Student interest in energy units can be motivated by an initial discussion about energy consumption and the geopolitical implications of our dependence on oil. Many advocate using other sources of energy and conserving what energy we have. US tolerance of autocratic oil-rich regimes, the ecological risk of more accidents like the Valdez oil spill, the Chernobyl meltdown that caused 20,000 deaths, and deadly sulfur pollution in China from coal are all related to energy consumption. The concepts addressed by the five Energy Conversion units help students understand these issues and debate them more knowledgeably.

To launch this discussion, ask students find out:

"How much energy does an average person consume in the US, England, China, Afghanistan, Zimbabwe, and other countries?"

"Where are the major fossil energy reserves?" [Oil, gas, and coal.]

"What are the most important non-fossil energy sources being used?" [Hydro, nuclear fission, wind, solar.]

"What new sources of energy might become important?" [Nuclear fusion, ocean thermal differences, solar.]

"What are the risks of each energy source to workers who produce the energy, to the environment, and to world political stability?"

If this discussion seems lively, you might assign a report due after the five units are completed. Ask each group of students to become expert in one form of energy and have each member of the group address one these questions:

"How can your form of energy be converted to electricity?"

"How would your form of energy result in power for your car?"

"What is the maximum global amount of energy available in your form of energy per year?"

"If all the world used only your form of energy, when would we run out of it?"

In this set of units, we ask students to look closely at different kinds of energy and energy conversions. Students are helped by wonderful tools that allow close looks at fleeting effects. The temperature probe, light probe, voltage and current probe, and SmartWheel all help students study energy and energy conversions, particularly when energy levels are changing. Each probe generates computer records that make it easy to see and analyze small, fleeting events. Records from two probes can easily be compared to determine how much of one form of energy makes it into another.

It is important to create an atmosphere that encourages careful and critical observation. Having great tools is of no use unless students understand and carefully observe the data that the tools capture. Science is based on looking carefully and closely to the world around us. The tools give us new ways of capturing details about the world, but students will only learn from these tools if they see the details and reflect about their significance. When students have questions, keep returning them to the data, even if you know the answer. Ask

"What did you see? What does the graph reveal? What evidence supports that idea? What experiment would you do to investigate that question?" (Questions like this are particularly handy if you are unsure of your answers!)

The core idea of this unit is that energy can be converted from one form to another. The unit also gives students some familiarity with thermal, electrical, mechanical, and light energy. It shows how each form of energy can be converted into thermal energy. Because this can be done with 100% efficiency, the amount of heating caused by each form becomes a way to quantify energy.

To underscore the importance of measuring energy by its ability to warm, the materials use a "heat cell" that has an important property: it requires ten joules of energy to warm it one degree Celsius. By using the very sensitive temperature probe, the rise in temperature of the heat cell can be easily monitored. If a student measures, for instance, that the heat cell warms 3.5 C, then heat energy in joules equal to ten times that-35 joules-must have been dumped into the cell.

Students find energy confusing, because we rarely define it directly. For instance, it is impossible to say how much heat energy is in something, only how much has been added or subtracted. Similarly, the potential energy that an object contains is a slippery concept too, because it is always measured relative to something. For instance, a cart might have one potential energy when measured above the floor, but if that floor is on the 50th floor of a building, the cart's potential energy above the street is much higher. The same cart might have a negative potential energy relative to the roof!

Because heat and potential energies cannot be determined directly, the units all talk about the change in energy during an experiment. We may not know how much heat energy is in a heat cell, but if it warms from 15 C to 25 C, we know exactly how much heat energy has been added. It may be impossible to tell how much potential energy a cart has, but if we know its mass and it is lifted up two meters, then we can easily tell how much potential energy has been added.

Kinetic energy is different, though. If an object isn't moving it has zero kinetic energy. If it moves, it has kinetic energy. It is impossible to have negative kinetic energy. Light energy is similar: when there is no light, there is no light energy. Again, there is no negative. Electrical energy is slightly different. When there is no electricity flowing, there is no electrical energy flowing either. But it can flow two different directions, so there can be negative electrical energy flow.