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


Garden
PolesBuilding 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?
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 centerofmass 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.
