To introduce students to energy through the idea of energy transformations and conversions, and to develop students’ ideas of what energy is and how it can be measured.
In this lesson, students will study energy through the idea of energy transformations and conversions. They will do this by exploring some Internet resources as well as engaging in some hands-on activities.
This investigation could be the beginning of a unit on energy. At this early stage, there may be some confusion in students’ minds between energy and energy sources. Focusing on energy transformations may get around this somewhat.
Introduce the investigation by letting students use their Converting Energy student esheet to explore Building a Better Pyramid on the Atoms Family website, which is part of the Science Learning Network. In this online activity, students explore energy conservation by adding insulation to the pyramid. Once students have done the online activity, discuss with them what they discovered about inslulation, especially how many layers would be the most efficient and why. You could ask them questions like these:
- What happens when you add one layer of insulation to the pyramid?
- What happens when you add two layers? How about three, four, and five layers?
- Is there a point where it doesn't seem beneficial to add more layers?
Then have students go to Raceways where they can explore various forms of energy and may be a good way to provide a context for student thinking on potential and kinetic energy. Have students do the activity and then discuss the questions found on the site.
Energy can be a difficult concept because we use the word so often in so many different ways in everyday life that it seems like a familiar concept. The familiarity is an advantage in getting a discussion of energy started, but can get in the way of deciding on a definition that can lead to experimental measurements and testing of ideas about energy.
Have students read the introduction and first chapter of The Energy Story, an online book found on the Energy Quest website; it consists of 15 brief chapters that focus on a variety of energy topics such as electricity, hydropower, and fossil fuels.
To focus student attention on the ideas in the related benchmarks, ask them to jot down notes as they read, based on these questions:
- What is "energy"?
- Is there more than one kind of energy?
- Can one kind of energy be changed into another?
The class should then discuss their ideas about energy. Students will probably come up with several kinds of energy as examples of what energy is. Make a list of students' ideas of energy types. Some examples are listed below:
- heat (warming a house, warming up liquids such as water)
- mechanical work (moving things around)
- electrical (lighting, cooking, lightning)
- chemical (burning in engines, explosions)
- light (solar cells and solar heating)
- nuclear (power plants, atomic bombs)
The ideas about interconversion of one form of energy into another will be implicit and explicit in student examples and discussion. In the above list, for example, we have the conversion of light energy into electrical energy in solar cells and light energy into heat energy in solar heating. Direct student attention to these conversions and get them to come up with as many as possible. Try to steer the student discussion toward the idea that all the kinds of energy they can describe and name can be converted into heat (to warm something up) and/or mechanical work (to move objects around). Work can also be converted to heat (rub your hands together briskly and feel the heat created by friction) and heat to work (in engines). We usually like to think about heat and mechanical work a bit separately, because work represents directed energy and heat is undirected. (At the molecular level, heat energy causes random molecular motion to speed up, but doesn't affect the randomness.) When students are satisfied that all the kinds of energy they know about can be converted to heat and/or mechanical work, they have as good an idea of what energy "is" as they need.
The discussion of forms of energy and their interconversion should lead to a further discussion of how energy can be measured. The objective is not to determine a numerical value for an input of energy to a system. Rather, students should be thinking about how they could tell whether a different amount of energy is input one way or another. Any kind of energy can be converted to heat energy that can be detected by warming things up. What will be warmed up and how will we know it has been warmed?
Students should discuss readily available, safe, and easy-to-handle substances to be warmed as well as how to detect the warming. Water probably will be among the substances suggested. Its advantages are accessibility and low cost, as well as ease of measurement of warming with a finger or thermometer immersed in the liquid.
Hand out the Heat Experiment student sheet. Divide students into groups and provide each group with two glass beakers and a heating source. Students should fill each beaker with different amounts of water. Let them decide how much water to use in each beaker but be sure that they measure and record the amounts on their student sheets. Then, students should heat the water for a set amount of time, say 10 minutes. Again, students can determine the amount of time so long as they record it.
Allow students to vary their experiments by trying different amounts of water, different temperatures, etc.
Among the questions the students need to explore experimentally are:
- Does it matter how much water is used?
- Does it matter what temperature the water is?
- Do different amounts of energy have different effects?
Discussion of the results students get from the above activities should lead to conclusions such as:
- The amount of water makes a difference: the more water, the smaller the amount of warming by the same amount of heat energy.
- The amount of heat energy makes a difference: longer heating time with the same amount of water leads to more warming.
- The initial temperature of the water probably has little effect. (Very cold or very warm water will gain or lose, respectively, heat energy from the room and this effect will be in addition to whatever heat energy source is used. Measurements with simple equipment will probably not show these effects.)
Middle-school students may think of energy as something that makes things happen and then is expended in the process. Students may not think of energy as measurable and quantifiable. After this investigation, for example, students should understand that some of the heat energy used to warm the water was transferred to the water, but also that some of the heat energy was transferred to the room air. To make sure that students understand this, have them make drawings of their investigations that show what happened to the heat energy.
Poor Richard's Energy Almanac on the Energy Quest site provides an interesting comparison of energy used in homes during Benjamin Franklin's time and the energy we use in homes today. Also on Energy Quest, Super Scientists, A Gallery of Energy Pioneers contains brief biographies and historical photographs of some of the men and women who contributed to our understanding.
On the Exploratorium Science Snacks the activity called Solar Brightness shows you how to make a photometer which can be used to compare the brightness of the sun to the brightness of a lamp.