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Content Benchmark P.8.C.4
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 Physical Science Matter Force and Motion Energy P.8.C.1 P.8.C.2 P.8.C.3 P.8.C.4 P.8.C.5 P.8.C.6 Content Areas Nature of Science (NOS) Life Science Earth Science Physical Science

Students know energy cannot be created or destroyed, in a chemical or physical reaction, but only changed from one form to another.  E/S

Energy cannot be created or destroyed in any kind of physical or chemical reaction. Energy can only change from one form into another. Commonly, energy will transform into more than one form during a physical and/or chemical reaction. The Law of Conservation of Energy states that energy cannot be created or destroyed, but only changed from one form to another. This assumes that the total amount of energy in the universe is constant. Likewise, in any closed system the total amount of energy remains constant. A closed system is any system in which the energy cannot escape.

To help understand what a system is, consider the following example. Kaitlyn and Jose are building a model roller coaster for their science project. The students are trying to make a ball, which represents the train of a coaster, complete the entire length of the track without jumping off the track. After setting up their coaster, they find that the ball keeps jumping the track. Jose lowers the height of the starting hill and finds that the ball will no longer make it to the end of the course. Jose and Kaitlyn are having a conceptual problems understanding about the conservation of energy. Kaitlyn remarks that if they keep the hill high, they have too much energy, “and if we lower the hill too much we don’t have enough,” said Jose

This example will be used to illustrate the content behind this benchmark, and in this example, we would say that they roller coaster is the closed system.

Potential and Kinetic Energy
The most fundamental forms of energy are potential and kinetic energy. Potential energy is the energy that an object has due to its position. Kinetic energy is the energy an object has due to its movement. When the roller coaster train is standing still at the top of a hill, it has potential energy (due to its relatively high position in the gravitational field). As it falls, this potential energy is transformed into kinetic energy (movement). The total amount of energy in the system is equal to all its potential energy and all of its kinetic energy added together at any point in time and can be expressed mathematically as Total Energy = Potential Energy + Kinetic Energy (TE = PE + KE). In the closed system of the model roller coaster, the potential energy and kinetic energy associated with the moving ball are changing (i.e., transforming between the two forms), but the total energy remains constant.

KEi + PEi = KEf + PEf
Figure 1. Energy transformations in a roller coaster.
(From http://www.glenbrook.k12.il.us/GBSSCI/
PHYS/CLASS/ENERGY/u5l2bb.html
)

A pendulum can also help us understand the total energy in a system.
In the absence of friction and other outside forces, the system is closed and will not experience a change in total energy.

Figure 2. A pendulum helps demonstrate how energy is conserved in a closed system. At point A and A’, the potential Energy of the pendulum is at its maximum. At point C the kinetic Energy is at its maximum and in the absence of friction would be equal to the energy at point A or A’. Point B is the point at which the amounts of potential energy and kinetic energy are equal and each 50%
of the total energy in the system.
(From http://albertgrasmarti.org/agm/recerca-divulgacio/pendulum-TPT.pdf)

In reality, the pendulum cannot continue to swing back and forth without stopping. Why does the total energy seem to decrease? The kinetic energy of the string movement causes heat transfer to occur from the pendulum to the support structure (i.e., the particles in the pin holding the string have increased kinetic energy due to conduction). Therefore, a real pendulum is not a closed system. Energy is still conserved, but the total energy in just the pendulum is not constant.  In all systems, some of the total energy is always transformed to increased random particle motions. For this reason perpetual motion is not possible.

This following website offers a great example of conservation of energy using the light bulb. The site also has a good visual of energy changes from kinetic to potential energy in a spring at http://fi.edu/guide/hughes/energyconservation.html.

This website describes the work-energy relationship. It uses mathematical formulas and graphics to explain the concepts of conservation of mechanical energy and applies it to pendulums and roller coasters.

