Hands-on Activity: Gone with the Wind - Sail Cars!

Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

A photograph in a classroom shows a boy positioning a toy-sized sail car in front of a box fan while a girl operates the fan control switch.
Students test their wind-powered sail car.
copyright
Copyright © 2014 Wyatt Champion, College of Engineering and Applied Science, University of Colorado Boulder

Summary

Students explore the use of wind power in the design, construction and testing of "sail cars," which, in this case, are little wheeled carts with masts and sails that are powered by the moving air generated from a box fan. The scientific method is reviewed and reinforced with the use of controls and variables, and the engineering design process is explored. The focus of the activity is on renewable energy, as well as the design, testing and redesign of small cars made from household materials. The activity (and an extension worksheet) includes the use of kinematic equations using distance, time traveled and speed to enforce exponents and decimals.

Engineering Connection

The use of renewable forms of energy is a major focus for today's engineers. Wind power is one of the simplest and least expensive sources of renewable energy. By designing wind-powered model cars, students experience the iterative steps of the design process while exploring and gaining a better understanding of how wind power may be utilized.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

Suggest an alignment not listed above

Learning Objectives

After this activity, students should be able to:

  • Describe how wind forms.
  • Describe different sources of energy.
  • Explain that wind energy is a renewable and sustainable form of power production.
  • Relate how different shapes and angles affect sail (and wind turbine) design and performance through the testing and improvement stages of the engineering design process.

Materials List

Each group needs:

  • 2 coffee stirrers, to serve as axles
  • 4 Life Savers® mints (ring-shaped hard candies), to serve as wheels
  • 8 plastic beads, such as pony beads
  • corrugated cardboard rectangle, 3 x 5 inches (7.5 x 12.5 cm); when cutting the pieces, make sure to orient the cardboard so the inner channels in the two-ply cardboard run parallel to the short side of the rectangle, so as to line up to hold the stirrers as axles for the car base
  • choice of mast material: 2-3 Popsicle sticks OR 1-2 wooden skewers
  • choice of sail materials: 12 x 12-inch (30.5 x 30.5-cm) piece of aluminum foil OR 12 x 12-inch (30.5 x 30.5-cm) piece of tissue paper OR 5 index cards
  • paper and pencils, for design drawings
  • Sail Car Test Table

To share with the entire class:

  • hot glue gun, glue sticks, scotch and duct tape, wooden skewers and scissors, for sail car construction
  • smooth floor or flat cardboard test track, 36 inches (~90 cm) long
  • colored tape, for setting up the track
  • box fan
  • stopwatch
  • projector and computer to show Renewable Energy: Sail Cars! Presentation, a PowerPoint® file
  • (optional) pennies taped together for car weight
  • (optional) stickers to decorate cars

Introduction/Motivation

The combustion of fossil fuels is considered a polluting, non-renewable form of power production. It is the job of future engineers to develop clean and sustainable means of producing energy—mostly for generating electricity, but also to power our vehicles.

Can you think of any interesting natural sources of power? (Listen to student ideas.) Maybe lightning, volcanoes or large storms? In fact, the last of these examples (storms) is currently being used today—in a sense! Wind power offers one of the simplest, least expensive, and safest sources of renewable power production.

(Continue on by showing the 14-slide Renewable Energy: Sail Cars! Presentation, a PowerPoint® file. The slides are animated, so clicking brings up the next text, image or slide.)

(Slide 1) Today, we'll be designing and building wind-powered cars!

(Slide 2) Who can tell me, in your own words: what is energy? (Example possible answers: The power to do work, heat is a type of energy, what we use when we move, what it takes to make changes to something.) Energy is defined as the ability to do work. Energy comes in many forms, such as chemical, electrical, heat, light, mechanical and nuclear energy.

(Slide 3) Now, we know something special about energy (and mass for that matter!): It can never be destroyed... only changed from one type to another. Let's think about that. When your parents drive a car and step on the gas pedal, fuel is burned and turned into heat and kinetic energy, which are used to turn the wheels of the car. Do you think all the energy from the fuel is used to turn the wheels? (Answer: No, less than 25% is used to move the car; the rest is lost to friction, waste heat and sound. So in this example, no energy is "lost," but a lot of it is useless to the job of moving the car.)

(Slide 4) Does anyone know why wind is considered a renewable source of energy? (Answer: Because we will never run out of wind. Make sure students do not confuse this with the false concept that renewable energy is renewable because we can use it over and over again, which is a common misconception. Instead, enforce the idea that renewable energy sources are renewable because we will never run out of the source, that is, water, solar, wind, etc.)

