Energy and Its Transformations
From wiki.NGSciEd.org
Contents |
Grade Level Targeted:
9-11 Physical Science
GPS Addressed:
SPS7 Students will relate transformations and flow of energy within a system.
a. Identify energy transformations within a system (e.g. lighting a match).
SPS8 Students will determine relationships among force, mass, and motion.
c. Relate falling objects to gravitational force.
SCSh1 Students will evaluate the importance of curiosity, honesty, openness, and skepticism in science.
e. Exhibit the above traits in their own scientific activities.
f. Recognize that different explanations can often be given for the same evidence.
g. Explain that further understanding of scientific problems relies on the design and execution of new experiments which may reinforce or weaken opposing explanations.
SCSh2 Students will use standard safety practices for all classroom laboratory and field investigations.
b. Demonstrate appropriate techniques for all laboratory situations.
SCSh3 Students will identify and investigate problems scientifically.
a. Suggest reasonable hypotheses for identified problems.
b. Develop procedures for solving scientific problems.
c. Collect, organize, and record appropriate data.
d. Graphically compare and analyze data points and/or summary statistics.
e. Develop reasonable conclusions based on data collected.
f. Evaluate whether conclusions are reasonable by reviewing the process and checking against other available information.
SCSh4 Students will use tools and instruments for observing, measuring, and manipulating scientific equipment and materials.
a. Develop and use systematic procedures for recording and organizing information.
SCSh5 Students will demonstrate the computation and estimation skills necessary for analyzing data and developing reasonable scientific explanations.
e. Solve scientific problems by substituting quantitative values, using dimensional analysis, and/or simple algebraic formulas as appropriate.
SCSh8 Students will understand important features of scientific inquiry. Students will apply the following to inquiry learning practices:
a. Scientific investigators control the conditions of their experiments in order to produce valuable data.
b. Scientific researchers are expected to critically assess the quality of data including possible sources of bias in their investigations’ hypotheses, observations, data, analysis, and interpretations.
Background:
Energy is “the ability to cause change” (McLaughlin, Thompson, & Zike, 2008, p. 100). Anything that can change its environment has energy, and it takes many different forms. There is electrical energy that causes a lightbulb to turn on which has to do with “the movement or flow of electrically charged particles” (“Electricity”). There is also chemical energy which is stored in chemical bonds, such as in the bonds in the food you eat. Radiant energy reaches us from the Sun, and thermal energy that we feel as heat.
Money can be used as an analogy to make energy easier to understand. If you have $100, you can change the form of money you have. You could have cash, traveler's checks, put it in a bank account, or even have it in gold coins. No matter what form you have it in, you still have $100. The same is true of energy. It can change forms, such as when electrical energy is used to power a lightbulb that produces radiant energy and thermal energy. However in the end, it's still energy.
Energy is often associated with motion, and “the energy a moving object has because of its motion” (McLaughlin, Thompson, & Zike, 2008, p. 102) is called kinetic energy. You can calculate the amount of kinetic energy in a system using the following equation: KE=1/2mv2. The joule (kg m2/s2) is the SI unit for energy, and it is abbreviated J. Kinetic energy depends on an object's mass and speed.
Potential energy is energy that an object has stored because of its position, and it is also measured in joules. “Even motionless objects can have energy” (p. 103). There are several different kinds of potential energy. One kind of potential energy is elastic potential energy which is stored in something that stretches or compresses, such as a spring. Another kind is chemical potential energy which is energy stored in chemical bonds, such as in natural gas which can be burned to release energy. Gravitational potential energy (GPE) is another form of potential energy that is stored due to an objects position over Earth's surface. GPE depends on an object's mass and height and can be calculated using the following equation: GPE=mgh. If two objects are located at the same height over Earth's surface, then the more massive one will have the greater GPE. If objects of the same mass are located at different distances above Earth's surface, then the higher object will have the greater GPE. The objects that initially had more potential energy would have more kinetic energy when they hit Earth's surface.
Integration of Science Concepts:
Students will be able to visualize several types of energy through the Bouncing Ball lab. They will be able to observe how changes in mass or distance from the ground influence GPE. They will also be able to observe the change from potential to kinetic energy. They will also observe elastic potential energy differences in the different types of balls. They may observe energy being transferred to the surface the ball is bouncing off of, hear it being transferred to sound, or infer that some is being transferred as heat.
