Summary
Mint candies aren’t just a tasty treat; they are useful in learning about engineering concepts! In this activity, students design, build and test model race cars made from simple materials (lifesavershaped candies, plastic drinking straws, Popsicle sticks, index cards, tape) as a way to explore independent, dependent and control variables. They measure the changes in distance travelled with the addition of mass to the vehicles. Students also practice the steps of the engineering design process by brainstorming, planning, building, testing, and improving their "mintmobiles."Engineering Connection
When developing a new product or device, engineers go through many iterations of the engineering design process. First, they imagine lots of ideas and share them with their teammates. Then, the team decides on one best design and plans its final materials, specifications, functionality and aesthetics. Before building a fullscale prototype, they create a small model on which they perform many tests with different independent variables to optimize performance and cost. Once a model has been perfected, they build at full scale.
Learning Objectives
After this activity, students should be able to:
 Explain the steps of the engineering design process.
 Define criteria and constraints for a specific design problem.
 Identify dependent and independent variables.
 Identify control variables.
 Predict future performance of design based on gathered data.
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
NGSS Performance Expectation  

MSETS11. Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions. (Grades 6  8) Do you agree with this alignment? 

Click to view other curriculum aligned to this Performance Expectation  
This activity focuses on the following Three Dimensional Learning aspects of NGSS:  
Science & Engineering Practices  Disciplinary Core Ideas  Crosscutting Concepts 
Define a design problem that can be solved through the development of an object, tool, process or system and includes multiple criteria and constraints, including scientific knowledge that may limit possible solutions. Alignment agreement:  The more precisely a design task's criteria and constraints can be defined, the more likely it is that the designed solution will be successful. Specification of constraints includes consideration of scientific principles and other relevant knowledge that is likely to limit possible solutions. Alignment agreement:  All human activity draws on natural resources and has both short and longterm consequences, positive as well as negative, for the health of people and the natural environment. Alignment agreement: The uses of technologies and any limitations on their use are driven by individual or societal needs, desires, and values; by the findings of scientific research; and by differences in such factors as climate, natural resources, and economic conditions.Alignment agreement: 
NGSS Performance Expectation  

MSETS12. Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem. (Grades 6  8) Do you agree with this alignment? 

Click to view other curriculum aligned to this Performance Expectation  
This activity focuses on the following Three Dimensional Learning aspects of NGSS:  
Science & Engineering Practices  Disciplinary Core Ideas  Crosscutting Concepts 
Evaluate competing design solutions based on jointly developed and agreedupon design criteria. Alignment agreement:  There are systematic processes for evaluating solutions with respect to how well they meet the criteria and constraints of a problem. Alignment agreement: 
NGSS Performance Expectation  

MSETS14. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved. (Grades 6  8) Do you agree with this alignment? 

Click to view other curriculum aligned to this Performance Expectation  
This activity focuses on the following Three Dimensional Learning aspects of NGSS:  
Science & Engineering Practices  Disciplinary Core Ideas  Crosscutting Concepts 
Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs. Alignment agreement:  Models of all kinds are important for testing solutions. Alignment agreement: The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.Alignment agreement: 
Common Core State Standards  Math

Represent and analyze quantitative relationships between dependent and independent variables.
(Grade
6)
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Summarize numerical data sets in relation to their context, such as by:
(Grade
6)
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Construct and interpret scatter plots for bivariate measurement data to investigate patterns of association between two quantities. Describe patterns such as clustering, outliers, positive or negative association, linear association, and nonlinear association.
(Grade
8)
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International Technology and Engineering Educators Association  Technology

Students will develop an understanding of the attributes of design.
(Grades
K 
12)
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Students will develop an understanding of engineering design.
(Grades
K 
12)
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Evaluate designs based on criteria, constraints, and standards.
(Grades
3 
5)
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Modeling, testing, evaluating, and modifying are used to transform ideas into practical solutions.
(Grades
6 
8)
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Troubleshooting is a problemsolving method used to identify the cause of a malfunction in a technological system.
(Grades
6 
8)
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State Standards
Colorado  Math

