Total marks: ______/ 30
Learning Goals for this Lesson / StandardsStandard 3: Energy and Its Effects: Energy takes many forms. These forms can be grouped into types of energy that are associated with the motion of mass (kinetic energy), and types of energy associated with the position of mass and energy fields
Students Will Know
· Elastic potential energy (EPE) is a form of stored “potential” energy in a stretched or compressed material.
· The amount of stretch or compression of a substance when a force is applied is related to the structure of the substance. This relationship between force and stretch or compression is called the elastic constant. The elastic constant is different for every elastic material.
· The elastic force, the elastic constant, and the distance that the elastic material is stretch or compressed can be related mathematically. This relationship is commonly stated using the equation F = kx; where x is the distance the elastic material is stretched or compressed, k is the elastic constant for that particular elastic material, and F is the elastic force.
· All elastic materials have an elastic limit, which is the point at which the material no longer will return to its original shape and no longer behaves like an elastic material.
· The amount of EPE is influenced by the type of elastic material and the amount of stretch or compression of this material. It is more heavily influenced by the amount of the material’s stretch or compression since the relationship between the amount of stretch/compression and EPE is exponential. (i.e., if the stretch is doubled, the EPE is quadrupled)
· An object’s EPE can be quantified by multiplying the constant ½ by the elastic constant and the square of the object’s stretch/compression. EPE = ½ k x2 / Students Will Be Able To
· Recognize that the relationship between the Elastic Potential Energy and the elastic stretch / compression is not simple (i.e. if the stretch or compression is doubled, then the EPE is quadrupled).
· Quantify the EPE of an object using mathematical equations.
· Recognize that every material has a unique property that determines the elasticity of the material known as the elastic constant.
· Recognize that each elastic material has an elastic limit, which is the point where the elastic material is stretched or compressed such that it will no longer return to its original shape.
· Recognize that in most examples EPE is transformed into KE; a good example of this is earthquakes.
Lesson Essential Question
How are elastic forces and their stretch related?
Activating Strategy:
Show the Olympic pole vault picture (Energy Across Systems Investigation 4 ppt, slide #2)
Have students discuss with collaborative partners the following questions:
1. List some examples of elastic materials and describe how you think these materials would store elastic potential energy.
2. Do elastic materials always return to their original shape and/or position? If not, what might cause them not to do so?
Have students share their thoughts with each other; and then share out with the class. Remind students of the transfer and transformation of energy reviewed in earlier lessons; as well as the Law of Conservation of Energy.
Key vocabulary to preview
Elastic- force, constant, and limit
Slope, linear regression
Elastic force (f) = kx (distance)(elastic constant)
Vocabulary Strategy
Have students create T-charts in notebooks; one column for word, one column for definition. Provide the definitions for any words the students do not know; have all students write the formula for Elastic force. Explain that it will be used later in the investigation.
Lesson Instruction
Learning Activity 1
Partner read page 1 of Investigation 4 Elastic Energy student guide (pole vault). Provide the focus question for the investigation: How are elastic forces and their stretch related?
Depending on the facility, either present as teacher demonstration or have students work in groups of 2-4 to complete.
**Teacher should set up investigation (force probe and computer) ahead of time.
Have groups either a.) each answer one question s (1-7), or answer all questions.
Assessment Prompt for Learning Activity 1
Exit ticket- How are elastic forces and their stretch related? / Graphic Organizer
·
Learning Activity 2
Investigation- Elastic forces and elastic energy- Complete investigation as whole group demonstration, or have students complete in small groups.
Focus question- How is EPE related to the stretch or compression distance of the elastic material?
Answer questions 1-3 (in student packet, p. 11)
Assessment Prompt for Learning Activity 2
Exit ticket- How is EPE related to the stretch or compression distance of the elastic material?
Assignment
Sports and Elastic Potential Energy
Read through page 16 in student packet (whole group or partner reading). Can show sports clips (baseball, car races, tennis, pole vault, etc.)
Question- What other examples can you think of to illustrate how EPE is used in sports? Write a paragraph explaining your examples.
Learning Activity 3
Making sense of energy- EPE and Earthquakes
Read through ages 13-14 in student packet- as whole group or through partner reading.
Complete investigation (page 15) as teacher demonstration
Assessment Prompt for Learning Activity 3
Investigation analysis and reflection questions:
1. Does each movement of the block (the earthquake) happen predictably? Are there any patterns that arise from the experiment?
2. A student observes the graph and states that the bungee earthquake stored more elastic potential energy than did the rubber band earthquake. Can the student justify his conclusion using the information provided on the graph? Explain.
Summarizing Strategy
Investigation 4 formative assessment.
Investigation #4: Stretching the Limits
Investigating Elastic Energy and Earthquakes
Energy is all around us and in many cases it is stored as potential energy. The stored energy doesn’t have to be in the form of Gravitational Potential Energy though; it can be stored in stretched or compressed materials as elastic potential energy. We make use of stored elastic potential energy (EPE) everyday. In many cases, such as in an earthquake, the stored EPE is released and changed into another form of energy such as KE.
In the sport of track & field, the pole vault stands out as a great example of energy transfer and energy transformation. The athlete runs as fast as her or she can, gaining KE, with a pole. The pole slides into a specially designed hole near the crossbar over which the athlete must vault. As the pole starts to bend, the athlete’s KE is transformed into EPE in the pole. The energy stays as EPE for only a short while, quickly converting back to KE in the athlete as he or she goes soaring over the crossbar.
· What makes some materials better able to store EPE?
· How do materials store EPE?
· Are all materials elastic?
