# Hands-on Activity:Car Collision Testing & Tradeoffs: Don’t Crack Humpty

### Quick Look

Grade Level: 7 (6-9)

Time Required: 3 hours

Takes 2 to 5 hours depending on the number of redesign steps permitted and the number of educational standards addressed.

Expendable Cost/Group: US \$3.00

The activity also uses some non-expendable (reusable) items such as a wooden ramp with a variable angle and four-wheeled car bases. See the Materials List for details.

Group Size: 4

Activity Dependency: None

Subject Areas: Algebra, Science and Technology

### Summary

Student groups are provided with a generic car base on which to design a device/enclosure to protect an egg as it rolls down a ramp at increasing slopes. During this in-depth physics-science-technology-math activity, student teams design, build and test their prototype creations to meet the design challenge, and then perform basic mathematical calculations using collected data, including a summative cost-benefit ratio. The activity has great potential to build on with additional physics and math explorations. Many student handouts are provided.
This engineering curriculum meets Next Generation Science Standards (NGSS).

### Engineering Connection

Automotive manufacturers hire engineers to redesign cars in order to make them safer. This process always involves a trade-off between cost of manufacturing a new design and level of safety. After this activity, students will be able to recognize this trade-off and understand the concept of cost to benefit ratio.

### Learning Objectives

After this activity, students should be able to:

• Explain the engineering design process.
• Explain the relationship between distance, time and speed.
• Describe how one can use math to solve a problem.

### 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.

###### NGSS: Next Generation Science Standards - Science
NGSS Performance Expectation

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?

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 agreed-upon 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:

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NGSS Performance Expectation

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?

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:

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NGSS Performance Expectation

Apply Newton's Third Law to design a solution to a problem involving the motion of two colliding objects. (Grades 6 - 8 )

Do you agree with this alignment?

This activity focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Apply scientific ideas or principles to design an object, tool, process or system.

Alignment agreement:

For any pair of interacting objects, the force exerted by the first object on the second object is equal in strength to the force that the second object exerts on the first, but in the opposite direction (Newton's third law).

Alignment agreement:

Models can be used to represent systems and their interactions—such as inputs, processes and outputs—and energy and matter flows within systems.

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:

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NGSS Performance Expectation

Apply scientific and engineering ideas to design, evaluate, and refine a device that minimizes the force on a macroscopic object during a collision. (Grades 9 - 12 )

Do you agree with this alignment?

This activity focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Apply scientific ideas to solve a design problem, taking into account possible unanticipated effects.

Alignment agreement:

If a system interacts with objects outside itself, the total momentum of the system can change; however, any such change is balanced by changes in the momentum of objects outside the system.

Alignment agreement:

Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects.

Alignment agreement:

Criteria and constraints also include satisfying any requirements set by society, such as taking issues of risk mitigation into account, and they should be quantified to the extent possible and stated in such a way that one can tell if a given design meets them.

Alignment agreement:

Criteria may need to be broken down into simpler ones that can be approached systematically, and decisions about the priority of certain criteria over others (trade-offs) may be needed.

Alignment agreement:

Systems can be designed to cause a desired effect.

Alignment agreement:

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###### Common Core State Standards - Math
• Solve unit rate problems including those involving unit pricing and constant speed. (Grade 6 ) More Details

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• Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin. (Grade 7 ) More Details

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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 ) More Details

Do you agree with this alignment?

• Know that straight lines are widely used to model relationships between two quantitative variables. For scatter plots that suggest a linear association, informally fit a straight line, and informally assess the model fit by judging the closeness of the data points to the line. (Grade 8 ) More Details

Do you agree with this alignment?

###### International Technology and Engineering Educators Association - Technology
• The development of technology is a human activity and is the result of individual and collective needs and the ability to be creative. (Grades 6 - 8 ) More Details

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• Requirements are the parameters placed on the development of a product or system. (Grades 6 - 8 ) More Details

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• Design is a creative planning process that leads to useful products and systems. (Grades 6 - 8 ) More Details

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• There is no perfect design. (Grades 6 - 8 ) More Details

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• Requirements for design are made up of criteria and constraints. (Grades 6 - 8 ) More Details

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• Brainstorming is a group problem-solving design process in which each person in the group presents his or her ideas in an open forum. (Grades 6 - 8 ) More Details

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• Modeling, testing, evaluating, and modifying are used to transform ideas into practical solutions. (Grades 6 - 8 ) More Details

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• Specify criteria and constraints for the design. (Grades 6 - 8 ) More Details

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• Make two-dimensional and three-dimensional representations of the designed solution. (Grades 6 - 8 ) More Details

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• Test and evaluate the design in relation to pre-established requirements, such as criteria and constraints, and refine as needed. (Grades 6 - 8 ) More Details

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• Make a product or system and document the solution. (Grades 6 - 8 ) More Details

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• Transportation vehicles are made up of subsystems, such as structural propulsion, suspension, guidance, control, and support, that must function together for a system to work effectively. (Grades 6 - 8 ) More Details

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###### Massachusetts - Math
• Apply and extend previous understandings of multiplication and division to divide fractions by fractions. (Grade 6 ) More Details

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• Fluently add, subtract, multiply, and divide multi-digit decimals using the standard algorithm for each operation. (Grade 6 ) More Details

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• Apply and extend previous understandings of arithmetic to algebraic expressions. (Grade 6 ) More Details

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• Recognize and represent proportional relationships between quantities. (Grade 7 ) More Details

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• Solve multi-step real-life and mathematical problems posed with positive and negative rational numbers in any form (whole numbers, fractions, and decimals), using tools strategically. Apply properties of operations to calculate with numbers in any form; convert between forms as appropriate; and assess the reasonableness of answers using mental computation and estimation strategies. (Grade 7 ) More Details

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• Compute unit rates associated with ratios of fractions, including ratios of lengths, areas and other quantities measured in like or different units. (Grade 7 ) More Details

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• Analyze proportional relationships and use them to solve real-world and mathematical problems. (Grade 7 ) More Details

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• Investigate patterns of association in bivariate data. (Grade 8 ) More Details

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• Understand that patterns of association can also be seen in bivariate categorical data by displaying frequencies and relative frequencies in a two-way table. Construct and interpret a two-way table summarizing data on two categorical variables collected from the same subjects. Use relative frequencies calculated for rows or columns to describe possible association between the two variables. (Grade 8 ) More Details

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• Summarize, represent, and interpret data on a single count or measurement variable (Grades 9 - 12 ) More Details

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• Describe the effects of approximate error in measurement and rounding on measurements and on computed values from measurements. Identify significant figures in recorded measures and computed values based on the context given and the precision of the tools used to measure. (Grades 9 - 12 ) More Details

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###### Massachusetts - Science
• Given a design task, identify appropriate materials (e.g., wood, paper, plastic, aggregates, ceramics, metals, solvents, adhesives) based on specific properties and characteristics (e.g., strength, hardness, and flexibility). (Grades 6 - 8 ) More Details

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• Identify and explain the steps of the engineering design process, i.e., identify the need or problem, research the problem, develop possible solutions, select the best possible solution(s), construct a prototype, test and evaluate, communicate the solution(s), and redesign. (Grades 6 - 8 ) More Details

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• Demonstrate methods of representing solutions to a design problem, e.g., sketches, orthographic projections, multiview drawings. (Grades 6 - 8 ) More Details

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• Describe and explain the purpose of a given prototype. (Grades 6 - 8 ) More Details

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• Explain how such design features as size, shape, weight, function, and cost limitations would affect the construction of a given prototype. (Grades 6 - 8 ) More Details

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• Given a transportation problem, explain a possible solution using the universal systems model. (Grades 6 - 8 ) More Details

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Suggest an alignment not listed above

### Materials List

One-time costs:

• a wooden ramp with adjustable incline; 6-ft long, 7-8 inch wide track, elevation 0º to 90º; 1 per class; see the Ramp Construction Method for details on how to build
• 5 x 8-inch wooden base, 1 per group
• screw eyes, 4 per group
• threaded rod to fit through screw eyes or wooden dowel, 2 per group
• wheels, 4 per group; use hobby wheels or cut them from a wooden dowel
• e-clips or washers, 4 per group
• stopwatches
• meter stick
• protractor
• balance
• string
• stapler
• scissors

Suggested materials:

• eggs, at least 1 per group
• (optional) wooden eggs for practice
• an assortment of construction materials and supplies, such as: cardboard squares, pipe cleaners, twist ties, small and large rubber bands, cotton balls, soda straws, craft sticks, masking and scotch tape, string, soda bottles, super glue, packaging peanuts, paper and plastic cups, bubble wrap, binder clips, staples

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### Pre-Req Knowledge

Students should have a basic understanding of ratios, proportions, Newton's laws, linear motion calculations, data collection and graphing.

### Introduction/Motivation

You and your team are members in the research and development department of a major car manufacturing company. You are in charge of testing a prototype safety harness on the latest line of cars. Your research team has provided you with instructions to create the device. Now it's your job to construct and test this prototype and determine how effective it is.

In a real lab situation, the car would be accelerated into a wall. Since you do not have the facilities to perform this test, you will use a ramp to simulate acceleration of a model car. To do your test, run your prototype car down the ramp starting at the lowest angle and see how well it performs. If it passes one angle, increase the slope and run the experiment again. If it fails, record the angle and stop testing. Compare your results with those of the other tests in the class to determine the average angle at which the prototype's safety mechanism failed. Based upon your results, make a recommendation as to whether or not the safety mechanism is effective. The company standards require that the safety mechanism be able to withstand an impact at a 50º incline run.

### Procedure

Before the Activity

• Gather materials.
• Make copies of the student handouts in the Attachment section: Design Constraints Handout and Cost of Materials and Data Table Handout.
• Review the Notes by a Teacher for a background about pertinent math, physics and cost/benefit concepts for the activity.
• Make sure that when students are figuring the total cost calculations they include only the cost of the materials used in the final devices. They may have redesigned their devices while constructing and decided not to use some of the materials initially chosen. For purposes of this activity, do not charge them for materials that they did not end up using in the final product.

Overview

1. Introduce the challenge: To design a safety device that can hold an egg (passenger) on the model car and keep it from breaking as the car rolls down the ramp at increasing slopes. The target goal is to protect the egg during a roll down the ramp at a 50-degree angle without cracking. Give extra credit to groups that can achieve success at steeper angles.
2. Explain the constraints.
3. Conduct the activity (see detailed steps below).
4. After activity completion, discuss the importance of having the "cost-to-performance" ratio and review the physics principles that can be observed in each device prototype. (Refer to the Notes by a Teacher for details.)

With the Students

1. Divide the class into groups of four students each and distribute the student handouts.
2. Have teams brainstorm, discuss and draw possible solutions and then agree upon the best ideas. (Make a brainstorming/sketch a graded component of the project.) This is a possible breakpoint for a shortened activity; see the Activity Scaling section for an explanation.
3. Verify that each group has a unified drawing or idea, and then permit each group to "purchase" materials.
4. Give the engineering teams 30-60 minutes to construct their devices.
5. Direct students to calculate their materials cost. This is another possible breakpoint.
6. Have one group present to the class its design, describing the construction, explaining the logic behinid its design, and reporting the construction cost.
7. Record the construction cost in the design database (such as a chart on the wall or a projected spreadsheet) for the class to see. Then the teacher revisits the design constraints and verifies that the device meets the requirements.
8. Have each group measure the mass of its device and record in the data table.
9. Then test the device at a low ramp slope.
10. Record in the data table the time it takes to move down the ramp and the incline number of the ramp.
11. Repeat the test for this device until the highest slope is reached or the egg is broken to any observable degree.
12. If a device needs minor repairs between runs, give the design team a set amount of time (perhaps 1-2 minutes) to make minor repairs (remember to re-record the mass of newly designed devices).
13. Repeat this process to check and test each device.
14. (optional) Determine angle measurements for each incline number.
15. Have teams calculate weight, speed and cost/performance ratio.* Use the Performance vs. Cost Projection Sheet/Handout (Excel file) to project the results on a classroom screen or wall.

* Note: Divide the fictional dollar cost from the "Cost Account" sheet by the highest ramp level survived to create the cost/performance ratio.

### Assessment

Rubric: Refer to the Example Grading Rubric to guide grading.

Hypothetical Bonus Exercise: If cooperation and doing one's fair share of the work are issues, consider giving the engineering team a fictional "\$10,000 bonus" to anonymously divide amongst its group members at project end, split as they deem fair; this is often very revealing! Or use the Team Member Peer Evaluation Form.

Graphing/Analysis: Have students graph cost vs. speed from the data table and discuss their relationship (if any). Ask the students if the more money they spend, the better/faster their car will be. Is the relationship linear? Another option is to graph weight vs. speed. Are heavier cars faster?

### Safety Issues

Watch students' use of the incline ramp to avoid pinched fingers and toes.

### Troubleshooting Tips

To save on broken eggs, use wooden eggs for the design and build phases.

An option if plenty of materials are available is to not charge for materials used in designs that were not tested. This encourages more experimentation. For purposes of this activity, the cost should be the finished cost (manufacture cost) not the development cost. It should be the cost of the materials needed to make the car they dropped.

### Activity Extensions

• If time and enthusiasm permit, have students re-design their solutions at home for presentation to the class at a later date.
• Have students evaluate their own devices: What is good/bad about the design solution and why? How could it be improved?
• Explore what formula might provide a fairer cost/performance ratio.
• Explore how to mass-produce the best design(s). All of the standards related to manufacturing could be addressed through the production process.
• Use weight of the device constructed as a design constraint.
• Refer to the Notes By a Teacher, created by Joshua Abrams of Meridian Academy, which explores possible activity extensions, scaling and concepts addressed by the activity from the physics and math perspective.

### Activity Scaling

Depending on the level of the class, make use of the "possible breakpoints" indications in the Procedure section. If materials are limited or unavailable, stop at the point at which students draw device sketches. Have them explain their designs and discuss how they might be successful or not. Another possibility is to have students bring in their own materials for the cars, although this makes the car bases uneven across the class, but the physics principles can still be observed in the devices they build.

### Additional Multimedia Support

Learn more about the steps of the engineering design process at https://www.teachengineering.org/engrdesignprocess.php.

### Contributors

Scott Beaurivage; Justin Riley; Ryan St. Gelais

© 2013 by Regents of the University of Colorado; original © 2005 Worcester Polytechnic Institute

### Supporting Program

K-12 Outreach Office, Worcester Polytechnic Institute

### Acknowledgements

This project was developed as a WPI Interactive Qualifying Project by undergraduate engineering students at Worcester Polytechnic Institute, and funded in part by Pratt & Whitney.