Building bridges involves precise calculations and certain geometric forms to make structures able to hold thousands of pounds without collapsing. Though you can explain this to your children, a practical demonstration will illustrate the point more effectively. Challenge your students or children to create a sturdy bridge using only paper.

• Building bridges involves precise calculations and certain geometric forms to make structures able to hold thousands of pounds without collapsing.
• Challenge your students or children to create a sturdy bridge using only paper.

Stack two sets of two hardcover books on top of each other. The stacks should be as close to the same size as possible. Place them so they're about 22.5 cm (9 inches) apart.

Turn your paper horizontally. Grip the upper right and left corners and fold the paper down 1.3 cm (1/2 inch). Fold the paper back 1.3 cm (1/2 inch), then forward again. Continue this way until you have a long paper accordion.

Stretch your accordion out gently. Place it horizontally across the two stacks of books. 2.5 cm (1 inch) of each end of the paper bridge should sit on each stack of books.

Place coins on the bridge. The bridge should hold the coins easily. The triangles created by folding the paper into an accordion make the paper rigid and able to hold more weight.

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Try placing an unfolded piece of paper across the books. It won't hold the coins; discuss why. Try ripping the paper into strips and weaving them into a stronger structure. Talk about which is stronger, the accordion bridge or the woven one.