If you've looked at bridges, you've probably noticed that they can be made of different materials. Some are wood, some are steel, some are concrete, and some are even made from stone. If you want to build a simple, sturdy miniature bridge using something you have lying around the house, what's the best material to use? Try this activity to find out!
What materials should engineers use to build a bridge? The decision depends on many factors. Where is the bridge located? How long will it be? What will go across the bridge (people, cars or trains) and how heavy will the total load be?
You probably know that different materials have different properties. You might think about the properties of various materials using your senses—for example, how something looks or feels; is it light or dark; smooth or rough? There are also properties that describe how strong a material is. These are called mechanical properties. For example, how hard is a material to stretch, squish or bend? When you bend the material and then let go does it stay bent or go back to its original shape? If you bend the material so far that it breaks, does it happen very slowly or snap suddenly and unexpectedly?
You might have experienced these different properties in everyday life without realizing it. When you bend a paper clip it stays bent; it's also hard to make the paper clip "snap" suddenly. Compare that with a wooden ruler. If you were to flex the ruler a little bit, it will bounce back to its original shape; but if you were to bend it too far, it would snap. Some materials, such as rubber, are easy to stretch or squish. Other materials, such as rocks, are much stiffer. You can probably imagine what properties would be important for a bridge. If a heavy truck drives over a bridge, do you want the bridge to sag a lot? Do you want the bridge to return to its original shape after the truck leaves? In this activity you'll explore these properties with various household materials and decide which one would make the best bridge.
You probably found that paper made the strongest bridge. You might have been surprised to find out that the aluminum foil bridge wasn't the strongest. After all, isn't metal stronger than paper? An object's strength depends not just on its material but also on its dimensions. A thick piece of paper can be harder to bend than a thin piece of metal—and aluminum foil is very thin.
If you watched closely, you also might have noticed that the bridges did not all collapse in the same way. The paper bridge might have started to sag gradually, eventually falling and dropping the coins. The aluminum foil and wax paper bridges might have failed much more suddenly—mostly holding their original shapes and then rapidly collapsing. How would you take this information into account when building a bridge of your own?
This experiment was selected for Science at Home because it teaches NGSS Disciplinary Core Ideas, which have broad importance within or across multiple science or engineering disciplines.
Learn more about how this experiment is based in NGSS Disciplinary Core Ideas.