The forces that affect buildings and other structures can be modeled inexpensively and quickly by using the humble drinking straw. Usually, the projects built with drinking straws are rapid build. Storage can be an issue if you plan on having students work the design over multiple classes, or saving the structure for reference. This really becomes a problem if you are doing the same project with a full load of 5 classes. By doing the project in a single class period, you can easily reuse the straws, having students discard any cut ones and replenish them with new for the next group.
For fasteners, there are a few options. Tape can work, but is hard to remove if you are reusing straws. This can be good if you are aiming for a more durable product. Sewing pins can be used over an over again. Having students count out the pins they need and keeping them in plastic cups is works for multiple classes. As a new batch of kids collects their supplies, they just check to see that the last group left the right number of pins in the cup. This can occur at the same time they get the straws they will need. Some towers are built with paper clips as the fastener. If you do this, you may give the option of using wire cutters and pliers to modify the pins.
In introducing the ideas of the project, you will want to discuss the forces of tension, compression, torsion and shear. As students build, they should be able to recognize the forces that affect buildings and other structures and devise ways to compensate for them.
Often in straw towers, you will want to incorporate the differences between live load and dead load. Sometimes called dynamic load and static load, you can model them by having the tower hold a weight, representing the live or dynamic load. You can also have students become more aware of factor of safety and failure analysis of their structure.
The building of these towers can lead to a competitive situation. You can have students all build with the same materials, and set the grades on how high the towers stand while holding the live load. One way of doing the calculation is to set the highest and lowest possible grade, 100 and 75 for example. Then you measure the towers, identifying the tallest structure. If the tallest tower is 50 inches, then each inch is worth 1/2 point. The group with the tallest load bearing tower gets the 100. A tower that holds the live load at 40 inches would get a 95. The group that has the ball on the floor gets the 75. The other groups in between get grades based on the height of the ball, or other load.
You can also use a project like this to examine the forces affecting a building during an earthquake.
Have you built a straw tower as a student, or have you used the project as a teacher? How well does a project like this work in homeschooling? What techniques work well, and what resources are really helpful?
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