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  • Subject: Technology
  • |
  • Grade(s): 6-8
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  • Duration: Three class periods

Lesson Plan Sections


Students will understand the following:
1. Bridges are categorized into three primary types: suspension, beam, and arch.
2. Each is designed and built according to certain principles of engineering.


Students will need research materials on bridge engineering, including a computer with Internet access. Each group will need the following materials:
Twenty drinking straws
One meter of masking tape
Two stacks of books or blocks of wood
Jar of pennies


1. Divide your students into groups, provide each group with the necessary materials, and challenge each group to build a bridge that will span 25 centimeters.
2. Set the following rules:
  1. For the two ends of the span, students will use two stacks of books or wood blocks placed 25 centimeters apart.
  2. The only materials students may use for the bridge itself are 20 drinking straws and 1 meter of masking tape.
  3. The straws may be shortened, bent, or cut.
  4. No part of the bridge may touch anything between the two ends of the span.
3. Allow each group one class period to research bridge engineering. They should find out the basic principles of the three main kinds of bridges: suspension, beam, and arch.
4. Allow each group another class period to brainstorm ideas, make sketches, and choose a final design for their bridges.
5. Students will use a third class period to build their bridges with the materials provided.
6. After all bridges have been completed, have students test their bridges by seeing how many pennies they will hold. Students may modify their bridges, at this point, and then see if they will hold more pennies.
7. Have groups present their bridges and testing results to the class. Ask students to speculate about why some bridges were more or less successful than others. What factors went into the strength or weakness of each bridge? What flaws were inherent in the building materials? How were those flaws overcome?
8. Students who enjoyed this activity can try a more challenging level by increasing the span to more than 25 centimeters.

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Rather than requiring students to do their own research on bridge engineering, provide students with a few basic plans to choose from in constructing their bridges.

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Discussion Questions

1. Suppose all the bridges in a large city (New York City, for example) were closed. What effect would that have on that city? What are some specific ways that people would adapt to not using bridges?
2. Discuss how each of the three basic types of bridges—suspension, beam, and arch—transfers loads from the bridge to the ground. Describe where tension and compression occur on each type of bridge.
3. Many bridges are icons for their city or region. Why do you think people associate certain bridges with certain cities, while other bridges seem unremarkable?
4. Compare and contrast a beam bridge and an arch bridge. List at least three ways they are similar and three ways they are different.
5. The U.S. government requires states to inspect and rate all bridges at least once every two years. Describe ways that technology can be used to make monitoring and inspection of bridges more efficient and effective.
6. The earthquake in October 1989 in the San Francisco Bay area caused great structural damage to many of the bridges in the area. What features would you design as part of a bridge to make it better able to withstand an earthquake? Explain your ideas.

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You can evaluate groups on their projects using the following three-point rubric:
  • Three points: worked cooperatively; carefully prepared plans and sketches; thoroughly researched principles of bridge engineering and applied principles learned
  • Two points: worked cooperatively; prepared plans and/or sketches; researched and applied some principles of bridge engineering
  • One point: had difficulties working cooperatively; failed to prepare plans or sketches; research insufficient; only a few principles of bridge engineering applied

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Celebrity Bridges
Many bridges are icons for the cities or regions in which they are located. Almost everyone associates the Golden Gate Bridge, for instance, with San Francisco, or the Brooklyn Bridge with New York City. Have your students prepare posters or multimedia presentations on famous bridges from around the country and world. Students should include in their presentations descriptions of the designs and features of the bridges, including pictures or diagrams and brief descriptions of the areas in which the bridges are located. They should also include brief histories of how and why the bridges were built and the current uses and states of the bridges, including any repair plans. You might also ask them to include any famous cultural references to bridges, like quotes from poems or songs ("London Bridge is falling down," for example). An excellent starting point for finding information is Netscape's Bridge Search.  

Constructing with Bridges in Mind
Some engineering principles used in bridge building are also used in the design and construction of other structures. Ask your students to research the three primary types of bridges and investigate how these engineering principles are used in the design and construction of other structures. Then have them build models of structures, incorporating one or more of these engineering principles in their designs. In addition to building models, students should write explanations of the engineering principles they discovered and the ways in which they incorporated those principles into their projects. When their models and explanations are complete, have the students present their work to the class.

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Suggested Readings

Engineers of Dreams: Great Bridge Builders and the Spanning of America
Henry Petroski. Knopf, 1996.
This book contains captivating stories about the men who designed and built the bridges that span America. See how the personalities of these engineers have played as much of a role as their technical know-how in getting bridges built. The book discusses well-known American bridges and includes a photograph and technical drawings of each one.

