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Physics HS/Science Unit: 06 Lesson: 01 Suggested Duration: 10 days Conservation Laws and the Work-Energy Theorem Lesson Synopsis: This unit begins with an overview of energy transformations. Students list quantities that are conserved in nature and examine the energy transformations. Students then investigate gravitational potential energy through an excellent simulation. The work-energy theorem is presented in detail. Students will use the mouse trap car to struggle with practical energy transformations and research an energy topic of interest to society. TEKS: P.6 P.6A P.6B Science concepts. The student knows that changes occur within a physical system and applies the laws of conservation of energy and momentum. The student is expected to: Investigate and calculate quantities using the work-energy theorem in various situations. Readiness Standard Investigate examples of kinetic and potential energy and their transformations. Readiness Standard Scientific Process TEKS: P.2 Scientific processes. The student uses a systematic approach to answer scientific laboratory and field investigative questions. The student is expected to: P.2E Design and implement investigative procedures, including making observations, asking well-defined questions, formulating testable hypotheses, identifying variables, selecting appropriate equipment and technology, and evaluating numerical answers for reasonableness. Demonstrate the use of course apparatus, equipment, techniques, and procedures, including multimeters (current, voltage, resistance), triple beam balances, batteries, clamps, dynamics demonstration equipment, collision apparatus, data acquisition probes, discharge tubes with power supply (H, He, Ne, Ar), hand-held visual spectroscopes, hot plates, slotted and hooked lab masses, bar magnets, horseshoe magnets, plane mirrors, convex lenses, pendulum support, power supply, ring clamps, ring stands, stopwatches, trajectory apparatus, tuning forks, carbon paper, graph paper, magnetic compasses, polarized film, prisms, protractors, resistors, friction blocks, mini lamps (bulbs) and sockets, electrostatics kits, 90-degree rod clamps, metric rulers, spring scales, knife blade switches, Celsius thermometers, meter sticks, scientific calculators, graphing technology, computers, cathode ray tubes with horseshoe magnets, ballistic carts or equivalent, resonance tubes, spools of nylon thread or string, containers of iron filings, rolls of white craft paper, copper wire, Periodic Table, electromagnetic spectrum charts, slinky springs, wave motion ropes, and laser pointers. Organize and evaluate data and make inferences from data, including the use of tables, charts, and graphs. Communicate valid conclusions supported by the data through various methods such as lab reports, labeled drawings, graphic organizers, journals, summaries, oral reports, and technology-based reports. P.2F P.2J P.2K GETTING READY FOR INSTRUCTION Performance Indicator(s): • Research and develop a written report on energy conservation, efficiency, and energy conversions in a small appliance. (P.2K; P.6A, P.6B) 4J; 5B, 5G AND Design and perform a laboratory investigation demonstrating how potential energy is transformed into kinetic energy. (P.2E, P.2J, P.2K; P.6A, P.6B) 1E; 3F; 5F Key Understandings and Guiding Questions: • • • The work-energy theorem follows directly from Newton’s 2nd law and states that the net work done on a mass is equal to the change in kinetic energy of that mass. — What is the definition of work? — How is work related to energy? Work and the various forms of energy have specific definitions in physics, which are used to calculate the values of these quantities. — What are the equations that allow calculations of work and energy? Power is the rate at which energy is used or transformed. — How are energy and power related? ©2012, TESCCC 01/10/13 page 1 of 9 Physics HS/Science Unit: 06 Lesson: 01 Vocabulary of Instruction: • • • • • • • • speed mechanical energy elastic energy heat thermal energy chemical energy work-energy theorem transformation • • • • • • • • kinetic energy work Hooke’s law conservative force electrical energy conservative force Conservation of Energy non-conservative force • • • • • • potential energy friction pendulum power efficiency solar, light energy Materials: Refer to Notes for Teacher section for materials. Attachments: • • • • • • • • • • • • • • • • • • • • • Teacher Resource: Video: Conservation of Mass Teacher Resource: Video: Conservation of Momentum Teacher Resource: Video: Conservation of Energy Teacher Resource: Video: Fire Syringe Handout: Energy Research Questions (1 per student) Teacher Resource: PowerPoint: Pre-Lab Questions Handout: Skateboard Physics (1 per student) Handout: Skateboard Physics Lab Report (1 per student) Teacher Resource: Skateboard Physics Lab Report KEY Teacher Resource: Sample Roller Coaster Project Handout: Work-Energy