|I didn't realize how cool
this project would be until I had actually built and tested it. Click
on the images to see MPEG movies.
|I took an old bike, scavenged
a motor from another project to power it, and ran chain around the rear rim.
I find it so mesmerizing it's almost dangerous to turn it on; I might
spend an hour watching the various shapes travel through the moving chain.
|Though this phenomenon is
probably best described by pages upon pages of differential equations,
my best simple explainantion is this: think of a length of chain hanging
and not moving. If you hit it, something like a wave will propagate
away from the point at which you struck. Now fix yourself to a point
on the chain, start it moving, and hit it again. From your perspective
the wave propagates as before, at equal speed in both directions, yet from
the perspective of a fixed external observer, the wave's speed and the chain's
speed add in one direction along the chain, and subtract in the other. So
for chain speeds close to the wave speed, waves will appear to sit at the
same relative position or to move slowly along.
This "slowing down" effect is one of the reasons why I am so fascinated. In the moving chain, shapes that would otherwise change too fast to enjoy can be clearly seen.
movie clips and additional pictures