(Slides 5-6) Does anyone know why we have wind? Have you ever been to a reservoir, lake or the ocean? If so, was the water warmer or cooler than the land? (Listen to any students experiences.) Water takes a lot more energy to heat and cool, so on a hot day, it is often cooler than the land. A difference in temperature between land and water, or even between different parts of the land, results in a difference in temperature in the air above those surfaces. Cold air is heavy and causes high pressure, hot air is light and causes low pressure. This pressure difference results in flow of air in a direction—wind!

(Slide 7) These photographs show two examples of how engineers have designed ways to capture solar energy. The PV (photovoltaic) panels on the left function a lot like plants, but instead of making sugars with the energy from the sun, they produce direct current (DC) electricity. The concentrated solar plant on the right is very efficient due to the high temperatures produced in the middle, where the solar concentrators are aimed. As part of the process, molten salt is used to absorb the thermal energy from all the sunrays aimed at it, and this high temperature is used to boil water and produce steam, and eventually to spin turbines to generate electricity.

(Slide 8) A turbine is a device that is spun by a moving fluid. The spinning causes a magnet to rotate inside of spooled wire, which causes electrons to flow and current to be produced.

(Slide 9) Turbines are used to produce power from both wind and water. A hydroelectric dam produces electricity from the movement of falling water, which spins turbines to generate electricity.

(Slide 10) Other types of renewable energies include slow but steady tidal power, geothermal power (only possible in some areas, tapping heat from deep in the Earth), and biofuels (fuels derived from plants and algae).

(Slide 11) Are you ready to apply your design skills to move a car using wind power? This is your engineering design challenge: In groups of two, design a sail (including a mast) to propel your car forward, catching the "wind" from a box fan. You'll get a car base with axles and wheels. You'll design a mast and sail that uses your choice of materials from a provided supply. This is your chance to be creative!

(Slide 12) How will you make your sail? How will it best catch the wind? Think of the different masts and sails you have seen. Here are pictures of two different sail types; one is rigid like a surfboard, the other is flexible like fabric. Notice how they are shaped and positioned. Think of your experiences with the wind. Brainstorm with your teammate. Use your imagination to come up with the best mast and sail shapes using the provided materials.

(Slide 13) We'll be doing some testing as part of today's activity. That's how you will test your designs to see if they work and think of improvements. Let's recall an important aspect of the scientific method of experimentation. What are our controls? (Possible answers: The car base and power source [wind speed and direction].) What are our variables? (Possible answers: Sail and mast material and design.) Can you think of other constants or variables? (Possible answers: Track start/stop locations, length and road surface.)

(Slide 14) For this activity, you are acting as engineering teams challenged to design masts and sails. Like engineers everywhere, you'll be following the steps of the engineering design process. Take a look at these steps. In your teams, you'll be brainstorming ideas (imagine, develop possible solutions), planning and sketching your best idea, building and testing your ideas as prototype cars, then redesigning by making improvements and testing again—until you are satisfied with your design and ready to test it against the designs of other teams.

Vocabulary/Definitions

control: A factor (or group of factors) that does not change during an experiment.

energy: The ability to do work. Comes in many forms including mechanical (kinetic), potential (including gravitational and chemical), electrical, thermal (heat, which may be considered kinetic), electromagnetic (including visible light), and nuclear.

gravitational potential energy: The energy possessed by an object due to its location in a gravitation field (most often that of Earth). More height = more distance to fall = more gravitational potential energy.

kinetic energy: The energy an object has due to its motion. It is related to the mass of the object, as well as the square of its velocity.

variable: A factor (or group of factors) that is changed during an experiment.

wind: The perceptible natural movement of air, especially in the form of a current.

wind farm: A group of up to several hundred wind turbines located in an area with relatively consistent winds, for the purpose of producing energy.

wind turbine: A device that converts the kinetic energy of the wind into electrical energy.

Procedure

Background

Wind power has been harnessed by humans for thousands of years. Previously used for agricultural purposes (moving water, grinding grain, etc.), wind power offers tremendous potential for energy production in many areas of the world. Using a turbine, which transforms the kinetic energy of wind into electric energy, wind mills (or wind turbines) enable clean power production. Once a wind turbine or a collection of turbines (wind farm) has been built, it produces no emissions (pollution), and provides reliable power output. As always, some downsides to the technology exist; wind turbines can kill birds, emit a loud buzzing noise, and are considered by some people to be "ugly" in the landscape.

It is important to think of power production in a long-term, sustainable fashion. Currently, about 51% of power production in the U.S. comes from the burning of coal, with another 24% from natural gas. These are both nonrenewable energy sources. Looking ahead, we want to shift to a more extensive use of clean power. This is where you fit in! You can be a person who works to help transition our society into a renewable future!

