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Cross that Bridge!

Grades: 6-8
Author: Kathy Crooks


This hands-on inquiry activity sets up a problem for students (design a bridge) and gives them specific constraints (type of materials, amount of materials, length of bridge, etc.) under which to work. The participants will work in groups to brainstorm and test multiple bridge designs. Throughout this lesson, the best teaching practices of inquiry approaches, hands-on/minds-on learning, and applications to the real world, will be emphasized.


What should students know as a result of this lesson?

  • Students will explain how to design a project, given constraints.
  • Students will explain that scientific thinking is helpful in daily life.

What should the students be able to do as a result of this lesson?

  • Students will be able to find an answer to a problem using scientific reasoning skills.
  • Students will be able to design a bridge using given constraints.


Per group:

  • Seven drinking straws
  • 14 paper clips
  • Meter stick or centimeter ruler (one per group)
  • One sheet 8 1/2" x 11" paper
  • 2 books or blocks to act as the bases of the bridge
  • Scissors

For the class: At least 100 pennies, washers or small weights that can be shared to test the strength of the bridges.



As an introduction, follow the lesson plan for:

Assessment: Ask the students what they discovered about the various shapes. Ask the students to explore building 3-dimensional shapes and explore their strengths and weaknesses.


Follow the lesson plan for building a bridge at:

Assessment: How many pennies did the students' bridges hold? Which designs were successful and which were not? What did the successful designs have in common? Discuss what is meant by constraints. Ask the students what constraints they had to consider in their current bridge designs.


See the section entitled "The Big Idea" at both, and


Give the students a piece of legal size paper and ask them to build a bridge to hold a hundred pennies. You can also provide them with paper clips in order to strengthen their bridges.

Assessment: Have the students discuss the problems with the longer bridge span. From their own bridge observations, how do engineers handle this design problem? What constraints were different in this experiment? What other constraints are faced by those who design and build bridges?


Students should have a basic knowledge of how to conduct an experiment and how to work together in small groups.

Best Teaching Practices

  • Science/Technology/Society
  • Authentic Problem Based Learning
  • Hands-On/Minds-On

Alignment with Standards

NGSS Standards:

  • MS-PS2-2 Plan an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object.
  • 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.

Common Core Standards:

  • RST.6-8.1 Cite specific textual evidence to support analysis of science and technical texts.
  • RST.6-8.3 Follow preciesly a multistep procedure when carrying our experiments, taking measurements, or performing technical tasks.
  • WHST.6-8.2 Write informative/explanatory texts, including the narration of historical events, scientific procedures/experiments, or technical processes.

National Standards:

  • Content Standard A: 5-8 Science as Inquiry
  • Content Standard E: 5-8 Science and Technology

Ohio Standards:

  • Grades 6-8 Scientific Inquiry Benchmark A
  • Grades 6-8 Science and Technology Benchmark B

Content Knowledge



Students should use basic laboratory safety skills.

Paper clips, if straightened or broken, can have sharp edges.

Advise the students that pennies are for the bridge testing only and are not to be thrown or otherwise used inappropriately.


The sustainability of an ecosystem is a function of the delicate balance between abiotic and biotic factors. Animal populations rise and fall over time based on the degree these factors shift. Slight changes in air or water temperature, for example, could dramatically impact animals with a narrow range of tolerance. A fluctuation in food supply, biotic factor, could increase or decrease the population of a species.

We commonly hear or read statistics about animals that are put on the threatened or endangered species lists. How is the total population of a species determined? Understanding the concept of sampling and the application of simple mathematics in which to analyze the data will help students learn how population studies are conducted and how this information can be effectively used.


Have the students view footage of the Tacoma Narrows Bridge disaster ( ). Discuss the importance of considering various constraints. What issues must engineers take into consideration when designing a structure? (Example: environmental, economic, or societal issues). Can one of these be more important than another?

Other Considerations

Grouping Suggestions Students can work in lab groups of 2-3 or could work individually if necessary.

Pacing/Suggested Time: This lesson can be conducted in one class period.

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