I'm going to try to explain this as well as I can. Two masses M1 and M2 are connected by chain and hung over a sprocket connected to the output shaft of a motor. We can assume M1 and M2 are equal. Normally, the weight of M1 counteracts the weight of M2 and there is no motion. If I want to accelerate M2 upwards at acceleration A1, what would be the force required? I thought this was simple at first, but the weight of M1 that is initially counteracting the weight of M2 diminishes as the acceleration A1 grows. If A1 is greater than the acc. of gravity then the weight of M1 is completely negligible. Is this correct?