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What It Is (continued)

At the end of the session, record their accomplishments through video or photography or by having the students draw pictures of their structures. Then have the students deconstruct the materials so that they can be used again at the next session.

For the next session, introduce the cantilever. A cantilever is a projecting beam or other structure which is supported at only one end (e.g., awnings, flagpoles, tree limbs). Challenge your students to build a cantilever out from a wall or out from a tabletop. Use the same rules for building as above with the following addition:

• Sticks may be taped to the wall, fence, or tabletop with a reasonable amount of duct tape.

Challenge the students to do one of the following:

• With 35 garden stakes, how far out from the wall or tabletop can you build a structure?

• Can you build a cantilever 11 feet out from the wall or tabletop?

• What is the strongest cantilever you can build 7 feet out from a wall or tabletop?

• Can you build a cantilever 9 feet out from the wall or tabletop that will hold one film canister of sand?

Choose or adjust the difficulty of the challenge based on the age and level of building skills of your students.

The question of rules and what is fair inevitably arises in these challenges. Questions such as, "Are the structures allowed to droop, and if so, how much?" and "How do you measure distance from the wall or tabletop?" almost always come up for these cantilevers. Setting these rules by class discussion enhances sensitivity to these problems. "Where is it fair to hang the weights?" is another question that often arises. The place where weights are hung is critical for cantilevers. When we hear students protest "it's not fair" when a group hangs their weight in close to the wall or table, we know that they have understood an important aspect of torque.