Summary
Students learn how the aerodynamics and rolling resistance of a car affect its energy efficiency through designing and constructing model cars out of simple materials. As the little cars are raced down a tilted track (powered by gravity) and propelled off a ramp, students come to understand the need to maximize the energy efficiency of their cars. The most energyefficient cars roll down the track the fastest and the most aerodynamic cars jump the farthest. Students also work with variables and plot how a car's speed changes with the track angle.Engineering Connection
The energy use and pollution associated with transportation is one of the largest issues facing society today. By building energyefficient cars, engineers can lower the negative impacts that cars have on the environment and ultimately help improve our lives. The energy efficiency of a car is affected by a variety of factors, including size, aerodynamics, weight, and the rolling resistance of the wheels. Engineers must know all about these factors to design better cars.
PreReq Knowledge
Some graphing skills.
Learning Objectives
After this activity, students should be able to:
 Describe the characteristics that affect a car's energy efficiency.
 Explain how rolling resistance affects a car's energy efficiency.
 Describe how a car's shape and size are related to aerodynamics.
 Explain the steps of the engineering design process.
 Explain the difference between an independent and dependent variable.
 Plot the results of a simple experiment on a graph.
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Building upon their understanding of forces and Newton's laws of motion, students learn about the force of friction, specifically with respect to cars. They explore the friction between tires and the road to learn how it affects the movement of cars while driving.
Educational Standards
Each TeachEngineering lesson or activity is correlated to one or more K12 science,
technology, engineering or math (STEM) educational standards.
All 100,000+ K12 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.
Each TeachEngineering lesson or activity is correlated to one or more K12 science, technology, engineering or math (STEM) educational standards.
All 100,000+ K12 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.
NGSS: Next Generation Science Standards  Science

Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost.
(Grades 3  5 )
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Do you agree with this alignment?
This Performance Expectation focuses on the following Three Dimensional Learning aspects of NGSS:Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts Define a simple design problem that can be solved through the development of an object, tool, process, or system and includes several criteria for success and constraints on materials, time, or cost. Alignment agreement:
Possible solutions to a problem are limited by available materials and resources (constraints). The success of a designed solution is determined by considering the desired features of a solution (criteria). Different proposals for solutions can be compared on the basis of how well each one meets the specified criteria for success or how well each takes the constraints into account. Alignment agreement:
People's needs and wants change over time, as do their demands for new and improved technologies. Alignment agreement:

Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.
(Grades 3  5 )
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Do you agree with this alignment?
This Performance Expectation focuses on the following Three Dimensional Learning aspects of NGSS:Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts Generate and compare multiple solutions to a problem based on how well they meet the criteria and constraints of the design problem. Alignment agreement:
Research on a problem should be carried out before beginning to design a solution. Testing a solution involves investigating how well it performs under a range of likely conditions. Alignment agreement:
At whatever stage, communicating with peers about proposed solutions is an important part of the design process, and shared ideas can lead to improved designs.Alignment agreement:
Engineers improve existing technologies or develop new ones to increase their benefits, to decrease known risks, and to meet societal demands. Alignment agreement:
Common Core State Standards  Math

Multiply a whole number of up to four digits by a onedigit whole number, and multiply two twodigit numbers, using strategies based on place value and the properties of operations. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models.
(Grade 4 )
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Represent real world and mathematical problems by graphing points in the first quadrant of the coordinate plane, and interpret coordinate values of points in the context of the situation.
(Grade 5 )
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International Technology and Engineering Educators Association  Technology

Asking questions and making observations helps a person to figure out how things work.
(Grades K  2 )
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The design process includes defining a problem, brainstorming, researching and generating ideas, identifying criteria and specifying constraints, exploring possibilities, selecting an approach, developing a design proposal, making a model or prototype, testing and evaluating the design using specifications, refining the design, creating or making it, and communicating processes and results.
(Grades 9  12 )
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State Standards
Colorado  Math

Multiply and divide within 100.
(Grade
3 )
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Represent and interpret data.
(Grade
3 )
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Appropriate measurement tools, units, and systems are used to measure different attributes of objects and time.
(Grade
4 )
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Graph points on the coordinate plane to solve realworld and mathematical problems.
(Grade
5 )
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Represent real world and mathematical problems by graphing points in the first quadrant of the coordinate plane, and interpret coordinate values of points in the context of the situation.
(Grade
5 )
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Colorado  Science

