## Bridging the Gap

Summary: Civil engineers are people who design bridges. To test the strength of a bridge they build models. Your group's challenge is to design and test a model bridge with a 40-cm gap. Your bridge will have to support the weight of 100 pennies.

1. Plan It

Make five paper tubes that are 21-cm (8 1/2 in.) long. Use 8 1/2 in. by 11 in. paper.

• First decide on the diameter of the tubes you want to test.
• Calculate the size of the rectangle needed for each tube. Use C = ¼ x d to find each circumference. Allow an extra 1-cm for the tube to overlap itself.
• Cut the paper to the size you want. Roll the paper and secure the tube with tape.
• Measure to be sure the tubes have the diameters you want.

Our planning completed

2. Put It Together

A. Put two desks close to each other.

• Hang a paper cup over the tube.
• Place the tube over the space between the desks.
• Put two rolls of 50 pennies in the paper cup.
• Gently pull the desks apart, only 1 cm at a time until the tube falls.
B. Create a chart. Create a chart using the example on page 227 of your textbook, or the Calculations Chart here on Education Place. Record the longest gap before the "bridge" falls.

C. Repeat. Repeat the steps with the other tubes.

Our experiments completed

3. Wrap It Up

A. Discuss. Discuss your data. What have you learned from your experiment? Which design works best?

B. Design. Design a bridge that can span a 40­cm gap and support the weight of 100 pennies.

• Specify the length, the diameter, and the span of the tube or tubes in your diagram.

Model completed

4. Discuss Your Results

• How well did you use measurement?
• How well did you design your bridge?
• Is the data on your chart clear and complete?
• Did your group work together and share ideas?
• Explain how well your final diagram worked.

Review completed

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