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What happens to knots in zero gravity? Do they behave any differently?

I've tried to do some reading on it, but I can't find anything related to knots in zero gravity.

uhoh
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LLLK7
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    Why would anything happen to them? – Organic Marble Jul 21 '23 at 16:54
  • Well I got an answer elsewhere. GPT says knots become useless without gravity, like I suspected. – LLLK7 Jul 21 '23 at 17:07
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    If you trust GPT, you are making a mistake. – Organic Marble Jul 21 '23 at 17:33
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    Do knots spontaneously untie themselves whenever you drop them? Of course not. The functioning of knots has nothing to do with gravity. – Christopher James Huff Jul 21 '23 at 17:55
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    GPT can only generate sentences that sounds natural and no more. It's basically butchering statements from everywhere then frankenstein them into a new statement while following the grammar. There's a high chance that the generated statement is a non-fact. – user3528438 Jul 22 '23 at 08:30
  • Knots reduce the breaking strength of the rope in which they are made to about 40 to 80 % of the original strength. So if ropes used in spacecrafts should be as light as possible with high reliability, knots should be avoided and splices used instead. – Uwe Jul 22 '23 at 11:12
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    Prior to the first human spaceflight it was wondered if astronauts would be able to swallow in zero gravity, since there would be no gravity to pull the food or liquid down. But that was actually easily answered on the ground by simply standing on your head and swallowing something. It seems like the same test can easily be done with knots by testing them both right side up and upside down. – Steve Pemberton Jul 22 '23 at 12:11
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    Hmmm.. It used to be the quickest way to get an answer was to post a wrong one; is "GPT agrees" the newer lazier version? – JCRM Jul 22 '23 at 15:17
  • @StevePemberton good point, but the analogy is a bit of a stretch, both literally and figuratively. Operated under ideal conditions the esophagus is a polarized, one-way device and the flow is always in one direction, so the upside-down test (reminiscent of Musks double vacuum stress) can be seen as an accelerated stress test - if we can swallow fighting gravity, we can also do it in absence of it. But generally knots are static devices and being stretched (thus the literal) and tensioned from multiple directions. – uhoh Jul 23 '23 at 01:01
  • @StevePemberton Of course the static friction that makes knots stay knotted comes from internal forces not gravity (i.e.a paperclip still works in microgravity but a paperweight not so much) So I think analogizing the question in terms of paperclip vs paperweight is a better fit than an an esophagus with the stomach at the top vs at the bottom. – uhoh Jul 23 '23 at 01:03
  • @Uwe I believe we're using knot in the common english sense that doesn't recognize a distinction between knots, splices, and hitches. – Darth Pseudonym Jul 23 '23 at 04:51
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    @uhoh - I think you may have missed the point which is that some people erroneously thought that swallowing wouldn't work in space because gravity is required, when it isn't. I don't recall anyone wondering if a paperclip or paperweight will work in space. People used to wonder how things would work in space, and as the question shows people still have similar questions. My other point was that sometimes there are ways to test these questions on the ground. Thirdly my comment was a point of interest based on something that I remembered that I thought others might find interesting. – Steve Pemberton Jul 23 '23 at 07:43
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    Or again, you could just drop something tied with a knot, and observe that the knot generally survives its time in freefall without any change. How popular would shoelaces be if they came untied every time you jumped? – Christopher James Huff Jul 23 '23 at 18:21

2 Answers2

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Knots in free fall...are knots. There's no reliance on gravity to hold knots closed.

Here's a whole bunch of knots tied in cord holding cables bundled together in the ISS. Seems to be working just fine.

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Cropped from NASA original https://images-assets.nasa.gov/image/iss036e017599/iss036e017599~orig.jpg

Organic Marble
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Knots generally function based on friction and tension, which doesn't have much of anything to do with gravity. Now, as said, there are some kinds of knot that depend on tension in the line to stay tight, and will work themselves loose over time if tension isn't maintained (a bowline, for example). In theory, if you had such a knot and it was being used to hold an otherwise unsupported object, it might stay tight under normal gravity and slowly work loose in freefall, but that's not from any innate nature of knots. It's just because gravity is one way you can come up with line tension. As long as you have tension from some other source (such as spring force or momentum), it wouldn't be an issue.

Darth Pseudonym
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