In a lecture I heard that if we suspend two objects of different masses (and the system is accelerating) on both sides of a pulley of no resistance with a mass-less string then the tension on both sides of the string is same - this is fine till now. To explain that the tension is same, it was said that if we take a very small piece of the string and see the two opposite forces acting on them - they must be equal. If these forces are not equal then there will be Infinite Acceleration. 1. What is this Infinite Acceleration in this context (the system is already accelerating)? What will happen if there is infinite acceleration? Does this mean the string will rupture? 2. Why Mass-Less string is important here?