GOALS: In this lab investigation, you will …
· Recognize that the relationship between the Elastic Potential Energy and the elastic stretch / compression is not simple (i.e. if the stretch or compression is doubled, then the EPE is quadrupled).
· Quantify the EPE of an object using mathematical equations.
· Recognize that every material has a unique property that determines the elasticity of the material known as the elastic constant.
· Recognize that each elastic material has an elastic limit, which is the point where the elastic material is stretched or compressed such that it will no longer return to its original shape.
· Recognize that in most examples EPE is transformed into KE; a good example of this is earthquakes.
Investigation Overview: A synopsis of this lesson is as follows…
In this lesson you will start investigating another form of energy called elastic potential energy (EPE). The factors that influence the EPE of a material will be investigated as will how these factors combine mathematically to quantify the amount of EPE in a specific material when it is stretched or compressed. The elastic constants and elastic limits of materials will also be investigated. The EPE stored in rock layers at fault zones is used as a practical example of the EPE to KE transformation process in a physical system.
CONNECTIONS
Scientific Content –
· Elastic potential energy (EPE) is a form of stored “potential” energy in a stretched or compressed material.
· The amount of stretch or compression of a substance when a force is applied is related to the structure of the substance. This relationship between force and stretch or compression is called the elastic constant. The elastic constant is different for every elastic material.
· The elastic force, the elastic constant, and the distance that the elastic material is stretch or compressed can be related mathematically. This relationship is commonly stated using the equation F = kx; where x is the distance the elastic material is stretched or compressed, k is the elastic constant for that particular elastic material, and F is the elastic force.
· All elastic materials have an elastic limit, which is the point at which the material no longer will return to its original shape and no longer behaves like an elastic material.
· The amount of EPE is influenced by the type of elastic material and the amount of stretch or compression of this material. It is more heavily influenced by the amount of the material’s stretch or compression since the relationship between the amount of stretch/compression and EPE is exponential. (i.e., if the stretch is doubled, the EPE is quadrupled)
· An object’s EPE can be quantified by multiplying the constant ½ by the elastic constant and the square of the object’s stretch/compression. EPE = ½ k x2
Scientific Process -
· Data will be collected, analyzed, and presented in a graphical form.
· Computer-based probes will be used for data collection and analysis.
Math/Graphing -
· Graphical displays will be used to communicate energy flow in a system.
· Calculations of EPE will be performed.
MAKING SENSE OF ENERGY … Elastic Forces & Elastic Potential Energy
Gravitational potential energy is not the only type of potential energy. Potential energies are referred to as “energies of position” because the potential energy is gained or lost when the position of the object is changed. For example, as an object’s position above the surface of the Earth (its height) increases so does the amount of its gravitational potential energy (GPE).
Another important form of potential energy is elastic potential energy (EPE). Elastic potential energy is the energy stored by elastic materials. An elastic material is anything that can be bent, stretched, or compressed, and return to its original shape and/or position when released. Energy is stored in these materials because they have been forced to change shape or position.
Journal Entry #1: List some examples of elastic materials and describe how
you think these materials would store elastic potential energy.
Journal Entry #2: Do elastic materials always return to their original shape
and/or position? If not, what might cause them not to do so?
When an elastic material is stretched or compressed, a force is applied to do work (i.e. transfer energy). The relationship between the force and the distance the elastic material is stretched or compressed is related to the properties of the material. This relationship is communicated by a numerical value called the elastic constant. The elastic constant is a number that tells how difficult a material is to stretch or compress. Like density (the ratio of mass to volume), the elastic constant is unique to each elastic material. It is represented in equations by the letter (k). The amount of elastic energy stored in an elastic material depends upon the force placed on that material and the distance that the material is stretched or compressed.
Let’s Investigate … Investigating Elastic Materials
We will first start our investigation into elastic energy by looking at how some common elastic objects, such as bungee cords and rubber bands, respond to forces when stretched or compressed. We will then turn our attention towards an investigation into how elastic materials store energy. Elastic materials, and any other thing that stores energy, can be dangerous so follow the directions and your teacher’s instructions very carefully.
Focus Question: How Are Elastic Forces and Their Stretch Related?
Directions:
1. Gather the materials needed for this investigation. Clamp the wooden block to the lab table using the C-clamp. (Your teacher may have alternative arrangements if your classroom does not have lab tables) Attach the spring, bungee cord, or other elastic material to the eyelet in the block of wood.
2. Attach the force probe to the other end of the elastic material, then plug the probe into the computer. Open the file: Investigating Elastic Materials. The force probe should be set for 50 Newtons. Make sure the elastic material is not stretched at this point.
3. Tape a meter stick to the table beside the force probe, placing 0 at the edge of the force probe. This will be used to measure how far the elastic material is stretched.
4. Click the Zero button on the tool bar so the force probe reads 0 Newtons.
5. Click the Collect button. It will turn red, and the Keep button will be activated.
6. Pull on the force probe along the edge of the meter stick until the edge that was on zero is now at 2 cm. Click the Keep button and a dialog box will appear. Enter the distance in the dialog box, but remember that 2 cm is .02 m. Click OK.
7. Repeat step 6, increasing the distance by 2 cm each time, until you have 10 data points. (Some materials may require that you only stretch the material 1cm for each trial; your teacher will adjust the directions if this is necessary.)
8. Click the Stop button. From the Experiment menu, select Store Latest Run or click on the filing cabinet icon.
9. Repeat steps #3 through #8 with a different elastic material. You will test at least three objects (a bungee cord, a rubber band, and a spring).
10. Make a copy of your graph in your journal or on a separate piece of paper. Include notes about each material that you tested.
Investigation Analysis & Reflection:
1. When scientists interpret their data after an investigation, they look for patterns that emerge. What patterns emerge from your data?