The Internet as the great leveler. Any idea that I may have, has already been done. On the other hand, it's a great time saver. Whole projects one does not need to do. Explanations already explained. Videos on YouTube. When I was a wee lad, I visited the Franklin Museum in Philadelphia, PA. There was an exhibit I would describe as "a bicycle wheel with rubber bands where the spokes go." An infrared lamp shone on part of the wheel, and the wheel turned. Already covered here, with BillW's statement to search "rubber band heat engine." A word about that. The description below the exhibit said something like "Rubber has an interesting property. See?" Well, I didn't know what the heck they were trying to show me, maybe something about the rubber bands changing length when heated. In fact, if you happen to mistakenly conclude that they stretch when heated (I did), that wheel would still turn. So, all I ever got out of that was, "there's something interesting about rubber". The exhibit had a push button so you could turn the light on or off. Hence, interactive. I remember one other exhibit involving a copper disc you could turn, and a large electromagnet you could activate, wherein the disc would become difficult to turn. From that, we get eddy currents, homopolar generators, regenerative braking...all from simple exhibit. Great stuff. I returned to that place some years later only to find the "Exploratorium" [1] aspects had all been removed and everything returned to boring-museum status. What attracted me to this discussion, though, was the rubber-band thing. Somewhere else I had read that if you stretch a rubber band and feel it, it gets warm. I then worked out, on my own, that if I let it return to room temperature, and then relax it, it would take up that same heat and get cold. I think this is a fundamental thing most non-technical people don't understand. They get that things can be made cold, but they don't understand the "taking heat from surroundings" thing. So, the rubber band is an excellent demonstration of this, and then could be extended (heh) to the trick of absorbing heat in one place, transporting it somewhere else, and releasing it (the Refrigeration trick). I kind of doubt it would be an efficient method, but for demonstration purposes it would be quite an interesting thing. And you explain the principle of refrigeration without cans of Freon--you just hand out some rubber bands. [1] Exploratorium, an extremely interactive museum in San Francisco, CA. On Sat, Sep 8, 2012 at 4:16 AM, RussellMc wrote: > > One could conceivably make a "refrigerator" using a rubber band that > is operated as a "driven belt", and stretched and contracted along > different parts of it's path. Could make for an impressive > demonstration. > > Russell > > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .