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Tension and Compression

In structural engineering, there are two basic forces at work in any structural element: compression and tension. Compression is the force applied when two objects are pushed together. Think of a stack of heavy stones. The force crushing down on the bottom stone is compression. Tension is the force applied when an object is pulled or stretched. A good example is the surface of a trampoline. When someone jumps down on the trampoline, the material stretches.

Engineers talk about the tensile strength of materials. This is the maximum force that can be applied to a material without pulling it apart. Bundles of steel cables have an incredibly high tensile strength, which is why they're used in the world's longest and heaviest suspension bridges. Even a single steel cable only 1 centimeter in diameter can hold the weight of two full-grown elephants [source: Yes Mag].

Now let's think about a typical structure in Jenga. If you remove the center piece in a row, then you create two simple beam-and-column structures on either side of the tower. A beam laid across two columns experiences both compression and tension at the same time. The weight bearing down on the top of the beam compresses it inward toward the center of the beam. And even though you can't see it with your naked eye, the underside of the beam is being stretched outward.

Imagine if the beam was made of rubber. The weight would stretch it into a "U" shape. That's why rubber makes such a lousy construction material. Structural engineers choose (and sometimes design) materials with the best compression and tension characteristics for the job. Stone is excellent under compression, but remarkably easy to pull apart. That's why a stone arch lasts a lot longer than a stone beam. Reinforced concrete is an ideal building material, because the concrete gives it compression strength and the embedded steel rods give it tensile strength.

Jenga towers don't get tall enough or heavy enough to apply serious compression or tension on the wooden pieces, so there's very little concern of splitting a beam. But in real construction projects, engineers need to carefully consider each element's strengths and weaknesses.

Now we'll explain why it's always better to leave two supports at the bottom of the Jenga tower.

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