Summarize numerical data sets in relation to their context.
(Grade
6)
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Use variables to represent two quantities in a realworld problem that change in relationship to one another.
(Grade
6)
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Visual displays and summary statistics of twovariable data condense the information in data sets into usable knowledge.
(Grade
8)
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Construct and interpret scatter plots for bivariate measurement data to investigate patterns of association between two quantities.
(Grade
8)
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Materials List
Each group needs:
 Note: for mintmobile construction supplies, the exact amounts required depend on the team's vehicle design; rough estimates are provided
 plastic drinking straws (estimated 46; make sure the straw diameter is smaller than the mint candy's hole diameter)
 Popsicle sticks (estimated 24)
 lifesavershaped candies, such as Lifesaver® mints (estimated 36)
 index cards (estimated 12; or thin cardboard or poster board scraps)
 tape, any type; duct or masking preferred
 scissors
 paper and pencil
 Design Worksheet, one per student
For the entire class to share:
 ramp, for testing, made from sturdy poster board, rigid cardboard or thin wood
 Gather two pieces of poster board, rigid cardboard, or thin wood of different lengths, for testing the independent variable of ramp length
 meter stick, for measuring the distance traveled
 pennies, for added mass during testing (estimated 1030 pennies; depending on robustness of mintmobiles, individually tape pennies on vehicles, or tape a little baggie of pennies to the design
 tape, for securing the ramp, meter stick and pennies
 (optional) hot glue gun and glue sticks
Worksheets and Attachments
Visit [www.teachengineering.org/activities/view/cub2537exploringvariablesmintmobilesmiddleschool] to print or download.PreReq Knowledge
Ability to make measurements using a meter stick.
Introduction/Motivation
(Write Figure 1 on the board as each step is discussed. Start by drawing an arrow in the shape of a circle.)
What do you think engineers do first when they begin to create a new product, say a new type of race car, a new style of backpack, or a new type of skis? That's right, the first thing engineers do is ask; that is, they ask what the product will do, what need they are addressing and what others have done. This also requires conducting research of the problem. Then, an engineer imagines all the possible features and qualities of the product. This takes a lot of creative brainstorming! After an engineer has made a list and some sketches of her/his ideas, all of the engineers in a team get together and share what they have come up with. As a team, they plan on one design by working with the best ideas. Once the details of the design have been decided, the team creates the product; then they get to test it out!
Tests are made on models of the product or device, which are often at a smaller than fullscale size. In the testing phase, the team pays attention to what needs to be changed to the model to make the product work better. The last step of the engineering design process is to improve the design.
While the engineering team designs the product, they first think about the criteria and constraints of their design problem. The criteria are all the things required of their product, or what the product must look like or be able to do in order to be considered successful. The constraints are all the things that limit the design. To help explain these terms, let’s apply them to an example.
Say I am an engineer designing a track for a roller coaster. What are some criteria that my design must meet if my goal is to design an exciting and fast roller coaster? (Allow three minutes for a group discussion. Student may say: include a large drop, lots of loops, long stretch so the cart can go fast, etc.) What are some constraints that limit my design? (Allow three minutes for a group discussion. Students may say: cost, amount of space available to build the coaster, other similar coasters nearby, safety requirements, etc.)
While the engineering team tests the product, they pay close attention to all the variables associated with their design. Two important types of variables are: independent and dependent variables. An independent variable is something that an engineer decides to change during each test to see how the results differ. A dependent variable is something that changes as a result of varying the independent variable. In testing, we also have what is called a control. A control is the part of the experiment that is neither changed by the engineer nor is affected by the independent variable. To help explain these new terms let's return to our roller coaster example.
Say I am an engineer testing a roller coaster. I want the cart to go as fast as possible on a track that I have already built. I can change some things to make the cart go as fast as possible—such as its mass, its length, or the type of wheels I use. Can anyone tell me what the independent and dependent variables are in this example? (The independent variables are the mass, length, and types of wheels that the engineer chooses. The dependent variable is the speed of the cart.) Control variables are independent variables that are held constant in an experiment. If you were testing variables that that influence a dependent variable, like speed, you would not test all the variables at the same time because then you would not know which variable(s) influenced the results. So, for example, if you were testing the influence of mass, you would hold the other variables (like length and type of wheels) constant, and test varying masses. So, length and type of wheels would be the control variables. On the contrary, if you were testing length, then you would hold mass constant and it would be a control variable. Thus, control variables are the variables you do not change in an experiment.
Today, working as engineers, we are going to follow the engineering design process and design and build mintmobiles! After identifying the criteria and constraints of your designs, you will get to choose an independent variable and investigate how changing that variable changes the distance your race cars travel. We'll send the cars down a ramp and measure the distance they travel, using a meter stick. Think for a moment: what are the independent and dependent variables in this activity and what is the control? (Allow about 10 seconds for students to individually think about this.) Now, share what you think is the correct answer with the person next to you. (Allow three minutes for a group discussion.) Now—are you ready to brainstorm? Great! Let's get started!
Procedure
Background
As this activity is written, student teams design their cars on paper first, working from a list of possible materials and then make a list of their needed supplies (including exactly how many wheels, straws, etc.) to request from the teacher. Activity variations are many. For example, limit the number of each type of material, require that each team use the exact same number and type of construction materials, or define a competitive objective to determine the best materials based on vehicle stability or speed with a certain mass.
Engineers use the engineering design process when they are creating new devices. The main seven steps of the engineering design process are: ask, imagine, research, plan, create, test, and improve. The improving step involves starting over again at the beginning of the design process with "ask," that is, "Where does this device need improvement? How can it be made to perform better?" Once a device has been built the first time, it is never complete! Engineers are always improving what they design. Imagine if the cellular phone had never been improved. Or cars, or computers.
Before the Activity
 Gather materials and list them on the board: plastic drinking straws, Popsicle sticks, lifesavershaped mint candies, index cards (or your own modified list of what's available).
 Set up the testing ramps by placing sturdy poster boards or a thin wooden board at an angle over a smooth surface (such as a tabletop). Use tape to secure the ramp; however, ensure that the ramp angle can be modified. Tape a meter stick from the bottom of the ramp along the table, so students can measure the distances traveled.
 Divide the class into teams of two students each.
With the Students
 Distribute copies of the Design Worksheet to students. Ask students to define the criteria and constraints of their mintmobile design problem. Record student ideas on the board, and have students record their ideas in the Design Worksheet. Criteria include: must be roll down the ramp smoothly, must travel in a straight line (not fall off the ramp), mustn’t fall apart, etc. Constraints include: can only use given materials, car must be small enough to fit on the ramp, etc.
 Ask students to list different independent, dependent, and control variables that they discussed with their partner during the activity Introduction/Motivation. List the variables on the board. Have students select one independent variable to test, discuss which independent variables would require the easiest modification to their race cars. Have students record their independent variable on the Design Worksheet. Encourage each group to select a different variable from the group next to them.
Independent variables include: mass of the mintmobile, number of wheels, width and height of the mintmobile, angle of the ramp, height of the ramp.
 To begin planning their mintmobile designs, give the class three minutes for students to individually brainstorm what their designs might look like on their Design Worksheets. Point out the list of available materials listed on the board, and remind students of the criteria and constraints of their design.
 Next, working with their partners, direct students to share their ideas and make drawings of their final, agreedupon designs on their Design Worksheets. Require the drawings to list the materials and amounts needed to build their mintmobiles. Remind them that their designs must be able to test the effects of the independent variable they chose on the depended variable: the distance their mintmobile travels.
 Once teams have finished their designs, distribute materials and give them time to build.
 Test the mintmobiles by sending them down the ramp. This is a good time for students to make modifications to their designs to ensure quality results. What can be improved? Does it roll smoothly? Does it roll straight? Can it successfully test their independent variable? Allow students time to record modifications on their Design Worksheet and modify their designs to ensure they meet the criteria recorded on the board.
 Now, have the students begin testing their independent variables (see Figure 2). Have students sent their mintmobiles down the ramp and record the independent variable they chose and their measurements of distance traveled (the dependent variable).
 Have students change their independent variable. For example: increase the length of the ramp, add mass to the car, decrease the angle of the ramp, etc. See Figure 3. Have students test their mintmobiles again and record new measurements for the independent variable and distance traveled.
 Before they test their cars for a third time by changing the independent variable again, ask each group to predict which trial will travel the furthest and why they believe this. Have groups write their predictions and justifications on their Design Worksheets.
 Retest the mintmobiles and record the new distances traveled after changing the independent variable again.
 In the table on their Design Worksheets, have students record the independent variable measurements and distanced traveled. Students then use these data to determine the effect of changing their independent variable on the distance their mintmobile traveled. Ask each group which independent variable they chose and how that variable affected the distance their mintmobile traveled. Record student conclusions on the board.
 As a class, review the collection of results on the board. Conclude with a class discussion (using questions provided in the Assessment section) about the experiment variables, how changing different independent variables impacted the distance traveled by the cars, and the design process. During this discussion, address any misconceptions the students identified during their predictions.
Vocabulary/Definitions
brainstorming: A technique of solving specific problems, stimulating creative thinking and developing new ideas by unrestrained and spontaneous discussion.
control variable : A variable that is neither changed by the engineer/tester nor affected by the independent variable.
dependent variable: A variable that changes as a result of changing the independent variable.
engineering design process: The cycle engineers go through while creating a new device: Ask; Research; Imagine; Plan; Create Test; Improve.
independent variable: A variable that is intentionally changed by the engineer or tester.
variable : Something that changes while testing an idea, device or system.
Assessment
PreActivity Assessment
Identifying Criteria, Constraints & Variables: Have students identify criteria and constraints from different examples of engineering design (such as the roller coaster design problem in the Intro/Motivation section). Next, have students categorize variables from different examples as independent, dependent or control variables. For example (as thoroughly explained in the Intro/Motivation section), the variables associated with roller coaster design. Then, have students talk in groups to identify the different variables involved with this activity.
Activity Embedded Assessment
Brainstorming Design Work: Have students follow the engineering design process by brainstorming different designs on their Design Worksheet; then have them share these ideas with their teammate(s). Have them draw their final group design, listing the exact materials they plan to use.
Theory to Practice: While researching their designs, have students identify (and list) the independent variables they will be testing, as well as the dependent, and control variables. (Note: Regardless of which independent variable a group selects, the dependent variable is the distance the cart travels, and the controls are the independent variables that students do not change during testing.)
Prediction: Before testing the cars in Run 3, ask each group to predict which trial will travel the furthest and why they believe this. Have groups write their predictions and justifications on their Design Worksheets.
Graphing: Have students plot the distances the cars go for the three different runs (or tests) of their mintmobile. Allow students to interpret results graphically and relate their independent variable to distance traveled.
PostActivity Assessment
Class Discussion: Ask students the following questions and discuss as a class.
 What were the independent, dependent and control variables in this test? (Possible answer: The independent variable was the angle of the ramp, the dependent variable was the distance the cart travels, and the controls included the length of the ramp and mass of the car.)
 Looking at everyone's results, how did changing each independent variable affect the distance traveled by the mintmobile? Did it travel a shorter or greater distance? (Answers will vary. Expect students to provide a statement on the effect of their independent variable on distance traveled and begin to explain why they think the distance traveled changed. For example, mass as the independent variable: Adding mass caused the cars to travel greater distances; the greater the mass, the further the cars travel.)
 How could you design a mintmobile to travel a longer distance than any of the mintmobiles you made or saw today? (Have students combine results from theirs and other groups. Possible answers: Increase the mass of the mintmobile by using heavier materials and improve the design to reduce drag and friction.)
 What sorts of things did you do at each step of the design process? (Have students share their own experiences, in their own words, that describe the repeating sevensteploop of the engineering design process: ask, research, imagine, plan, create, test, improve.)
Investigating Questions
 What independent variables could affect the distance traveled by the mintmobiles? (Possible answers: The material used on the ramp, the mass of the cart, the type of materials used to build the cart, the slope and length of the ramp, the number of wheels, the stability of the cart.)
 What is another dependent variable in this activity that might be of interest to an engineer designing a real race car or roller coaster cart? (Possible answers: Speed, stability.)
 What are the dependent variables that would be affected by these changes? (Possible answers: Speed, distance traveled, and stability.)
Troubleshooting Tips
If students use the straws as axles and find that the straws are bigger than the candy hole diameter, they can use scissors to slit the straws lengthwise, then curl and tape them tighter (so they are narrower) to make straws that spin better in the candy holes.
The mintmobiles roll best on smooth surfaces rather than the textured surfaces of carpets, so build the testing ramp on a tabletop and place a thin poster board at the bottom of the ramp.
If students' mintmobiles are quite small, they may not be able to hold many pennies. If so, tape on a few pennies at a time to determine a reasonable maximum amount.
Activity Extensions
Team Test Your Instructions: In addition to each team designing a mintmobile with a sketch and list of materials (see the Design Worksheet), have them write instructions on how to build the mintmobile and exchange designs with another group. Tell the students to build the other team's mintmobile following the instructions using only the supplies listed. This exercise sharpens students' awareness of the importance of accuracy and clear communication in their engineering plans. Or similarly, conduct The Universal Language of Engineering Drawings activity, in which students practice the ability to produce clear, complete, accurate and detailed design drawings for a mintmobiletype model car, using only specified materials. Teams trade drawings and attempt to construct the model cars in order to determine how successfully the original design intentions were communicated through sketches, dimensions and instructions.
Activity Scaling
 For lower grades, select mass as the independent variable for all groups to test. See Exploring Variables While Testing & Improving MintMobiles (for Elementary School).
 For upper grades, have students focus on following the engineering design process to build and test their mintmobiles while balancing tradeoffs between safety, design materials, and cost. Then, students test how changing the mass of their mintmobile mass affects distance traveled. See Exploring Variables While Testing & Improving MintMobiles (for High School).
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Copyright
© 2020 by Regents of the University of ColoradoContributors
Lesley Herrmann; Stephanie Rivale; Denise W. Carlson; Sabina SchillSupporting Program
Integrated Teaching and Learning Program, College of Engineering, University of Colorado BoulderAcknowledgements
The contents of this digital library curriculum were developed under grants 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.
This curriculum was revised and adapted in 2020 from its original to serve middle school students by TeachEngineering.org.
Last modified: December 13, 2021
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