C HAPTER
15 TE Fluid Forces
Chapter Outline
15.1 CHAPTER15: FLUIDFORCES
15.1. Chapter 15: Fluid Forces www.ck12.org
15.1 Chapter 15: Fluid Forces
Chapter Overview
All fluids exert pressure because their particles are constantly moving. Pressure is the amount of force per unit area, expressed in the SI unit N/m2, which is called the pascal (Pa). Factors that affect the pressure of fluids include depth and density. According to Pascal’s law, a fluid transmits pressure equally throughout the fluid. According to Bernoulli’s law, the faster a fluid is moving, the less pressure it exerts. Buoyancy is the ability of a fluid to exert an upward force, called buoyant force. According to Archimedes’ law, buoyant force on an object equals the weight of the fluid displaced by the object.
Online Resources
See the following Web sites for appropriate laboratory activities:
With the inquiry lab at the following URL, students will design an experiment that demonstrates Bernoulli’s law.
• http://www.nvscience.org/files/Bernoulli_Doesn_t_Suck_It_Blows1.doc
In the lab at the URL below, students are challenged to make a mini-submarine that behaves in certain ways (sinks to the bottom, stays down for at least 10 seconds, rises back up to the surface). The lab requires students to design their own experiment, identify independent and dependent variables, outline their procedure, and demonstrate their mini-submarine.
• http://serc.carleton.edu/sp/mnstep/activities/27604.html These Web sites may also be helpful:
The following URL provides several interesting activities that demonstrate the properties of fluids under a variety of circumstances. They show the role of pressure in fluid behavior and also relate fluid pressure to everyday experiences.
• http://mypages.iit.edu/~smile/ph95p1.html
At the following URL, you can find several simple demonstrations that will help students understand basic principles relating to air pressure.
• http://mypages.iit.edu/~smile/ph8901.html
Use the ideas and activities at the URL below to teach the physics of the Bernoulli effect.
• http://mypages.iit.edu/~smile/phma2000.htm
The following URL provides a collection of lessons relating to fluid pressure and buoyancy. The lessons begin with a discussion of fluid pressure, buoyant force, and Archimedes’ law. Interesting demonstrations and activities using common objects support the discussion. The activities give students hands-on experience with fluid forces.
• http://www.sbceo.org/~impact2/pdf/pkts2011/RyanHubbard/RyanHubbardComplete.pdf
Pacing the Lessons
T
ABLE15.1:
Pacing the LessonsLesson Class Period(s) (60 min)
15.1 Pressure of Fluids 1.5
15.2 Buoyancy of Fluids 3.0
15.2. Lesson 15.1 Pressure of Fluids www.ck12.org
15.2 Lesson 15.1 Pressure of Fluids
Key Concept
All fluids exert pressure because their particles are constantly moving. Pressure is calculated as the amount of force per unit area, and the SI unit for pressure is the pascal (Pa), or N/m2. The pressure of fluids is greater at greater depths, and denser fluids exert greater pressure than less dense fluids. Pascal’s law states that a change in pressure at any point in an enclosed fluid is transmitted equally throughout the fluid. Bernoulli’s law states that pressure in a moving fluid is less when the fluid is moving faster.
Standards
• SCI.CA.8.IE.9.f; SCI.CA.8.PS.8.a
• NSES.5-8.D.1.8
• AAAS.6-8.1.A.4; AAAS.6-8.3.A.3; AAAS.6-8.3.C.3; AAAS.6-8.9.B.3; AAAS.6-8.11.C.3; AAAS.6-8.12.D.4, 11
Lesson Objectives
• Describe pressure and how to calculate it.
• Relate fluid depth and density to pressure.
• State Pascal’s and Bernoulli’s laws.
Lesson Vocabulary
• Bernoulli’s law: law stating that pressure in a moving fluid is less when the fluid is moving faster
• pascal (Pa):SI unit for pressure, equal to 1 newton per square meter (N/m2)
• Pascal’s law: law stating that a change in pressure at any point in an enclosed fluid is transmitted equally throughout the fluid
Teaching Strategies
Introducing the Lesson
Introduce fluid pressure with the simple but effective “Water in a Cup” demonstration, which is described at the following URL. It demonstrates the effects of air pressure and shows that it acts in all directions. The document includes teacher notes and follow-up questions for class discussion.
