Algodoo

Interesting scene, but I don't know why anyone would want to do this because Algodoo already has tracers. But I did play around a little with your scene and I made a couple of minor changes that seem to work well. I made the spawned circles non-transparent, and I turned off circle cake. Here is a copy of my spawned circle script:

scene.addCircle({
radius = radius;
color = [0, 0, 1, 1];
density = 0.01;
timeToLive = 0.5;
glued = true;
collideSet = 0;
pos = pos;
angle = angle;
drawBorder = true;
drawcake = false

EDIT - I found another scene that makes a "fake" tracer:

Solid Tracer!

Thank you for helping me.Sorry for my english

Fayree - Your English is just fine! Don't worry about it.