Bridges: A History of the World's Most Famous and Important Spans
Judith Dupre. Black Dog & Leventhal Publishers, 1997.
This magnificent, one-of-a-kind book about bridges bears witness to the creativity and intelligence of engineers. You'll find photographs and location maps for each bridge featured.

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West Point Bridge Designer
West Point, home of the oldest engineering college in the Country, offers a free download of great Bridge Design software that will proivde hours of fun and intuitive learning for your students.

Bridges: Bridge Project Menu
Step by Step hand drawing procedures for designing model wooden bridges which could be adapted to a computer assisted drawing "CAD" program such as West Point's free "Bridge Designing Software."

Truss Bridge Laboratory
From the menu at this University of Florida engineering website, click on "Education Activities" and from a list of engineering projects, find the "Truss Bridge Laboratory."

The collapse of the Tacoma Narrows Bridge
Photographs, text and a short MPEG movie explain how the phenomenon of resonance caused the collapse of the Tacoma Narrows Bridge in 1940. This disaster is one of the biggest design blunders of all times, and no was hurt.

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Click on any of the vocabulary words below to hear them pronounced and used in a sentence.

speaker    composite
Definition: Made up of distinct parts.
Context: Chemists and engineers are creating strong yet lightweight composite materials that are now being used in everything from tennis rackets to airplanes.

speaker    resonance
Definition: A vibration of large amplitude in a mechanical or electrical system caused by a relatively small periodic stimulus of the same or nearly the same period as the natural vibration period of the system.
Context: The magnified sways and twisting of the Tacoma Narrows Bridge were caused by the resonance of 40-mile-per-hour winds and the natural oscillations of the bridge.

speaker    stay
Definition: A large, strong rope usually of wire used to support a mast.
Context: One of the diagonal steel stays that supported the bridge broke, but the structure remained standing.

speaker    tension
Definition: Either of two balancing forces causing or tending to cause extension.
Context: The heavy weight of concrete and steel causes a great deal of tension on the cables that support a bridge.

speaker    viaduct
Definition: A long elevated roadway usually consisting of a series of short spans supported on arches, piers, or columns.
Context: In Europe, there are still viaducts over deep valleys that were built by the Roman Empire.

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This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.
Grade level: 6-8
Subject area: physical science
Understands motion and the principles that explain it.
Understands effects of balanced and unbalanced forces on an object's motion (e.g., if more than one force acts on an object along a straight line, then the forces will reinforce or cancel one another, depending on their direction and magnitude; unbalanced forces such as friction will cause changes in the speed or direction of an object's motion).

Grade level: 6-8, 9-12
Subject area: science
Understands the scientific enterprise.
Benchmark 6-8:
Knows that people of all backgrounds and with diverse interests, talents, qualities, and motivations engage in fields of science and engineering; some of these people work in teams and others work alone, but all communicate extensively with others.

Benchmark 6-8:
Knows various settings in which scientists and engineers may work (e.g., colleges and universities, businesses and industries, research institutes, government agencies).

Benchmark 9-12:
Knows that throughout history, diverse cultures have developed scientific ideas and solved human problems through technology.

Benchmark 9-12:
Understands that individuals and teams contribute to science and engineering at different levels of complexity (e.g., an individual may conduct basic field studies; hundreds of people may work together on a major scientific question or technological problem).

Benchmark 9-12:
Knows that science and technology are essential social enterprises, but alone they can indicate only what can happen, not what should happen.

Benchmark 9-12:
Knows that creativity, imagination, and a good knowledge base are all required in the work of science and engineering.

Grade level: 6-8, 9-12
Subject area: technology
Understands the relationships among science, technology, society, and the individual.
Benchmark 6-8:
Knows ways in which technology has influenced the course of history (e.g., revolutions in agriculture, manufacturing, sanitation, medicine, warfare, transportation, information processing, communication).

Benchmark 6-8:
Knows that technology and science are reciprocal (e.g., technology drives science, as it provides the means to access outer space and remote locations, collect and treat samples, collect, measure, store, and compute data, and communicate information; science drives technology, as it provides principles for better instrumentation and techniques, and the means to address questions that demand more sophisticated instruments).

Benchmark 6-8:
Knows ways in which technology and society influence one another (e.g., new products and processes for society are developed through technology; technological changes are often accompanied by social, political, and economic changes; technology is influenced by social needs, attitudes, values, and limitations and cultural backgrounds and beliefs).

Benchmark 9-12:
Knows that mathematics, creativity, logic, and originality are all needed to improve technology.

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Don DeMember, science resource teacher, Kingsview Middle School, Germantown, Maryland.

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