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Rope has lower bending stiffness than a rod?

11/23/2007 5:55 PM

Can someone explain qualitatively why a rope has a lower bending stiffness than a rod of the same diameter, but would have about the same axial tensile stiffness

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#1

Re: Rope has lower bending stiffness than a rod?

11/23/2007 6:50 PM

Can't you work it out intuitively?

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#2
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Re: Rope has lower bending stiffness than a rod?

11/23/2007 7:38 PM

yes.

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#3

Re: Rope has lower bending stiffness than a rod?

11/24/2007 12:31 AM

There is a simple yet profound reason, you just need to use lateral thinking.

Many centuries ago in the land then controlled by the British Raj, there were folks who sometimes needed to escape in an efficient and speedy manner.

Thus in the fullness of time, a method was developed by the more clever inhabitants of that region.

Because there were many of these sudden disappearances, and to hide the fact it did really happen, it was decided to call it a magical trick, so nobody could be blamed for the disappearances.....

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#4
In reply to #3

Re: Rope has lower bending stiffness than a rod?

11/24/2007 1:59 AM

oh my god, that is the most brilliant answer for that question!! haha.

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#5
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Re: Rope has lower bending stiffness than a rod?

11/24/2007 2:59 AM

I'm so happy to oblige.

As the gardener said, after picking up the coins which had fallen from his pocket with a hole in it, into the compost bin: "Never lose your cents off humus". (Another original, especially made now, just for you)

Kind Regards from New Zealand...

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#6

Re: Rope has lower bending stiffness than a rod?

11/24/2007 9:50 AM

The rope is made of lots of strands , each strand has a very low coefficient of bending stiffness. the overall stiffness will be vaguely proportianal to the number of strands...but they are not rigidly joined to eachoer and thus won't be as stiff as a single strand.

Stiffness of a cantilevered beam is proportional to the cube of it's thickness. therefore on e thick beam will be mush stiffer than the the sum of many indivicual beams.

eg. 1 beam of thicknes 3 gives a stiffnes of 33=27

3 beams of thicknes 1 is say 3x 13 = 3 (even if you allow a factor of 5 to allow for the beams(fibres of rope) being twiated together this would give 15...still not stiff.

Dunno why I'm really answering this as someone else said isn't it intuitively obvious that this is the nature of rope... ?

In otherwords...mulpiple strands give a high coefficient of floposity.

Del

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#7
In reply to #6

Re: Rope has lower bending stiffness than a rod?

11/24/2007 10:51 AM

Hi, Del,

Have you by any chance just got back from the pub? (No offence intended).

John

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#8
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Re: Rope has lower bending stiffness than a rod?

11/24/2007 11:26 AM

Thash mell chequer ishnt as clever ash what she stinks he is (hic).

I'm smertinly not under the affluence. ( no infense unattended swotsomever )

Del

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#9
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Re: Rope has lower bending stiffness than a rod?

11/24/2007 11:53 AM

My mistake !

I can only offer an unreserved withdrawal of my unseemly allegation, and humbly crave your forgiveness .

()

John

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#10
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Re: Rope has lower bending stiffness than a rod?

11/24/2007 12:09 PM

Where do you guys find the funky emoticons... eh?...eh?..go on...tell Del.

I promise I won't myself out of the bag!

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#11
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Re: Rope has lower bending stiffness than a rod?

11/24/2007 5:36 PM

Confession time - just 'tween you 'n' me .

I found myself a nice chat-site (not telling you where - I stumbled on it while searching for info. about an exotic vegetable - but some of them are quite strange ).

Registered and contributed - then did lots of "right click - Save as...", 'cos it was a fun site to chat on, but they also had a load of "brilliant" smilies.

Some of the ones I've hoarded get treated to a little massage (Jasc Paintshop + Animation Shop) before they're ready to be unleashed, but that's about it. My dark & dirty secret exposed.

Guess I can expect a visit from the web cops any time now.

(Sorry to anyone who's tracked me back from xxxxxxxxxxx, but I have had a good time with you guys & hope I've given you a laugh)

Have also found some very nice ones right here on CR4 - but I save them in a 'special place for use elsewhere, thereby avoiding treading on any toes.

Think I'm just about done, now, so it's off to the pub for a wee doch an dorus.

(my personal favorite),

John

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#12
In reply to #10

Re: Rope has lower bending stiffness than a rod?

11/24/2007 7:59 PM

Hello Del,

I "collect" emoticons (Never from smiley Central, because that website has lots of GIF Bugs)

I Right Click/Save interesting pics to my own PC, rename them as required, and keep them in folders under "My Pictures", and enjoy animated ones too.

I use Google Images search, type in what I want, and let the Search Engine locate what I need - and Right click/Save to my PC what I like the look of.