Review Sheet (1 per student) Handout: W-E Application Problems (1 per student) Teacher Resource: W-E Application Problems KEY Handout: Elastic Potential Energy Hooke’s Law Force Vernier Version (1 per student) Handout: Elastic Potential Energy Hooke’s Law Force Pasco Version (1 per student) Optional Handout: Pasco Motion Detector Review (1 per student) Teacher Resource: Teacher Notes on Mouse Trap Car Design Handout: Mouse Trap Car Rules (1 per student) Handout: Basic Mouse Trap Car Design (1 per student) Handout: Mouse Trap Car Design Report (1 per student) Teacher Resource: Video: Mouse Trap Car Resources and References: • • • Texas Education Agency, STAAR Physics Reference Materials (look under "Specific STAAR Resources)," "Science": http://www.tea.state.tx.us/student.assessment/staar/ Phet simulation website: http://phet.colorado.edu/new/simulations/sims.php?sim=Energy_Skate_Park College Board- Table of Information and Equation Tables for AP Physics Exams: http://www.collegeboard.com/prod_downloads/ap/students/physics/physics_equation_tables.pdf Advance Preparation: 1. Gather support stands and clamps to position oscillating springs in place. 2. Examine the Handout: Teacher Notes on Mouse Trap Car Design. Students will be asked to bring materials from home with the remaining supplies obtained by the teacher. (Among the needed materials are box cutters, which may need to be approved by administration and must be used under strict supervision. One method would be to have students make cutting marks and then the teacher makes the actual cuts.) 3. Install software needed for activities and homework. Make certain needed software is compatible with computers and networks: ©2012, TESCCC 01/10/13 page 2 of 9 Physics HS/Science Unit: 06 Lesson: 01 • Microsoft Word and Excel • Ultrasonic motion detector software • Internet Explorer with plug-ins for showing films, etc. • Either Pasco – Data Studio or Vernier – Logger Pro software and appropriate experiment files 4. Prepare attachment(s) as necessary. Background Information: The focus of this unit is the concept of conservation of energy and how it may transform from one type to another, the identification of types of potential energies and the corresponding conservative forces. Energy is a quantity that can be transformed from one form to another without loss – if we include thermal energy! Newton’s laws of motion describe classical motion, but they are sometimes difficult to apply in a given situation because every detail of that situation must be known and utilized in the solution to a problem. Conservation laws are easier to use and apply very broadly as it is not necessary to know every detail of the problem. For example, we know from conservation of mass that the mass of a piece of clay does not change even if the shape or number of pieces changes. The same is true of energy. If we do not lose energy from a system, the total remains constant. We are quickly able to reach significant conclusions with a limited amount of information. Energy has the additional advantage of being a scalar and, thus, easier to manipulate mathematically than the force vectors used in applying Newton’s laws. It is important to note, much of the language in layman use is similar to, but has a different meaning from, the use of the same words in a physics class. Students should understand the difference between conservation of energy and energy conservation, as used by the public. In the unit on thermodynamics, students will see that, while energy is conserved, useful energy does invariably decrease. Finding efficient ways of transforming energy is an important task we face. This unit is essentially a study of the different forms of energy and their characteristics. GETTING READY FOR INSTRUCTION SUPPLEMENTAL PLANNING DOCUMENT Instructors are encouraged to supplement and substitute resources, materials, and activities to differentiate instruction to address the needs of learners. The Exemplar Lessons are one approach to teaching and reaching the Performance Indicators and Specificity in the Instructional Focus Document for this unit. Instructors are encouraged to create original lessons using the Content Creator in the Tools Tab located at the top of the page. All originally authored lessons can be saved in the “My CSCOPE” Tab within the “My Content” area. INSTRUCTIONAL PROCEDURES Instructional Procedures Notes for Teacher ENGAGE – Conservation Principles and Energy NOTE: 1 Day = 50 minutes Suggested Day 1 1. Announce that today we will begin a new unit exploring energy and the conservation of energy. Energy is a very important and often controversial topic in society because it is associated with the quality of life, politics, and global resources. Some of that language is similar to that which will be used in this unit. However, from a physics point of view, energy is an important tool in describing nature. 