Before the Activity

  • Gather materials and make copies of the Sail Car Test Table, one per group. Note that two tables are provided on each table attachment to save paper; just cut them apart.
  • For each group, prepare a car base composed of a piece of cardboard with axles, beads and wheels installed (see Figures 1-2). To do this, slip a wooden skewer between the cardboard layers (going "with the grain") where you want to place the axles, in order to widen the cardboard channels a bit, making for easier insertion of the stirrers as axles. Then insert the two stirrer axles. For each wheel, slip onto the stirrer end a bead, the ring-shaped candy, and a second bead. Next, trim the stirrer axle (if way too long) and tape the stirrer end (hub) to keep the items from slipping off. The beads help keep the wheels from wobbling. Note: By providing each group with an identical sail car base, students are able to focus on mast and sail design alone. Explain to students that by controlling the car base we can reliably compare the performance of each sail independently. It is impossible to make experiment runs perfectly independent.
  • (optional) Build an example sail car to show students. See Figures 1-3.
    A photograph shows a hand holding a 3 x 5-inch piece of corrugated cardboard with a wooden skewer pushed through the short side via a channel between the cardboard paper layers at one end and a red plastic coffee stirrer inserted through a similar paper channel at the other end. This shows how to place the stirrer axles for the sail car base.
    Figure 1. To make the car base, use a wooden skewer to widen two cardboard channels a bit so the stirrers/axles slide in easier.
    copyright
    Copyright © 2014 Wyatt Champion, College of Engineering and Applied Science, University of Colorado Boulder
    A photograph shows a view from above of two plastic coffee stirrers run through the cardboard layers of a 3 x 5 piece of corrugated cardboard, making axles in a car chassis base. Where the stirrers extend outside of the cardboard at four spots, wheels are attached by placement of a plastic bead and then ring-shaped hard candy, with the stirrer ends duct-taped.
    Figure 2. A sail car base assembled with cardboard, stirrer axles, beads, mint candies and duct tape.
    copyright
    Copyright © 2014 Wyatt Champion, College of Engineering and Applied Science, University of Colorado Boulder
  • Decide if you want to add to the activity a budget constraint (a typical real-world engineering design constraint!) by assigning a monetary value to each supply type and a maximum budget amount per team. Write these values on the classroom board; for example, index cards $20 each, foil $20 per square foot, etc., and $150 per team total budget. Then require that students keep track of their expenses as they request materials and redesign.
  • On Day 1, to present background information on renewable energy and wind power, be ready to show students the Renewable Energy: Sail Cars! Presentation, a PowerPoint® file.
  • On Day 2, set up the test track at the beginning of the hour while students are finishing up their sail fabrication. On an area of smooth floor (such as linoleum, or on a large piece of cardboard), use colored tape to mark a straight track that is about three feet long. Indicate the start and finish lines. Place the fan at the start of the track, facing towards the finish line. The fan is more powerful when angled down (which could serve as another variable).

With the Students—Day 1

  1. Present the Introduction/Motivation content, including the background information on renewable energy and wind power provided in the presentation. Make sure students understand what renewable energy is (give examples), and how students can help to make a difference in the future.
  2. Show the class an example sail car base made from the cardboard piece, axles, beads and wheels and explain that this is the "control," and that they will influence the "variable"—the sail (including mast) material and design. Because every team's base is the same, we can compare the added sails as the only variable in our testing.
  3. Divide the class into groups of two students each. Give each group a half-sheet of paper and pencils for drawing. Show students the available materials.
  4. In their teams, have students brainstorm, decide on materials and draw sketches of their mast and sail designs (see Figure 3). If implementing a budget constraint, explain the "cost" of the supplies, the team maximum budget, and the requirement to keep track of their expenses as they request materials and redesign.
  5. After teacher design approval, have one student in each group collect materials.
  6. Once they have materials, they are ready to work in their teams to fabricate their sails.
  7. With 5-10 minutes left in class, have students clean up and store their in-progress car prototypes and drawings in the classroom.
  8. Wrap up by requesting each group to briefly discuss its current mast and sail design, including the logic for its material selection and shape.
    A 3D line drawing shows a rectangular (cardboard) base with two (coffee stirrer) axles and four (ring-shaped candy) wheels to which is attached vertically in the center of the base a (wooden skewer) mast with a rectangular (pink tissue paper) sail.
    Figure 3. An example drawing of a sail car design, showing the car base, mast and sail.
    copyright
    Copyright © 2014 Wyatt Champion, College of Engineering and Applied Science, University of Colorado Boulder

