To understand how and why heat is produced from things that give off light, from machines, or when one thing is rubbed against another.
This lesson is intended to give students a general idea of how heat is produced from human-based activities and mechanical and electrical machines.
At these grade levels, students do not need to develop formal concepts of energy. However, one type of energy which students at this age can begin to explore is heat, which is produced almost everywhere. In their science and technology activities during these years, students should be alerted to look for things and processes that give off heat—lights, radios, television sets, the sun, sawing wood, polishing surfaces, bending things, running motors, people, animals, etc.—and then for those that seem not to give off heat. Also, the time is appropriate to explore how heat spreads from one place to another and what can be done to contain it or shield things from it. (Benchmarks for Science Literacy, p. 82-84.)
Many of your more advanced students may begin to ask why things or activities like flashlights, pencil sharpeners, and hand rubbing create heat. In this case, you may want to offer a simplified, general explanation, like: heat is produced by the movement and collision of tiny ("excited") atoms or molecules. (Science for All Americans, p. 49-52.) Though many students may not be able to grasp the more technical reasons, let this be considered the more challenging part of the lesson that they do not have to completely understand.
It is important to keep in mind that students' ideas about heat are inexact. In some situations, cold is thought to be transferred rather than heat. Some materials may be thought to be intrinsically warm (blankets) or cold (metals). Objects that keep things warm—such as a sweater or mittens—may be thought to be sources of heat. Only a continuing mix of experiment and discussion is likely to dispel these ideas. Furthermore, students need not come out of this grade span understanding the difference between heat and temperature. In this spirit, there is little to be gained by having youngsters refer to heat as heat energy. The overall goal here is for students to make qualitative approximations and gain a better understanding of the general heat energy story. (Benchmarks for Science Literacy, p. 82-84.)
While teaching, it is also important to be aware of the many misconceptions that students at this level have about heat energy and energy transformation. For example, even after instruction, students don't always give up their naive notion that some substances (for example, flour, sugar, or air) cannot heat up or that metals get hot quickly because "they attract heat," "suck heat in," or "hold heat well." In addition, the transformation of motion to heat seems to be difficult for students to accept, especially in cases with no obvious temperature increase. Finally, it may not be clear to students that some forms of energy, such as light, sound, and chemical energy, can be used to make things happen.
Here are examples of items that can be used to demonstrate activity-based, mechanical, electrical, and light-producing heat. There are also examples of non-heat producing items. In case you are unable to locate the items, the first column of the When Things Start Heating Up student sheet is left blank so that you may fill in whatever eight items or ideas you can come up with to fulfill the teaching objective. You will need to come up with at least one or two activities for each of these categories:
- Mechanical pencil sharpener
- Roller skate
- Fly swatter
- Electric pencil sharpener
- Light bulbs
- Cardboard box
To best orient students on the basics of heat production and motion through human activity and by machines, begin by having the class stand up to perform a number of physical activities that produce heat. You should say to students something like, "OK, class, I would like you to stand up and begin rubbing your hands together like this [demonstrate]." After 15 to 30 seconds, have the class stop and ask questions like these:
- In what kinds of situations would you do something like this? Why?
- How do your hands feel right now? Why?
- Why is rubbing your hands together useful or helpful?
(Accept all answers, but ask students to support their views with explanations.)
To further extend their awareness, have students then either: jog in place, stomp their feet, wave their arms up and down, or bend down to touch their hands to their feet again and again. After a brief period, have students stop the activity to discuss their similar heat-based reactions. You may wish to give them the impression that they are "little heat producers" when they are physically active.
When appropriate, lead the class into a discussion of heat itself in more general terms. You may wish to review Heat Energy for general background information. Discussion questions may include:
- Why do people need heat?
- In what kinds of specific everyday situations do we need heat?
- What are some of the major sources of heat that we rely on?
- What kinds of machines produce heat when being used?
(Accept all answers, but ask students to support their views with explanations.)
Allow the heat-based discussion to lead into an orientation and warm up about the different categories on the When Things Start Heating Up student sheet. To peak student interest, you may just simply write the corresponding categories on the chalk board (Human, Electrical, Mechanical, Light-Producing) and ask them what they think the categories represent (and, if necessary, how they might relate to heat). You can have them brainstorm to come up with a number of heat-producing activities or machines and have them decide to which categories they would belong.
When all four categories have been filled up on the board, finish off the activity by adding the additional category of Non-Heat-Producing Situations, explaining that it is important to be aware that there are many objects in the world that do not produce heat. Have them brainstorm again and fill the category with specific objects or situations. (If appropriate, students may revisit this chart in the Assessment section if they need to modify any of their answers based on what they learned in the lesson.)
Now distribute the When Things Start Heating Up student sheet so the class can undertake a number of hands-on activities that will help them better identify and investigate how heat is and is not produced under a number of situations and conditions. Read over the chart with the class for general comprehension. As mentioned earlier, you could have either filled in the eight activities in the first column or have students do it themselves at each of the eight activity stations. As suggested by the second column, students should identify where specifically on the object or in the situation heat is being produced. In the third column, have students estimate the level of heat produced by the activity (on a scale of one to six). Finally, in the fourth column, encourage them to decide in which of the previously discussed five categories the activity belongs.
As indicated in the charts, the eight activities will need to demonstrate how heat is produced or not produced in at least one:
- Human-based activity (erasing board, rubbing book against desk)
- Mechanical activity (sharpening pencil, spinning roller skate wheels)
- Electrical activity (computer, radio)
- Light-producing activity (flashlight, light bulb)
- Non-heat-producing situation (boxes, plants)
As previously mentioned, activities may vary depending on the availability of items and stations for each activity that will need to be set up throughout the classroom.
Between activities, have students take short breaks to discuss their findings (for further guidance, insight, and reinforcement). Overall, it is important that students come to understand that all of the situations that produce heat involve motion—either observable (activity-based and mechanical) or molecular (electrical and light), and that simple, stationary objects do not produce heat.
Review with students what they have learned about how heat is produced by the activities we undertake and by many of the mechanical and electrical machines around us. To further broaden their understanding, you may ask them to ponder and respond to questions like these:
- Which of the activities did you find most surprising? Why?
- What are some of the benefits and dangers of heat being produced in human, mechanical, and electrical situations?
- What would life be like if we didn't have these kinds of heat-producing situations?
- In what ways has this lesson changed the way you think about heat? Explain.
This lesson is part of a series of lessons dealing with energy transformations. The other lesson in the series is The Warmth of the Sun (K–2).
This lesson may be supplemented by Energy Sources and Uses, which introduces and examines the advantages and disadvantages of renewable and non-renewable sources of energy.
The Energy Story, from the California Energy Commission, provides a simple, colorful, and comprehensive exploration of the various forms of energy in the universe. (For more advanced students.)