Hands-on Activity Creative Engineering Design:
Mouse Trap Cars

Learning Objectives

After this activity, students should be able to:

• Understand and apply the Engineering Design Process (EDP).
• Describe how the EDP is used at each step of the mousetrap car design challenge.
• Explain how their mousetrap car functions.
• Improve on the mousetrap car design by iterating the EDP.

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

Materials List

For each student:

• 1 mousetrap 
• 10 craft sticks 
• 36” fishing line, string or heavy thread
• 2 sticks hot glue 
• 2 BBQ skewers 
• 2 straws 
• Unlimited cardboard 
• Unlimited duct tape 

Materials for wheels that can be provided in class or provided by students:

• Bottle tops
• Small plastic plates
• Toilet or paper towel roll
• CDs
• Film canisters 
• Jar lids, etc.

Optional materials for car body:

• Wood 
• Boxes
• Plastic bottles or containers, etc.

Worksheets and Attachments

Introduction/Motivation

Today we will begin our next design challenge making sure we perform each step of the EDP. For our next design challenge, you are going to design and build a car powered solely by a standard mousetrap.

The purpose of the design challenge is that the final car for each person will travel as far as it can. In order to get there, however, this project will undergo several iterations – the first build will not be the final project. We will start with prototypes, and then experiment with various modifications before deciding on a final design and materials.

Also, the car itself will only represent a small portion of the mark – so there is nothing to lose by taking risks. What really counts is what you learn from the processes of design, construction, analysis, problem solving, and so on. The car will be designed and built by each of you, and each student will submit their analysis report when the final results are in. We will have class time dedicated to car builds, but you may need some time outside class as well.

Materials:

The car may be of any size and made of any material, but no pre-fabricated car parts may be used. You may not use prefabricated wheels or tires. Some suggested materials are CD's, metal rods, wooden dowels, balsa wood and rigid plastic tubing. The wooden stir sticks from a paint store are good as well. Glue, nails, screws and staples etc are acceptable as fasteners. The mousetrap may be attached to the car in any position and by any means desired. 

Some materials will be provided - mousetraps, hot glue, craft sticks, BBQ skewers, straws, cardboard, duct tape, and fishing line/string. It’s not possible to anticipate everyone's needs on this open design challenge, plus storage is limited. As such, you will be required to gather some of the project materials yourself, which are open-ended for the most part.

Power:

The car is powered by the mousetrap. No other electrical, mechanical or chemical energy may be used to power the vehicle. You may use elastic bands if you wish, but they may NOT be stretched at the start of the run. The car will be started from a standstill by gently setting off the trap (so the trap must be left intact!). An initial push is not permitted. As a car, forward motion is generated by powered wheels which push against the floor - the car may not push off any other object or surface.

Procedure

Background

A mousetrap car is a model car made from simple materials that is powered by a mousetrap. Mousetrap cars can be made from cardboard or balsa wood with CD’s for wheels and axles of wood or brass tubing. Power to drive the wheels is provided by a mousetrap to which a wand and string is attached to the snap arm. Winding the string around the axle pulls back the snap arm and releasing the snap arm pulls the string, turning the wheels. Because of their simplicity, low cost and the nearly endless variation of ways to build a mousetrap car, they are a great project to help students learn about the engineering design process and conducting investigations to test designs. This activity provides the opportunity for students to participate in a design-build-race contest to test their different model car designs to engage with and learn from their peers.

Design considerations:

The basic concept is fairly simple. The classic design is an axle fixed to one or two wheels, and a string is wound around the axle and tied to the mousetrap. When the trap is released the spring pulls the trap arm forward, which turns the axle and drives the wheels. 

• A small axle and large wheels will help maximize distance, with lower acceleration.
• Extending the length of the arm has a similar effect to widening the wheels – increased distance.
• An intermediate gear or pulley between the trap and the axle can also increase the distance/decrease the drive force.
• If the total drive ratio (wheel rotation distance to trap swing distance) is too large, the car may not be able to overcome the resting friction. 
• Greater acceleration means more chance of spinning the wheels.
• The more mass the car has the more traction it will have and the more momentum it will have, but more mass also means lower acceleration and lower top speed.
• The more moving parts your car has the more energy will be lost to friction.

A variety of online resources are provided to help you in the design and construction of your mousetrap car.

Test Races:

The cars will be run indoors on a smooth hard surface, such as the floor in the classroom, gym or auditorium. This decreases the rolling friction, allowing for a greater distance, but can also lead to the cars spinning their wheels. This should be considered during the design process. All cars must be ready to run on the designated days. Students will record the average distance traveled for their initial and iterated mousetrap car designs, as directed by the teacher.

