Summary
Introduction
Have you ever seen a geodesic dome? Geodesic domes are approximately sphere-like structures made up of interconnected triangles. A famous geodesic dome is Spaceship Earth at EPCOT in Walt Disney World, Florida, but geodesic domes are also commonly found as climbing domes at playgrounds. In this science activity, you will get to build a simple geodesic dome using gumdrops and toothpicks. Once it is built, you may be surprised by how strong it is! Get ready to do some tasty engineering!Materials
- Gumdrops (11). Alternatively, jelly beans or other semi-firm, chewy candies may be used.
- Toothpicks (25)
Instructions
- Attach five toothpicks together using the gumdrops to form a flat pentagon (five-pointed) shape. You should have a gumdrop at each point and a toothpick along each edge.
- Poke two more toothpicks into each gumdrop, arranging the new toothpicks so that they are pointing up.
- Take five new gumdrops and attach them to the top of the new toothpicks, putting two toothpicks into each gumdrop, to form triangles. (The pentagon should form the base of the triangle, and the new gumdrops should form the top point.) You should end up with five triangles this way.
Why do you think the geodesic dome is made out of triangle shapes?
- Attach a toothpick between the top points of the triangles you just made, connecting the triangles together. This uses five toothpicks, and will create another pentagon shape, this time at the top of the dome.
- Take five more toothpicks and poke one into each of the five gumdrops that make up the top pentagon. Arrange the new toothpicks so that they are pointing up. Then poke all five toothpicks into a gumdrop in the middle, and at the top, of the dome. Your geodesic dome is complete!
- Gently press down on the top of your geodesic dome. If it does not break, try carefully pressing down on it a little more.
How strong is your dome? Are you surprised by how well it can support your hand as it presses down on the dome?
What Happened?
A geodesic dome's design allows it to support a surprisingly large amount of mass compared to the structure's own mass and size. Because of this, you should have seen that the geodesic dome could easily support your hand as it pressed down on the top of the dome, even when you increased the pressure a little. You would need to apply a lot of pressure before the dome would fail. The struts (the toothpicks in the model you made) of a geodesic dome are arranged to make triangles. This rigid network of triangles distributes any forces applied to the top of the dome to the rest of the structure.
You may have also noticed that since the geodesic dome approximates a sphere, it has a relatively low surface-area-to-volume ratio (meaning, its volume is relatively large compared to its surface area), and it can enclose a large amount of volume compared to the mass of the structure itself. In other words, it makes for a roomy space inside with very little building materials.
Digging Deeper
A geodesic dome is a structure made of struts that are connected to each other to approximate the shape of a sphere (or part of a sphere). Richard Buckminster "Bucky" Fuller, an American inventor, architect, author, engineering, designer, and futurist, patented the geodesic dome in the 1940s and made it popular. Spaceship Earth at EPCOT in Walt Disney World is one famous example of a geodesic dome that is a complete sphere shape, but many other geodesic domes are only part of a sphere, such as climbing domes at playgrounds and some greenhouses.
Typically, the struts of a geodesic dome are joined together in triangles, with the points of the triangles being approximately on the sphere's surface. In this activity, a geodesic dome design is used where all of the struts are the same length, which is known as a V1 design. Other designs have struts of different lengths, and this allows more triangles to cover over the same area of the dome. Typically, the more differences in strut lengths, the more triangles there are, and the rounder the shape of the dome is. In addition to adding more weight-bearing capacity, the added capacity also increases the stability of the dome. For more information on different dome designs, see the Desert Domes website.
Ask an Expert
For Further Exploration
- Try doing this activity again but this time use long, wooden skewers instead of toothpicks. Is one geodesic dome stronger than the other? If so, which one is stronger and why do you think this might be?
- Try adding some mass on the top of your dome, such as heavy envelopes. How much mass can your dome support before failing? Are you surprised by how strong it is? When the dome fails, how does it fail? Can you figure out a way to make it even stronger?
- The geodesic dome you made in this activity uses a relatively simple design. You could try making a more complicated one, or a larger one, by looking at the resources in the "More to explore" section, on the next page. Can you build a much larger geodesic dome? What about one that uses multiple different strut lengths? How does a more complicated design compare to the one used in this activity?
Related Resources
Project Ideas
Links
- Blog Post: Family Math: Making a Geodesic Dome from Straws
- Blog Post: Beyond Winter White: A Burst of Color for Winter Engineering
- Blog Post: Egghead Science: The Strong and the Weak of It
