Educators' Guide: Hands-On/Mini-Activity: Sponge Beam

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Bending A combination of forces that causes one part of a material to be in compression and another part to be in tension.

Illustration: sponge with scoring lines.

1. With a permanent marker, draw a series of lines crosswise on the top and bottom of a soft kitchen sponge.

Illustration: sponge plane curving.

2. Pass the sponge around. Have kids bend the sponge into a U-shape, and observe what happens to each set of lines. (The lines inside the U get closer together and the lines on the outside spread farther apart.) Ask: Where is this sponge in compression? (On the inside.) In tension? (On the outside.) Bending is common in structures; for example, a horizontal beam that supports a floor or a bridge deck experiences bending. Reinforced concrete resists bending because of its combination of materials: concrete, which resists compression well; and steel bars, which resist tension well.

Try the Forces Lab.