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BUILDING BIG
Bridges
Domes
Skyscrapers
Dams
Tunnels
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The Educators Guide
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  Mini-Activity: Human Arch
Activites Index | Glossary Educator Support  

Definition Arch A curved structure that converts the downward compression force of its own weight, and of any weight pressing down on top of it, into a force along its curve. This results in an outward and downward force along the sides and base of the arch. 
Buttress A side support that counteracts an outward pushing force, the way bookends keep books on a shelf from sliding sideways. Buttresses are often used to support the sides of arches and tall cathedral walls, where they counteract the outward thrust.


1. Have two kids form an arch by placing their palms together and leaning toward each other, sliding their feet as far back as they can. Caution them not to lose their balance. Ask: Where do you feel a push or a pull? (pushing on their hands) 
2. Have a third kid gently pull down on the top of the arch to test its strength. Ask: How difficult is it to break the arch? (not difficult)  
Illustration: kids forming an arch. 3. Have the group brainstorm ways for two more kids to join the arch and make it stronger, but without breaking up the space beneath the arch. Guide them to the idea of adding buttresses by asking the arch-makers how stable their legs feel. Then repeat Step 2 and compare the results. (The buttresses exert an inward force on the sides of the arch that balances the outward force created by the load pressing down on the top of the arch.)

Video Connection "Roman Bridges" from Bridges (see the Program Description)

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