Hello everyone I'm quite confused here and would really appreciate help. Consider a spring standing upright with a box on top of it. Now according to statics there are two forces acting on the spring: the weight of the box G and the support of the ground -F. But when we calcuate the compression of the spring, it is G/k not G+F/k . Why is this? I have been told that this is because F is a reaction force so it is not taken into account. But I thought the reaction force must be directed at a different body than the action force?