Crane Thumbnail
A crane is a good example a cantilever structure. Click on the image for larger view.


Garden Poles--Building Out

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Discussing Results (continued)

Finally, ask your students about how building on this scale differs from their experience on a smaller scale. How is it the same?

What's Going On

In building on this scale, the physics phenomena are more clearly seen and discussed. For example, the superior strength of the triangle and need for diagonal bracing becomes easily apparent. Tension, compression, and the effect of weight at a distance from its support (torque) become very obvious. During the building process, balance and stability are constantly challenged, and students resolve these problems in a variety of interesting ways. The relative strength and weakness of the building material are revealed through this challenging building experience.

In addition, students develop an intuitive sense of how the weight and strength of materials compare at this large scale. When you scale up, as in this activity, weights increase more than strength so everything seems flimsy. When working on this scale, the center-of-mass of the cantilevers gets far away from the supporting wall or table very rapidly. This creates much greater torque on the cantilevers, causing a great tendency toward twisting and turning.

  • You can extend this activity by having students build structures of varying dimensions and with various parameters on the type and number of connectors.

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