Key Concepts
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Physics -
Engineering -
Materials -
Force -
Strength
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Introduction
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!
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Background
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.
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- An adult helper
- Two thick books or small boxes
- Paper
- Wax paper
- Aluminum foil
- Scissors
- Tape
- At least 25 pennies (If you don’t have enough pennies, you can use fewer heavier coins, such as quarters, or other small objects to use as weights, such a rocks, bolts, etc.)
- Ruler or measuring tape (optional)
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Preparation
- Cut your wax paper and aluminum foil into sheets the same size as the piece of paper
- Space your books roughly 10 inches apart
- Fold each of your three sheets of material into a bridge shape. First, fold them in half lengthwise at least twice. Then fold up the edges to make walls. Tape the edges to prevent the bridges from unfolding. Make sure your bridge is wide enough to hold pennies sitting flat. Which material do you think will make the sturdiest bridge
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Procedure
- Rest one of your bridges across the gap between the books.
- Place a penny in the middle of the bridge.
- Keep adding more pennies to the bridge one at a time. Space the pennies evenly along the length of the bridge. This simulates how real people or cars travel across a bridge; they aren't all piled on top of one another.
- Watch the bridge carefully as you keep adding pennies. Does the bridge hold its shape or start to sag?
- If you fill the entire surface of the bridge with pennies, start a second layer. Keep adding pennies until the bridge collapses. How many pennies did it take to make the bridge collapse?
- Repeat the procedure for each of your other bridge materials. Which bridge held the most pennies? Did the bridges all collapse in the same way (i.e. did some collapse suddenly and did some collapse gradually)?
- Extra: Build a fresh bridge from each type of material. Add some pennies to each bridge—but not enough to make it collapse—and then remove the pennies. Does the bridge completely return to its original shape—or is it permanently deformed?
- Extra: The shape of an object also affects its strength. Try changing the geometry of your bridges, adjusting, for example, the width of the bottom or the height of the walls or the number of times you fold each sheet in half. How does changing the shape affect how many pennies the bridge can hold?
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Observations and Results
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?
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Safety First & Adult Supervision
- Follow the experiment’s instructions carefully.
- A responsible adult should assist with each experiment.
- While science experiments at home are exciting ways to learn about science hands-on, please note that some may require participants to take extra safety precautions and/or make a mess.
- Adults should handle or assist with potentially harmful materials or sharp objects.
- Adult should review each experiment and determine what the appropriate age is for the student’s participation in each activity before conducting any experiment.
Next Generation Science Standard (NGSS) Supported - Disciplinary Core Ideas
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.
Engineering Design (ETS)1: Engineering Design
Grades K-2
- K-2-ETS1-1. A situation that people want to change or create can be approached as a problem to be solved though engineering. Such problems may have many acceptable solutions.
- K-2-ETS1-1. Asking questions, making observations, and gathering information are helpful in thinking about problems
- K-2-ETS1-1. Before beginning to design a solution, it is important to clearly understand the problem.
Grades 3-5
- 3-5-ETS1-1. Possible solutions to a problem are limited by available materials and resources (constraints). The success of a designed solution is determined by considering the desired features of a solution (criteria). Different proposals for solution can be compared on the basis of how well each one meets the specified criteria for success or how well each takes the constraints into account.
Grades 6-8
- MS-ETS1-1. The more precisely a design task’s criteria and constraints can be defined, the more likely it is that the designed solution will be successful. Specification of constraints includes consideration of scientific principles and other relevant knowledge that is likely to limit possible solutions.
Grades 9-12
- HS-ETS1-1. Criteria and constraints also include satisfying any requirements set by society, such as taking issues of risk mitigation into account, and they should be qualified to the extent possible and stated in such a sway that one can tell if a given design meets them.
Grades K-2
- K-2-ETS1-2. Designs can be conveyed through sketches, drawings, or physical models. These representations are useful in communicating ideas for a problem’s solutions to other people.
Grades 3-5
- 3-5-ETS1-2. Research on a problem should be carried out before beginning to design a solution. Testing a solution involves investigating how well it performs under a range of likely conditions.
- 3-5-ETS1-3. Tests are often designed to identify failure points or difficulties, which suggest the elements of the design that need to be improved.
- 3-5-ETS1-2. At whatever stage, communicating with peers about proposed solutions is an important part of the design process, and shared ideas can lead to improved designs.
Grades 6-8
- MS-ETS1-4. A solution needs to be tested, and then modified o the basis of the test results, in order to improve it.
- MS-ETS1-2. There are systematic processes for evaluating solutions with respect to how well they meet criteria and address constraints of a problem.
- MS-ETS1-3. Sometimes parts of different solutions can be combined to create a solution that is better than any of its predecessors.
- MS-ETS1-2. Models of all kinds are important for testing solutions.
Grades 9-12
- HS-ETS1-3. When evaluating solutions, it is important to take into account a range of constraints including cost, safety, reliability, and aesthetics and to consider social, cultural, and environmental impacts.
- HS-ETS1-4. Both physical models and computers can be used in various ways to aid in the engineering design process. Computers are useful for a variety of purposes, such as running simulations to test different ways of solving a problem or to see which one is most efficient or economical; and in making a persuasive presentation to a client about how a given design will meet his or her needs.
Grades K-2
- K-2-ETS1-3. Because there is always more than one possible solution to a problem, it is useful to compare and test designs.
Grades 3-5
- 3-5-ETS1-3. Different solutions need to be tested in order to determine which of them best solves the problem, given the criteria and the constraints.
Grades 6-8
- MS-ETS1-3. Although one design may not perform the best across all tests, identifying the characteristics of the design that performed the best in each test can provide useful information for the redesign process – that is, some of the characteristics may be incorporated into the new design.
- MS-ETS1-4. The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.
Grades 9-12
- HS-ETS1-2. Criteria may need to be broken down into simpler ones that can be approached systematically, and decisions about the priority of certain criteria over others may be needed.
Earth & Space Science (ESS)3: Earth and Human Activity
Grades K-2
- K-ESS3-3. Things that people do to live comfortably can affect the world around them. But they can make choices that reduce their impacts on the land, water, air, and other living things.
Grades 3-5
- 5-ESS3-1. Human activities in agriculture, industry, and everyday life have had major effects on the land, vegetation, streams, ocean, air, and even outer space. But individuals and communities are doing things to help protect Earth’s resources and environments.
Grades 6-8
- MS-ESS3-3. Human activities have significantly altered the biosphere, sometimes damaging or destroying natural habitats and causing the extinction of other species. But changes to Earth’s environments can have different impacts for different living things.
- MS-ESS3-4. Typically, as human populations and per capita consumption of natural resources increase, so do the negative impacts on Earth unless the activities and technologies involved are engineered otherwise.
Grades 9-12
- HS-ESS3-3. The sustainability of human societies and the biodiversity that supports them requires responsible management of natural resources.
- HS-ESS3-4. Scientists and engineers can make major contributions by developing technologies that produce less pollution and waste and that preclude ecosystem degradation.
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