When you are in a box it is difficult to know the difference between if the box is accelerating in space or you are standing in the box on the surface of a planet. That is correct is it not? In both the accelerating box and on the surface of the planet you can weigh yourself and if the gravity and acceleration are equivalent you will weigh the same. Also if you have a standing vertical spring instead of yourself then it will compress the same in both circumstances. But, it occurred to me that if the spring were attached to the underside of the box that is accelerating then it will be stretched instead of compressing. Does this have any meaning when it comes to gravitational equivalence?