Common Energy Transformations
Energy can be more commonly described in terms of (1) chemical energy, (2) radiant energy, (3) electrical energy, and (4) thermal energy. These types of energy are combinations of both potential and kinetic energy, and relate to how these energy forms are experienced. Some common energy transformations include chemical to motion, radiant to chemical, electrical to thermal and electrical to radiant. In these transformations, energy begins in one form and then transforms into another. In a radiant to chemical transformation light energy from the sun (radiant) is transferred to our planet in the form of electromagnetic waves. Energy from these EM waves is stored in plants. Through the process of photosynthesis, energy from waves is stored in the plant (biomass-chemical potential energy). This chemical energy can be transformed into motion (kinetic energy) when an animal eats the plant and breaks down the chemical bonds in the biomass. The breaking of the bonds releases energy which can be stored in the animal, or used by the animal (kinetic and/or thermal energy).

http://www.think-energy.co.uk/ThinkEnergy/11-14/activities/EnergyTrans.aspx.

Examples of Energy Transformations
Energy transformations can be shown within systems. For example, we can think of the Earth as a system, and we can show energy transfers within that system. Earth’s energy budget shows energy transfers from the sun to the earth and how this energy moves within and between the atmosphere, biosphere and hydrosphere. Internal energy from geologic process are a part of Earth’s energy budget, however this internal energy is a relatively small source in comparison with the input from the sun.

Figure 3. This diagram shows the earth’s energy budget in terms of
power (energy per time, in units of Watts) per square meter.
(From http://stephenschneider.stanford.edu/
Graphics/tn_EarthsEnergyBalance.jpg
)

In this diagram solar energy enters our atmosphere in the form of radiant energy (electromagnetic waves). Some of this radiant energy is reflected back into space. The remainder provides energy for our planet. It warms our air, land and oceans through conduction and convective modes of heat transfer and also through chemical energy transformations. This energy is transformed into kinetic energy of the wind and ocean currents. Some of the energy causes evaporation, where the energy is used to change the phase of water (i.e., the radiant energy causes a change of the water’s molecular potential and kinetic energy). Because of this energy input from the Sun, the Earth’s temperature increases and it transfers some of this energy back to space; again, as radiant energy in the form of electromagnetic waves.

The photosynthetic process is another system that demonstrates energy transformations within a system. Again, we start with solar energy. This is then transferred to the plant which uses the energy in the photosynthetic process. The biomass of the plant now has chemical potential energy that may be transferred to other organisms either in the form of chemical energy used to generate thermal energy inside the organism and/or kinetic energy to allow the organism to move.

Figure 4. The Basis Photosynthetic process is represented in this diagram.
(From http://grapevine.net.au/~grunwald/une/KLAs/science/photosynthesis.html)

Electrical energy is easily converted into other forms of energy as it is transferred. For example, in an electrical circuit, electrical energy is transformed to radiant and thermal energy in a light bulb, kinetic and thermal energy in a hair dryer, and/or radiant and sound energy in a television. During transfer, some useful electrical energy is always transformed to the kinetic energy of random particle motions. It is important to note that this energy does not disappear; however, it is no longer useful.

Figure 5. This diagram shows how a hair dryer transforms
electrical energy into other energy forms.
(From http://my.hrw.com/tabnav/controller.jsp?isbn=0030305217)

ks-3-how-electricity-transfers-energy/
.

MS TIPS Benchmark P.8.C.6.

Energy can also be transferred from the mass of an atom. In nuclear fission, the atom is split and in doing so, some of the resting mass of the atom is transformed into energy.

Figure 5. This diagram illustrates how mass is converted to energy
when the nucleus of a uranium-235 atom is fissioned
(From http://grapevine.net.au/~grunwald/une/
KLAs/science/photosynthesis.html
)

A really nice flash animation of energy transformation inside a nuclear power reactor can be seen at http://www.atomeromu.hu/mukodes/lancreakcio-e.htm.

This website contains a story-like explanation of energy conversion. Vocabulary is highlighted and scientific principles related to energy transfer are given in the margin. To learn more about various energy transfers, go to http://www.ftexploring.com/energy/energy-1.htm.

Efficiency of Conversions

When energy is transformed from one form to another form, we know that some of the energy is always transferred into some other form of energy that is not useful. For example, when you put gas in your car, the primary goal is transforming the fuel’s chemical energy into kinetic energy, which rotates the wheels and propels the car forward. In addition to making the wheels turn, some of the energy is transformed into random particle motions which increase the thermal energy inside the car’s materials, and also make sound as the particles vibrate. These random particle motions are not useful to moving the car forward. Because some of the energy goes to an unintended purpose, the car is not 100% efficient. The less efficient a car is the less energy will be available for a useful purpose.

