Bridge Unit Study - Lesson 2: Draw Bridge

My son built a draw bridge model.

Do you think a draw bridge is a beam bridge, arch bridge or suspension bridge?

Well drawbridges are a type of movable beam bridge. They were used extensively during the middle ages to prevent entry into fortifications. Before cannons were invented, residents could simply pull up the bridge, and it was very difficult for invaders to enter.

Here is a medieval draw bridge turned permanent bridge from William the Conquerer's castle in Normandie, France.

Draw bridges are also used today, but they are not quite so common. In my town, there is a drawbridge that raises to allow boats with tall masts to pass underneath and enter the channel. Most of the time it stays down, but during the summer months it often goes up and can cause some minor traffic back-ups.

After reading about draw bridges in the book Bridges: Amazing Structures to Design, Build & Test (Kaleidoscope Kids), my son followed the directions to create his own using an empty cereal box, string, and a straw.

 It's a pretty simple design. Just punch four holes in the box and lace the string through. Put the string through the straw and cut the string to the desired length for opening and closing.

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