Okay here is my question. Assume that you are pulling a spring with 3N from one end and 5N from the other one. How can we apply Hooke's Law in this case? And let's assume that the spring isn't stretching anymore just to simplify things, but it is accelerating. If we divide the spring into eight segments. I feel like the net force on the end of third segment is zero (3N is applied to first segment). If that idea is true then we can apply Hooke's Law to each side. But I couldn't prove that idea and the springs got me really confused.