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TE Lesson: Puttin' It All Together
Related Curriculum
Learning Objectives (Return to Contents) After this lesson, students should be able to:
Introduction/Motivation (Return to Contents) The previous lessons and activities in this unit provided examples that demonstrate the physical science concepts of mechanical energy, work and power, momentum and collisions, and friction and drag. While waterwheels were used as a demonstration of work and power, if you look deeper into a waterwheel system, you will see aspects of mechanical energy, momentum, and friction as well. Water turns the wheel by going from a high potential energy to kinetic energy. Also, if there were no load on the waterwheel and the water supply ran out, the wheel would keep turning, showing signs of momentum. However, friction would eventually bring the wheel to a stop. It is important to note that in real-world physical systems, these energy of motion concepts are commonly interconnected with each other. Much of our everyday lives and safety depend on engineers designing vehicles and structures with a firm understanding of these concepts and their interaction. For example, skateboards, scooters, roller coasters, trains, cars, planes, trucks, elevators, etc. In this lesson, we put all of these concepts together to understand how they work collectively in a hands-on, inclined ramp activity. Lesson Background & Concepts for Teachers (Return to Contents)
PE = mass x g x height and where g is gravity measured as 9.81 meters/sec2 (32.2 feet/sec2) at sea level. As an object goes from a high to a low position or height, its potential energy is converted into kinetic energy. Naturally, as kinetic energy increases, the objects velocity increases and the object gains momentum. Momentum is defined as: Momentum = mass x velocity with units measured in kg-meter/sec. With momentum, two types of collisions exist: elastic collisions, in which momentum is conserved, and inelastic collisions, in which momentum is not conserved. A rubber ball and a ball of silly putty are good examples of objects that experience elastic and inelastic collisions. A rubber ball experiences elastic collisions and the silly putty experiences inelastic collisions.
FF = μ × W where FF is the force of friction measured in Newtons (N) or pounds (lbs), μ is the coefficient of friction which is unit-less, and W is the weight of the object. μs and μk are used in the cases of static friction and kinetic friction. Work and power were also discussed in previous lessons. Work is defined as force acting over a distance, or: Work = force × distance and power is defined as work divided by time, or: Power = force × distance ÷ time In the case of the skateboard coming to a stop, friction and drag would be doing work to bring you to a stop. However, this is a special case because the frictional forces would be acting in a direction opposite to your motion. Normally the force and distance are going in the same direction which gives a positive value of work. Conversely, the value of work is negative for frictional forces. Vocabulary/Definitions (Return to Contents)
Associated Activities (Return to Contents)
Lesson Closure (Return to Contents) Engineers learn these principles of physical science in order to design vehicles for recreation and transportation. From skateboards and scooters to roller coasters and light rail trains, engineers must understand these concepts to design for safety. You would not want a scooter with wheels that do not provide any friction, or climb on a roller coaster that does not have enough momentum to make it back to the start of the ride. On a larger scale, you would not want to be on a train that has too much momentum to stop, or in a car that does not provide an inelastic collision during an accident. You would not want to fly a plane that does not have enough power to take off on the runway, or creates too much drag and runs out of fuel. Much of our everyday lives and safety depends on engineers designing with an understanding of these energy of motion concepts. Assessment (Return to Contents) Pre-Lesson Assessment Matching: Create a list of all the equations used in this lesson. Randomly write the left sides of the equations on the left side of the board and the right sides of the equations on the right side of the board. As a class, have the students match the correct sides together. For example, Momentum mass × g × height Potential energy force × distance Vocabulary: Ask the students to write down the vocabulary words and definitions on a sheet of paper or in their science journals. Question/Answer: Have students answer the following questions to gauge their understanding of the lesson concepts.
Post-Introduction Assessment Discussion Question: Ask the students and discuss as a class how the waterwheel was an example activity that showed a combination of energy, work and power, momentum, and friction. Ask students to suggest another example from the previous energy of motion lessons and activities that also shows a combination of energy, work and power, momentum, and friction. (Example answer: In the Lesson 4 Introduction / Motivation section, bobsledders were cited as real-life example of minimizing friction and drag. While going down the track, bobsledders also convert potential energy into kinetic energy. They also gain momentum to carry them through the turns and must have a powerful start when pushing the sled to help decrease their time.) Lesson Summary Assessment Pairs Check: Have students work in pairs to answer following questions.
Lesson Extension Activities (Return to Contents) As an open-ended design activity, propose to the students that they have been contracted by an amusement park to design a new roller coaster. Have the students sketch their design and explain how they took mechanical energy, momentum, work and power, and friction into consideration. Remind the students that too much or too little of one thing may be disastrous. For example, too much friction, too little momentum, or too little potential energy in the beginning will cause the ride to stop in the middle of the track. However, too much momentum or kinetic energy might cause the ride to jump off of the track. References (Return to Contents) Asimov, Isaac. The History of Physics. New York, NY: Walker & Co., 1984. Jones, Edwin R. and Richard L. Childers. Contemporary College Physics. Reading, MA: Addison-Wesley Publishing Co., 1993. Kahan, Peter. Science Explorer: Motion, Forces, and Energy. Upper Saddle River, NJ: Prentice Hall, 2000. Railroad Commission of Texas, Investigation Water Wheel activity: http://www.rrc.state.tx.us The Physics Classroom: Momentum and Its Conservation, at: http://www.physicsclassroom.com/Class/momentum/momtoc.html Waterwheel Factory, at: http://www.waterwheelfactory.com. Owner (Return to Contents) Integrated Teaching and Learning Program, College of Engineering, University of Colorado at BoulderContributors Chris Yakacki, Malinda Schaefer Zarske, Denise CarlsonCopyright © 2004 by Regents of the University of Colorado.The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0226322. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government. Last Modified: June 11, 2007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