Content Benchmark P.8.C.3

Students know energy cannot be created or destroyed, in a chemical or physical reaction, but only changed from one form to another.  E/S

Common misconceptions associated with this benchmark

1. Students incorrectly believe that energy is destroyed in energy transformations.

When students watch a pendulum swing back and forth it is easy for them to note that the pendulum does not swing as high with each successive swing. Some students assume that energy has been destroyed. When we ask students where this energy has gone, many are not able to tell you. Ask students to rub their hands together, and observe what they feel afterwards. Students should feel a temperature rise that is accompanying the energy transformation from kinetic energy (rubbing hands) to thermal energy. Students may also be able to feel warmth in the string where it rubs against their hand when they are swinging a ball on a string (the pendulum).

2. Students incorrectly think that energy can be changed completely from one form to another without any additional energy transformations or loss from the system.

Perpetual motion is a concept that many students believe is possible. There are advertisements on television and the Internet proposing that 100% efficiency is possible. An imaginary perpetual motion machine operates such that energy can be transformed into another form and then transformed completely back into a useful form without putting any additional energy from outside the system into the machine.

This following web site chronicles past attempts at perpetual motion machines and describes the science behind them including why they don’t work. To access the site, click on http://www.lhup.edu/~dsimanek/museum/unwork.htm.

3. Students incorrectly believe that there is no relationship between matter and energy.

Students have a hard time grasping the equivalence of matter and energy. Einstein’s famous equation (E=mc²) represents this equivalence in mathematical form. Nuclear physics is beyond the capabilities of most middle school students, and therefore it is important to talk about energy and matter in a way they can understand. The process of nuclear fission is a great way to discuss the relationship of matter and energy. By discussing what happens inside each splitting uranium atom as a chain reaction is taking place, teachers can demonstrate the equivalence of mass and energy.

The following website shows a great animation of a nuclear chain reaction occurring.
http://www.lon-capa.org/~mmp/applist/chain/chain.htm.

4. Students often ask the question “if energy is conserved, why are we running out of it?”

Students often confuse energy resources with energy forms. They also do not fully understand the concept of efficiency. They do not understand that once you have transformed energy, you cannot change it back to a more useful source without putting additional energy from outside the system.

The following website provides excellent energy resources. The site can be used to help students to separate forms of energy from energy sources and understand more about non-renewable energy sources.
http://www.eia.doe.gov/kids/energyfacts/science/formsofenergy.html

Another website has information about energy conversion and efficiency. It also explains a sample energy bill and the calculations on it.
http://www.uwsp.edu/cnr/WCEE/keep/mod1/Rules/EnConversion.htm

Content Benchmark P.8.C.4

Students know energy cannot be created or destroyed, in a chemical or physical reaction, but only changed from one form to another.  E/S

Sample Test Questions

1st Item Specification: Identify and describe differences between kinetic and potential energy.

Depth Of Knowledge Level 1

1. Kinetic energy is
1. the energy stored in an object.
2. the energy of a moving object.
3. stored and moving energy.
4. loss of all energy.
1. Potential energy is
1. the energy stored in an object.
2. the energy of a moving object.
3. stored and moving energy.
4. loss of all energy.

Depth Of Knowledge Level 2

1. Below is a figure of a pendulum. The letters represents specific points that the pendulum passes through in its swing. Use this figure to answer the next question.

In the figure above

1. position A is the point of maximum potential energy and minimum kinetic energy.
2. position B is the point of maximum potential energy and minimum kinetic energy.
3. position A is the point of maximum kinetic energy and minimum potential energy.
4. position B is the point of maximum kinetic energy and minimum potential energy.
1. Below is a figure of a pendulum. The letters represents specific points that the pendulum passes through in its swing. Use this figure to answer the next question.

In the figure above, the letter representing the point where kinetic energy and potential energy are equal is

1. Point A
2. Point B
3. Point C
4. Point A'

2nd Item Specification: Describe common energy transformations (e.g. chemical to motion, radiant to chemical, electrical to thermal, electrical to radiant).

