Balsa Towers
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.
The Sears Tower, Chicago, IL
Civil engineers design and build structures all around us. The bridges, roads, and skyscrapers are all projects that take time to plan, prototype, and create. Students act as if they are civil engineers, and make balsa wood towers to meet a design requirement. They use the engineering design process to brainstorm, design, test and redesign their model towers.
After this activity, students should be able to:
- Draw structurally sound 2D designs on paper.
- Construct 3D structures from 2D designs.
CCSS.Math.Content.6.RP.A.3 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
Do you agree with this alignment?CCSS.Math.Content.6.SP.B.4 Display numerical data in plots on a number line, including dot plots, histograms, and box plots.
Grade 6
Do you agree with this alignment?CCSS.Math.Content.6.SP.B.5 Summarize numerical data sets in relation to their context, such as by:
Grade 6
Do you agree with this alignment?CCSS.Math.Practice.MP2 Reason abstractly and quantitatively.
Grades K-12
Do you agree with this alignment?
Students will develop an understanding of the attributes of design.
Grades K-12
Do you agree with this alignment?Students will develop an understanding of engineering design.
Grades K-12
Do you agree with this alignment?Students will develop abilities to apply the design process.
Grades K-12
Do you agree with this alignment?There is no perfect design.
Grades 6-8
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
Do you agree with this alignment?Structures rest on a foundation.
Grades 6-8
Do you agree with this alignment?Buildings generally contain a variety of subsystems.
Grades 6-8
Do you agree with this alignment?STEL-7P Illustrate the benefits and opportunities associated with different approaches to design.
Grades 6-8
Do you agree with this alignment?STEL-7Q Apply the technology and engineering design process.
Grades 6-8
Do you agree with this alignment?STEL-7R Refine design solutions to address criteria and constraints.
Grades 6-8
Do you agree with this alignment?STEL-7S Create solutions to problems by identifying and applying human factors in design.
Grades 6-8
Do you agree with this alignment?
MS-ETS1-1 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
This resource focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices- 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.Do you agree with this alignment?
Disciplinary Core Ideas- 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.Do you agree with this alignment?
Crosscutting Concepts- 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.Do you agree with this alignment?
- All human activity draws on natural resources and has both short and long-term consequences, positive as well as negative, for the health of people and the natural environment.Do you agree with this alignment?
Do you agree with this alignment?- 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.
MS-ETS1-2 Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.
Grades 6-8
This resource focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices- Evaluate competing design solutions based on jointly developed and agreed-upon design criteria.Do you agree with this alignment?
Disciplinary Core Ideas- There are systematic processes for evaluating solutions with respect to how well they meet the criteria and constraints of a problem.Do you agree with this alignment?
Do you agree with this alignment?- Evaluate competing design solutions based on jointly developed and agreed-upon design criteria.
MS-ETS1-4 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
This resource focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices- Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs.Do you agree with this alignment?
Disciplinary Core Ideas- Models of all kinds are important for testing solutions.Do you agree with this alignment?
- 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.Do you agree with this alignment?
Do you agree with this alignment?- Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs.
CCSS.Math.Content.6.RP.A.3 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
Do you agree with this alignment?CCSS.Math.Content.6.SP.B.4 Display numerical data in plots on a number line, including dot plots, histograms, and box plots.
Grade 6
Do you agree with this alignment?CCSS.Math.Content.6.SP.B.5 Summarize numerical data sets in relation to their context, such as by:
Grade 6
Do you agree with this alignment?CCSS.Math.Practice.MP2 Reason abstractly and quantitatively.
Grades K-12
Do you agree with this alignment?
7.P.1.2 Explain the effects of balanced and unbalanced forces acting on an object (including friction, gravity and magnets).
Grade 7
Do you agree with this alignment?
- 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 (PDF), one per student
Source for balsa wood and glue: http://www.specializedbalsa.com/
Your engineering design challenge today is to build a structurally sound tower with a favorable strength-to-weight ratio using only the materials provided. 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!
- Gather materials and make copies of the Structural Strength Testing Handout (PDF), one per student.
- Divide the class into groups of three or four students each. Hand out the large-sized paper and writing implements.
- Direct the teams to brainstorm and imagine possible solutions 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.
- 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 strength-to-weight 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 strength-to-weight 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 strength-to-weight ratio of their towers? Give groups time to redesign and reinforce their towers, and test again.
- Compare designs and have teams share their designs to the class.
- 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.
- lateral force
- A force that impacts a structure horizontally, such as winds and earthquakes.
- deflection
- The amount a structure bends or moves from its "at rest" position.
- civil engineering
- The field of engineering pertaining to non-moving structures such as roads, sewers, towers, buildings and bridges.
- strength-to-weight ratio
- A ratio of the amount of weight a structure can hold to the mass of the structure itself.
- 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)?
- 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.
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.
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
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.
Copyright
2013 by Regents of the University of Colorado; original © 2004 Duke University