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Mini Bridge Rating: 4

 Level: Beginner Duration: 2 - 4 class periods Grade Level: NA Author: Pitsco Materials:  Toothpick Bridge Tester, Toothpick Bridges Teacher’s Guide, CJ600 Digital Scale, Toothpicks, glue, graph paper, test block, pencil, ruler, scissors or hobby knife, sand or other mass, tape, two solid surfaces to use as supports, notebook paper, calculator, waxed paper .

Objective

Design and build two bridges with the same efficiency, with one bridge weighing half as much as the other.

Description

Using the materials provided, design a toothpick bridge that maximizes efficiency. That is, it holds the maximum load using the least possible amount of materials. The bridge must have a roadbed. It may also have any substructure and/or superstructure you choose. The bridge must be at least 10 inches long and at least two inches wide.

Procedures

Use a ruler and pencil to draw on the graph paper a design for the roadbed, the bridge sides, and any other parts of the bridge. Draw the parts of the bridge full size. Indicate where glue will be applied. Design a second bridge that will weigh half as much as the first bridge but will have the same efficiency.

Place the toothpicks on the designs. Cut any toothpicks to the proper length, if necessary. Use tape to hold the toothpicks in place. Place drops of glue at each joint and allow the glue to dry. After the glue has dried, remove the tape. Assemble the parts of the bridge into a complete bridge. Use tape to hold the bridge parts to one another. Place glue at the bridge joints that connect the parts of the bridge together. Allow the glue to dry and then remove the tape.

Locate the digital scale and measure the mass of the bridge and record the mass.

Test the completed bridge:

·         Place a bridge across the space between two supports.

·         Find the mass of the test block, container, and accessories that will hang from the bridge.

·         Add enough sand or other mass to the container to increase the total mass of the testing block, container, materials, and hardware to 4.5 kg (10 lb).

·         Place a test block along the roadbed.

·         Attach a container to the test block so that the container hangs straight down from the block.

·         Gradually add sand or other mass to the container until the bridge breaks.

·         Measure the amount of mass, or load, the bridge supported.

Calculate the efficiency of the bridges. Efficiency equals load supported by the bridge divided by the mass of the bridge.

Discussion

Write a report summarizing your designs and the efficiency of the bridges. Explain how well the bridges met the goals set in this activity. Explain what could be done to make the bridges better meet the goals of the activity.

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