2. Introduce Conservation Principles and Energy. Ask: • If you gave me a dollar and asked for change, how many dimes would you want back? (10) • How many quarters? (4 – In some sense, money is conserved in that you can keep books on it, and if you don’t lose any, it can change forms and you still have just as much.) • What physics quantities are conserved? (Energy, momentum, mass, charge, not volume, force, etc.) Answers will vary. • Name different kinds of energy? Several possible answers, including kinetic, potential, light and work. ©2012, TESCCC 01/10/13 Materials: (optional for demonstrations) • play dough ball • balance • ring magnets on a pole • Newton’s Cradle apparatus • tennis ball • basketball • bowling ball pendulum or 2 liter bottle pendulum (filled with water) • spool mobile • 2 balls of same size, color and material (1 room temperature, 1 frozen) • generator • radiometer page 3 of 9 Physics HS/Science Unit: 06 Lesson: 01 Instructional Procedures Notes for Teacher 3. Perform a series of demonstrations illustrating conservation. Facilitate a class discussion after each demonstration asking students what they think occurred. This will help to uncover some common misconceptions. You may use the optional in-class demonstrations or videos. See notes below for discussion ideas and material suggestions. 4. Demonstrate conservation of mass or show the Teacher Resource: Video: Conservation of Mass. • Put a ball of putty (play dough works well) on a scale, and balance the scale. Then, ask if the mass would be more, less, or the same if it were broken into two pieces. (Answer: Most will say the same – and when demonstrated, it should be close – do not worry about fine balance, this is an illustration.) • Using ring “magnets on a pole” in the attract configuration, balance the scale. Adjust the magnets so that most float above the others. Ask the students if the mass will measure more, less, or the same as before? (Answer: There will be uncertainty and a variety of answers – but the mass will be the same.) • Explain that conservation principles are useful because they allow us to meet new situations and know the answer to questions without examining all the variables in detail. If students remember E=mc 2 at this point, acknowledge that the conservation of mass principle has been modified. 5. Demonstrate conservation of linear momentum or show the Teacher Resource: Video: Conservation of Momentum. • Show the popular Newton’s Cradle demonstration indicating that both momentum and kinetic energy are conserved. (No explanations at this time) • Carefully drop a tennis ball resting on a basketball to surprisingly “launch the tennis ball”, or show similar demonstration with commercial apparatus. • Explain that conservation of momentum is a concept that will be used to study collisions later in the year. • • Fresnel lens paper Attachments: • Teacher Resource: Video: Conservation of Mass • Teacher Resource: Video: Conservation of Momentum • Teacher Resource: Video: Conservation of Energy Instructional Notes: In the introduction to this unit, several demonstrations are recommended. These serve to introduce students to the concepts of conservation of mass, energy and momentum. Videos of these demonstrations are provided, but optional in-class demonstrations are recommended. Other demonstrations may be used based upon material availability. Misconception: • Students may think momentum is the same as force. 6. Demonstrate conservation of energy and energy concepts, or show the Teacher Resource: Video: Conservation of Energy. • Use a bowling ball pendulum to show the exchange between gravitational potential energy and kinetic energy. (Most teachers do not have a bowling ball pendulum, but a 2 liter bottle filled with water works well.) • Spool mobile: elastic potential energy converts to kinetic energy • Happy ball – sad ball: gravitational potential energy to kinetic potential energy — The sad ball’s (non - bouncing ball) energy ends up as thermal energy of the ball • Generator (Does the generator work harder if the lights are turned off?): mechanical energy to electric energy to light and heat energy • Generator – motor: mechanical energy to electrical energy to mechanical energy • Radiometer: light and/or heat energy to mechanical energy • Burn paper with a Fresnel lens: solar energy to fire 7. Give students advance notice that they will need to bring in materials for an ©2012, TESCCC 01/10/13 page 4 of 9 Physics HS/Science Unit: 06 Lesson: 01 Instructional Procedures Notes for Teacher upcoming activity. See Day 7 Elaboration Activity Instructional Procedures for materials students will need to bring to class. EXPLORE/EXPLAIN – Conservation Principles and Energy Transformations 1. Ask students to brainstorm in groups for an operational definition and characteristics for the concept of “work.” This should be a review of middle school concepts. 