Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Cut each manila folder in half.
2. Cut the sandpaper into 15 pieces, one for each group.
3. Set up the testing stations.

1. Obtain a paperclip, Bunsen burner or candle and a bottle cap.
2. Unbend the paperclip so that a free end is exposed.
3. Light the burner or candle.
4. Using tongs, heat the free end of the paper clip in the flame.
5. Place the hot paperclip in the center of the cap and lightly press to make a hole.
6. Position the hole of the cap, flat side down, onto the motor shaft (see Figure 4). Press the cap all the way down so it is flush with the motor and the shaft protrudes through the hole.
   {14058_Preparation_Figure_4}
7. Secure the motor in the clamp and attach the clamp to the support stand.
8. Set the fan 20 cm from the motor, facing the cap attached to the motor.
9. Using alligator cords, connect each wire from the motor to a lead of the multimeter. Note: It may be necessary to strip some of the insulation form the motor wires for a good connection.
10. Repeat steps a–i to construct the second testing station.
11. The large end of the corks that students use for the central hubs of their rotors will fit snugly in the cap. Hold the cap securely and twist the cork into the cap to avoid bending the motor shaft. The shaft should press into the cork to help secure the cork in the center of the cap (see Figure 5).

Safety Precautions

Exercise caution when heating the paperclip over a flame. Use tongs to hold the paperclip at the opposite end from the flame or wear heat resistant gloves. Exercise caution when handling sharp bamboo skewers. Sandpaper may be used to smooth rough edges. Wear eye protection.

Disposal

Materials for the testing stations may be stored for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Part A of this laboratory activity can reasonably be completed in one 50-minute class period. Part B can be started during the first class if time permits. Rotor modification results (Part B) should be measured and shared among the groups during the second lab period. The prelaboratory assignment may be completed before coming to lab, and the post-lab questions may be completed the day after the lab.
• Keep a “scoreboard” in a central location displaying power produced by each group’s rotor after Part A. This allows groups to see where their turbine ranks and if the more successful rotors had any common characteristics before they decide what modifications to make.
• Limit each group to one type of material for the blades. Students should determine the blade size and shape before they begin cutting to avoid waste.
• If students use bamboo skewers to attach the blades to the corks, they will need to cut them. The best way is to cut partway by scoring around the skewer with scissors, and then break the skewer by applying pressure on either side of the partial cut. Rough edges should be sanded smooth.
• Determine whether or not students are limited to the materials provided. For example, may students use paper clips to attach the blades to the hub? The more variables introduced, the more difficult it is to analyze the results.
• With this design challenge, each group may achieve success as long as the modified design results in greater power output. For a class competition, several categories may be presented.
  • The design with the greatest power output
  • The modified design with the greatest increase or percent increase in power output from its original design
  • The design with the greatest power-to-weight of rotor ratio

Teacher Tips

• Discuss with your class whether or not your area of the country is ideal for harnessing wind energy. See the link to the Wind Energy website in the References section featuring a U.S.A. Wind Resource Map displaying wind power found in different regions of the country.
• Since students may make several modification to their rotor designs, they most likely will not know exactly what effect each change has on the performance of the rotor. Use this opportunity to discuss variables and the importance of changing one variable at a time.
• A hand-crank generator is a great demonstration tool to show how a generator converts mechanical energy to electrical energy. The Genecon Generator, available from Flinn Scientific (Catalog No. AP6585) has a clear plastic housing so students can see the inner movements of the components.

Answers to Prelab Questions

1. Why is wind considered a renewable energy source?

   Wind is considered a renewable energy source because using it today will not result in any less of the resource available in the future.

2. A spinning rotor is attached to a multimeter. The meter displays 18 V and 6 A. How much power is produced by the rotor?

   P = 18 V x 6 A =108 W

3. The current of the model rotors in this activity will actually be measured in milliamps (1 mA = 0.001 A) and the power output will be calculated in milliwatts (mW) using Equation 2.

1. Calculate the power output of a spinning rotor in mW with meter readings of 0.15 V and 7.8 mA.

   P = 0.15 V x 7.8 mA = 1.17 mW

2. What is the power output of the rotor from 3a in watts?

Sample Data

Part A. List and/or draw specifications of chosen rotor design.

