Algodoo

Don't have enough time to check this out completely. Got to go to work.

So far I see:

"density := density;" listed twice
"_spawn := _spawn" may cause infinite recursion
code should probably be in "controllerAcc :={...}" instead of "_spawn := {...}" in which case you will need to remove "controlleracc := controlleracc;"

P.S. Tried some more. Can't figure it out. Maybe needs some "scene.my" variables. I'm giving up.

why don't just use simple scene.my.variavble

The changes that I made gets rid of spawning more circles (unnessary), and works directly on the radius of the circle. I put lower and upper limits on the radius to prevent the circle from disappearing (radius = 0), and from getting too big. Check out my response scene and tell me what you think about it.