Students need ample time to build their designs, analyze graphs from the sensor devices, and brainstorm how to improve their designs. Allow two class periods per activity, which should provide time for debriefing when the unit is completed. Your students will be able to construct the solar ovens by themselves and most components of the wind generator. Be careful with the hot glue gun. Teachers may want to ask for parent volunteers to help with the wind generator activity. It requires a hot glue gun for two phases of the design. It would also help if the children cut out the pinwheel patterns the day before doing the activity. The small electric motors are inexpensive -- $1.00-$2.00 at science supply stores. You will also need temperature sensors and voltage sensors, along with USB connectors to allow data from the sensors to generate graphs.
Two full class periods for experimentation, one full class period for optimizing the design solutions and debriefing.
This unit engages students in engineering design to learn about transformation of energy in a wind generator and a solar oven. Students will construct a pinwheel wind generator and a solar oven made from common household items. Each activity includes analysis of data created by temperature sensor and voltage sensor devices that automatically generate graphs via a USB software interface. Students will begin to develop understanding of the purpose of insulation in a good oven design and the importance of blade shape in building the best wind generator. The activities will also promote appreciation of the process of engineering design.
The driving question of the Wind Generator activity is: What is the best blade design for collecting energy from the wind? Wind turbines work by using an internal generator to convert the mechanical energy of the spinning turbine shaft into electricity. The construction paper pinwheel is quite different from the wind turbines you see across the country, but either design requires blades that efficiently capture the wind's kinetic energy. When the wind blows, it pushes against the blades of the wind turbine, making them spin. They power a generator to produce electricity (in this activity, the pinwheel will power a small electric motor). When the pinwheel is spinning, the motor will generate a small amount of electricity -- students will be measuring it with a voltage sensor.
The driving question of the Solar Oven activity is: Can you cook with sunshine? The answer is yes! A solar oven works like a mini-greenhouse, but with a few differences. The light-absorbing surface is enclosed in a tightly-sealed, well-insulated box. Sunlight comes in through a transparent material and is then absorbed and changed into heat by the black surfaces inside the box. The biggest design challenge is finding insulation material that will keep the heat in. Students will work in teams to design an oven, then attach temperature probes to figure out which design does the best job of heating up and retaining the heat.
Children in this grade band often think there is a "right answer" in designing a structure or system. This activity will help them understand that real engineers work through an iterative process that involves brainstorming, building models, testing their models, comparing their own designs with other people's work, redesigning to make their structure better, and communicating their results to others. Designs that are best in one respect may be inferior in others. For example, one oven design might heat up very quickly but fail to heat evenly, while another design heats slowly but maintains an appropriate cooking temperature. Many of the best inventions in the world were invented through trial and error! And all engineering design depends on a knowledge of science to build a good structure or device.
Students at this age understand that sunlight warms objects. But they often misunderstand that different objects absorb sunlight in different ways. In addition to building the solar oven, it may help for students to compare light absorption in dark and light-colored objects. They also frequently overlook the role of light intensity. If the sun is directly overhead, the sunlight will be more intense and the solar cookers should heat up more quickly. It would be interesting to allow a follow-up for students to analyze differences in the solar cooker efficiencies between morning and afternoon classes. You might anticipate that students will have trouble identifying the forms of energy and how they are transformed in the wind generator and the solar oven. At this age, we don't expect students to have a sophisticated view of energy transformation, but they should understand that the sun provides radiant energy that is transferred by light waves. When light energy from the sun interacts with matter, it can be transformed into thermal energy. At this level, it's best not to get too deep with explanations of heat or thermal energy. Although we don't introduce kinetic and potential energy at this level, students should be able to understand that objects in motion have energy......the faster the motion, the greater the energy the object possesses. The wind generator activity will help them build a foundation to understand that motion energy can be transformed into electrical energy.
Allow one full class period for each experiment, with one day for students to prepare and share reports on their data analysis findings.
Wind Generator: What would be a good design for wind generator blades?
Let students brainstorm a few minutes before they use the Drawing Tool in the interactive model. Teachers: The blades in a windmill or wind generator are intended to slow down the speed of the wind. As the wind blows, it pushes against the blades to make them spin. An inclined blade makes it easier to push the air than a perpendicular blade.
Explain how you think a solar cooker could help change people's lives. (Responses will vary. You may want to guide the conversation by talking about the health benefits of cooking food and the convenience of using electric or gas-powered ovens and cooktops in our homes. What if your family couldn't afford electric appliances? What if you live in a part of the world that doesn't have reliable electric power? Why do we need to be sure some foods (like meat) are fully cooked?
From the National Energy Education Development Project (NEED): Like old-fashioned windmills, todayís wind turbines use blades to capture the windís kinetic energy. Wind turbines work because they slow down the speed of the wind. When the wind blows, it pushes against the blades of the wind turbine, making them spin. They power a generator to produce electricity. Most wind turbines have the same basic parts: blades, shafts, gears, a generator, and a cable. (Some turbines do not have gear boxes.) These parts work together to convert the windís energy into electricity:
Prediction: If there is more wind, will the pinwheel turn faster? Will it generate more voltage? Explain why you think so. Students may not yet be able to accurately predict how the voltage sensor will respond with a faster-turning pinwheel. Teachers might want to explain that voltage is a measure of electric force, but otherwise let students create their individual responses.
What was the maximum voltage you were able to generate? (Answers will vary.)
What was the best place to position the pinwheel in front of the fan? (Acceptable responses will indicate that the pinwheel "blades" need to be turned at an angle to the fan.)
How did your propeller compare to the pinwheel in producing a voltage? (Answers will vary, but encourage students to think carefully about why one design was better or worse than the other and be sure they back up their conclusion with data from the voltage sensor readings.)
Prediction: How warm do you think you can make your solar cooker? Hot enough to warm up a cookie (60 degrees C)? Hot enough to boil water (100 degrees C)? Hot enough to cook an egg (150 degrees C)? Guess what you think the maximum temperature will be. Students should construct predictions without interference.
Describe your graph? What was its shape? What was the maximum temperature of your oven? (Answers will vary.)
Did your maximum temperature go up or down when you added aluminum foil to the design? (If done correctly, the temperature should've gone up.)
What type of insulation materials did you use? What happened to the temperature graph after you added the insulation? (Answers will vary. In general, student responses should discuss HOW the temperature was affected. Did it rise higher? Did the temperature sensor show a more stable temperature, or was it erratic? Did the cooker retain its heat longer after you took it out of the sun?)
1. Describe and draw the design that seemed to generate the most voltage. (Students will use the interactive Drawing Tool to draw and describe their pictures.)
2. Make a list of the features of your propellers that seem to affect the voltage and the features that seem to have no effect. (Answers will vary, but in general, expect students to recognize that the propeller needs to have some slant to be able to capture and push the wind.)
3. How did your propeller performance compare to the propellers of other teams? (Responses will vary.)
4. What is the best blade design for collecting energy from the wind? (Ask students to be prepared to defend their conclusions with scientific data, not just with an opinion.)
Solar Oven Activity
Background Information: Solar ovens come in two basic varieties:
1. After conducting the 3 temperature sensing experiments, what would you do next to improve your solar oven? Make a drawing of your best idea for design. (Students will use the interactive Drawing Tool to draw and describe their pictures.)
2. What was the maximum temperature of your oven? Explain what features worked well to increase the temperature. (Responses will vary, especially as students discuss how well their oven performed with addition of insulation materials. In general, a box-type solar cooker will produce a temperature range from approximately 200-250. You might ask students to consider whether the sun was directly overhead. If the class was held in early morning or late afternoon, this would affect the intensity of the sunlight.)
3. Explain what features worked well to increase the temperature. (Anticipated responses would include reference to adding aluminum foil as a light reflector and reasons for choosing particular insulation materials.)
4. Which meals would work best in a solar oven? (Kids will have fun responding to this question, but may not have enough cooking experience to know. Even a great solar cooker may only get up to about 250 degrees Fahrenheit (121 degrees Celsius). This is hot enough to cook lots of meals, but not all kinds of food. You might want to lead a classroom discussion to get kids brainstorming what sorts of meals can cook slowly for several hours. Ask if their parents have ever cooked slow-roasting meats on a grill or casseroles that they leave in the oven to cook all day. Ask them if you could cook a batch of cookies in their box cookers (probably not). On the other hand, would the cookers work to warm up the cookies if they're already baked? (Yes!)
Choice A: Design and construct a larger solar oven (large enough for a real cooking pot). Cook a meal, such as rice, oatmeal, or hard-boiled eggs. What were you able to cook, and how long did it take?
This task is a good choice if there is adequate time for the engineering design process in building a second product. You may want to provide information about panel cookers to see if children want to experiment with another design style (see photos above). If they choose to try a panel cooker, make sure to start early in the day because these cookers don't reach as high a temperature as the box cookers.
Choice B: Try your solar oven at different times of the day and in different weather. Investigate these questions: 1) Will it still work when there are clouds? 2) Will it still work early or late in the day when the sun is low in the sky? 3. Will it still work if the sun is coming in through a window?
This task is a good choice if time is limited. Ask students to predict answers to the 3 questions above. After finishing the investigation, responses should fall within this general framework: 1) Yes, the oven will still work, but cooking time will be slowed down. If it's fully cloudy, the cook time will be extended a lot. 2) The cooker will heat up fastest in mid-day when the sun is directly overhead. It heats up slowest in the morning. If it's really hot with no clouds, you need to keep an eye to be sure you don't overcook the food. 3) Generally, trying to use a solar cooker next to a window is not very effective unless you have old windows. Teachers: Newer windows have UV inhibiting materials, which significantly slows the rate of solar cooking.