Algodoo

this is a simulation of a chemical reaction that happens in two
different directions, discription is on the scene. but the Green and
Red balls have halfe the radius that of the Blue and Yellow balls, So
there is more chance for the reaction to happen in the direct way
( B+Y -> G + R) than the indirect way ( G+R -> B+Y), so Xf will be bigger than
Xmax/2=150.