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The Brooklyn Bridge is a suspension bridge. It is held together by cable, a wire rope that is so flexible that
it can move in the wind. Yet the bridge is very stiff. Even when you cross it on a very windy day,
you probably wouldn't feel it moving. How is that possible?
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Think of a spider web. It keeps its shape even in the wind and rain. Many of its threads are
attached to things that don't move.
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The bridge stays still because its
cables are in tension, pulled tight by several forces.
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The bridge cables are secured to the stone towers,
while the weight of the road bed pulls them down and the anchorages hold them down on each side of the river.
Like spider web threads, the cables can move a little bit - just enough to make them withstand the wind,
but not enough to make them shaky. Here are some more comparisons between a spider web and a suspension bridge;
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| SPIDER WEB |
SUSPENSION BRIDGE |
| web made with flexible spider silk |
bridge made with flexible steel wire rope and cables |
| web wheel "spokes" |
main bridge cables |
| web wheel "orb" |
suspender cables and diagonal stays |
| web spokes secured to inanimate found objects (tree branches, walls, etc.) |
main cables secured to inanimate man-made stone towers and anchorages |
| spider repairs web after wear and tear from weather and other insects |
workmen repair bridge after wear and tear from weather, automobiles, and people |
Can you think of some other similarities? How about some differences?
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