Copyright © 2010,2011 Joseph Mack
v20110327, released under GPL-v3.
Abstract
A video of a lesson on the Platonic solids, given to 3rd graders, about May 2009.
Material/images from this webpage may be used, as long as credit is given to the author, and the url of this webpage is included as a reference.
Table of Contents
For about the last 10yrs, the science teacher at my son's school, Lyn Streck, has let me teach a science class to her 3rd graders. There's four classes in the grade and I give all lessons in one day.
The students cut out and assemble the NOAA Surface of the Earth Icosahedron Globe (http://www.ngdc.noaa.gov/mgg/fliers/04mgg02.html).
The maps are low cost ($0.50 ea), and printed on cardstock making a nice finished globe (I have them on my desk at work and home).
 | Note |
|---|---|
| You can download a pdf of the maps and print them yourself, but you'll need a large format printer, lots of ink and your own cardstock. It's cheaper and more convenient to buy them from NOAA. | |
A new version (2008) of the map has press out tabs, which I haven't used (I've been using the ones which need cutting out). With the older version of the maps each student needs
- a map
- scissors
- a table with a square edge
- double sided sticky tape
The class is 40mins and can only just be done in the time. The instructions are relatively complicated, and the cutting takes time. Adults need to be on hand to help the kids. Despite my best attempts to give clear directions, some student will wind up cutting off the flanges (tabs) and others turn their scissors around and cut from the inside out, gouging the map (see the video for directions). Following a large mistake, there isn't time to start again, and an adult will have to handle patching the globe. You want every kid to walk out with a functional globe. The last part of the taping (closing the globe) is tricky and usually has to be done by an adult.
Besides building the icosahedral globe, other material covered in the class is
- the Platonic Solids (http://en.wikipedia.org/wiki/Platonic_solid).
- viruses (since some have icosahedral capsids)
trusses (since the icosahedron is made of triangles).
The tetrahedron, octahedron and icosahedron have triangular faces and are rigid, when you press on them. The cube (hexahedron, with square faces) and the dodecahedron (pentagonal faces) are floppy. Early in the class I ask the kids if they can figure out why some of the Platonic solids are rigid and some floppy. I encourage them try out the models themselves during the class and, if they have an answer, to let me know quietly (so not to let the cat out of the bag to the rest of the class). About half the time, some student figures it out (or already knows, I can't tell which).
The trusses and the earlier versions of the Platonic solids were made from toothpicks and hot glue. These took several sunday afternoons. (Buy your toothpicks all at once; toothpicks bought a year later, at the same store, in the same type of box, were a different length.)
One problem was convincing the students that some of the solids were intrinsically rigid and some were instrinsically floppy. With the glue providing some rigidity at the vertices, the usual answer was that the rigid solids had more glue. While the kids saw the glue providing rigidity, they wouldn't look further to structural elements as the answer. My first approach was to tell them that it wasn't the glue. Quite reasonably kids don't trust adults, who are in charge, make arbitary rules and can make a kid's answer wrong any time they want. It took several years before seeing the futility of this approach. I needed models with demonstrably floppy vertices. This led to the models with rubber tubing vertices. Since I've added these models, students have stopped proposing glue as the agent of rigidity.
- using the colours on the globe as a guide, locate and discuss high (mountains) and low places (oceanic trenches) on earth. This reinforces mountain building and plate tectonics, which they've had in class.
By the wonders of digital editing, on combining videos from four different classes, the students give correct answers to all the questions.
Errata. A volunteer at the school kindly edited the videos of the four classes for me in their spare time and I wasn't able to get the following fixed.
- a screen shows bacteria causing plague; they cause plaque.
- The coloured scale showing elevation is a legend, not a ledger.
With only a few minutes at the end for the kids to explore trusses and their globe, an extra 5 mins, if you can find it, can make or break the class. In 2011 I made these changes to the class
At the suggestion of the teacher's assistant, I precut the cardboard sheets (paper cutter/guillotine; a sharp one helps) removing extraneous cardboard and separating the legend and base from the map. This eliminated the first cutting step for the kids.
Several stages of checking are required (cut out, fold along all the black lines) so that the final map folds to a globe. Previously when the first student was ready, I stopped the class and demonstrated the next stage to everyone. However the kids are busy with their efforts and don't have attention for much else and they can't listen.
This is particularly so when the first student reaches the last stage - applying the double sided sticky tape - at which time some students are still back two stages - cutting out. I would have to repeat the taping instructions individually to confused students a few minutes later as they reached the taping stage. Instead, in 2011, as student(s) were ready, I showed them individually how to apply the tape. The tape and the to-be-taped globe were right infront of the students, who could see exactly how I did it. Initially only the first student was ready, then a group of four more students were ready... Using this approach, few students had to return for clarification, reducing the time on this step.
With these changes, after assembling their globes, the students had time to gather around the rubber and drinking straw platonic solids, to figure out why some were rigid. Talking and poking, they collectively figured it out and when I asked for the answer, they all knew it was triangles. Over the previous 10yrs of this class, only a couple of times has a student figured out the answer. I'd concluded that the problem was too difficult for them, when all that was missing was a few minutes poking the platonic solids.
I then had about 5 extra minutes at the end of the class to talk about the trusses and explore oceanic trenches and the location of mountain ranges on their globe. You still have about 1/4 of the class with uncompleted globes, which are handled by the adults, while you're talking.
The 240 piece icosahedral jigsaw globe of the earth, seen in the video, comes in 3 versions, with 240, 560 and 960 pieces (search in the internet with "3-D puzzle of the world" or "icosahedral puzzle globe of the earth"). Presumably they're all icosahedrons. An icosahedral globe will have multiples of 20 pieces (4-fold as for my 80 faced toothpick icosahedron as seen in the video, or 3-fold as seen for the 60 subunit capsids of icosahedral viruses).
I have no vested interest in the use of these maps. I like maps and bought a few of these to decorate home and work, several years before I met Lyn. I think everyone should get a chance to build one of these.