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
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.
To learn more about closed and open systems, go to
http://www.users.globalnet.co.uk/~noelh/OpenClosedSystems.htm.
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.
To access the site, go to http://fi.edu/guide/hughes/energyconservation.html.
To learn more about conservation of energy, please go to
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/energy/u5l2bb.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).
To learn more about energy transformations, go to
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.
To learn more about the Earth’s energy budget, go to
http://okfirst.mesonet.org/train/meteorology/EnergyBudget2.html.
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 )
To learn more about energy transformations in photosynthesis, go to
http://arnica.csustan.edu/boty1050/Photosynthesis/photosynthesis.htm.
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)
To learn more about electrical energy transformations, go to
http://www.slideshare.net/scienceinteractive/ks-3-how-electricity-transfers-energy/.
This website has a very useful slideshow that explains energy usage and transfer.
More information about electrical energy transformations can also be found at 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.
More information about efficiency can be found at
http://er100200.berkeley.edu/handouts/Week_4_Section_Handout.pdf
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).
To learn more about this common energy transformation, go to
http://www.materialworlds.com/sims/Pendulum/sim.html. This site allows you to adjust the
friction and gravity acting on an interactive pendulum. You have to download free software to
run the program.
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
Questions and answers will be provided on a separate document
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
Answers to Sample Test Questions
Questions and answers will be provided on a separate document
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.