I had this discussion while driving home to California from a trip to Washington state with a friend. We were discussing the stability of a completely rigid, untethered, ring-structure around Earth, and I did not know how to explain to him that such a thing must be tethered by rigid towers lest one portion of it begin a runaway acceleration towards the planet's surface, crashing into the ground. Certainly, this is the case, right? There is no restoring force to bring the ring back to its original position when even the slightest drift occurs, and, even if the ring were to be spinning in geostationairy orbit, that does not impart any additional stability, does it? The apsis wouldn't suddenly begin rotation around the planet, so, since the perigee is closer to the surface and experiencing a stronger gravitational pull than the rest of the rigid ring, it would overall experience a net force leading to the perigee slamming right into the ground, as far as I am aware. Anyway, if I'm correct, I'd like to have some kind of thought experiment or layman's terms explanation to convey the information I can't easily explain to him. This is my first thread, also, so I apologize for any silent rules about this process that I am ignorant of.