Management Considerations:
When students are bouncing the balls, be sure to remind them to only use the balls for the lab and not to use them inappropriately. Remind them to just drop the balls and not throw them down which would skew their data. In addition have them hold a meter stick vertically next to the drop zone so that they can approximate the height of the bounces.
Common Misconceptions on this Topic:
When the balls bounces get shorter, the energy is going away. The ball's energy is not going away, because energy is being conserved. It is simply changing forms and perhaps being transferred as sound, heat, or kinetic energy in vibrations. The Bouncing Ball lab addresses this misconception that energy is lost by prompting students to look for energy transfers further and not to just accept that it is gone. By actually making a concentrated effort to look for the energy, they will see that it has gone several other places, but it is not just “gone.”
You only observe energy when objects are in motion. Energy has many forms, such as kinetic and potential, chemical, electrical, and thermal. You observe energy when you hear something, see an object sitting on a high shelf, or turn on a light. The Bouncing Ball lab addresses this misconception by purposefully guiding students to look for energy that is not just related to the ball dropping. They have to account for the bouncing ball stopping, so they must look for energy in other places.
Bouncing Ball Lab - Inquiry Lab Instructions:
Prelab:
1.Why is it important to drop the balls from the same height?
2.How could you use a cardboard box in this lab?
What happens when you drop a ball on to a hard, flat surface? It starts with potential energy. It bounces up and down until it finally comes to rest. Where did the energy go?
Question:
Why do bouncing balls stop bouncing?
Materials:
- Tennis ball
- Rubber ball
- Golf ball
- Table tennis ball
- Balance
- Masking tape
- Meterstick
- Cardboard boxes
- Book
- Paper towel stack
In this lab, you will use the materials above to observe where energy goes when a bouncing ball stops bouncing. Which balls will bounce highest on which surfaces and what makes the difference? Below, write your hypothesis for what type of ball and surface will yield the highest bounce. Afterwards, write the step-by-step procedure you will follow to test your hypothesis.
Hypothesis:
Procedure:
Data:
Construct a data table recording the type of ball, the surface, and the height of the bounce (cm).
Construct a bar graph to compare the heights of the bounces for each type of ball/surface.
Discussion:
1.Compare the height of the bounces for the different ball/surface combinations. Which produced the highest bounce? Why do you think this combination produced the highest bounce? Which produced the lowest bounce? Why do you think this combination produced the lowest bounce?
2.Calculate the gravitational potential energy (GPE) of each ball before dropping it.
3.Describe how the gravitational potential energy and the kinetic energy of a ball changes as it falls.
4.Infer what happens to the kinetic energy of a ball when it hits the floor.
5.Explain why the balls bounced to different heights using the concept of elastic potential energy.
Conclusion:
Was your hypothesis supported? If you could do your experiment again, would you change anything, and if so, what would you change?
Internet Resources:
- “Energy Rules!” (http://www.uwsp.edu/cnr/wcee/keep/Mod1/Rules/EnTransfer.htm) outlines several different types of energy transfer as well as relevant, easy-to-understand examples that students observe in their day-to-day lives.
- “Moving Stores of Energy (http://www.sep.org.uk/samples/energynow/files/animations/energy8_main.swf) shows students how energy is conserved when a wheel spins on a block and thermal energy is measured. They also can see how the mass of the wheel affects the amount of energy.
- “Transformation of Energy” (http://www.tutorvista.com/content/physics/physics-i/work-energy-power/energy-transformation.php) includes a tutorial on energy transformations and then concludes with have students match a change to its corresponding energy transformation.
- “Build a Pizza Box Solar Oven” (http://www1.eere.energy.gov/kids/roofus/pizza_box.html) outlines the steps of an activity such that students can create a product that transfers energy.
- “Energy Transfer in a Trebuchet” (http://www.teachersdomain.org/asset/hew06_vid_trebuchet/) shows how historians construct a trebuchet and depend on an understanding of energy transfer in order to make it work properly.
References:
- “Electricity.” (n.d.). Retrieved September 23, 2009 from http://en.wikipedia.org/wiki/Electricity
- McLaughlin, C. W., Thompson, M., and Zike, D. (2008). Physical Science. New York: The McGraw-Hill Companies.
