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What Gives?


Today's challenge is to design and construct a suspension bridge. Can you build a bridge out of cardboard that won't collapse under the weight of a pile of books?

  • Target Age: 8-10
  • Skills/Subjects: Science
  • Related Episode: Episode 313: Dog of the Rings

WHAT TO DO

1. Get what you need:

  • 2 chairs with backs
  • 3 11" x 17" sheets of corrugated cardboard
  • Duct tape
  • String
  • Hole puncher
  • Scissors
  • Yard or meter stick
  • Paper and pencil
  • 4 people

2. Learn the parts of the suspension bridge:
The deck (or road) is suspended from hangers. The hangers are attached to the cables. The cables are draped over the towers, and then secured to the ground on either end of the bridge by solid rock or huge concrete blocks called anchors.

suspension bridge, with labeled parts

 

3. Set up the deck and suspension cables:
Tape 3 pieces of cardboard together to make the deck and place across 2 chairs. (Only 3" of the deck should rest on each seat.) Make 2 cables out of string, each 3 yards long, using scissors and the yard stick. Drape the cables over the towers (the chair backs) so they hang above the deck.

chairs set up as bridge here

4. Brainstorm and design:
Figure out the best way to attach the cables to the deck. The goal is to make a sturdy, strong bridge. Talk ideas over and sketch out designs. Follow the building rules:

  • Don't tape the deck to the chairs.
  • Don't tape the cables to the chairs or floor.
  • Don't tie the cables to the chairs.

5. Revise your design, if necessary:
Is your bridge working the way you want it to? Test it by putting an object on the deck. If it's not holding up, redesign.

6. Test your bridge:
Pile books on the deck, one at a time, while the anchors pull the cables. How many books can your bridge hold? Take turns being anchors so that everyone has the chance to feel the pull on the cables from the books. What's supporting the weight of the bridge? What would happen if you let go of the cables?

CHEW ON THIS!

Suspension bridges are among the strongest and longest of bridges. How do they work? The deck is suspended from vertical hangers that are attached to two heavy cables. The cables are pulled over the towers and secured by heavy anchors at each end. Weight pushes down on the deck, but the cables and hangers holding it up transfer the weight to the strong towers, which support the weight of the bridge.

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