Teaching the science of energy, force, and motion through an engineering design challenge Solar energy is clean, free, and abundant worldwide. The challenge, however, is to convert it to useful forms that can reduce our reliance on fossil fuels. This article presents an activity for physical science classes in which students learn firsthand how solar energy can be used to produce electricity specifically for transportation. The activity introduces students to solar-powered mass transit currently in use and then challenges them to create their own vehicle (Figure 1). When students create a successful solar-powered mass transportation vehicle, they use the engineering-design process to create designs that solve problems and carry out relevant scientific investigations (see box, p. 32, for connections to the Next Generation Science Standards). Engaging students Directly or indirectly, people and products are transported by fossil fuels that are mined or drilled from the Earth, then burned with many environmental consequences; there is a growing need for cleaner sources of energy. After describing this problem, give students a miniature toy solar car, a Matchbox car, and a shop light (Figure 2; see On the web for sources for materials and parts). Explain that energy from the light transforms into motion for the solar car. Share images of solar transportation--of say, the Solar Impulse or the Turanor (see sidebar, p. 29)--or let students browse the internet for images, videos, and news stories related to solar transportation. Plan on one class period for the pretest on energy and motion (included in the complete curriculum; see On the web); learning about solar trains, planes, boats, and automobiles; and the investigation with the toy solar and Matchbox cars described above. [FIGURE 1 OMITTED] [FIGURE 2 OMITTED] Testing the components Next, students will prepare to design their own solar vehicles by devoting a few class periods to testing the various design components: the solar cells, motors, gears, and wheels. Solar cells Distribute the solar panels for students to examine. Ideally, one panel should be rated for high voltage and low current (5.0 V and 100 mA) and another for low voltage and high current (1.0 V and 415 mA). Have students compare them by measuring surface area, counting the number of cells within the panels, and observing the wires beneath the plastic surface. Challenge them to use a light source and multimeters to determine how much energy the solar cells produce (Figure 3). (See On the web for a video on how to use a multimeter.) Have students use the multimeters' direct current (DC) settings to measure voltage and current. Many will be familiar with the former but not the latter. Both are important for understanding how much energy a solar cell can produce. Have students test the solar cells in series and in parallel to see which configuration produces more power over time. The overhead light in the classroom might be sufficient as a power source, but we find it better to conduct this activity outside in the sunshine or with shop lights in the classroom. (Safety note: When using shop lights, 150-watt incandescent bulbs are ideal but get very hot. Mount the shop lights so that students do not have to touch them and remind students to keep all hands and solar panels at least 50 cm away.) After testing, students might create a data chart similar to the one in Figure 4. FIGURE 4 Data collected from solar cells. Voltage Current Energy per second Power Solar cell (volts) (amperes) (joules/second) (watts) A B A+B in series A+B in parallel [FIGURE 3 OMITTED] Electric motors Distribute inexpensive electric motors typically used for hobbies and robotics. Ideally, one should be rated for high speed and low torque and another for lower speed and higher torque. …