With the Students—Day 2

  1. Ask students: Why are we building these sail cars? (Listen to student answers. As necessary, clarify the engineering design challenge.) Our challenge is to work as engineers to develop efficient cars that use the wind power of wind—a renewable energy source! In your team, prepare and test your sail and mast design. Then from what you learn in the testing, redesign it to make improvements. Do this as many times as necessary to make it ready to be raced in a class competition.
  2. Have students pull out their drawings, materials and sail cars, as left from Day 1. Direct them to continue to build.
  3. As students are ready, test each group's sail car, one at a time, by turning on the fan, placing the car in front of the fan at the start line, and letting go. Direct students to take advantage of these tests to observe their cars' performances and make adjustments in design and materials. For example, fixing wobbly wheels, strengthening the mast and making sure it does not drag on the ground, altering the sail materials, design or orientation, etc.
  4. Once teams are happy with their cars' performances, use a stopwatch to time how long it takes each car to travel the track distance. Record the times on the classroom board, and fill in the test table and run through the calculations with them. Encourage students who have tested to continue to make improvements as the other teams test their cars.
  5. Conclude with a race between the fastest two cars to determine the fastest sail car in the class.
  6. Lead a wrap-up class discussion in which students summarize their successful mast and sail design improvements. Also ask students the post-activity questions in the Assessment section.

Attachments

Safety Issues

Supervise students while they use hot glue guns.

Watch that students do not stick their fingers into the fan blades or get too close with long hair.

Troubleshooting Tips

An oversized sail can cause the sail car to tip forward. If this happens, add weights to the base to rebalance the car.

Fan management is key and can get out of control. Before each test, have teams identify who will operate the fan, time the test and record the timing measurement.

Assessment

Pre-Activity Assessment

Topic Exploration: Ask students the following:

  • Think of the windiest day you can remember. How strong did the wind feel? Could it have pushed you over? Do you think the power of the wind could be used for anything other than making you fall down? Have you seen wind push other objects? Did they move fast? Kinetic energy is interesting, because speed is much more important than mass (exponential compared to linear).
  • Think of examples of plants and animals that use the power of the wind. What are some examples? (Possible answers: Dandelion, tumbleweed, birds.)
  • What do you know about renewable energy? What is your definition of a renewable energy source? Why are oil and coal not considered renewable energy sources?

Activity Embedded Assessment

Test Table: As a class, fill in the Sail Car Test Table with the team data, doing the calculations together. The teacher may use a calculator and try to make estimates with the class along the way.

Post-Activity Assessment

Quick Wrap-Up: Lead a concluding class discussion with questions such as:

  1. What were your design improvements? Which were successful?
  2. How can you apply this practice to wind turbine design, or even real-world sail car construction?
  3. (multiple choice) Why are renewable energy sources (such as wind, solar, water, etc.) called "renewable"? Select the correct answer:
  • a. They can be used over and over again.
  • b. These energy sources do not cost money.
  • c. We will never run out of these energy sources (This is the correct answer.)
  • d. These energy sources have no disadvantages.
  1. Name one advantage of wind energy (Possible answer: It is a renewable energy source that is inexpensive and effective.)
  2. Name one disadvantage of wind energy (Possible answers: It can be loud, ugly (to some people) and kill birds.)

Activity Extensions

As an activity extension, hand out the Sail Car Test Worksheet, which further incorporates kinematic equations into calculating acceleration and final velocity from the measurements taken from testing. Note that this might be challenging for fifth graders and will most likely require teacher guidance to go through the worksheet and help with the necessary algebra.

Have students explore different sail materials, and even combining the given materials together to make a "composite."

Have students test their sail cars outdoors on a windy day. Have them check the wind speed online and compare it to their car speeds (calculated by timing how long it takes their cars to move a known distance, say 5 or 10 feet).

Challenge students to build larger-scale sail cars. Use different materials, such as LEGO wheels or small model car wheels and axles. Have them compare sail size and weight of the small and large sail cars.

Hold a classroom- or school-wide sail car race!

Activity Scaling

  • For higher grades, assign students the Sail Car Test Worksheet as homework instead of doing it in class. In that case, record times for each group on the board as usual, and make sure students record them. They will use the times and the fixed track distance to perform the calculations on their own. See the Activity Extension section for details.
  • For higher grades, have students also design the base itself. However, note that this changes the controls in the experiment.
  • For lower grades, do not use the Sail Car Test Table; instead, simply record run-times on the board for comparison.

References

Fuel Mix for U.S. Electricity Generation (2001-2013). Energy and You, Clean Energy, U.S. Environmental Protection Agency. Accessed December 18, 2014. (a great bar graph compares the use of coal, petroleum coke, oil, natural gas, other gas, nuclear, hydro, other, wind, solar, biomass and geothermal every year since 2001) http://www.epa.gov/cleanenergy/energy-and-you/

Contributors

Emily Gill, Kristi Ekern, Wyatt Champion, Denise W. Carlson

Copyright

© 2013 by Regents of the University of Colorado

Supporting Program

Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

Acknowledgements

This digital library content was developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. DGE 0338326. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

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