Timeline for "You can't push a rope" [closed]
Current License: CC BY-SA 3.0
20 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Feb 14, 2016 at 18:37 | comment | added | Ben McKay | en.wikipedia.org/wiki/Pushing_on_a_string | |
| Feb 14, 2016 at 18:21 | history | closed |
Mikhail Katz Franz Lemmermeyer Chris Godsil Stefan Kohl♦ Felipe Voloch |
Not suitable for this site | |
| Feb 14, 2016 at 15:11 | review | Close votes | |||
| Feb 14, 2016 at 18:21 | |||||
| Feb 14, 2016 at 15:07 | answer | added | Michael Renardy | timeline score: 10 | |
| Feb 14, 2016 at 15:05 | history | made wiki | Post Made Community Wiki by Todd Trimble | ||
| Feb 14, 2016 at 14:27 | answer | added | Bob R Cherry | timeline score: 1 | |
| Dec 11, 2015 at 13:33 | answer | added | Jack | timeline score: 4 | |
| Jul 17, 2012 at 8:59 | comment | added | Federico Poloni | @S. Carnahan: in my comment I meant a rope on an Euclidean plane, without gravity. It is not clear to me whether it is possible or not: for instance, with n=2 points it should be equivalent to the classical "how to balance a rod on your nose" example problem in control theory. | |
| Jul 17, 2012 at 5:40 | answer | added | dab | timeline score: 6 | |
| Jul 11, 2012 at 5:01 | comment | added | S. Carnahan♦ | @Federico Poloni: You could put the rope in a nearly-frictionless trough with a "V"-shaped cross-section. (Also, I think most real-life ropes have small but nonzero restoring forces, due to their nonzero cross-section). | |
| Jul 10, 2012 at 14:07 | comment | added | Federico Poloni | Actually, it would be interesting to solve it as a control theory problem. Model a rope as a large number of points connected by short incompressible rods, and suppose that initially they are perfectly aligned and horizontal. Then you can "push the rope" by applying a horizontal force which will be propagated through the rods. But this is an unstable equilibrium; is it possible to determine vertical "control" forces that keep the rope in a neighbourhood of the unstable equilibrium point, while pushing the rope horizontally at the same time? | |
| Jul 10, 2012 at 12:55 | comment | added | Boris Bukh | @Alexander: Веревку невозможно толкать. | |
| Jul 10, 2012 at 10:03 | comment | added | Alexander Chervov | How this should be translated into Russian ? "Вы не можете нажать на веревке" - translate.google.com - does not make sense for me ... | |
| Jul 10, 2012 at 8:46 | comment | added | Asaf Karagila♦ | I remember once pushing a rope when it was on the ground... perhaps the saying has a second part "unless it is on the ground". :-) | |
| Jul 10, 2012 at 7:59 | history | edited | David Feldman | CC BY-SA 3.0 |
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| Jul 10, 2012 at 7:44 | comment | added | Douglas Zare | I have no background in engineering, but I remember saying "You are pushing on a rope," a few times. Rather than something deep, I think these boiled down to $P \implies Q. ~Q \therefore ~...$ | |
| Jul 10, 2012 at 7:26 | comment | added | David Feldman | Amit Kumar Gupta, that is certainly useful for me to hear! Of course a solid beam has few significant internal degrees of freedom, so a small state space, and just the opposite for a rope. So to me the literal interpretation seems paradigmatic for any situation where a long causal chain has small errors that will accumulate and overwhelm the desired effect or signal. I first heard this decades ago from an MIT student who definitely thought he was getting a broad message, but one he couldn't quite explain to me. | |
| Jul 10, 2012 at 7:09 | comment | added | Amit Kumar Gupta | When I was an engineering student, I had a professor who said it, and meant it literally. I remember drawing structure diagrams with arrows representing forces at all the nodes. A solid beam could have compression and tension forces at either end, but ropes or cables could only have tension. | |
| Jul 10, 2012 at 7:08 | comment | added | Johan Wästlund | Perhaps you can post it as an answer to mathoverflow.net/questions/3559/… and wait for comments ;) | |
| Jul 10, 2012 at 6:31 | history | asked | David Feldman | CC BY-SA 3.0 |