Hands-on Activity: Balsa Towers

Contributed by: Techtronics Program, Pratt School of Engineering, Duke University

Photograph shows street view looking up at very tall glass-covered skyscraper that reflects the blue sky and nearby tall buildings.
The Sears Tower, Chicago, IL

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 strength-to-weight ratio.
This engineering curriculum meets Next Generation Science Standards (NGSS).

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

  • Students will be able to draw structurally sound 2D designs on paper.
  • Students will be able to construct 3D structures from 2D designs.

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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.

  • 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) Details... View more aligned curriculum... Do you agree with this alignment?
  • Display numerical data in plots on a number line, including dot plots, histograms, and box plots. (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Solve real-world and mathematical problems involving area, surface area, and volume. (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations. (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Summarize numerical data sets in relation to their context, such as by: (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Design is a creative planning process that leads to useful products and systems. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • There is no perfect design. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Requirements for design are made up of criteria and constraints. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Design involves a set of steps, which can be performed in different sequences and repeated as needed. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • 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) Details... View more aligned curriculum... Do you agree with this alignment?
  • Modeling, testing, evaluating, and modifying are used to transform ideas into practical solutions. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Test and evaluate the design in relation to pre-established requirements, such as criteria and constraints, and refine as needed. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Structures rest on a foundation. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Buildings generally contain a variety of subsystems. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Summarize numerical data sets in relation to their context, such as by: (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Solve real-world and mathematical problems involving area, surface area, and volume. (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations. (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Display numerical data in plots on a number line, including dot plots, histograms, and box plots. (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Predict the effect of a given force or a change in mass on the motion of an object. (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Understand force, motion and the relationship between them. (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Understand motion, the effects of forces on motion and the graphical representations of motion. (Grade 7) Details... View more aligned curriculum... Do you agree with this alignment?
  • Explain the effects of balanced and unbalanced forces acting on an object (including friction, gravity and magnets). (Grade 7) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

  • markers
  • large sheets of paper, such as butcher paper
  • quick drying epoxy glue (90-second or 5-minute)
  • 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/

Introduction/Motivation

Your engineering design challenge today is to build a structurally sound tower with a favorable strength-to-weight 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 "strength-to-weight 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 strength-to-weight ratio? Let's get started!

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 non-moving 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.

strength-to-weight ratio: A ratio of the amount of weight a structure can hold to the mass of the structure itself.

Procedure

  1. Gather materials and make copies of the Structural Strength Testing Handout, one per student.
  2. Divide the class into groups of three or four students each. Hand out the large-sized paper and writing implements.
  3. Direct the teams to brainstorm and then sketch their tower ideas and designs on the large-sized paper. One possible tower-building technique is to build each side (either 3 or 4) and then attach each side together. Or, take a ground-up 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.
  4. Distribute the building materials.
  5. Explain safety techniques that pertain to the utility knives, epoxy glue and dremmel tool. See the Safety Issues section.
  6. 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.
  7. Give the teams time to build the towers on their own.
  8. If some groups finish early, suggest that they decorate their towers, keeping in mind the strength-to-weight ratio objective.
  9. Hand out the worksheets for students to record their testing data and the data from other groups.
  10. 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.
  11. Have students calculate strength-to-weight ratios and graph the class results on the worksheets.
  12. Lead a class discussion: Compare results. Which team design was the most successful? Why?
  13. 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 strength-to-weight ratio of their towers? Give groups time to redesign and reinforce their towers, and test again.

Attachments

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.

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?

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)?

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 Burnham

Copyright

© 2013 by Regents of the University of Colorado; original © 2004 Duke University

Supporting Program

Techtronics Program, Pratt School of Engineering, Duke University

Acknowledgements

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 GK-12 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: August 10, 2017

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