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6-8 > Physical Science
Grade level: 6-8 Subject: Physical Science Duration: Two class periods
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Students will:
1. Understand the benefits and drawbacks of different types of bridges.
2. Think about the challenges involved in building bridges.

The class will need the following:
Computers with Internet access (optional but very helpful)
Reference materials on bridges
Each group of three or four students will need the following:
Research material about a particular bridge (Web sites and books suggested below)
One long piece of butcher block paper
Pencils, colored markers, and crayons
Each student will need the following:
Classroom Activity Sheet: Bridge Research (see printable version)
Take-Home Sheet: Longest Suspension Bridges in the United States (see printable version)

1. Introduce the lesson by showing the class a picture of a popular bridge, such the Golden Gate Bridge (San Francisco) or the Brooklyn Bridge (New York City). Ask students to imagine what might happen if all the bridges in New York City or San Francisco were suddenly shut down. Then help the class brainstorm some ways that bridges affect our lives. For example, you could remind students that food and other essential supplies are often transported across bridges.
2. Gather an assortment of bridge photos from library books and Web sites. Ask students to look at some pictures and discuss ways in which the bridges are similar. Then ask the class to speculate on why many bridges are shaped differently and made of different materials. Finally, help students make a list of some of the challenges that successful bridge designers must overcome. Some possible answers include earthquakes, strong winds, and changes in temperature. For this step and the group activity that follows, see Resources to find Web sites and books about bridges, including famous bridges. .
3. Divide students into small groups of three or four. Ask each group to select a photograph and research the bridge. Students can write their findings on the Classroom Activity Sheet: Bridge Research. Each group should try to find the following information:
  • When and where was the bridge built?
  • What type of architecture characterizes the bridge?Is the architecture consistent with an arch, beam, suspension, cable-stayed, cantilever, or moveable design?
  • What were some special challenges that the bridge architects and engineers faced? How did they overcome those challenges?
  • How much time did construction crews need to complete the bridge?
  • Approximately how many cars use this bridge each week (or year)?
  • What interesting stories can be found about this bridge? For example, are any fun facts associated with its design, construction, name, or use?
4. Have students in each group draw the bridge on butcher block paper. Specify a scale, such as 1 inch = 1,000 feet, and ask students to write the scale in a corner of the illustration. To demonstrate the scale, instruct students to draw a stick figure that represents a person 5 feet tall. Note: The scale may depend on the available wall space in the classroom or school hallway. As a concluding activity, have the groups imagine that they are bridge tour guides. Ask each group write a short tour script and then select one person to present the tour to the class. Make sure that each group has a turn giving a tour.
5. For homework, assign the Take-Home Sheet: Longest Suspension Bridges in the United States. The assignment will give students understanding of nationwide bridge locations.
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To help older students delve further into bridge architecture, have them conduct research on bridges of the future. What kinds of materials will be used to build future bridges? Will bridges take on new shapes? This Web site can serve as a springboard for their research:Buildings, Bridges and Tunnels. Based on the research, ask students to use butcher paper and markers or 3-D manipulatives such as K’nex to show an example of future bridge design.
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Discussion Questions

1. Thousands of cars drive over bridges each day. What are some techniques used to enable bridges to withstand this level of wear and tear? What keeps the bridges from falling down?
2. In October 1989, a strong earthquake in the San Francisco Bay Area caused tremendous structural damage to many bridges. What are some ways that such bridge damage might be avoided in the future?
3. What is the longest bridge in your area? Why was it built? What factors determined the materials used to design and build it? Did the builders face any special challenges?
4. Does a career as a bridge builder or engineer sound interesting to you? Why or why not? What challenges do you think would be particularly frustrating?
5. The U.S. government requires states to inspect and evaluate all bridges at least once every two years. What are some ways that technology can be used to make the inspection of bridges more efficient and effective?
6. In addition to being functional, bridges frequently become attractive landmarks for a town or region. Which bridges do you think are most visually appealing? Why?
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Use the following three-point rubric to evaluate students’ work during this lesson. Students should be able to work cooperatively in their groups, answer the research questions, complete their drawings of the bridge, write tour scripts, and present their tour to the class.’
  • Three points:students worked well in their groups; answered all the research questions; completed an accurate illustration of a bridge drawn to scale; wrote a creative and interesting tour script; made a clear presentation to the class
  • Two points:students worked somewhat well in their groups, answered most of the research questions; completed an illustration of a bridge drawn to scale; completed their tour script; presented the information to the class in a straightforward fashion
  • One point:students completed some of the group work; answered two or three research questions; completed a not-to-scale illustration of a bridge; wrote most of their tour script; presented some information to the class
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Build It and They Will Come
Divide the class into small groups. Give each group a small collection of materials, such as drinking straws, rubber bands, paper clips, and tape, to use to build a model bridge. Ask students to construct a bridge between the backs of two chairs that are approximately 2 feet apart. The bridge must be able to handle the weight of a model car or a tennis ball rolling across it. If their bridge cannot meet the load criterion, have them make adjustments until it can support the weight.

