Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Unfold the 8 plastic binder pockets completely.
2. Using scissors, cut the binder pocket down the middle as shown.
   {12414_Preparation_Image_1}
3. Make enough copies of the three-blade and four-blade template for each student group.

Safety Precautions

Do not handle electrical cords with wet hands. Exercise caution when using scissors and hot glue. Wear protective eyewear when operating the windmill in front of the fan. The hex nut may spin at unanticipated speeds—stop the trial if this happens. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Disposal

All materials used in this laboratory activity may be saved for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Depending on the time allotted, the assembly and experimental testing may be completed either on the same day or on separate days.
• Depending on the fan speed, it is usually better to operate on low speed. If the fan speed is too high it pushes the windmill away, causing too much friction between the freely rotating pieces of the straw and the glued pieces. In this case students will need to tap the end of the straw back toward the fan so it keeps spinning without getting caught.

Further Extensions

Alignment with AP^® Environmental Science Topics and Scoring Components

Topic: Energy Resources and Consumption. Renewable Energy (Solar energy; solar electricity; hydrogen fuel cells; biomass; wind energy; small-scale hydroelectric; ocean waves and tidal energy; geothermal; environmental advantages/disadvantages).
Scoring Component: 7-Energy Resources, Renewable Energy.

Answers to Prelab Questions

1. When deciding where to place a windmill on a piece of land what factors should be taken into consideration?

   Make sure that the windmill is at least 500 horizontal feet away from any tall obstructions like a house or tree. Also make sure that the lowest point of the blade is at least 30 vertical feet above the highest obstruction on the property.

2. If a windmill is being installed for use as a pump, what characteristics should it have?

   If a windmill will be used for a pump it should have greater torque and less speed. Therefore it usually has four or more blades.

Sample Data

Mass of string + hex nut = ___3.14 g___

Answers to Questions

1. Calculate the average times required to lift the weight for the three-blade windmill and the four-blade windmill. Record in Data Table 1. {12414_Answers_Equation_4}
2. On average, which windmill was able to lift the weight faster? Explain.

   Students should find the four-blade windmill was able to lift the weight faster. This is because the curved area facing the wind is greater on the four-blade windmill than the three.

3. Using Equation 3 from the Background section, calculate the force in Newtons required to lift the hex nut and string. Hint: Remember to convert grams to kilograms. Record in Data Table 2.

   Force = mass (kg) x 9.8 m/s²
   Force = 0.00314 kg x 9.8 m/s²
   Force = 3.08 x 10^–2 Newtons

4. Calculate the work done in Joules by each windmill to lift the hex nut and record the results in Data Table 2. How does the amount of work compare for each windmill? Explain.

   Work (w) = force (N) x distance (meters)
   Work = 0.0308 Newtons x 0.3 meters
   Work = 0.00924 Nm
   Each windmill does the same amount of work because both are lifting the same weight over the same distance.

5. Using Equation 1 from the Background section, calculate the power in watts of each windmill.

   Power (W) = work (Nm)/time (seconds)

   Three-Blade Windmill

   = 0.00924 Nm/6.6 seconds
   = 0.0014 Watts

   Four-Blade Windmill

   = 0.00924 Nm/2.8 seconds
   = 0.0033 Watts

6. Why are wind farms usually found in the country as opposed to more urban areas?

   Wind turbines are traditionally found in the country because they thrive in areas of steady, unobstructed wind. They require a distance of at least 500 horizontal feet from any buildings or trees. This type of location is nearly impossible to find in urban areas.

7. Explain the energy transfer that occurs between the fan, the windmill, and the weight beginning when the fan is turned on to after it is turned off.

   The fan has a motor that converts electrical energy (from the outlet) into mechanical energy and powers the fan, causing the blades to move, and creating wind. Kinetic energy of the wind is transferred to kinetic energy of the spinning windmill, which turns the dowel rod and lifts the nut. This results in the nut having stored gravitational potential energy. Once the fan is turned off, the nut will be pulled by gravity and its potential energy is transferred to kinetic energy as the dowel rod turns and the nut is pulled downward.

Teacher Handouts

12414_Teacher1.pdf

References

Adams, B. Wind at Work. Science and Children. Volume 34. 2008, p 54.

How and Why to Permit for Small Wind Systems. American Wind Energy Association. www.aewa.org/smallwind (accessed March 2011)

Moyer, R. H. & Everett, S. A. Windmills are Going Around Again. Science Scope. 2011, 34, pp 8–15.

Introduction

With fuel prices soaring to new heights, green energy is more popular than ever! Learn the basic principles of wind energy by constructing two different windmills and compare the power of each model.

Concepts

• Wind energy
• Alternative energy
• Power

Background

Wind energy has been utilized for thousands of years. The design of wind energy units has changed over time but their purpose remains the same—using wind to produce mechanical power. The blade of a windmill or wind turbine captures energy from the wind and turns a shaft, generating mechanical power or electricity.

Historically wind energy has been used to move sail boats, pump water and grain, and also to generate electricity. By the 1930s many rural areas were wired for electricity and the use of windmills decreased. In the 1970s the price of fossil fuel began to rise rapidly, leading to increased demand of alternative energy sources such as windmills. Today wind energy is the fastest-growing renewable energy source in the United States.

Wind is a type of solar energy caused by the uneven heating of the atmosphere, irregularities of the Earth’s surface, and the Earth’s rotation. Wind patterns are altered by variations in the Earth’s surface such as rivers, lakes, crops, and also by man-made barriers such as buildings. The term wind energy is used to describe the process which uses the kinetic energy of wind to produce mechanical power or electricity.

