Bridges make it possible to cross over water, roads and railways. Children can better understand types of bridges and how they are constructed by learning what they are used for, the materials used to make them and which bridge shapes are the strongest. Children can also understand the structure of bridges by making their own simple models and playing online bridge-building games.
Arch bridges date back to ancient times, when they were constructed from stones or bricks. Bridges built during the Middle Ages usually rested on basic stone arches with heavy support structures. Children can learn about the structure and design of arch bridges by making their own using a piece of cardboard about 1 inche by 11 inches. The cardboard is positioned on a table to resemble an arch and a stack of books placed at each end. This helps children understand how arch bridges withstand compression and distribute weight.
A beam bridge is basically a horizontal beam supported by piers that takes the weight of the beam and traffic passing over it. Concrete is often used in making beam bridges because it isn’t expensive and withstands compression, which happens when weight pushes down on the beam, pushing the beam’s top edge together. Children can make a beam bridge using a flat eraser or a small sponge and slicing a shallow V-shaped indentation at the top and bottom of the sponge or eraser. Place stacks of books at each end for support, then press down on the center of the bridge and see what happens. The Lake Ponchartrain Causeway is the world’s longest beam bridge. It is 24 miles long and the beams are joined together in what is known as a continuous span.
Suspension bridges are lightweight but strong and can 2,000-7,000 feet long. They are held together by cables extending the full length of the bridge. Early suspension bridges were made with twisted grass. Children can better understand the concept of suspension bridges using a simple experiment with a newspaper and a book. Folding the newspaper twice lengthwise and folding it into a tube should make it strong enough to hold the book. The Tacoma Narrows Bridge near Washington is a famous suspension bridge.
Older children can build a virtual bridge, test how strong its structure is and even knock it down and start again using online learning projects. Students can view one another’s designs and share what they have learned with their peers. Younger children can also try their hand at building a bridge using an online game on the PBS website.