Content Benchmark P.12.C.2
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Students know energy forms can be converted. E/S

Energy is the capacity to produce physical changes. The word capacity is important because change may or may not be actually occurring (i.e., energy can be thought of as being “stored” in some situations). Physical change is often equated with “work,” a term in physics defined as the product of force and distance. But change mechanisms associated with energy include not only work, but also heat and electromagnetic radiation.

Figure 1. A schematic of the many connections within energy (from http://hyperphysics.phy-astr.gsu.edu/hbase/enecon.html).

Energy is a scalar quantity, which means energy values do not have a directional component. The SI unit for energy is the Joule (J), where 1 J = 1 kg × 1 m/s²× 1 m = 1 kg·m²/s². To learn more about energy units and conversions, go to
http://www.physics.uci.edu/~silverma/units.html

Energy is broken down into two types: potential and kinetic. Potential energy can be thought of as “stored” energy of an object because of its position. For example, the position of an object within a gravitational field gives it potential energy. On Earth, the higher an object is above the ground, the greater its gravitational potential energy. Another example is potential energy stored in a spring. In this case, an elastic object is deformed and will have potential energy until it moves back to a neutral (i.e., non-deformed) state. The greater the compression or elongation of the spring (in other words, the greater the deformation) the greater its potential energy.

To learn more about potential energy, go to
http://hyperphysics.phy-astr.gsu.edu/hbase/pegrav.html#pe

Kinetic energy is associated with moving objects. If an object’s velocity increases, its kinetic energy will rapidly increase. Also, the more massive a moving object is, the greater its kinetic energy. The equation that describes kinetic energy is , where m is mass of object in kilograms and v is the velocity of the object in meters/second.

A detailed discussion of kinetic energy is found at
http://www.physicsclassroom.com/Class/energy/U5L1c.html.

In a system, the total energy is the sum of the potential and kinetic energies. Within the system, potential energy may be transformed into kinetic energy and vice versa. If the system is closed (no energy can enter or leave), the total energy will remain the same even though energy may be transformed from one kind to another within the system. This principle is called the Law of Conservation of Energy.

The Law of Conservation of Energy also applies to open systems, where energy may enter and leave the system boundaries. In an open system, the net change in total energy is equivalent to the amount of energy added or removed from outside the boundaries, regardless of energy form. In other words, if net energy is added to a system, then the total energy is equal to the original amount of potential and kinetic energies plus the new amount of potential and kinetic energies added. On the other hand, if net energy is removed from a system, then the total energy is equal to the original amount of potential and kinetic energies minus the new amount of potential and kinetic energies subtracted.

Simply stated, the Law of Conservation says that energy can neither be created from nothing nor destroyed completely, but it can be converted from one form into another.

To learn more about the Law of Conservation of Energy, go to http://www.eia.doe.gov/kids/energyfacts/science/formsofenergy.html.

Figure 2. In a pile driver, energy is transferred from potential energy (PE) to kinetic energy (KE) to do work on the post (i.e., a force moving the post downward). (from http://www.physicsclassroom.com/Class/energy/U5L1d.html)

At its most fundamental level, energy is some combination of potential and kinetic. Energy can be more commonly described in terms of (1) chemical energy, (2) radiant energy, (3) electrical energy, and (4) thermal energy. These can be thought of as more complex combinations of potential and kinetic energy, and sometimes it is easier to talk about energy transformations in these terms. For example, the chemical energy in food, which is a combination of the potential and kinetic energy of molecules within the food, can be converted to kinetic energy of muscle motion in animals causing them to move.

Figure 3. Common examples of energy transformations. (from http://www.eia.doe. gov/kids/energyfacts/ science/formsofenergy.html)

It is common to refer to heat as energy, but heat is actually a process where energy is transferred from a high temperature object to a lower temperature object. Therefore, an object does not possess heat. The appropriate term for the microscopic energy is thermal energy. Thermal energy is a combination of the potential and kinetic energies associated with microscopic particles within a material.

Electromagnetic radiation, more commonly called light, is also commonly referred to as an energy form. But, just as with heat, light is a process that transfers energy. Besides being a wave, light also has a particle nature, where each particle of light is called a photon. The total energy transferred via a photon is directly dependent on the light’s frequency. For example, high frequency light, such as x-rays have greater photon energies than low frequency light such as radio. The total energy transferred by an individual photon is calculated using Einstein’s photoelectric effect equation.

Details about the photoelectric effect can be found at
http://galileo.phys.virginia.edu/classes/252/photoelectric_effect.html.

