 10 m
   3. 14.7 m
   4. 76 m
   5. 100 m
3. A solid has a density . If a second solid having the same volume has three times the mass of the first, what is the density of the second solid?
   1. 
   2. /3
   3. 3
   4. 6
   5. 9
4. A tube with a radius of 42 mm holds an organic fluid that has a specific gravity of 0.92. The tube has a depth of 640 mm. What is the pressure at the bottom of the tube?
   1. 100 Pa
   2. 580 Pa
   3. 1.7 kPa
   4. 5.8 kPa
   5. 1.0 MPa
5. When a solid is submerged beneath the surface of a liquid, the buoyant force acting on the solid is equal to the
   1. viscosity of the liquid
   2. the surface tension of the liquid displaced
   3. the weight of the liquid displaced
   4. the weight of the liquid directly above the surface of the solid
   5. the density of the liquid
6. The two pistons in a hydraulic lift have radii of 26.7 mm and 200 mm respectively. What force must be applied to the 26.7 mm piston so that a 19.6kN weight resting on the 200 mm piston is lifted?
   1. 35 N
   2. 0.27 kN
   3. 0.35 kN
   4. 1.5 kN
   5. 3.0 kN
7. Which of the following is independent of the density of a liquid in a cylinder?
   1. the total force at the bottom of the cylinder
   2. the pressure at the surface of the liquid
   3. the pressure at the bottom of the cylinder
   4. the force on the sides of the cylinder
   5. the pressure on the sides of the cylinder
8. The ratio of an object's weight density to its mass density is
   1. less than 1
   2. is greater than 1
   3. unitless
   4. equal to g
   5. the absolute pressure
9. A cube of cork weighs 2 N. When placed in water exactly half of its volume is submerged. The weight of the displaced water is
   1. 0.5 N
   2. 1 N
   3. 2 N
   4. 4 N
   5. 9.8 N
10. If the flow rate of a liquid moving through a 40 mm diameter pipe is 0.008 m³/s, the average fluid speed in the pipe is
    1. 0.064 m/s
    2. 0.640 m/s
    3. 1.00 m/s
    4. 2.42 m/s
    5. 3.20 m/s
    
    

answers: 1 (e), 2 (b), 3 (c), 4 (d), 5 (c), 6 (c), 7 (b), 8 (d), 9 (c), 10 (b)

Suggested Problem Assignments: