Saturday, December 20, 2014

Winter break activity: Build a geodesic dome from plastic straws

Materials:
  • Straws ( got mine at a grocery store)
  • Mini brads
  • Paper punch (about 1/16" diameter)
  • Ruler
  • Scissors

Topic:
  • How to calculate a triangle if you know the angle and one of the length? If your students are high school, you can use trigonometry. 
  • Triangle is the strongest and more economical shape. Talk about angles in a triangle
  • Constraints. My straw length is about 7". The longest straw should be no longer than the material.

Activity:
If you have a middle schooler, you can relate this with trigonometry. For this activity, I have a "cheat sheet" from youtube. https://www.youtube.com/watch?v=Z1ZLoQc0ay0
 If the outside of pentagon = N, the R for the pentagon is Nx0.8696 or Nx1.0224 for hexagon.

If the longest straw is 5.5" = N, the r for pentagon is a 5.5"x0.8686 = 4.78"

Cut straws to 2 sizes:
Green: 5.5" ( about 35 pieces)
Blue: 4.75" ( about 30 pieces )
Hole punch both ends and connects it with brads.


Starts by making a big circle using 10 green straws

Connect them with blue straws. Add vertical blue straws on the middle of the blue pentagon. Connect the top of the blue straws with green straws to make this shape


 Then connect horizontal lines using green straws. Then add the vertical blue straws as pictured.


Connect the last brad.
You made a model from straw. Want to be more creative? Instead of straw, try using rolled newspaper... See how big it can get. 

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