2 large books of the same size
2 strips of posterboard (3"x28")
1 ruler
1 toy car
1 11x14" piece of paper
Stand the books on end approximately 12" apart. Open the covers so they don't fall over but keep the two inside covers parallel to each other.
Make a bridge by placing one of the posterboard strips across the books. Put the car in the middle of the bridge. What happens?
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The arch is frequently used to strengthen bridges. Make an arch by putting one of the posterboard strips between the two books.
Adjust the distance between the books so that the top of the arch is as high or slightly higher than the top of the books. Put the other posterboard strip back on top of the books. Put the car in the middle of the bridge. What happens?
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Finally, let's try a truss bridge. Take a large sheet of paper and fold it in half long ways. Fold it long ways again so that it's folded in quarters and again so that it's folded in eighths. Open it flat and fold it like a fan or accordion. Open it slightly so that it's 2-3" wide.
Remove the arch. Put the truss across the books and then put a posterboard strip on top for a roadway. Put the car in the middle of the bridge. What happens?
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We found that the arch can be used to strengthen bridges. What geometric shape did we use for the truss bridge? (Hint: look at the truss from the end.)
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