Activity 2: Grades 5-8 Geodesic Domes

Questions
1. Did you need to use the ruler to measure the length of each tube?
(No. The ruler was only needed to measure the lengths of one long and one short tube. These two tubes could then be used as templates from which to obtain the measures for the remaining tubes.)
2. What was the basic geometric shape of this frame? (Triangle)
3. What other shapes did you observe?
(Pentagons, rhombus, hexagons)
4. What was the maximum number of tubes that came together at any one joint?
(Six)

EXTENSIONS

How would increasing the number of component triangles affect the shape of the dome?
(The more triangles that are used, the closer the shape resembles a true sphere.)

Small Scale Model
The plans for building a geodesic dome are scalable. In fact, you can use the steps above to build versions using either plastic straws or wooden toothpicks. Suppose you needed to scale the measurements to straws that are 20 cm long. If you opted to use the uncut length of the straw as the longer rod, what length would the shorter one need to be cut to? Explain.
(Using the ratio 26:24, we uncover a proportionality constant of about 0.92. When you multiply the 20 cm length by the constant, you arrive at a length of about 18.5 cm for the shorter support.)