3 ms·
> What happens next? It falls to the ground, of course. At the scale of something that long steel isn't any more rigid than rope is.
by Symmetry 8y ago
> What happens next?
It falls to the ground, of course. At the scale of something that long steel isn't any more rigid than rope is.
- lmilcin 8y agoNot sure why your comment is being downvoted. It is obvious that the shell theorem only applies to Earth and not the steel ring (it's not the ring that is within a shell) and only to the plane of Earth that is in the plane of the ring. While the single plane (crossection) of Earth would not see gravitational gradient from the ring it is only because each part of that crossection of Earth is being attracted to all parts of the ring in a way that all forces cancel each other. For the ring itself, each part of the ring is being attracted by the Earth that is beneath it. There is no magic, the Earth is not a shell around that part of the ring and and full force of attraction is felt. The compressive force on the steel would just squash it immediately. No known material would be strong enough to support itself in this configuration. Think about an arch that is 5 feet high standing on the Earth. Now start making the span wider while keeping its height. The arch gets shallower and shallower until the radius of the arch is the same as radius of Earth. The wider the span and the shallower the arch the stronger the material needed and the less force it can carry.
- ColinWright 8y agoThe idea is that we're in "Puzzle World". This is one of the things that most people take for granted, that the way this is set up has the ring being rigid, even though that's not genuinely feasible. We assume that in the same way as we are assuming that the Earth is a perfect, homogeneous sphere. I might add a note to that effect - thanks for highlighting this. Added in edit: I've now added a note to the page to address this question/issue. And when I say "address", I really mean "try to avoid".
- noir_lord 8y agoYep, sometimes a good puzzle needs a spherical chicken to be tractable.
- ColinWright 8y agoI think you mean spherical cow ... But yes. To avoid adding yet another semi-off-topic comment in the thread I'll add this here: Yes, absolutely, "Spherical [cow|chicken|horse|other]." Cheers!
- noir_lord 8y agoThere are variants of the joke for both spherical cows and chickens going back decades. > "Postulate a spherical chicken ...", as presented in a 1973 letter to the editor of the journal Science titled A Spherical Chicken. Turing discussed spherical horses even earlier :).
- Symmetry 8y agoThere's nothing wrong with an infeasible thought experiment. Frictionless surfaces and spherical cows are a staple of learning physics. The problem is when the author describes them as "greased surfaces" or "watermellon shaped cows" and asks you to treat them as perfectly frictionless or spherical. Describing the rope as being "steel" instead of "rigid" is just needlessly confusing.
- ColinWright 8y agoIf you're inside the world of physics, "rigid" carries exactly the meaning you say it has. But it's a code word, it's got a technical meaning, and for people not in the world of physics, using the word "rigid" would, I think, be confusing. So I've updated the side-box to try to make it clearer. You might like to check it out to see what you think.