testing physical theories of knots

[X11]

@DerekSmith post:42

@X1 post:39

Derek, we had agreed that the Symmetric Sheet bend is not a practical knot

Really? When did ‘we’ agree to this?

Really !

http://igkt.net/sm/index.php?topic=3716.msg21506#msg21506

@DerekSmith post:29

I would be happy to comment on this knot as it is truly an excellent example of cogging dynamics, and I agree with you that a simple knot is an ideal starting point to examine the machinations of a knot’s workings.

However, This is the ‘Practical Knots’ board, and this is never going to be a ‘Practical Knot’ and I believe we have a duty not to promote it as such.

While I must agree with you that this exact form of dressing is strong and stable under load, it only takes a tiny tug on one of the ends to convert it into one of the two other massively cogging forms.

Even though it is one of the few knots which ‘dresses itself’ to the extent that it won’t eat any of the tails as it is loaded, it is none the less only safe as a ‘cerebral exercise’. To suggest to anyone with less understanding of a knot’s functionality than you have Xarax, is I believe, foolhardy and irresponsible.

To that end, if the topic finds itself over in ‘cerebrionics’ then I will be happy to fawn over it.

Derek

It would be “foolhardy and irresponsible” (sic) to suggest it to anyone as a Practical knot, but we can suggest to anyone to melt the free end of a practical knot, that would otherwise be unknotted at a glance ! THAT would require a lot of “cerebrionics” to understand…

@DerekSmith post:42

Most knots have limits to their practical usage, but few of those knots are deemed impractical simply because they have a usage limitation.

So, now it is me the one who will try to narrow the field of “practical” knots…What a difference a few days can make !
I had come to believe that if the dressing of a knot is unstable, i.e. if the knot should be dressed to one stable form that very easily ( by a " tiny tug" ) degenerates to another, less stable or completely unstable form, from which it can easily be untied, then it should not be considered as a “practical” knot.
Of course, if the knot demands melting, gluing, fastening with metal parts, the involvement of segments of other rope, etc., it is not a 'practical knot" either.
I have to remind that I am the least able to speak about the practicality or impracticality of a knot, because I never use knots for practical purposes ! I use knots to admire them as rope mechanisms, as potential tools, and in an effort to understand what a knot is…

@DerekSmith post:42

a Girth Knot formed utilising a loop of cord is not impractical.

You would have to adress this statement to knot tyers of other universes, to get a reply ! Try 4 dimensions…

@DerekSmith post:42

making a stopper knot by back splicing a braid is certainly not impractical, be it used to block slippage through a strangle or any other knot. So, even in this simple and highly practical example of a stopper knot, you are presented with yet another example of a practical knot which does not rely on friction for its function.

I doubt that any back splicing of a braid would remain in place in the complete absense of friction - unless it replicates a “Gordian knot” that I had mentioned. If it does, it would be probably so complex and hard to tie that it would NOT qualify as a practical knot.
I myself had tried to figure out a knot that does not rely on friction ( or topology, of course ! ), and I had presented the Gordian links and bends I had mentioned. If you would find another such knot, you should present it properly, not by talking only about it, but by pictures !
So, I am NOT presented with yet another example of a practical knot that does not rely on friction, just because I am not presented with EVEN ONE example of a practical knot that does not rely on friction - because to say that any knot or hitch, when it is wrapped around the pole, bollard, hook or ring, and you hold both its ends by the friction of the fingers of your hands, is such an example, is a great misunderstanding of what I was talking about - and of what an example, any example, is ! It is a tautology, void of any meaning, good only for rhetoric purposes, of which we have enough in this Forum. Knots, presented with pictures, THAT is what we do not have ! So, try to figure out a tangle of ropes that is not topologically linked in the first place, but can remain tangled even in the absense of any friction. It is called “Gordian knot”. You will soon discover that it is NOT so easy as you think…

Please, let us move our discussion at (1), because I feel guilty I have destroyed this very interesting thread. Sorry, bcrowell, it was my fault.

1). http://igkt.net/sm/index.php?topic=4183.0