Hi, in my previous course on basic Physics we learned to solve problems concerning simple mechanical systems like this: The method consists in analyzing separately the two degrees of freedom of the system, computing for each degree the acceleration of each body (or whathever) and the sum both of them to obtain the overall result. Can someone tell me where I can find information about this approach? What does assure me that the sum of the quantities give me the correct result? I would like to understand in detail where the theorical backgroud lies. Thank you.