Challenge 5: What's the Big Deal About Entropy?
(45 minutes)
During “What’s the big deal about entropy?” students are presented a series of engaging challenges involving a solar panel, a gas generator and a hand-cranked generator. First, students experiment with covering up a solar panel connected to a solar-powered radio. They are then asked to determine if the solar panel is creating energy. Then they observe a gas powered machine and debate if it is creating energy. Most groups assert confidently that the “passive” solar panel isn’t creating any energy, unlike the gas being burned in a generator. Your students learn that neither of these technologies creates any energy; that all technologies are only transformers of energy and that energy cannot be created or destroyed. So then what’s all the hype about an energy crisis? To figure that out, they are challenged to use two small hand-cranked generators and a couple of wires to find out what happens every time energy changes from one form to another. It turns out, every time energy transforms into another form, it becomes less useable and organized to do work. This phenomenon is called entropy (i.e., the second law of thermodynamics).
Materials (for whole-class demonstration):
Procedure:
- 1 Solar cell powering some easily observable device like a radio or small car
- 1 Automobile or other gas powered equipment
- 2 Genecons, each with a pair of wires (aka, small hand-cranked generators available from many science education supply companies)
- Demonstrate a solar powered radio or solar powered model car. Ask volunteers to experiment with covering the panel.
- Have students break up into their Challenge Trail groups to answer, “Is the solar panel creating energy?” (3-minutes). While rotating among the groups, play devil’s advocate when appropriate.
- Do not process as a whole group yet.
- Demonstrate a gas-powered device. Turn it on and off a couple of times.
- Have each group answer, “Is the gas generator creating energy? (3-minutes) Continue to circulate and ask students to explain their reasoning. Try to play off of the dissonance that might occur between their different reasoning between the solar panel and gasoline generator.
- Invite the whole class to share their answers to both questions. Facilitate a whole class discussion by playing devil’s advocate. When you think the discussion has peaked, state the following:
It’s reasonable to think that both the solar panel and the gas generator are creating enough energy to
help operate things. But GET THIS. They’re not creating any energy. Neither the solar panel in all of its grand
quietness, nor the gasoline engine, in all of its fury, is creating any energy. It’s true.
The solar panel is just changing the sun’s energy from light energy into electrical energy.
Same deal with the gasoline generator. For something that makes so much noise, and seems to have so
much power, it doesn’t create an ounce of energy. Like the solar panel, it is only a transformer.
So here are a couple of important punch lines. First: All technologies are only transformers of energy.
Second: Energy cannot be created or destroyed. The amount of energy that existed in the Universe at its
creation is the same amount of energy that exists right at this moment. The amount of energy that exists at
this moment will be the same for generations to come.
So what then is the big deal? Why not drive the big cars with low gas mileage? Why not wear the cotton
clothes that require more energy to create than the hemp? Why not just keep eating the processed foods
rather than the fresh ones? Why not just collect more and more stuff: TV’s, SUVs, some of these, some of
those?”
Ah, if life was so simple. You see there’s a catch.
If energy can’t be created or destroyed, why worry? Well actually, something incredibly powerful happens
every time energy is transformed, and for that matter, every time matter changes form. Some say the fate of
humanity depends on how well we’ll respect this power.
Your challenge is to help you experience what happens when any energy changes from one form into
another. So...
7. Write the following challenge on the board: “By using 2 small hand-crank generators and four wires demonstrate that whenever energy is transformed from one form to another, it becomes less ordered, less available, and less useable to do work. Be sure to crank only one of the Genecons at a time.” Ask for one volunteer from each of the four groups who are willing to work together to solve this problem in front of the class. Tell them they have 5 minutes. If they don’t solve the problem by then have another 4 students, one from each group, take their place.
8. You may provide hints that lead them to connecting the two Genecons with the wires. If they crank one of the Genecons 30 or more times, ask them to notice how many times the handle on the other Genecon turns. Then ask, “Why didn’t the second handle turn the same number of times?”
9. If necessary, explain, “It’s because every time energy changes from one form to another, no matter how big or small that energy is, it becomes less organized, and less available to do useful work. This is called entropy.” Share this chart on the board and ask them to find an example of an energy transformation that doesn’t do this.
8. You may provide hints that lead them to connecting the two Genecons with the wires. If they crank one of the Genecons 30 or more times, ask them to notice how many times the handle on the other Genecon turns. Then ask, “Why didn’t the second handle turn the same number of times?”
9. If necessary, explain, “It’s because every time energy changes from one form to another, no matter how big or small that energy is, it becomes less organized, and less available to do useful work. This is called entropy.” Share this chart on the board and ask them to find an example of an energy transformation that doesn’t do this.
10. Put the following on the board and discuss: “Consider this: entropy is increasing at an exponential rate. This means that increasingly more and more amounts of energy are becoming unavailable, and unusable at a faster and faster rate.”
11. Tell your students they can pick an Earthstone for working so hard at trying to understand a very complex concept.
11. Tell your students they can pick an Earthstone for working so hard at trying to understand a very complex concept.