2. Facilitate a class discussion where students come up with an operational definition for work, and suggest to students to consider the idea of “work” as a member of the energy family. Work is interchangeable with energy – is like energy and has the energy unit of Joule. • Work is defined as (Force)(distance) – when they are parallel. • We typically deal with constant forces in a single direction. For this condition, the work done by a force on an object is the average force times the distance an object is moved. • If F and the displacement are perpendicular, then there is no work done. • If the object does not move (pushing against a wall), then no physics work is done. • You carry an object across the room, the force is up but the displacement is horizontal, thus no physics work is done. 3. Review with students that the language of work is specific and important. Examples: • When you lift a weight up – you do work on the weight, the weight does negative work on you. • When you lower an object – you do negative work on it, the weight does positive work on you. • If you hold an object – no work is done. 4. Demonstrate the fire syringe – or show the Teacher Resource: Video: Fire Syringe emphasizing force and distance (work into thermal energy). Suggested Day 2 Materials: (optional for demonstration) • fire syringe apparatus • cotton fabric Attachments: • Teacher Resource: Video: Fire Syringe • Handout: Energy Research Questions (1 per student) STAAR Note: The STAAR Physics Reference Materials include the formulas for work, power, energy, kinetic energy, potential energy, gravitational potential energy, elastic potential energy and mechanical energy. Misconception: • Students may think that momentum and kinetic energy are the same. 5. Ask students to work in their groups to recall definitions for the following concepts. These should be review for students, but you may want to provide other resources. • Units of work and energy (SI units): Joule • Kinetic energy – energy of motion: KE = ½ mv2 • Potential energy – energy stored in one form or another. There are different equations for different types of potential energy. The energy is stored by doing work on a system against a conservative force. • Example: gravitational potential energy = mgh; where a force lifts an object a distance h against the force of gravity: Fg = mg 6. Ask students to share their definitions with the class, and assist them with summarizing and elaborating on concepts. Ask students to take notes in their science notebooks. 7. Mechanical potential energies (like gravitational) are referenced to some zero location, which is chosen for convenience. There is no instrument that ©2012, TESCCC 01/10/13 page 5 of 9 Physics HS/Science Unit: 06 Lesson: 01 Instructional Procedures Notes for Teacher can measure potential energy. Ask these questions to check for understanding: • What is the definition of work? Work is a force moving an object through a distance, and one condition of work is that the force and the distance displaced are in the same direction. • How is work related to energy? Energy is needed to provide the force to move an object or to do work. 8. Distribute the Handout: Energy Research Questions. Students select one of the topics to research. It is suggested that students be allowed to select the topic that seems most interesting to them. Tell students they will be presenting a very short summary presentation of the information to the class at the end of the unit. Check for Understanding Science Notebooks: Students summarize definitions and notes in their notebooks. 9. Allow time for questions and to choose topics. EXPLORE/EXPLAIN – Skate Park Lab 1. Announce that for the next two days, students will be exploring the physics of roller coasters and skate boarding through a simulation. The investigation will be conducted with a focus on the concept of energy. 2. The Teacher Resource: PowerPoint: Pre-Lab Questions may help students visualize the simulation and graphing. 3. Distribute the Handout: Skateboard Physics and the Handout: Skateboard Physics Lab Report. Have students read the handouts. 4. You will need to divide the students into groups based on the number of computers you have access to in your classroom or computer lab. 5. Very briefly, demonstrate the Phet simulation website Skate Park Lab simulation: http://phet.colorado.edu/new/simulations/sims.php? sim=Energy_Skate_Park by displaying it to the class and assisting with the vocabulary terms at the start of the lab. Suggested Days 3 and 4 Attachments: • Teacher Resource: PowerPoint: Pre-Lab Questions • Handout: Skateboard Physics (1 per student) • Handout: Skateboard Physics Lab Report (1 per student) • Teacher Resource: Skateboard Physics Lab Report KEY • Teacher Resource: Sample Roller Coaster Project Instructional Notes: Students usually do quite well at manipulating the features of this lab, as the lab report instructions are very detailed. 6. Remind students they will need time to design the project track and perform the energy analysis of Part II. Assist students as needed. There is a Teacher Resource: Sample Roller Coaster Project available for reference. 