Wind turbines use wind to make electricity. Wind pushes the blades of the turbine, rotating the shaft that connects the turbine to a generator. A generator is a magnet surrounded by several coils of wire. The generator begins to spin and the electricity produced is carried through wires and sent to power stations (see Figure 1).

Wind turbines can range in power from 100 kW to several megawatts. Turbines below 100 kW are considered small turbines and are used for homes, water pumping, etc. Larger turbines are usually grouped together on wind farms and provide bulk power to an electrical grid.

When deciding to install a wind turbine, ideal geographical placement is crucial. Wind turbines are mounted on a tower to capture the greatest amount of energy from the wind. At greater heights the turbines are able to access steady, unobstructed wind. Ideally, wind turbines are placed on the highest point of the property.

The bottom of the turbine blade should be at least 30 feet higher than the highest vertical object and 500 feet away from the nearest horizontal object (see Figure 2). A wind farm often consists of hundreds of wind turbines and covers hundreds of miles. Wind farms are typically located in open regions such as plains, mountain gaps, and shorelines where ideal wind conditions are prevalent. The land surrounding the wind turbine can still be used for agricultural purposes because the height of the crops or animals does not obstruct the wind source. Wind turbines are designed in several different ways. They can rotate around either a vertical or horizontal axis. The most common type observed is a horizontal-axis wind turbine (HAWT). The number of blades on a wind turbine is based on aerodynamic efficiency, component costs, system reliability, and aesthetics. Furthermore, the number of blades depends upon the job of the specific turbine. If the turbine is being used for electricity production it needs to operate at a high speed but does not need much torque. These turbines usually have two to three blades. Turbines that will be used as pumps need more torque and less speed, and usually have more blades than turbines used for electricity.

The power produced by a windmill can also be analyzed in the following manner. Power measures the relationship between work and time. See Equation 1. In order to calculate power, one must first calculate work. Work is the product of force acting through a distance. See Equation 2. Work is measured in Newtonzmeters also known as Joules. Force is calculated by multiplying the mass in kilograms by the gravitational constant, 9.8 m/s². See Equation 3.

Experiment Overview

The purpose of this experiment is to determine the power generated by a three-blade windmill compared to a four blade windmill. Each windmill will be exposed to wind to test the time required for the torque of the windmill shaft to lift a hex nut 30-cm.

Materials

Prelab Questions

1. What factors should be taken into consideration when deciding where to place a windmill on a piece of land?
2. If a windmill is being installed for use as a pump, what characteristics should it have?

Safety Precautions

Do not handle electrical cords with wet hands. Exercise caution when using scissors and hot glue. Wear protective eyewear when operating the windmill in front of the fan. The hex nut may spin at unanticipated speeds—stop the trial if this happens. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Fan Assembly

1. Cut out the templates for the three-blade fan (hexagon) and the four-blade fan (square).
2. Place the templates underneath the plastic sheet and trace each template using a permanent marker. Note: Trace all markings onto the plastic sheet.
3. Using scissors cut out the hexagon and the square.
4. Cut along the dotted lines of each shape. Do not cut along the solid lines.
5. Using the hexagon, grab one of the corners with an asterisk (*) and fold it in to the center as shown in Figure 3.
   {12414_Procedure_Figure_3}
6. Hold the pieces in the center and continue folding all of the asterisk corners toward the center (see Figure 4).
   {12414_Procedure_Figure_4}
7. Insert a pushpin through the center of the resulting three-blade windmill. Note: If the pieces do not stay in place with the addition of the pushpin, place one small drop of hot glue underneath the first piece as it is folded toward the center. With the pin through each of the four layers hold the windmill together tightly until the glue dries. Set aside.
8. Repeat steps 5–7 to construct a the four-blade windmill from the square.

Stem Assembly

9. Obtain a dowel rod and a straw. Cut the straw into the following pieces—four 2-cm long pieces and two 5-cm pieces.
10. Using a glue-gun, attach the straw pieces to the dowel rod as shown. The 2-cm pieces should be glued to the rod while the 5-cm pieces are allowed to float freely (see Figure 5).
    {12414_Procedure_Figure_5_Straw attachment to dowel rod}
11. Using a ruler, measure 40 cm of string.
12. Tie one end of string to a hex nut. Trim off the excess string from the knot.
13. Measure the string from the knot of the hex nut to the opposite end. Trim it as needed so the distance between the hex nut and the end of the string is 30 cm.
14. Place the string and hex nut on a balance. Record the mass on the worksheet.
15. Place a strip of hot glue around the middle of the dowel rod.
16. Carefully wrap the string one full rotation around the center of the glue. Caution: Glue is very hot.
17. Add a small piece of clay to the end of the dowel rod. See Figure 6 for the completed shaft assembly.
    {12414_Procedure_Figure_6_Complete shaft assembly}

Experimental Procedure

18. Use the pushpin to insert the three-blade windmill into the clay at the end of the shaft. If possible insert the pin through the clay between the straw and the dowel rod for increased stability.
19. One partner should hold the apparatus by the two moveable straw pieces and lower the unit in front of a fan, approximately one foot away, to obtain optimal spinning speed.
20. Once an ideal location has been identified, mark the table or floor with masking tape so all trials can be carried out at the same distance from the fan.
21. The second partner should time how long the windmill should be kept in front of the fan until the hex nut reaches to the shaft. Record the data on the Wind Energy Worksheet.
22. Repeat steps 19–21 four more times.
23. Remove the three-blade windmill from the shaft and attach the four-blade windmill.
24. Repeat steps 19–22 five times using the four-blade windmill.

Student Worksheet PDF

12414_Student1.pdf