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Content Benchmark P.12.C.2

Students know energy forms can be converted. E/S

Common misconceptions associated with this benchmark:

1. Students incorrectly believe that energy can be made, used, and lost.

The Law of Conservation of Energy states that energy is not created or destroyed only transferred from potential to kinetic (or vice versa). Students should understand that just because they cannot see energy transfer (into and from some forms) does not mean that the energy has been destroyed.
A discussion about the Second Law of Thermodynamics should aid in the explanation of energy transformation. The Second Law of Thermodynamics concerns entropy and its increasing amount in the universe and exploring this topic should deepen student understanding about how energy has been transferred via heat to a more disorganized kinetic energies of random molecular motions.

To learn more about the Second Law of Thermodynamics, go to
http://www.grc.nasa.gov/WWW/K-12/airplane/thermo2.html.

2. Students incorrectly use the terms “energy” and “force” interchangeably

In Star Wars Episode IV, Obi Wan Kenobi tells Luke Skywalker that “The Force is an energy field created by all living things.” This statement typifies confusion about the terms energy and force. An appreciable part of this confusion resides in misconceptions about the relationship between force and motion. Many students incorrectly believe that a moving object must have an “impetus” force causing it to stay in motion. Students incorrectly believe that this impetus force is applied to an object by a collision with another object (i.e., hitting a baseball with a bat) and that this “impetus force” then resides within the object even after it has lost contact with the original impactor, causing it to continue moving until this impetus is somehow dissipated.

To learn more about the impetus misconception, go to
http://modeling.asu.edu/R&E/forceConceptionTaxon92.doc

Before Galileo, the prevailing scientific thought upheld the belief of force impetus, where some incorrectly believed that this force depended on the speed and mass of the object. Note how closely the incorrect idea of force impetus relates to correct understandings about kinetic energy. Starting with Galileo and Newton, scientists now know that an object will remain in constant motion (either at rest or traveling in the same direction with the same speed) unless acted upon by a net force. Therefore, force is not required for motion, but only to change an object’s motion (direction and/or speed). Forces act upon objects, but are not an inherent quality within the object.

A detailed discussion of Newton’s First Law of Motion is found at
http://www.physicsclassroom.com/Class/newtlaws/U2L1a.html

On the other hand, energy is an inherent quality of an object. If the object is moving, it has kinetic energy. Also, within the object there exists internal kinetic energy associated with molecular motions of the object’s material. The object would also have potential energy due to position within a gravitational, electrical, magnetic, and/or other type of force field.

An overview about the forms of energy can be read at
http://www.eia.doe.gov/kids/energyfacts/science/formsofenergy.html

3. Students incorrectly believe that energy is a substance, such as gasoline fuel.

Many students often view energy as a type of material or substance that acts similarly to that of matter. This may stem from common use of fuels, such as gasoline, and the misconception that the fluid itself is energy. The bonds that hold the hydrocarbon together to form gasoline are stored chemical potential energy that is released with a minimal amount of activation energy. Gasoline, or any fuel, can be viewed as a “storage container” for energy. Energy is not a substance, but a quantitative way to measure how a system is changing or potentially can change.

To learn more about the energy as a substance misconception and other energy
misconceptions, go to http://www.uwsp.edu/cnr/WCEE/keep/Mod1/Whatis/energyforms.htm.

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Content Benchmark P.12.C.2

Students know energy forms can be converted. E/S

Sample Test Questions

1^st Item Specification: Explain that heat is often produced as a byproduct when one form of energy is converted to another form (e.g., when machines and living organisms convert stored energy to motion).

Depth of Knowledge Level 1

1. Which of the following examples has the greatest thermal (internal) energy?
1. 5 kg of water with a temperature of 150°C
2. 8 kg of water with a temperature of 110°C
3. 10 kg of water with a temperature of 90°C
4. 100 kg of water with a temperature of 28°C

2. A toy car with initial kinetic energy rolls to a stop along a flat track. Because of friction, some of kinetic energy was transferred to
1. thermal energy.
2. gravitational potential energy.
3. elastic energy.
4. chemical energy.

Depth of Knowledge Level 2

3. A ball is initially dropped from a height 4 meters. After the ball bounces it returns to a height of only 2 meters. How much of the ball’s initial gravitational potential energy was transformed between the initial position and the final position of the ball?
1. One fourth of the total energy.
2. Half of the total energy.
3. Double the total energy.
4. Four times the total energy.

