Revisiting the Candle Experiment

Sag calculations are of great importance to electrical engineers designing overhead power transmission lines. In principle I can't see the difference between calculating power line sag and working out how much sag would be present in JD's experiment.

https://electricalengineerresources.com/2018/01/13/sample-calculation-of-sag-and-tension-of-transmission-line/

The parameters we need for the calculation are:

W1 = Unit weight of the line (N/m)
H1 = Tension in the line (N)
S = Span length (m)

And using these we will calculate the expected drop/sag (m) (D).

The calculation for drop is given in the quoted article as: D = H1/W1 (cosh(S / (2H1/W1)) -1)

Using this product: 3-Ply 84 lb. Tensile Strength Jute Tying Twine - 5,000 feet (https://www.interplas.com/84lb-jute-tying-twine-p-twj-500) we have a 5000 foot roll of 84lb tensile strength twine weighing in at 10lb. From this we can calculate...

W1 = 10lb / 5000ft = 0.002 lb per foot or 0.029 N/m
H1 = 84lb (i.e. we tension the line to 100% of its breaking point) or 373.78 N
S = 1320ft or 402.34m

Plugging these parameters in to the calculation gives an expected sag of 1.58m or 62 inches.

If we try to pull the twine any tighter, then according to the calculation, make no mistake, it will break. We could do better with something like dyneema, but JD did specify twine after all.

Yeah, twine it is. Wouldn’t want to mess that part up. We need to stay true.

As my old grandma used to say:

If you ain't got the twine, then don't waste your time.

Why not use a laser pointer?

Measure the height of the laser above the clear riser, in the PVC pipe setup, at each end and in the middle.
Surely that would give the level of accuracy needed to prove the principal.

Just a thought. 

Why not use a laser pointer?

Lasers are susceptible to atmoplanic refraction.

Quote from: Psychomech on November 12, 2019, 06:09:26 AM

Why not use a laser pointer?

Lasers are susceptible to atmoplanic refraction.

Atmospheric refraction is due to variations in air density. Over a quarter of a mile, with no major change in height, I am pretty sure that there would be discernible effect.

Got to be far more accurate that stretching the shit out of a piece of string. 

Didn't they try using a laser pointer on the behind the curve documentary on Netflix?

Quote from: markjo on November 12, 2019, 06:22:09 AM

Quote from: Psychomech on November 12, 2019, 06:09:26 AM

Why not use a laser pointer?

Lasers are susceptible to atmoplanic refraction.

Atmospheric refraction is due to variations in air density. Over a quarter of a mile, with no major change in height, I am pretty sure that there would be discernible effect.

Got to be far more accurate that stretching the shit out of a piece of string. 

Far more accurate than a piece of string. piano wire or even the best Dyneema fibre but the Earth's curvature is less than any of those could detect.
You need something like a very high-quality level or theodolite.

So ask a Geodetic Surveyor, they know!

Quote from: Psychomech on November 12, 2019, 06:37:19 AM

Quote from: markjo on November 12, 2019, 06:22:09 AM

Quote from: Psychomech on November 12, 2019, 06:09:26 AM

Why not use a laser pointer?

Lasers are susceptible to atmoplanic refraction.

Atmospheric refraction is due to variations in air density. Over a quarter of a mile, with no major change in height, I am pretty sure that there would be discernible effect.

Got to be far more accurate that stretching the shit out of a piece of string. 

Far more accurate than a piece of string. piano wire or even the best Dyneema fibre but the Earth's curvature is less than any of those could detect.
You need something like a very high-quality level or theodolite.

So ask a Geodetic Surveyor, they know!

A level, theodolite or total station would do it in a heartbeat, you wouldn't need to do the quarter mile either.

If the modern instruments are off putting  a good old mechanical theodolite would be just as effective.

Simple measurements aswell so no need to set up a full survey. Position your instrument and set up the two poles, measure the vertical angle of each pole, bit of high school trig and a decent surveyor will get you Earths R to +/- 2mm

As my old grandma used to say:

If you ain't got the twine, then don't waste your time.

If you can’t do the time, don’t do the twine.

What you need is long strong line with the specific weight matching water.
Such line you should be able to stretch in water without sagging.
Then you can see if it dives in the middle as you pull it straight through the curve.

With the Earth radius of 6371 km, and with the string of 1 km,
the middle should dip for about 2 cm (0.00002 km).
At 2 km string you should have 8 cm (0.00008 km) dip.

Is there such line?

What you need is long strong line with the specific weight matching water.
Such line you should be able to stretch in water without sagging.
Then you can see if it dives in the middle as you pull it straight through the curve.

With the Earth radius of 6371 km, and with the string of 1 km,
the middle should dip for about 2 cm (0.00002 km).
At 2 km string you should have 8 cm (0.00008 km) dip.

Is there such line?

Dynema (Rab's suggestion) might match that. It has a density of 0.97 g/ml.
But as it is slightly less dense, it will curve up slightly due to buoyancy.

Of course, some people might complain that you can't use a candle under water.

Anything over an extended distance will sag.
Super impractical experiment.

Didn't they try using a laser pointer on the behind the curve documentary on Netflix?

They probably didn't factor in aetherific eddification.

Anything over an extended distance will sag.
Super impractical experiment.

Well you might think that, I might think that too, however John Davis is quite convinced that the twine won't sag at all as far as I can see.

It would be quite interesting for someone (Gumwars said he was willing) to propose a properly specified experiment (e.g. type of twine/candle/sticks etc.) and a methodology to follow based on the little JD has explained and see if JD is willing to accept the chosen parameters and whatever results from the experiment.

I see two main problems, firstly, I doubt JD will be willing to unambiguously agree to anything proposed and secondly, there is a get-out clause in his original post:

If necessary, repeat this experiment a number of times and localities to rule out local variances skewing the results.

So how many times would the experiment have to be done to "rule out local variances" I wonder?

Quote from: Macarios on November 13, 2019, 02:27:02 AM

What you need is long strong line with the specific weight matching water.
Such line you should be able to stretch in water without sagging.
Then you can see if it dives in the middle as you pull it straight through the curve.

With the Earth radius of 6371 km, and with the string of 1 km,
the middle should dip for about 2 cm (0.00002 km).
At 2 km string you should have 8 cm (0.00008 km) dip.

Is there such line?

Dynema (Rab's suggestion) might match that. It has a density of 0.97 g/ml.
But as it is slightly less dense, it will curve up slightly due to buoyancy.

Of course, some people might complain that you can't use a candle under water.

That's a very clever idea!

The buoyancy of Dyneema would be equivalent to line with a density of 0.03 g/ml, so it would be equivalent to line with more or less the same strength, but weighing only 3% as much (unless Dyneema loses significant strength when wet).

The buoyancy of Dyneema would be equivalent to line with a density of 0.03 g/ml, so it would be equivalent to line with more or less the same strength, but weighing only 3% as much (unless Dyneema loses significant strength when wet).

Close. It would be equivalent to ~ -0.03 g/ml.
I wonder if any FEer would try to use this with the appropriate tension to keep it perfectly level and claim Earth is flat?

But that does also provide one key part:
If the region in the middle is lower than at the edges, then there is literally no way for a FE to explain it.
"Sag" in this case would be upwards.

It seems that at breaking point, over 1000 m, it would be higher by roughly 1.5 cm, while the curvature of Earth is roughly 2 cm.
That means it should still sag a big, but it would require 2.5 GPa.
Dropping it to 1 GPa would produce 3.7 cm upwards, meaning it would still go up.

So we need a heavier fibre.
Perhaps coat the fibre in something heavier than water to make it match water?

