Particles are really fun to play with. Here is another 2D example with line collisions. Click and drag to draw a line. You can also move the endpoints. Releasing an endpoint below or above the stage will remove a line. The collision detection is done by finding the intersection from the line and the moving path from each particle (672).
Particles and Lines require flash8.5player
Try your own bitmaps -default-size 256 384 -default-frame-rate 120 -optimize