Identify and predict how the direction or speed of an object may change due to an outside force
(Grade
2 )
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Analyze and interpret observable data about the impact of forces on the motion of objects
(Grade
2 )
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Materials List
Each group needs:
 5 Popsicle® / hobby sticks
 masking tape, ~24 inches
 4 Lifesavers® mint candies (Tip: Use the mintflavored candies because they do not get as sticky as the fruitflavored ones.)
 3 drinking straws (small enough diameter to fit inside the mint candy holes)
 3 index cards
 Car Design Worksheet, one per student
To share with the entire class:
 scissors
 play money (Monopoly® money works well)
 rain gutter section(s), ~7 ft in length
 duct tape (or other heavy duty tape)
 cardboard ramp
 electric fan
 projector, for showing the attached PowerPoint presentations
 stopwatch (if racing only one car at a time)
Introduction/Motivation
How far can a car travel on one gallon of gas? (Answer: It depends on the car, but usually between 6 and 70 miles.) Do you think all cars are the same? (Answer: No) How about a semitruck? (Answer: Definitely not.) What makes the difference in a vehicle's energy efficiency? A car's energy efficiency depends on many things, including its weight, its rolling resistance, and its aerodynamics. A car that is energy efficient can travel farther on the same amount of gas, which saves the driver money. Creating more energyefficient cars also decreases air pollution and helps decrease greenhouse gas emissions due to automobile emissions. Also, gasoline is made from oil, a fossil fuel. Oil is a nonrenewable energy source, which means that when it is used up, no more is available. For these reasons, engineers are continually figuring out ways to make cars more energy efficient by decreasing their air resistance, rolling resistance, and weight.
The aerodynamics of a car is dependent on how much air the car has to move out of the way as it travels along a road. Engineers often design cars to resemble aerodynamic animals and shapes in nature. Can you think of any aerodynamic animals? (Possible answers: Fish, birds, sharks.) These animals move through the air (or water) easily and use little energy because they are sleek in their shapes, having no sharp corners or flat surfaces facing the wind. This causes the air to flow smoothly (efficiently) over them. A sleek car moves more easily through the air than a semitruck does, which means the car is more energy efficient.
The amount of energy a car uses can also be affected by the resistance of a car's tires on the road surface. You need to be able to find the balance between the amount of resistance, or friction, needed to keep the vehicle on the road and the ability to move efficiently without it flying off the road or being "stuck" to the road. Engineers design tires that increase a car's energy efficiency by rolling smoothly while making sure they are "sticky" enough to stay safely on the road, especially through corners and on wet surfaces. A great example of this would be a NASCAR race. Have any of you watched racing on television? The tires they use are expertly engineered so that the cars can reach high speeds while staying on the track during the tight corners.
Finally, a car's weight affects its energy efficiency. Is it harder to push a loaded grocery cart or an empty one? (Answer: Loaded) How about if you had to push the grocery cart uphill? Would you rather do it empty or full? (Answer: Empty) A car's weight determines how much energy it takes to accelerate, or speed up, the car, and it also affects how much energy it takes to move the car up a hill. Heavier cars are less energy efficient than lighter ones. Engineers use newly created, innovative materials whenever possible to reduce the weight of cars, as well as find ways to build them smaller so fewer materials are needed, which in turn reduces the weight of the car.
All of these factors contribute to a car's energy efficiency, with some of them being more important at high speeds and others being more important at low speeds.
All of these factors are considered variables, or something that you can change in an experiment or test. Engineers perform experiments on the many different variables to design cars for different purposes. When engineers perform experiments, they test only one variable at a time, while making sure that all of the other potential variables are kept unchanged. A variable that is kept from changing during an experiment is called a control. At the end of this activity, we will conduct several experiments to see how changing the angle of the track affects the speed of a car. In this case, the angle of the track is called the independent variable because we intentionally change it to gauge its affect on our vehicles. The speed of the car is called the dependent variable because it will be affected by the changes we make to the angle of the track. Once we have chosen our variables, we need to be very careful to control all other factors so that we get really accurate results. Let's get started!
Vocabulary/Definitions
aerodynamics: The ability of an object to cut through air (or water) efficiently
control: A variable that you are careful to keep the same during an experiment.
dependent variable: A variable that changes in value when you change an independent variable. Usually this is the variable about which you collect data during an experiment.
energy efficiency: Being able to do more with less energy.
independent variable: A variable you intentionally change in an experiment. Usually, the intent of the experiment is to see how a change in this variable affects the dependent variable.
