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As I mentioned a few posts ago, Leo and I have started receiving Science Magazine, and each week, in addition to paging through the issue looking at interesting pictures, I try to find something that we can actually do together that is related to one of the papers (even if the relationship is tenuous).

This week Leo became interested in this paper:


Okay, so I’ll admit that, not only didn’t we actually read the paper, but I can only vaguely understand the abstract! However, what attracted our attention was this cool figure:


Leo has always liked complex molecular structures; since he was three, or so, he’s had a molecular construction kit, so these looked like fun!

What seemed most interesting about these molecules is that some of the structures appear to be rigid, while others appear to be floppy. Molecule 2.2, for example, seems to be floppy, whereas the 4.x structures (and 2.1) appear to be rigid.

Whether or not this ends up being really true (recall that we didn’t actually read the paper — see “tenuous” above! :-)), it’s a great excuse to explore rigid v. floppy structures, which we did!

It turns out to be surprising, and surprisingly simple to build structures that can be easily transformed from a rigid to a floppy structure, and back. This is a little hard to explain without seeing it, so here’s a video showing off these interesting structures, built out of Knex . All you need to do to transform it from the rigid form:


To the floppy form:


You’ll have to watch the video to see how the conversion works.

These are actually amazingly fun to manipulate, and it’s quite surprising when you discover that just by changing one link you completely change the flexibility of the structure!

It appears that if you add even one additional link to this particular structure, you convert it into one that only has a floppy conformation, although I can’t prove that. Here’s Leo manipulating a slightly larger structure: