Rope / String Strength Question

[Swarley]

I have no idea how to google this.

I have some cotton that can hold 2lb when tied with a granny knot.

I tie one end to a hook on a plank of wood, and the other to a fishing scale. I pull it back and when it gets to 2lb it snaps. I can understand this, my cotton has the tensile strength of 2lb when knotted to a hook by a granny knot.



Now this is my question.
I granny knot my 2lb cotton to the hook, then pass the cotton through the ring in the scale then tie it back
on to the hook. Then pull it till it snaps.
But this time it snaps at 3lb. Why?
Why can this configuration have a higher tensile strength, when at one point (the ring on the scale) it is only one strand of cotton? Sherly its weakest link is at the ring?

[cazzer]

Either that's homework or you're really really bored.

[Swarley]

Not homework. Its been a question that's been bugging me for years.

And yes I did have some spare time today.

[dilbert]

Where does it snap?

[Swarley]

Twice at the ring, once half way down the cotton on one side.

[cazzer]

It Quantum...probably.

[jagracer]

It's osmosis.

[dilbert]

Swarley said:

Twice at the ring, once half way down the cotton on one side.

But you don't say which configuration did what....

[soad]

Lovely drawings. That is all.

[Swarley]

dilbert said:

Swarley said:

Twice at the ring, once half way down the cotton on one side.

But you don't say which configuration did what....

Oh sorry
Twice at the ring, once half way down the cotton on one side, for the second test.

At a knot every time with test one.

[perdu]

cazzer said:

It Quantum...probably.

this

maybe

[wombat172a]

Go for test 3:

Two equal lengths of string, tied in the same manner as the first.

[mblade123]

Your halfing the loading. Each length of string now takes half the load in the double configuration.
Although I do wonder why it snaps at 3Lbs and not 4.
If you had 2 more scales at the "grany knot end" you would find each should register 1.5lbs

[K87]

Although there is now two strings there is only 3 mounts. So you haven't doubled the strength, or something like that.

[Jag-D]

because it rocks!!!

[dilbert]

I'm pretty sure it's something to do with Pirates.

[SimonV8ster]

jagracer said:

It's osmosis.

Photosynthesis surely ?

[DrTre]

perdu said:

cazzer said:

It Quantum...probably.

this

maybe

Thought string theory settled the uncertainty principle?

[Swarley]

mblade123 said:

Your halfing the loading. Each length of string now takes half the load in the double configuration.
Although I do wonder why it snaps at 3Lbs and not 4.
If you had 2 more scales at the "grany knot end" you would find each should register 1.5lbs

I agree. But at one point (the ring) there is only one strand of cotton that can only hold 2lb. So how can it get up to 3lb at that point?

[Swarley]

Oh and will it take off?