Depth Of Knowledge Level 1

1. A match is being lit to start a fire. As the match decreases in size and turns black, the chemical energy stored in the match is NOT
1. changed partially into thermal energy.
2. changed partially into light energy.
3. completely destroyed.
4. completely conserved.
1. During photosynthesis, light energy is converted into
1. chemical energy.
2. electrical energy.
3. nuclear energy.
4. thermal energy.
1. A hairdryer converts electrical energy into
1. chemical energy.
2. electrical energy.
3. nuclear energy.
4. thermal energy.

Depth Of Knowledge Level 2

1. The motor in a fan converts
1. potential energy into mechanical energy
2. electrical energy into kinetic energy
3. chemical energy into electrical energy
4. solar energy into nuclear energy
1. The sun is beating down on a child sitting on the sidewalk. This is an example of a transformation of
1. radiant energy to thermal energy.
2. radiant energy to chemical energy.
3. electrical energy to radiant energy.
4. thermal energy to radiant energy.
1. The diagram below shows a roller coaster. Use this diagram to answer the next question.

At what point in the journey of the roller coaster is potential energy transforming into kinetic energy?

1. Point A
2. Point B
3. Point C
4. Point D

Constructed Response P.8.C.4

1. Cross country runners sometimes eat pasta before they begin running.

1. In terms of energy, explain why the runners eat pasta before running?
2. Runners are often sweating when they finish their race. Using your knowledge of how energy changes, explain what happens to the pasta during the course of the run?

Content Benchmark P.8.C.4

Students know energy cannot be created or destroyed, in a chemical or physical reaction, but only changed from one form to another.  E/S

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

Constructed Response 3-point Answer and Score Rubric:

 3 points Response addresses all parts of the question clearly and correctly. The student correctly identifies pasta as a source of potential energy that changes to kinetic energy of running. Specifically, chemical energy in the pasta is transformed by the body to provide energy for the kinetic energy of the human muscles. This kinetic energy of the muscles allows the runner to move forward. The chemical energy is also transformed to thermal energy in the body, which raised the runner’s temperature. The sweat produced evaporates on the skin. This energy required to change the state of the water transfer thermal energy from the runner to the atmosphere. 2 points Response addresses all parts of the question and includes only minor errors. 1 point Response does not address all parts of the question. 0 points Response is totally incorrect or no response provided.

Content Benchmark P.8.C.4

Students know energy cannot be created or destroyed, in a chemical or physical reaction, but only changed from one form to another.  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 Transformation Webquest

This website contains a webquest for conservation of energy using a roller coaster example. Students are given various questions and web site links for help solving those questions and problems. The majority of the questions are from the Glenbrook physics classroom web site. You can pick and choose among the questions/tasks to suite your lesson.

The webquest can be found at http://physicsquest.homestead.com/quest3ap.html.

2. Debating Nuclear Power

This PBS website for the Frontline program titled “Nuclear Reaction: Why Do Americans Fear Nuclear Power?” is full of great information on nuclear energy, including how it works and its advantages and disadvantages. Safety information is given as well as historical information about Chernobyl and Three Mile Island. There is a great map that shows the location of nuclear power plants. There is a nuclear phobia quiz and a link to nuclear energy as it is portrayed in Hollywood. This website also has information on how nuclear radiation is measured, and how much would be harmful. A list of links to more information on nuclear energy is also given.

To access the site, go to http://www.pbs.org/wgbh/pages/frontline/shows/reaction/.

3. Energy Graphics Organizer

This hyperphysics site has a graphic organizer for almost every physics concept and how they are related to each other. In addition to relating the concepts, the concepts are explained in concise detail. Many have basic graphics to help explain the concept. In particular, the site has several pages dealing with energy transformations. Go to the index to see the list of physics concepts available. The website is also available on a disk.

Click on http://hyperphysics.phy-astr.gsu.edu/hbase/conser.html#isosys to get to the hyperphysics website.

4. Lesson Plan for Conservation of Energy and Perpetual Motion

This inquiry lesson plan asks students to build their own device for transforming between potential and kinetic energy. It also asks students to evaluate the possibility of perpetual motion. The lab activity takes about two class periods, but is worth the time to reinforce the principles behind the conservation of energy. Students use common classroom and laboratory materials to make the devices. Evaluation and assessment questions are available for the end of the lab.

The lesson is found at http://www.wested.org/werc/earthsystems/energy/conservation.html.