Imagine a spring that has its two ends attached to a wall at the same height. The spring will adopt a kind of a ''U'' shape (maybe a parabollic shape would be more precise). Why are the coils near the wall more distant from each others than the coils at the middle of the spring ? I think it is because the tension is higher, but the tension isn't suppose to be same everywhere in a spring ? How could I find the difference between the tension near the wall and the tension in the middle of the spring ?