So....my Pics collection here runs now at around 300GB of interesting Pics, any of which I can easily now upload to a Forum,or use elsewhere.

If I wanted a pic of an elephant, type in "elephant" into the Search box, if you want an animated elephant, try "elephant ani" (without quote marks, of course)

You ask about emoticons, so here's the drill for obtaining some:

In "Google Images Search for" type "emoticons" (without the quote marks.)

If you want animated emoticons, type "emoticons ani" into the search box.

Most of the Forum sites I got my emoticons from, are now "Register before Entry", and if the pic is animated, ensure you click on "see Fullsize Image" this ensures that the pic is properly animated, so when you Save it to your PC, the pic remains animated, not just a fixed thumbnail pic as located by Google Image Search.

You should soon get the idea - and don't limit yourself to emoticons.

So.........here's a nice animated pic of a Stirling Engine, "liberated" from somewhere else, saved to my PC, renamed so I can locate it, and uploaded here, so you can see it in full working glory - it does not animate when I insert it into the Edit box, but when I "Preview Comment" it does animate.

As you should find: When searching for a pic, you come across others which may prove useful later, I grab those as I go, because next time, they may not be there.

Have fun......

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#13
In reply to #12

Re: Rope has lower bending stiffness than a rod?

11/24/2007 11:10 PM

I had a pool cue made fom Indian rope trick rope amd it worked well for years, until one day it reverted to rope. I later found the swami who stiffened the rope and died and the magic went out of all his works

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#14
In reply to #13

Re: Rope has lower bending stiffness than a rod?

11/24/2007 11:35 PM

That is such a sad, sad story, aurizon.

I feel you have earned

along with some new cues

Go to: http://www.michaeljscues.com

Cheers....

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#18
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 5:02 AM

Link did not work for me....

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#15
In reply to #12

Re: Rope has lower bending stiffness than a rod?

11/25/2007 4:04 AM

Cheers Sparky...

Nice full reply!

Del

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#16
In reply to #6

Re: Rope has lower bending stiffness than a rod?

11/25/2007 4:33 AM

Thank's, "Del the cat" I was looking for a "Word Of The Week".

Yes, it's floposity.

Brilliant. I hope I never come down with a case of floposity.

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#17
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 4:45 AM

floposity - isn't that a synonym for brewers' droop?

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#19
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 6:06 AM

Don't know about the synonym but every morning, when straight out of bed, I use my flopopositor to relief myself.

When somebody, by sheer magyck, has put some rigidity into it, it cannot be used to relief yourself. Very upsetting

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#20
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 7:09 AM

...maybe to "relieve" someone else?

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#21
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 8:28 AM

Sorry but I have not the slightest idea what you are talking about

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#22
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 10:07 AM

Then you must be father to a "Grudge Baby", somebody had it in for you......

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#23
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 1:28 PM

Not many things I am sure about these days but she is defenitely mine, of that I am sure

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#24
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 2:12 PM

Its a very old English joke.....

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#25
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 2:25 PM

I tried to look it up on google but the link was pointed at something wrong. I did not bother to seek any further as I thought this was the gist of it.

Was it wrong?

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#26
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Re: Rope has lower bending stiffness than a rod?

11/25/2007 5:53 PM

No offense, but you would need to be born in the UK to see the joke......I should hold myself back a bit more, sorry!

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#31
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Re: Rope has lower bending stiffness than a rod?

11/26/2007 1:52 PM

floposity?

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#32
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Re: Rope has lower bending stiffness than a rod?

11/26/2007 2:12 PM

Insactly..its the reciprocal of stiffaciousness !

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#27

Re: Rope has lower bending stiffness than a rod?

11/26/2007 8:07 AM

Del was close but the one thing that's missing is that not only are the individual strands not ridgidly tied together they can slip past each other to some extent, depending on how tightly the rope is laid.

Don't ask me how they get the rope climbing trick to work....

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#28
In reply to #27

Re: Rope has lower bending stiffness than a rod?

11/26/2007 8:15 AM

I Del's defence, he did say "...but they are not rigidly joined to eachother..", which surely implies that they can slip past each other?

(at least, he tried to ... )

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#30
In reply to #27

Re: Rope has lower bending stiffness than a rod?

11/26/2007 12:32 PM

Cal1icoCat:

The rope trick:: They fill the pot with Viagra!

Hank

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#29

Re: Rope has lower bending stiffness than a rod?

11/26/2007 8:33 AM

Ah, you see, grasshopper, when the rope is divided into many small strands, they have the same cross sectional area as the original rod, and hence the same tensile strength. However, these strands are free to slide with respect to each other. Engineers call the resistance to sliding, shear modulus. If one were to weld all the individual strands of the rope to each other one would dramatically increase the shear modulus and create a rod.

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