7. Assist students as needed on Part I of the lab and in the design project and energy analysis report of Part II. 8. Check with students on the status of their research projects. You may want to allow time for students to visit a computer lab for additional research. EXPLORE/EXPLAIN – Work-Energy Review 1. Re-introduce questions from the previous activity about work and energy. Get students to begin thinking about work, potential energy and kinetic energy again. • Does doing work on an object always give it energy? Is the energy always kinetic energy? When positive work is done on an object, it does gain energy. However, the energy may be potential ©2012, TESCCC 01/10/13 Suggested Day 5 Attachments: • Handout: Work-Energy Review Sheet (1 per student) • Handout: W-E Application Problems (1 per student) • Teacher Resource: W-E page 6 of 9 Physics HS/Science Unit: 06 Lesson: 01 Instructional Procedures • • • • Notes for Teacher energy such as the lifting of a book. When I lift a book up from the table, is my lifting force the same force F that goes into F=ma of Newton’s second law? (No, the F in F=ma is the total net force; in this case, there is also gravity pulling down on the book.) Since I do work on the book, I give it energy. What kind of energy do I give it? (Potential) If I let go, the book falls. What force is doing work on the book? (Gravity, which gives it kinetic energy) What are the equations that allow calculations of work and energy? Answers will vary, but guide students to review the concepts from the previous day’s activity. 2. Inform students that the class will now study the theory associated with energy and work some example problems to illustrate some of those concepts. Application Problems KEY Instructional Notes: The goal for today’s activity is to formally introduce the Handout: WorkEnergy Theorem using the energy concepts and situations already studied. In addition, a number of related terms, such as power, efficiency, conservative forces, and simple machines, with be introduced and/or reviewed. Equations and examples for some common conservative forces will be also presented. 3. Distribute the Handout: Work-Energy Review Sheet. Explain that this sheet is more than a glossary, but less than a complete explanation of the material for this unit. Discuss the information on the handout. 4. Remind students that the language must be specific, as in “the force does work on the object”. This is necessary because there are always two forces doing work, the action force and the reaction force, and it is sometimes confusing to determine which force is being discussed. 5. Distribute the Handout: W-E Application Problems. Assist students as they work through the problems. 6. Continue to check with students to remind them of their research projects and to answer any questions they may have about the reports or the presentation itself. EXPLORE/EXPLAIN – Spring Kinetic Energy 1. Suggested Day 6 Divide the students into lab groups and distribute the Handout: Elastic Potential Energy Hooke’s Law Force Vernier Version or Pasco Version that is appropriate for your equipment. 2. If needed, distribute the Optional Handout: Pasco Motion Detector Review. 3. Provide assistance as needed to assist the students with the lab. Some students may have forgotten how to use the lab equipment. Also, make sure that if a printer is not available that you make adjustments in the lab. 4. Help the students stay on pace through the lab so that approximately 10 minutes can be used at the end of class for a post-lab discussion. 5. Conduct a post-lab discussion making sure that students understand conceptually what happened and how they should respond to the lab questions. 6. Once again, check in with students to see if assistance is needed with student research projects. Remind students of the time limits for presentations. ©2012, TESCCC 01/10/13 Materials: (per group) • spring • support stand • set of weights • ruler or meter stick Attachments: • Handout: Elastic Potential Energy Hooke’s Law Force Vernier Version (1 per student) • Handout: Elastic Potential Energy Hooke’s Law Force Pasco Version (1 per student) • Optional Handout: Pasco Motion Detector Review (1 per student) Instructional Notes: The goal for today is to have a realpage 7 of 9 Physics HS/Science Unit: 06 Lesson: 01 Instructional Procedures Notes for Teacher world laboratory experience with a conservative system. The spring is a good source to demonstrate conservation. Students should remember how to use the motion detector, but there are some instructions in the lab and a review document provided as well for the Pasco program. The file needed for the Pasco program is named spring.ds. ELABORATE 1. – Constructing a Mouse Trap Car Prepare classroom for construction of cars. Divide the class into partners or small working groups. If you have not already done so, please refer to the Teacher Resource: Teacher Notes on Mouse Trap Car Design. 