You’re the Engineer!
Two online challenges will help students improve their understanding of different kinds of bridges. On each Web site listed below, students will find several scenarios that conclude with a question about the best kind of bridge to build. Students must figure out how to resolve the problem.

The Bridge Challenge

NOVA Online Bridge Activity

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Suggested Readings

Steven A. Ostrow. MetroBooks, 1997.
The history of bridges and bridge-making is presented through color photographs and explanatory text, from the earliest Roman bridges to the most recent suspension types, from covered bridges on back-country roads to huge iron railroad trestles. The book shows how engineering and aesthetics can merge and create something both beautiful and useful.

Bridgescape: The Art of Designing Bridges
Frederick Gottemoeller. John Wiley & Sons, 1998.
This book offers an in-depth look at all the decisions that must be made while a bridge is bein designed. The text stresses the integration of the aesthetic dimension of design with its engineering aspects and provides examples through hundreds of photographs and illustrations.

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Bridges: Reaching Out
At Discovery Online's "Bridges: Reaching Out," explore the world's longest suspension bridge, learn about future bridges, and take a tour of the greatest and grandest bridges on planet Earth..

Technology & Bridge Design
Using internet resources suggested at this web page, students working in teams will prepare preliminary designs and prototypes (on paper) for a model bridge that could be built for a science fair.

How Bridges Work
From the ever-popular "How Stuff Works" web page, learn the basics of building beam, arch, and suspension bridges.

Bridge Building-Art and Science
Everything you always wanted to know about bridges, from the structural analysis of bridge stress to the soothing poetry and music inspired by by the world's great bridges.

West Point Bridge Designer
West Point provides FREE downloadable bridge design software. Design your bridge and test it in a virtual simulation. You might even be able to encourage a few of your students to enter West Point's "Bicentennial Engineering Design Contest."

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

speaker    arch bridge
Definition:A type of bridge in which its weight is carried outward along the curve to supports at each end.
Context:One of the oldest connecting structures, arch bridges can have a span of up to 1,700 feet. The Iron Bridge, located in England, is an example of a well-known arch bridge.

speaker    beam bridge
Definition:A simple type of bridge composed of horizontal beams supported by vertical posts
Context:Hundreds of workers helped build vertical supports for the beam bridge.

speaker    cable-stayed bridge
Definition:A bridge in which the roadway deck is suspended from cables anchored to one or more towers.
Context:Unlike suspension bridges, cable-stayed bridges do not block a driver’s view of the water.

speaker    cantilever bridge
Definition:A projecting structure supported only at one end, much like a shelf bracket or a diving board.
Context:A cantilever bridge has two towers located on opposite sides of a body of water.

speaker    span
Definition:The distance between two supports of a bridge.
Context:The Verrazano-Narrows Bridge has a span of 4,260 feet, the longest of any bridge in the United States.

speaker    stay
Definition:A long, strong wire rope that supports a mast.
Context:One of the steel stays that supported the bridge snapped, but fortunately, the structure didn’t collapse.

speaker    suspension bridge
Definition:A bridge in which the roadway is hung from strong cables that pass over two towers.
Context:The George Washington Bridge is the second longest suspension bridge in New York City.

speaker    tension
Definition:A force that stretches a material apart, often making the material longer.
Context:When cars travel on a suspension bridge, they put tension on the vertical cables.

speaker    truss
Definition:A rigid frame composed of short, straight pieces joined to form a series of triangles or other stable shapes.
Context:Many suspension bridges have a series of trusses beneath the roadway to prevent the bridge from twisting.

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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 the effects of balanced and unbalanced forces on an object’s motion (e.g., if more than one force acts on an object traveling along a straight line, 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 on an object’s motion).

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

Grade level:6-8
Subject area:Scientific Processes
Understands the scientific enterprise.
Knows that the work of science requires a variety of human abilities, qualities, and habits of mind (e.g., reasoning, insight, energy, skill, creativity, intellectual honesty, tolerance of ambiguity, skepticism, openness to new ideas).

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Jordan D. Brown, a freelance author specializing in materials for kids and teachers
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