4. Aluminum was once used as the wires in home construction. Recently, it was changed to copper wires. Which of the following statements BEST account for why aluminum was replaced with copper?
1. When electrical energy is passed through a copper wire, less of the energy removes copper atoms from the wire.
2. The electrical energy that a copper wire can transfer is less than
   an aluminum wire.
3. As a byproduct of transmission, more electrical energy is transformed to wasted thermal energy in aluminum wire than in copper
4. The electrical energy that passes through an aluminum wire cannot be directed as well as the energy passing through copper.

5. After a student stretches a rubber band many times, they notice that the rubber band is now very warm to the touch. Which of the following predictions should be made?
1. The rubber band collected heat from the surrounding air after
   continuous stretching.
2. The stretching transferred energy to the rubber band and some of that energy was transferred to heating the rubber band.
3. The chemical reactions activated by the stretching caused an increase in the rubber band’s temperature.
4. The rubber band must have been warm prior to stretching and cooled somewhat during the stretching process.

2^nd Item Specification: From an example, identify that energy cannot be created or destroyed, but only changed from one form to another.

Depth of Knowledge Level 1

6. Energy is created as the result which activity?
1. Burning gasoline in an internal combustion engine.
2. Damming a river for hydroelectric power.
3. Rolling a marble down an incline plane.
4. Energy can only be transformed, not created.

7. When a match is initially struck, some amount of chemical energy is transferred to
1. thermal energy.
2. elastic energy.
3. kinetic energy.
4. potential energy.

Depth of Knowledge Level 2

8. The diagram below is a representation of a person skiing down a hill with the potential (PE) and kinetic (KE) energies noted. Use the diagram to answer the following question.

(From http://www.physicsclassroom.com/Class/energy/U5L2bc.html)

Which statement best summarizes the energy represented in the diagram?

1. The total mechanical energy is 100,000 J.
2. The total mechanical energy is 50,000 J.
3. The total mechanical energy is 35,000 J.
4. The total mechanical energy is 0 J.

9. The figure below is a model of the electromagnetic spectrum. Use the diagram to answer the following question.

(From http://hyperphysics.phy-astr.gsu.edu/hbase/ems1.html#c1)

Which of the following statements would be true if an increase in photon (quantum) energy occurred?

1. The wavelength must have increased.
2. The direction must have changed.
3. The frequency must have increased.
4. The wave speed must have increased.

10. When a piece of wood is burning, the stored energy within the chemical bonds of the wood is being transferred into
1. a gas thus heating the surrounding area.
2. the heating of the surrounding area.
3. electrical energy causing ionization and forming fire.
4. matter which accounts for the ash and charred wood.

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Content Benchmark P.12.C.2

Students know energy forms can be converted. E/S

Answers to Sample Test Questions

1. D, DOK Level 1
2. A, DOK Level 1
3. B, DOK Level 2
4. C, DOK Level 2
5. B, DOK Level 2
6. D, DOK Level 1
7. A, DOK Level 1
8. B, DOK Level 2
9. C, DOK Level 2
10. B, DOK Level 2

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Content Benchmark P.12.C.2

Students know energy forms can be converted. E/S

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. Energy Modeling Unit
Arizona State University runs a physics modeling program, which research has shown that students experiencing the unit undergo conceptual change for better student understanding. The complete energy unit comes with teacher notes and resources that thoroughly explain mechanical energy, and discuss heat and radiation. The modeling strategy forces students to problem solve and formulate a mathematical model of behavior that syncs with current scientific knowledge.

To view the unit on energy, go to: http://modeling.asu.edu/Modeling-pub/Mechanics_curriculum/7-Energy/ . Please note that this link is an ftp site appearing as a folder containing several PDF files for download.

2. Renewable Energy Lessons and Resources
The New York State Energy Research and Development Authority has a program with schools in the state called School Power…Naturally, where solar panels are provided to schools for use in generating the schools’ electrical power. In association with the program, several curricular materials have been developed, including lessons that cover the nature of energy and conservation of energy.
Teacher materials, instructions, and links to resource can be found at http://www.powernaturally.org/Programs/SchoolPowerNaturally/InTheClassroom/

3. Energy Tutorial
The Physicsclassroom.com offers a comprehensive tutorial that explains the concepts of kinetic energy and potential energy. This site is useful for educators as a quick review of content and as a resource for students needing further clarification. The concepts are described well with many examples and the site has review questions for students to test their understanding.
To view the tutorial, go to http://www.physicsclassroom.com/Class/energy/energtoc.html.

4. Energy Lesson Plans
PhysicsFront.org is a Web site for Physics Educators that has a collection of ready to use lesson plans. The lesson plans are complete with labs and activities and further resources.
Lesson plans and activities for energy can be found at http://www.thephysicsfront.org/static/unit.cfm?sb=5

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