Attractors
This morning, I came across Attractors, yet another web page employing Flash as an experimental toy. Tiny dots (I call them BBs) spill out of the upper left hand corner of the display at slightly different trajectories and fall in parabolic arcs, as though under the effect of gravity. As they fall, they trace a shadowy comet tail, the better to let you watch their motion. When the BBs fall to the bottom of the screen, they are immediately injected back into play from the starting point. You can affect their motion through the placement of four tools: two large, rotatable platforms, off of which you can carom the BBs, and two spots (I call them black holes) with a powerful attractive force.
After tinkering briefly with attempts to create attractive patterns, I settled down to a somewhat more concrete goal: creating a stable and dynamic flow of BBs. This is harder than it might seem at first. A stable, static pattern is easy: simply angle the platforms together to form a cup, move the black holes far enough away to make their effect negligible, and let the BBs collect in the cup. This is neither interesting to achieve nor interesting to look at.
To keep things moving, you need to get the BBs orbiting one or both of the black holes in some fashion. A single black hole is insufficient. If a BB approaches close enough to a black hole, and slowly enough not to whip past on an escape velocity, it can circle the black hole several times, but the background gravity soon takes its toll, and the BB dips lower and lower until it drops away entirely. Two black holes alone are probably insufficient, too, though it should work in theory. The problem is that this is a chaotic system: small, even microscopic changes in input (in this case, the positions of the black holes and the initial velocity of the BBs) produce dramatic changes in output (in this case, the extended trajectory of the BBs). Placing the elements precisely enough to keep the BBs circling forever is effectively impossible; the tiniest variation in a BB’s flight can send it swinging more and more wildly, until it is flung free.
I was reduced to combining the two ideas: collect the BBs in a cup formed by the two platforms, and place the black holes inside the cup, closely enough to pick up any BBs that drop out of orbit, even if they settle in the bottom of the cup. I wasn’t entirely satisfied with the result—simply recovering fallen BBs by default seemed like cheating—but it does work. If anyone can do better, let me know. My best idea so far for a more efficient design hasn’t yet worked: a really tight configuration might allow one platform to do the work of two, if no BBs travel sideways too quickly to be recaptured by the black holes before they drop off one of the edges of the platform.