Before the Activity

• Gather materials and create copies of the worksheet for the students.
• Set up an area in the classroom or school to test how far the mousetrap cars can travel
• Create a way to record students’ average distance traveled for both the initial and iterated mousetrap car design.

With the Students

Day 1

1. Warm Up: Show the short video of a mousetrap car. Ask students to share what they observed. Ask them to explain how they think a mousetrap car moves.
2. Read the Introduction/Motivation section and review over the Materials section with the class.
3. (Ask) Introduce and then have students fill out the Ask section (part 1) of the worksheet.
4. After everyone has written down the problem/goal of the activity and what the project constraints are, have a short class discussion focused on the student learning objectives in relation to the activity goal and the constraints (limits) they need to work within to successfully complete solve the problem/reach the goal.

Day 2

1. (Research) Using the internet (google, YouTube, google images), students individually research good design ideas for a mousetrap car and complete the Research section (part 2) of the worksheet.
2. Reflection: Ask for a couple of students to share tips they learned from their mousetrap car research.

Day 3

1. Warm Up: In pairs, have students share their Research section (part 2) findings of their mousetrap car design ideas with a thought partner. Guide student pairs in sharing their ideas by asking: What mousetrap car design ideas do students have that are the same/different, what designs do they think will be the most/least successful and why, etc.
2. (Brainstorm) Next, students complete the Brainstorm section (part 3), independently and quickly sketch at least 2 potential mousetrap car designs. Have students self-assess and then select a final design idea for their mousetrap car.

Day 4

1. (Plan) Students then fill out the Plan section (part 4) of the worksheet. This includes materials they will use for the car body, the axles and wheels and how they will be attached to the car body, and how the energy from the mousetrap will make the wheels spin.
2. (Plan) Before students start building, have each student verbally explain to the teacher how the mousetrap car will be built and how their design will get the wheels to turn. 
3. (Create) If time allows, students start to build their car with the materials they have chosen.
4. Reflection: Ask for a couple of students to share their final design choice for their mousetrap car.

Days 5-6

1. Warm-Up: Review materials and options for materials for students to use in building their mousetrap cars.
2. (Create) Students build their car with the materials they have chosen. They should fill in the Create section (part 5) of the worksheet as they build their design.
3. (Test) If time allows, review the mousetrap car testing protocol. Explain the set-up of the testing track distance with single or multiple lanes, have students test in pairs—one student releases their car and the other marks where car stopped, record distance in cm or m using a tape measure or meter sticks, then switch roles and repeat.
4. Reflection: Have a short Q&A session on design-build issues and suggestions.

Day 7

1. Warm Up: Do a quick check-in with students to confirm if all cars are built and offer support, as needed. Review the mousetrap car testing protocol.
2. (Test) Once students have built their first prototype, they should test it three times and fill out the Test section (part 6) of the worksheet. Have students record their average distance traveled on the class data sheet (posted in an online doc or written on the whiteboard or a large post-it in the classroom)
3. (Improve) If time allows, have students start on improving (iterating) on their initial mousetrap car design, but to not retest yet.
4. Reflection: Ask students to share and record their average distance traveled for their initial mousetrap car design.

Day 8

1. (Improve) Have students complete the Improve section (part 7) of the worksheet as they redesign (iterate) and retest their mousetrap car improvements.
2. Have each student informally present their reflections and results of the individual mousetrap car design challenge. Have each student share their highest average distance traveled and indicate if it was their initial or iterated design that traveled the farthest. To keep students engaged, have a deliverable expectation during presentations (e.g., peer review rubric, contribute to Q&A, etc.)
3. Reflection: Provide an anonymous Exit Ticket asking students to share their thoughts and experiences on what they learned, found challenging, suggestions for improvement, and what they enjoyed in applying the EDP via the mousetrap car design project.

Days 9-10

1. Mousetrap Car Design Student Presentation. Each student prepares a short 2-3-minute presentation explaining their mousetrap car design, materials selected, achievements and challenges of the build, iteration pros and cons, furthest average distance traveled, ideas for further iterations and improvements.

Vocabulary/Definitions

design thinking: A solutions-focused, human-centered way to creatively problem solve and innovate throughout the engineering design process.

engineering design process: A series of steps that guides engineering teams to solve engineering problems.

iteration: The repetition of a process towards improvement.

prototype: First model.

Assessment

Post-Activity (Summative) Assessment

Making Sense Assessment: Have students reflect on the science concepts they explored and/or the science and engineering skills they used completing the Making Sense Assessment.

Copyright

Contributors

Supporting Program

Acknowledgements

This curriculum was developed under National Science Foundation grant numbers 1941524 and 1941701. Any opinions, findings, and conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.