2. Distribute and discuss the contest documents including the Handouts: Mouse Trap Car Rules, Basic Mouse Trap Car Design, and Mouse Trap Car Design Report. 3. Discuss the rules and assist students by answering any questions they may have about the assignment. 4. Give instructions, including basic safety instruction, regarding cutting of foam board, hot glue guns and the use of the materials. 5. Show the Video: Mouse Trap Car to give students an idea of what to expect from their creation. 6. Students will work in small groups and follow the rules provided in the Handout: Mouse Trap Car Rules. All cars will use the mouse traps supplied. If a lab group somehow destroys their mouse trap, the replacement must be identical to the official mouse trap. 7. Students may decorate their cars and may take them home for modifications, but the car design must be within the rules. 8. Monitor and assist students in the construction of the cars. 9. On the second day of the activity, hold the contest with the cars. 10. Allow time for a post-activity discussion and to answer any questions students may have regarding the results of the contest or the report. 11. Allow students to work on their reports. Monitor and assist students with any questions they may have. Each student should prepare their own report. Suggested Days 7 and 8 Materials: • mouse traps (1 per group) • old CDs for wheels • glue guns for construction (2 or 3 per class) • newspaper (to catch the dripping hot glue) • box cutter (teacher) • cardboard or cardboard boxes (protects the desks when cutting foam board) • wire coat hangers (use for the lever arm attached to the mouse trap and wheel axles) • bolt nuts or large beads • ¼ inch dowel rod • kite string • foam board Attachments: • Teacher Resource: Teacher Notes on Mouse Trap Car Design • Teacher Resource: Video: Mouse Trap Car • Handout: Mouse Trap Car Rules (1 per student) • Handout: Basic Mouse Trap Car Design (1 per student) • Handout: Mouse Trap Car Design Report (1 per student) Safety Notes: Warn students that the glue from the hot glue gun can burn their skin. The box cutters can cause cuts to both people and desktops. Be careful and use covers to protect the desks. You ©2012, TESCCC 01/10/13 page 8 of 9 Physics HS/Science Unit: 06 Lesson: 01 Instructional Procedures Notes for Teacher may want students to mark cuts and have only the teacher use the box cutter. Instructional Notes: The goal for the first day of the contest is to get most of the construction completed for the student mouse trap cars. Teams may take the basic car home for tuning and/or major repair. The goal of the second day is to hold the contest itself and assist students in preparing their reports. EVALUATE – Performance Indicators Performance Indicator • Research and develop a written report on energy conservation, efficiency, and energy conversions in a small appliance (P.2K; P.6A, P.6B) 4J; 5B, 5G 1. Students will use the Handout: Energy Research Questions as a resource for helping them complete the Performance Indicator. 2. If you have additional time, you may want to schedule a day to allow students to work on the compilation of the report in class. Research should be done on an individual basis during the unit. 3. Students should be prepared to lead a short summary discussion and/or answer questions on their topic. 4. If they wish to distribute any printed material, they should bring the handouts or make advance preparation for you to make copies. Keep the questions and presentations on schedule. Five minutes per report should be sufficient. 5. The presentations should be 3-5 minutes long with additional time at the end of class for questions and answers. The presentations have been noted in previous lessons, but may be omitted for time constraints. If you choose to omit the presentations, make sure to find a way to post materials or have a time for sharing of the written reports in another format such as partner sharing, etc. Suggested Days 9 and 10 Attachments: • Handout: Energy Research Questions (previously distributed) • Handout: Skateboard Physics Lab Report (previously distributed) Performance Indicator • Design and perform a laboratory investigation demonstrating how potential energy is transformed into kinetic energy. (P.2E, P.2J, P.2K; P.6A, P.6B) 1E; 3F; 5F 1. Students will use the Handout: Skateboard Physics Lab Report (1 per student) to analyze an investigation demonstrating the energy conversions that took place during the lab. They have previously designed an investigation during the explore phase of the unit, so the focus for the performance indicator may be on analysis of the investigation. 2. Although students have already designed and performed the investigation during the unit, you may want students to revisit the skateboard simulation to design and perform another investigation in order to show mastery of the concepts. ©2012, TESCCC 01/10/13 page 9 of 9