Summary
Students groups use balsa wood and glue to build their own towers using some of the techniques they learned from the associated lesson. While general guidelines are provided, give students freedom with their designs and encourage them to implement what they have learned about structural engineering. The winning team design is the tower with the highest strengthtoweight ratio.Engineering Connection
Students act as if they are civil engineers, and make balsa wood towers to meet a design requirement. They brainstorm, design, test and redesign their model towers.
Learning Objectives
After this activity, students should be able to:
 Draw structurally sound 2D designs on paper.
 Construct 3D structures from 2D designs.
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 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 )
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This Performance Expectation 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:
Common Core State Standards  Math

Display numerical data in plots on a number line, including dot plots, histograms, and box plots.
(Grade 6 )
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Solve realworld and mathematical problems involving area, surface area, and volume.
(Grade 6 )
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Use ratio and rate reasoning to solve realworld and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations.
(Grade 6 )
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Summarize numerical data sets in relation to their context, such as by:
(Grade 6 )
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International Technology and Engineering Educators Association  Technology

Design is a creative planning process that leads to useful products and systems.
(Grades 6  8 )
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There is no perfect design.
(Grades 6  8 )
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Requirements for design are made up of criteria and constraints.
(Grades 6  8 )
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Design involves a set of steps, which can be performed in different sequences and repeated as needed.
(Grades 6  8 )
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Brainstorming is a group problemsolving design process in which each person in the group presents his or her ideas in an open forum.
(Grades 6  8 )
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Modeling, testing, evaluating, and modifying are used to transform ideas into practical solutions.
(Grades 6  8 )
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Test and evaluate the design in relation to preestablished requirements, such as criteria and constraints, and refine as needed.
(Grades 6  8 )
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Structures rest on a foundation.
(Grades 6  8 )
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Buildings generally contain a variety of subsystems.
(Grades 6  8 )
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State Standards
North Carolina  Math

Summarize numerical data sets in relation to their context, such as by:
(Grade
6 )
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Solve realworld and mathematical problems involving area, surface area, and volume.
(Grade
6 )
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Use ratio and rate reasoning to solve realworld and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations.
(Grade
6 )
More Details
Do you agree with this alignment?

Display numerical data in plots on a number line, including dot plots, histograms, and box plots.
(Grade
6 )
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Do you agree with this alignment?
North Carolina  Science

Predict the effect of a given force or a change in mass on the motion of an object.
(Grade
5 )
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Understand force, motion and the relationship between them.
(Grade
5 )
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Understand motion, the effects of forces on motion and the graphical representations of motion.
(Grade
7 )
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Explain the effects of balanced and unbalanced forces acting on an object (including friction, gravity and magnets).
(Grade
7 )
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Materials List
 markers
 large sheets of paper, such as butcher paper
 quick drying epoxy glue (90second or 5minute)
 1/4 x 1/4 inch balsa wood strips
 1/8 inch balsa wood sheets
 (optional) dremel tool
 measuring rulers
 utility knives (for students, if possible, otherwise one for the teacher)
 newspaper, to protect table tops from glue
 scrapwood, to cut on (and protect the table tops)
 goggles, one per person
 scale, to weigh towers
 flat board, to set on top of a tower and on which to place weight for testing
 weights or many identical books, to use as mass/weight to test tower strength
 Structural Strength Testing Handout, one per student
Source for balsa wood and glue: http://www.specializedbalsa.com/
Worksheets and Attachments
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Introduction/Motivation
Your engineering design challenge today is to build a structurally sound tower with a favorable strengthtoweight ratio. Working in teams, you will experiment with various designs and come up with what you believe is the best one.
Who can tell me what we mean by "strengthtoweight ratio"? (Listen to student explanations. Correct and amend as necessary.) That's right, it is the ratio of the amount of weight a structure can hold to the mass of the structure itself.
Which team will succeed in building a tower with the highest strengthtoweight ratio? Let's get started!
Procedure
 Gather materials and make copies of the Structural Strength Testing Handout, one per student.
 Divide the class into groups of three or four students each. Hand out the largesized paper and writing implements.
 Direct the teams to brainstorm and then sketch their tower ideas and designs on the largesized paper. One possible towerbuilding technique is to build each side (either 3 or 4) and then attach each side together. Or, take a groundup approach and build all of the sides of the tower at the same time. Expect students to discover what shapes are the strongest in the design of a physical structure.
 Distribute the building materials.
 Explain safety techniques that pertain to the utility knives, epoxy glue and dremmel tool. See the Safety Issues section.
 Demonstrate for students on how to safely cut and glue together two pieces of balsa wood. Note that epoxy glue has two components: resin, and hardener. To use it, apply a small amount of the resin to the area to be glued, and then apply the hardener, which makes it dry practically instantly.
 Give the teams time to build the towers on their own.
 If some groups finish early, suggest that they decorate their towers, keeping in mind the strengthtoweight ratio objective.
 Hand out the worksheets for students to record their testing data and the data from other groups.
 Test each tower to see how much it weighs, and how heavy a load it can support. In order to test a tower's strength, place a flat board on the top of the tower. Then, carefully apply masses (such as a book at a time) to simulate a load. Remind students to record the results (tower weight and load weight at failure) for every team's tower test.
 Have students calculate strengthtoweight ratios and graph the class results on the worksheets.
 Lead a class discussion: Compare results. Which team design was the most successful? Why?
 After the initial testing, expect that students have learned a lot about what worked and what did not work. Point out that the engineering design process is "iterative," meaning it is a cycle that is repeated over and over so that improvements can be made from what is learned in testing, until a successful design is achieved. Do they have ideas to improve the strengthtoweight ratio of their towers? Give groups time to redesign and reinforce their towers, and test again.
Vocabulary/Definitions
buckling: When a column fails by bending at some point in the height of the column, usually towards the midpoint and caused by a vertical force.
civil engineering: The field of engineering pertaining to nonmoving structures such as roads, sewers, towers, buildings and bridges.
deflection : The amount a structure bends or moves from its "at rest" position.
lateral force: A force that impacts a structure horizontally, such as winds and earthquakes.
strengthtoweight ratio: A ratio of the amount of weight a structure can hold to the mass of the structure itself.
Assessment
 Did all group members participate in the design, construction and testing of the tower?
 How well did the towers perform, compared to expectations?
 What would students do differently next time (did they learn from their mistakes)?
Investigating Questions
 Which shapes/structures seem to be the strongest while using the least material?
 If you were going to tell someone how to build a strong and light tower, what instructions and advice would you give?
Safety Issues
 Several safety Issues must be taken into account when building the towers. Require students to wear safety goggles when cutting with utility knives, using epoxy glue and using the dremel tool. Also, since utility knives are very sharp, supervise their use at all times and direct students to always cut down and away from themselves and other people. Epoxy glue is very strong and dries very fast so students should be careful not to get any on their skin.
 If not enough adults are available to adequately supervise students using utility knives, use 1/8 inch square balsa wood strips because they can be cut with scissors.
Troubleshooting Tips
If a team's tower is weak or unstable, have students examine each region of the tower and think about how they can reinforce it.
If epoxy glue is not practical or students have trouble with it, super glue works as an alternative.
Activity Extensions
Lead a class brainstorming session in which you ask students what they would tell someone who wanted to build a strong tower and had no idea how.
Contributors
Kelly Devereaux, Benjamin BurnhamCopyright
© 2013 by Regents of the University of Colorado; original © 2004 Duke UniversitySupporting Program
Techtronics Program, Pratt School of Engineering, Duke UniversityAcknowledgements
This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.
Last modified: March 15, 2019
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