Quote from: Alpha2Omega on November 13, 2019, 01:07:31 PM

The buoyancy of Dyneema would be equivalent to line with a density of 0.03 g/ml, so it would be equivalent to line with more or less the same strength, but weighing only 3% as much (unless Dyneema loses significant strength when wet).

Close. It would be equivalent to ~ -0.03 g/ml.
I wonder if any FEer would try to use this with the appropriate tension to keep it perfectly level and claim Earth is flat?

But that does also provide one key part:
If the region in the middle is lower than at the edges, then there is literally no way for a FE to explain it.
"Sag" in this case would be upwards.

It seems that at breaking point, over 1000 m, it would be higher by roughly 1.5 cm, while the curvature of Earth is roughly 2 cm.
That means it should still sag a big, but it would require 2.5 GPa.
Dropping it to 1 GPa would produce 3.7 cm upwards, meaning it would still go up.

So we need a heavier fibre.
Perhaps coat the fibre in something heavier than water to make it match water?

But what happens if there is the slightest movement of the water? It all goes awry.

To anyone who has been involved in surveying on a professional basis, the idea of using lengths of string and candles to prove anything in regard to the topography of an area is just preposterous. The only thing it does prove is how divorced from reality the designer of this 'experiment' is.

To anyone who has been involved in surveying on a professional basis, the idea of using lengths of string and candles to prove anything in regard to the topography of an area is just preposterous. The only thing it does prove is how divorced from reality the designer of this 'experiment' is.

To be completley fair string is used quite a lot in surveying, but knowhere near the lengths suggested by the experiment.

Kerbs are set out with string prior to laying, and strings tangentially across kerbs are used to dip (calculate) the depths of bituminous materials required at 10m chainages

No
JohnD put out a compleyely assinine experiement - either forgetting that gravity exists or expecting it to not exist...

No
JohnD put out a compleyely assinine experiement - either forgetting that gravity exists or expecting it to not exist...

...to the amazement of all who witnessed it!

No
JohnD put out a compleyely assinine experiement - either forgetting that gravity exists or expecting it to not exist...

Or, he's using an unobtanium twine that is infinitely strong and nearly weightless.

So we need a heavier fibre.
Perhaps coat the fibre in something heavier than water to make it match water?

Dyneema / UHMWPE is 0.97
Nylon is 1.14

We can intertwine them in the desired proportion.
6D + 1N gives 0.9943, but then the used N can be slightly thicker for fine tuning.
Or the difference can still be kept to keep it floating until tense.

(Or we could skip Nylon and put series of rings on Dyneema with calculated spacing.)

But what happens if there is the slightest movement of the water? It all goes awry.

The experiment can be done on Bedford canal.

EDIT: It is 9.7 km long.

In the winter with no refraction

But it has to be safe from moonlight and heaven energies.

But it has to be safe from moonlight and heaven energies.

I've heard that enclosing the experiment in a Bismuth box might shield it from "heaven energies".

Yes, it might.

Quote from: Timeisup on November 14, 2019, 02:27:36 AM

To anyone who has been involved in surveying on a professional basis, the idea of using lengths of string and candles to prove anything in regard to the topography of an area is just preposterous. The only thing it does prove is how divorced from reality the designer of this 'experiment' is.

To be completley fair string is used quite a lot in surveying, but knowhere near the lengths suggested by the experiment.

Kerbs are set out with string prior to laying, and strings tangentially across kerbs are used to dip (calculate) the depths of bituminous materials required at 10m chainages

If you are into home improvements and laying out a patio/kerb then sure using 20 meters of mason's twine would be a good way to go, along with some other basic leveling items. The 'Clown' who started off this particular mad caper was suggesting using a line over 400 meters long! That's in a totally different ballpark. If you turned up on-site to do some meaningful measurements witha ball of string 400 meters plus, you would be medicated then sent home for your own good.
I'm not sure who the instigator of this stupidity was but one thing is for certain he knows less than nothing about basic surveying. Having read a few of the other discussions on this site it looks like it could be medication for quite a few is required.