Dear Friends, Two more questions that I could not find the resolution. If anyone knows where is resolved, or could give a little help, I will be so much agreed!!! One is about fluids mechanics: imagine one ball, in a fluid composed by much little balls. At much velocity, this big ball could adquire mass from this entorn, and be bigger. What's de velocity of equilibrium that makes that the ball has not acceleration. Imagine that the ball is little at principle, but it creates much big ball derivate of the material arround it. Another example could be a ball of snow running, at much velocity, much bigger... Another question is about biot-savart law, in fluids mechanics. I dont understand the meaning of the strength... is this the circulation? And another question is about demonstration of schrödinger equation by the formulae of continuity. I don't know how to do it. I desire all of you a very good day. R. Aparicio.