one of the cooler things i’ve learned in a bit...

i spent a large chunk of my afternoon at the main memphis library today to get some programming/research/writing the talk i give next week done. instead of going straight home though, i went to raid the math section and see if they had anything interesting or new since i last checked it out in may. amongst other things i found a book called "1089 and all that" which was a quick easy (150ish pages in about an hour) read, with lots of cute facts, most of which i knew already.

but one chapter amazed me. "the indian rope trick" is a magic trick where the magician throws a rope into the air and somehow, defying gravity, it stays in the air, and then a small child climbs it. if you google it, there's all kinds of speculation about how it's a hoax and how it might be pulled off.

however, inspired by this, the author looked at a different idea:
instead of a rope, think of a pendulum hanging from the ceiling and attach another pendulum to the bottom of that, etc., etc.... so it's like a giant stick that can bend in a bunch of places

now instead of attaching to the ceiling, attach the pendulum to the floor. clearly, if you let it be, it's going to collapse.

HOWEVER, the author proved that there's a "natural frequency" that if you move the base of your stick of pendulums UP and DOWN the right amount at the right speed, the stick will stay up... you can even push it up to like 40 degrees off center and it will correct itself.

the author's website has an illustration program. click on the upside down pendulum theorem at http://home.jesus.ox.ac.uk/~dacheson/1089comp.html

how cool is that?