Design 1
Material: polystyrene sheet
Shape and size: trapezoid of 23 cm total length; narrow end 5 cm, wide end 10 cm
Blades mounted parallel to each other; no angle. The spines of the blades (skewers) were inserted evenly around the center of the cork.

Design 2
Material: foam sheet
Shape and size: 4-blade pinwheel, 18-cm diameter, counterclockwise spin

Data Table A. Original Design (1)

Data Table A. Original Design (2) Part B. List and/or draw modifications to the rotor design.

Design 1
Shortened blade length to 20 cm, wide end 9 cm to prevent the blades from being pushed against the clamp.
Moved spines closer to front of hub, away from the clamp.
Angled the blades slightly in the same direction.

Design 2
Opened up pinwheel blades slightly to catch more wind, 20-cm diameter.
Changed spin to clockwise rotation to match the rotation of fan blades

Data Table B. Modified Design (1) Data Table B. Modified Design (2)

Answers to Questions

1. Calculate the amount of power the improved rotor design generated in Part B and record in Data Table B.

   See Sample Data.

2. Compare the power output of the original rotor to the modified rotor.
1. Did the rotor modifications result in greater power production?

   Yes, the original design 1 did not work and the modified design generated 2 mW of power. The modified design 2 increased the power output from 0.34 mW to 5.8 mW.

2. Are you able to determine which modifications made a difference in the power output? Explain.

   Design 1: Shortening the blades prevented them from bending back and hitting the clamp. Setting the blades at an angle may have helped, since the more successful designs in the class had angled blades.
   
   Both designs: Without testing each modification separately, it cannot be determined what effect each change had on the power output.

3. Traditionally a motor uses electric current to spin objects. In this laboratory activity the constructed rotor is connected to a motor but the motor is not attached to any source of electricity.
1. What makes the shaft of the motor spin?

   The wind from the fan makes the rotor turn. The spinning rotor hub turns the shaft of the motor.

2. As the shaft of the motor turns, electric current runs through the wires. What must be inside the motor for this to happen?

   A coil of wire turning through a magnetic field must be inside the motor.

3. What is the motor actually functioning as in this activity?

   The motor is functioning as an electric generator, converting mechanical energy into electrical energy.

4. Wind power provides less than 2% of the electricity in the United States, but may provide as much as 20% in the future.
1. List advantages of using wind power for electricity.

   Wind is a naturally occurring, clean, renewable source of energy.

2. What are some reasons why wind is not being used more as a resource to generate electricity?

   Wind is variable, not all areas are suitable for utilizing wind energy, cost of research, transporting materials, and construction, possible effect on birds and other wildlife, etc.

References

Hicks-Pries, C. & Hughes, Julie. “Powering the Future A Wind Turbine Design Challenge,” Science Scope (2011): 25–30.

“Wind Energy Basics.” Wind Energy Development Programmatic EIS. http://windeis.anl.gov/guide/basics/index.cfm (accessed January 2016).

Introduction

Wind is moving air. You cannot see air, but it is all around you. You can also not see wind, but you know it is there. Wind is energy in motion—kinetic energy—and it is a renewable resource. Wind turbines are being used today to harness the wind to power a generator and produce electricity.

Concepts

• Wind energy
• Energy transfer
• Wind turbines
• Electric generators

Background

Wind is a desirable energy source as it is both non-polluting and renewable. It does not emit air pollutants or greenhouse gases and using it does not diminish future supply.

So how does wind provide the energy to make electricity? Sunlight provides electromagnetic energy, which is absorbed by the Earth’s atmosphere and converted into thermal (heat) energy. The Earth’s surface does not heat uniformly and the uneven heating of Earth causes differences in temperature and air pressure. These pressure differences result in air moving from areas of high pressure to low pressure. Moving air is wind, containing mechanical energy. Mechanical wind energy pushes the blades of a wind turbine. That mechanical energy turns a coil of wire inside a generator within the turbine. The wire coil turns within a magnetic field, which causes electric current to flow in the wire. Figure 1 is a flow chart that illustrates the transfer of each energy type throughout the process.

A simple way to understand how wind turbines work is that they are essentially the opposite of an electrical fan. On a hot summer day a fan is plugged into an outlet and the electricity causes a motor to rotate, and the attached blades turn. With a motor, electric energy is converted to mechanical energy (see Figure 2). Conversely, wind turns the blades of a wind turbine that produces electricity. A generator converts mechanical energy to electrical energy (see Figure 3). The power output of a wind turbine is measured in watts (W) and can be determined by Equation 1. where

P = power measured in watts (W)
V = voltage measured in volts (V)
I = current measured in amps (A)

Experiment Overview

The purpose of this activity is to design and build a rotor (windmill blades attached to a central hub) out of the materials provided that produces the greatest amount of power. The voltage and amperage of the spinning rotor will be measured with a multimeter to determine the amount of generated power. Improvements will then be made to the rotor to increase the amount of power produced.

Materials

Prelab Questions

1. Why is wind considered a renewable energy source?
2. A spinning rotor is attached to a multimeter. The meter displays 18 V and 6 A. How much power is produced by the rotor?
3. The current of the model rotors in this activity will actually be measured in milliamps (1 mA = 0.001 A) and the power output will be calculated in milliwatts (mW) using Equation 2.

1. Calculate the power output of a spinning rotor in mW with meter readings of 0.15 V and 7.8 mA.
2. What is the power output of the rotor from 3a in watts?

Safety Precautions

Exercise caution when handling sharp bamboo skewers. Sandpaper may be used to smooth rough edges. Wear eye protection as rotor components may separate during testing. Never touch any bare wires in an electric circuit with a current. Please follow all laboratory safety guidelines.

Procedure

Part A. Designing and Building a Rotor

1. Read through the entire procedure before beginning.
2. Take 5–10 minutes to plan the rotor design using only materials provided by the instructor. Consider the following questions when planning the design:
1. How many blades will the rotor have?
2. How will the blades be attached to the hub (cork)? Note: The small end of the cork should face the fan that will be providing the wind.
3. What material will be used to make the blades?
4. What size and shape will the blades be?
5. Will increased weight produce more or less power?
3. Once the group has determined the rotor design, obtain the necessary materials from your instructor.
4. Using the design plans from step 2, assemble the rotor. Note: Do not glue the blades to the hub so adjustments may be made if necessary.
5. Take the completed rotor assembly to the testing station.
6. The instructor will attach the rotor to the motor at a set distance from the fan.
7. Turn the fan on high speed.
8. If the rotor turns, go on to step 9. If it does not turn, try to determine why not. Remove the rotor and go to step 13.
9. Set the multimeter to measure volts.
10. With the fan on high speed, note the highest voltage displayed in 20 seconds and record the value on the Generating Electricity with Wind worksheet. Note: If the voltage is a negative number, reverse the current by switching the connections to the multimeter.
11. With the fan still running, adjust the multimeter to register milliamps.
12. Note the highest amperage displayed in 20 seconds and record the value on the worksheet.
13. Observe other groups’ rotors as they are tested.
14. Once each group has tested its rotor, adjust the height of the motor on the support stand so the rotor hub is half way between the center and the top of the fan. Repeat steps 9–12 with the rotor in this new position. If the rotor does not turn in this position, go on to step 15.
15. Calculate the power output in milliwatts for each test using Equation 2 from the Prelab Questions. Record the value on the worksheet.

Part B. Design Challenge

The challenge is to make adjustments to your group’s rotor to increase the power output from Part A. If time allows, your enhanced rotor may be tested at the testing station to make sure it rotates and stays intact. This test will only determine functionality; the amps and volts will not be measured until the final test.

Consider the following as you redesign the rotor.

1. Make a list of problems, if any, the rotor experienced during testing and how modifications might be made to correct the problems.
2. If the rotor did not turn, then all forces acting on the blades were balanced, resulting in zero net force. How can the blades be modified to correct this?
3. The pitch of the blade is the angle of the blades in relation to the plane in which they are rotating. Was the pitch of the blades consistent throughout the testing?
4. Was the rotor well balanced and did it rotate smoothly? If not, how might the balance be improved?
5. How might changing the size or shape of the blades affect the outcome?
6. As other groups’ rotors were tested, did you observe any common variables in the rotors that worked well?
7. Does it matter if the end of each blade touches the hub or if there is space between the hub and the blades?
8. Based on the results from Part A, choose where your rotor will be positioned for the final test—either in line with the center of the fan or raised up as in step 14.

Student Worksheet PDF

14058_Student1.pdf