Build a Paper Bridge
Do you think you can you build a bridge out of paper? Try it out and then see if you can make it stronger with these tips.
1. Make two supports for your bridge by stacking books into two stacks that are the same height. They should rise several inches off of the table or floor and be about 6″ apart from each other.
2. Lay a plain sheet of paper across the stacks of books. There should be an even amount of paper over each stack.
3. Place a penny, paperclip, pencil, or other light object in the center of the paper. Does your bridge support the weight? If so, add more until it collapses. If not, try to make it stronger.
4. A sheet of paper is very thin and without anything to support it in the middle, it will collapse easily. Can you think of any ways to make your bridge stronger? You could move the supports (stacks of books) closer together, or try folding the paper in different ways to make it stronger. Here are some tips:
Arch Bridge Activity
Arches are one of the oldest types of bridge. Try this activity to learn more about them.
1. Take a thin piece of cardboard that is longer than it is wide and bend it into an arch shape.
2. Set it on the table, making sure it still has at least a slight arch.
3. Press on the top of the arch. What happens?
4. Now arch the cardboard again and place it between two stacks of books.
5. Press on the top of the arch again and notice what happens this time.
The stacks of books act as abutments or supports to keep the ends of the arch from collapsing from the weight you put on it. Without them, there was nothing to support the weight of your hand and keep the ends of the arch from pushing outward and falling down.
For another simple project, use sugar cubes to build an arch. Taper the sides of the cubes with an old nail file (or scrape them with a butter knife) so that they fit snugly against each other to form an arch. Be sure to use an odd number of cubes, so that there’s only one cube in the middle. If you used two cubes in the middle, the frictional force between those blocks would be overcome by the load force on the arch, causing it to buckle.
Suspension Bridge Activity
Make a model of a suspension bridge and learn why anchors for the cables are so important!
1. Pick two hardcover books that are the same height and about the same thickness. Stand them up on end, facing each other, several inches apart.
2. Tie a piece of string around the top of one of the books.
3. Letting the string hang loosely between the books, tie the other end to the top of the other book.
4. Now press on the center of the string suspended between the two books. What happens? (The books will fall over.)
5. Untie the string and set the books back upright, about 10″ apart.
6. Place a stack of books on top of one end of the string. Pull the string tight and hang it over the tops of the standing books, with some string hanging loosely between them.
7. Put the other end of the string securely under another stack of books, a few inches away from the standing book.
8. Now try pressing again on the string in the center. What happens this time?
Types of Bridges
Arch bridges were one of the first types of bridge. The Romans used arches in their bridges and aqueducts as well as in their triumphal arches and other great architecture. See a picture of Constantine’s Arch here. Arches are designed with an odd number of stones, with the top, middle one being the keystone on which the bridge’s weight rests. These stones have slanted sides so that they fit tight against each other. The downward force of the bridge’s weight spreads out to the stones on either side of the keystone. Arches used in bridges also have supports at each end of the arch called abutments. These supports keep the stones in the arch in place even when weight is put on top of them.
Suspension bridges use a combination of strong cables and tall, solid towers to achieve a balance of forces. The roadway of a suspension bridge is suspended from the tower and held up by incredibly strong cables. Most suspension bridges today use steel wires and cables, because steel is very strong. A steel wire only 1/10th of an inch thick can hold more than 1,000 pounds of weight without breaking! To make the cables used in bridges, thousands of strong steel wires are twisted and bound together to make them even stronger. The Brooklyn Bridge in New York is one of the most famous bridges, now not so much for its size as its beauty. Built in 1883, it was the first great suspension bridge and a feat of engineering. At the time, it was the longest suspension bridge ever built (though several larger ones have been built since). The stone and steel that Brooklyn Bridge was built with combined to make it both solid and graceful. See a picture of it here.
Learn more about another famous suspension bridge, the Golden Gate Bridge, located in California.
To learn more about different types of bridges, check out this site.
Architects & Engineers
In general, bridges are designed by two different types of people. Architects are responsible for how a bridge looks while engineers are responsible for how the bridge works and is supported. There are a lot of things to consider when designing a bridge. Physics is a field of science that studies matter, energy, forces, and more. People who design bridges need to understand some important physics concepts in order to make a bridge that will be strong, stable, and secure over time.
Some physics concepts that are considered when bridges are designed are compression and tension. These are both forces that happen every day on bridges and can act differently on different materials. Compression presses down or shortens an object. Try putting a marshmallow on the counter and pressing down on it with the palm of your hand. The force from your hand compressed the marshmallow! Tension stretches out or lengthens an object. When you stretch a rubber band, a toy slinky, or pull two ends of a string tight, that’s tension.
In addition to being able to support lots of weight, a bridge must also be able to stand up to lots of different types of weather, like high winds and sometimes even earthquakes!
Sometimes architects and engineers design special bridges that combine two or more types of bridges together to make the best possible bridge for a location. They have to be very careful to make sure the bridge design will still be stable and strong enough. Bridge designs must be tested quite well before a bridge is ever built.
Printable Worksheet & PDF
Use this worksheet to help kids review types of bridges. It also includes two simple activities.