A Paper Bridge

A bridge is a structure that provides a pathway across streams, ravines, or other obstacles. The earliest bridges were made by nature and consisted of materials  including fallen logs, rocks, or tangled vines growing across the gap.

Structural engineers are concerned with the design and construction of all types of structures, including bridges.  The first structural engineers were untrained and simply made improvements on nature’s bridges. For example, to improve on a fallen log bridge, another log could be rolled beside the first one. These bridges are now called now called simple beam bridges.

A flat piece of paper is not very strong, but if you fold the paper so that it has sides, it becomes stronger and can support weight.

magic-paper-bridge1

Discover For Yourself

Place two books about 6 inches (15 cm) apart. Make a bridge across the gap between the books using a strip of copy or notebook paper about 4 x 8 inches (5 by 25 cm). Place a button or coin (penny) in the center of the bridge. The results will be that the paper bridge collapses under the weight.

Remove the paper bridge and test how flexible it is. Do this by holding the ends of the bridge and try to bend it back and forth. You will find that the paper is very flexible, so much so that even the weight of a button or coin causes it to collapse.

A structural engineer’s job would be to change the paper bridge to make it less flexible and more supportive of  added weight. One way to do this is to add sides to the bridge. Instead of adding parts to the paper, sides can be formed by folding the paper so that it has two sides as shown.

Place the paper bridge across the gap between the books and add buttons or coins. How many will your paper bridge hold?

magic-paper-bridge2

Test the flexibility of the bridge by holding its ends and trying to bend it back and forth as before. You will find that the folded sides make the bridge less flexible and more capable of holding added weight.

Simple Ideas Can Be Science Projects

So, how can a paper bridge be used as a science project?

1. Testing the ability of the flat and folded paper can be of your research on bridges. Other things to research would be to read about bridges and the forces acting on them as well as how different structures increase their ability to span gaps and support weight. .

2. If your science project has to be an experiment, then you need to think of ways the paper bridge experiment can be changed. The part that you purposefully change is called the independent variable (see index for more information about independent variables.) Examples of independent variables are: the size of the paper, the type of paper, and the shape of the paper. CAN YOU THINK OF OTHER INDEPENDENT VARIABLES?

3. How could any of the changes in step 2 affect the paper bridge? This is the part that you are going to be observing and it is called the dependent variable. Examples of dependent variables are: the amount of weight the bridge can hold and the distance the bridge can span. Note: For each of these you have to have some way to measure them. The weight the bridge can support can be determined by determining how many buttons or coins it will support. The distance the bridge will span can be determined by using the same amount of weight for each test, but change the distance between the books. The results from the test has to be compared to something elese—which would be the control bridge (this is the bridge made with the original procedure.) CAN YOU THINK OF OTHER DEPENDENT VARIABLES?

4. Using the Variable Examples in steps 2 and 3, six different questions can be written. Note that each question compares ONE INDEPENDENT VARIABLE to ONE DEPENDENT VARIABLE.

  • How does the size of the paper affect the amount of weight the bridge will support?
  • How does the size of the paper affect the amount the distance the bridge will span?
  • How does the type of paper affect the amount of weight the bridge will support?
  • How does the type of paper affect the amount the distance the bridge will span?
  • How does the shape of the paper affect the amount of weight the bridge will support?
  • How does the shape of the paper affect the amount the distance the bridge will span?

5. Your project investigation should be to compare two things: ONE INDEPENDENT VARIABLE and ONE DEPENDENT VARIABLE. So, choose one of the questions from step 4 or design one of your own.

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For more ideas about other engineering activities, see Janice VanCleave’s Engineering for Every Kid

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