Math Forum - Project of the Month


September 1998 Project of the Month

Building a Mobile

September's Winner

This summer when I was camping in a state park in Illinois, I noticed something hanging from the front of one of the big campers. It looked like this:

Not very interesting. But then the next day I walked by and it looked like this!

Now that was interesting. The geometer in me wanted to figure out what it really was, so I looked at it a little bit longer. As I walked around the front of the camper, I got a view that looked like this:

I stared at it a little bit longer, and figured out a little bit more about it. It was made with only 90 degree angles, and all of the pieces were equal in length. Wow! This thing was really cool! I saw three more of them that trip, hanging on campers. I was determined, when I got home, to build one! And so I did.

Your task: Figure out how to build a three dimensional object that, when looked at from different angles, looks like the two dimensional pictures above. It must be made of congruent "edges", using only 90 degree angles to join the pieces. You must explain how to build one, how you figured it out, and point out some other interesting "2D" views. (I found three or four more after I built it and played around with it a bit.)

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