### 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 energy-efficient 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 energy-efficient 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.

### Pre-Req 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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###
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*.

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*.

###### 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) Details... View more aligned curriculum... Do you agree with this alignment?
- 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) Details... View more aligned curriculum... Do you agree with this alignment?

###### Common Core State Standards: Math

- Multiply a whole number of up to four digits by a one-digit whole number, and multiply two two-digit 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) Details... View more aligned curriculum... Do you agree with this alignment?
- 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) Details... View more aligned curriculum... Do you agree with this alignment?

###### International Technology and Engineering Educators Association: Technology

- Asking questions and making observations helps a person to figure out how things work. (Grades K - 2) Details... View more aligned curriculum... Do you agree with this alignment?
- 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) Details... View more aligned curriculum... Do you agree with this alignment?

###### Colorado: Math

- Multiply and divide within 100. (Grade 3) Details... View more aligned curriculum... Do you agree with this alignment?
- Represent and interpret data. (Grade 3) Details... View more aligned curriculum... Do you agree with this alignment?
- Appropriate measurement tools, units, and systems are used to measure different attributes of objects and time. (Grade 4) Details... View more aligned curriculum... Do you agree with this alignment?
- Graph points on the coordinate plane to solve real-world and mathematical problems. (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
- 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) Details... View more aligned curriculum... Do you agree with this alignment?

###### Colorado: Science

- Identify and predict how the direction or speed of an object may change due to an outside force (Grade 2) Details... View more aligned curriculum... Do you agree with this alignment?
- Analyze and interpret observable data about the impact of forces on the motion of objects (Grade 2) Details... View more aligned curriculum... Do you agree with this alignment?

### Materials List

Each group needs:

- 5 Popsicle® / hobby sticks
- masking tape, ~24 inches
- 4 Lifesavers® mint candies (Tip: Use the mint-flavored candies because they do not get as sticky as the fruit-flavored 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 semi-truck? (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 energy-efficient 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 non-renewable 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 semi-truck 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 30-degree 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, re-design 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.

### 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

**Pre-Activity 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.

**Post-Activity 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 Yowell### Copyright

© 2011 by Regents of the University of Colorado.### Supporting Program

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

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 GK-12 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.

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