• http://pzweb.harvard.edu/ucp/curriculum/pressure/s2_reinforcement_cup.pdf Demonstration
Help students visualize Pascal’s law with the demonstration described at the URL below. The demonstration could be done as a student activity instead. It clearly shows how pressure is transmitted throughout a fluid.
• http://www.sciencefair-projects.org/physics-projects/pascals-law.html Building Science Skills
The class activity described at the following URL demonstrates Bernoulli’s law. After the demonstration of the airfoil, give students a change to experiment with the position of the airfoil, the size of the contact surface at the front, and the length of the airfoil as an inquiry activity to build science skills. A question and answer session should close the activity. Ask, for example, what would happen if the airfoil was turned over (curved surface on bottom) and air was applied.
• http://epic.physics.missouri.edu/PDF%20files/Bernoulli_s_Principle_.pdf Differentiated Instruction
Give less proficient readers the following cloze prompts to complete as they read the lesson. This will help focus their attention on the most important ideas. Make sure students know that most of the blanks require at least a few words to fill in adequately. Sample answers are given in brackets.
1. Fluids are __________. [liquids and gases]
2. All fluids exert pressure because __________. [their particles are constantly moving and bumping into things]
3. Pressure can be represented by the equation __________. [Pressure=Force Area] 4. The SI unit for pressure is __________. [N/m2, or the pascal (Pa)]
5. Two factors that affect pressure in fluids are __________. [depth and density]
6. As you go deeper in the ocean, the pressure exerted by the water __________. [increases]
7. As you go higher in the atmosphere, the pressure exerted by the air __________. [decreases]
8. Pascal’s law states that __________. [a change in pressure at any point in an enclosed fluid is transmitted equally throughout the fluid]
9. An example of Pascal’s law is __________. [ketchup squirting out of the open end of a packet when the opposite end is squeezed]
10. Bernoulli’s law states that __________. [pressure in a moving fluid is less when the fluid is moving faster]
11. Bernoulli’s law explains how __________. [the wings of birds and airplanes create lift and allow them to fly]
Enrichment
Students who are interested in engineering might want to explore hydraulics in greater depth. Direct them to the first URL below, which starts with a video showing how hydraulic machines are used on a crab boat. They can also read about the use of hydraulics in large construction machines, including shovel excavators, skid loaders, and dump trucks. Videos showing each type of machine in operation are included. After students read the article and watch the videos, suggest that they take the hydraulic machines quiz at the second URL below.
• http://science.howstuffworks.com/transport/engines-equipment/hydraulic.htm
• http://science.howstuffworks.com/transport/engines-equipment/hydraulic-machine-quiz1.htm?answerId=2192
15.2. Lesson 15.1 Pressure of Fluids www.ck12.org Science Inquiry
Have small groups of students do the inquiry activity “Fluid Pressure—An Inquiry Introduction,” which you can find at the following URL. The activity uses the first tab of the simulation “Fluid Pressure and Flow” (at the same URL).
Students will investigate how pressure changes in air and water. They will also discover how they can change fluid pressure, and they will predict fluid pressure in a variety of situations.
• http://phet.colorado.edu/en/simulation/fluid-pressure-and-flow Common Misconceptions
Misconceptions about gases and pressure are common. Read the following list of misconceptions to the class. For each statement, ask students to raise their hands if they think the statement is true. Call on other students to restate the misconception so it is true and to explain why.
• Gas is not a fluid; only liquids are fluids.
• Gases do not have properties of mass and weight.
• Air pressure is greater in a downward direction.
• Moving air has pressure only in the direction it is moving; if there is no movement, there is no pressure.
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in theCK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 15.1 Quiz inCK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
If you’ve ever floated in water, you may have noticed that filling your lungs with air helps to keep you afloat.
• Why do you think having more air in your lungs helps you float in water?
• What other things float in water? What things don’t float? How do they differ?