1. The problem statement, all variables and given/known data I have a double Atwood machine; on left side there is a heavy thing which weight 4m, on right side there is another circle (this circle which go around in atwood machine) and on left there is heavy thing which weight m, on right - mass which weight 3m. Now the 3m thing starts to go down, m thing goes up. Why the 4m mass goes down, while the mass on both sides are the same mass? http://img10.imageshack.us/img10/9270/testttti.jpg [Broken] 2. Relevant equations I got this result from Lagrange equations 3. The attempt at a solution I tried to research how the forces in lines and masses are existing, but I couldnt find any soluton for this.. why this 4m mass is going down? thanks for answer!