rolling resistance: The force of friction acting on a rolling object by the ground to slow it down.
variable: Something that can be changed in an experiment.
Procedure
Before the Activity
 Decide which of two ways to set up the activity: To run the activity as a series of two cars competing against each other (that is, two separate cars being raced at once), set up two rain gutter race tracks at approximately a 30degree angle from the ground (see Figure 1). Tape the two gutters together to ensure the tracks are even. To run the activity with only one car racing at a time, use a single track and a stopwatch to record individual race times.
 Gather materials and make copies of the Car Design Worksheet.
 On Days 1 and 3, have the attached PowerPoint presentations ready to show.
 Set up race brackets, depending on number of student groups.
With the Students
Day 1 (or first hour)
 Show the Day 1 PowerPoint presentation, as part of the Introduction/Motivation.
 Divide the class into groups of two or three students each.
 Hand out the worksheets.
 Give $700 of play money to each group.
 Have students follow the steps in the worksheet (look at constraints, brainstorm ideas, draw a design, determine cost, redesign if over budget).
 Once groups have completed detailed designs that are within budget, have them purchase materials. Encourage them to reserve some funds to make later modifications (improvements) to their original designs.
 Have groups begin assembling their model cars.
Day 2 (or second hour)
 Briefly remind students of the activity goals.
 Have groups work on completing the assembly of their model cars.
 Have students test cars and make changes to improve the designs.
 Once all students have completed their model cars and made improvements, collect all of the cars at the front of the classroom.
 Race cars against each other using double elimination to find the most energy efficient car (that is, cars are raced twice; after each race, the winner moves on to the next round; if a car is deemed the "slowest" car in more than two races, it is eliminated from the trials). If a single track is being used, record times and eliminated the slowest cars after two runs down the track. Have students record on their worksheets the fastest time for each car.
 As a class, discuss why the winning car was the most energy efficient by examining its aerodynamics, rolling resistance, and size.
 If time allows, place a ramp about 6 inches away from the bottom of the rain gutters, as shown in Figure 2. If available, place a fan flat on the ground blowing air upwards. Have students run their model cars down the gutters and jump them off the ramp. Mark where each car lands.
 Discuss why specific cars jumped well and others did not.
Day 3 (or third hour)
 Using the Day 3 PowerPoint Presentation, introduce the topic of variables.
 Select the fastest car from the previous day's races to use to collect data.
 Race the cars at the track angles specified in the worksheet, and have students record the times.
 Have students practice graphing by having volunteers graph each data point on a graph drawn (or projected) on the board.
 Discuss the shape of the graph with the students.
 Have students predict the speed of the car at an angle that is less than 10 degrees and at an angle greater than 60 degrees. Record predictions.
 Test students' predictions by moving the track to the specified angle and timing the car.
Worksheets and Attachments
Safety Issues
Watch that students use care when using scissors.
Troubleshooting Tips
If students have trouble designing cars with rolling wheels, suggest that one way to do this is to use the the drinking straws as axles and the mint candies as wheels.
Make sure the fan is slightly elevated from the floor to create a good air flow.
Investigating Questions
What characteristics do the fast cars have in common?
What is the most important characteristic that made the cars go fast?
What effect does changing the angle of the track have on the car speed?
Assessment
PreActivity Assessment
Class Discussion: As a class, discuss the definitions of energy efficiency and aerodynamics. Have groups come up with three different factors they think will affect the energy efficiency or aerodynamics of their model cars. Write these factors on the board for all students to refer to during the design phase.
Activity Embedded Assessment
Car Design Worksheet: Have students follow the steps on the worksheet. Check the groups at each step and make sure they have adequately completed the associated task. For instance, the final design should include several different viewpoints and be adequately labeled.
PostActivity Assessment
Graphing Exercise: As a class, graph the results of the experiment together. Have volunteers graph individual points on the board while students complete the graphs on their worksheets. Discuss the shape of the graph and its meaning. See the sample worksheet for information on typical values.
Activity Extensions
Perform a second experiment, this time using the weight of the model cars as the variable. Record the speed of a car with different amounts of weight attached, and graph the data. Compare the data from the different experiments. Which variable had the greatest effect on the car's speed? How do the two graphs compare? Are they different or the same?
Contributors
Eszter Horanyi, Jake Crosby, William Surles, Janet YowellCopyright
© 2011 by Regents of the University of Colorado.Supporting Program
Integrated Teaching and Learning Program, College of Engineering, University of Colorado BoulderAcknowledgements
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education, and National Science Foundation GK12 grant no 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.
Last modified: February 26, 2019
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