# Can you detect the curvature of the Earth with a taut line 3 miles long? [No]

#### Greylandra

##### Active Member
Why recreate [the Wallace Experiment] when getting a result either way can be shrugged off (by either side) simply with "optics" or "refraction" 3 miles of 100lb test line a winch and boat would put this to rest definitively.

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#### Trailblazer

##### Moderator
Staff member
Why recreate this when getting a result either way can be shrugged off (by either side) simply with "optics" or "refraction" 3 miles of 100lb test line a winch and boat would put this to rest definitively.
How? What are you suggesting?

##### Senior Member.
Why recreate this when getting a result either way can be shrugged off (by either side) simply with "optics" or "refraction" 3 miles of 100lb test line a winch and boat would put this to rest definitively.
How? What are you suggesting?

If he's suggesting stretching a rope/string/twine type object the distance of 3 miles, then I think he's overlooking the dip that gravity will put in the rope, which will only muddy up your margin of error.

#### Greylandra

##### Active Member
If he's suggesting stretching a rope/string/twine type object the distance of 3 miles, then I think he's overlooking the dip that gravity will put in the rope, which will only muddy up your margin of error.
Something overlooked? You're absolutely right, gravity will pull the line down. This cannot work against a round earth argument. A line stretched above a body of water at, say, 3 feet of elevation must touch the water at the center point if spanning 3 miles. gravity pulling the line down will only add to this dip. But what if the line wasn't touching the water at all? I'm sure the first explanation out of the bag would be the newly discovered "antigravity rope/line effect" which has a measurable "center of taughtness"... lol

#### Mick West

Staff member
Something overlooked? You're absolutely right, gravity will pull the line down. This cannot work against a round earth argument. A line stretched above a body of water at, say, 3 feet of elevation must touch the water at the center point if spanning 3 miles. gravity pulling the line down will only add to this dip. But what if the line wasn't touching the water at all? I'm sure the first explanation out of the bag would be the newly discovered "antigravity rope/line effect" which has a measurable "center of taughtness"... lol

Well since the earth IS round then the rope is going to touch the surface. If you can't distinguish between the curvature of the Earth and the line's catenary, then it's not really very useful.

And with 3 miles, the center would only need to dip 1.5 feet to hit the ground in the middle.

#### Mick West

Staff member
And I'm not sure of the exact math, but suspect that three miles of line would have WAY more dip in the middle than three feet. You've only got 100lb of force at the ends holding about six pounds of cable.

Why don't you give it a go with 1000 feet, and report back

#### Auldy

##### Senior Member.
As much as I'd like to see your experiment in practice @Greylandra , its not really practical.

Say you used this rope, if you had it in one continuous length it would weigh around 140kgs. What kind of pulling force would be needed by the boat to keep a 3mile long, 140kg rope taught?

#### Rory

##### Senior Member.
A result either way can be shrugged off (by either side).
No matter what the experiment, it seems, this remains true.

#### Trailblazer

##### Moderator
Staff member
And I'm not sure of the exact math, but suspect that three miles of line would have WAY more dip in the middle than three feet. You've only got 100lb of force at the ends holding about six pounds of cable.

Why don't you give it a go with 1000 feet, and report back

Playing around with the calculator here:

http://www.spaceagecontrol.com/calccabl.htm

and using 46lb per nautical mile (0.00757lb per foot) for 1000lb line (quoted from http://blueoceantackle.com/commercial-fishing-supply/monofilament/) with 1000lbf of tension, I get 237ft of sag over three miles of line.

You'd need something like 75,000lbf of tension to get a drop of about 3ft... but that would break the line, so you'd need a much heavier line, which would need much more force to overcome the sag, which would break the line, so you'd need an even heavier line, which would...

I think you see where this is going.

#### NoParty

##### Senior Member.
As much as I'd like to see your experiment in practice @Greylandra , its not really practical.

Say you used this rope, if you had it in one continuous length it would weigh around 140kgs. What kind of pulling force would be needed by the boat to keep a 3mile long, 140kg rope taught?
While I don't view this as a serious topic, if one were determined to try it, wouldn't a better medium
--like the strongest, lightweight fishing line...extended ever so gently--
be more likely to succeed?

#### Trailblazer

##### Moderator
Staff member
As much as I'd like to see your experiment in practice @Greylandra , its not really practical.

Say you used this rope, if you had it in one continuous length it would weigh around 140kgs. What kind of pulling force would be needed by the boat to keep a 3mile long, 140kg rope taught?
If by taut you mean straight, then it is impossible. The sag will only be zero when the horizontal force is infinite.

With the rope in equilibrium, there has to be an upward component to the tension from the centre (lowest point) to cancel the downward force of gravity. The greater the magnitude of the tension, the shallower the angle needed to provide this vertical component, but although the angle will approach zero, it can never actually reach zero because this would require an infinite tension force in the rope.

#### Auldy

##### Senior Member.
While I don't view this as a serious topic, if one were determined to try it, wouldn't a better medium
--like the strongest, lightweight fishing line...extended ever so gently--
be more likely to succeed?

I went with rope because I thought a boat spooling out fishing line and pulling away from where it is tied down would be easy to snap.

#### Greylandra

##### Active Member
OK back to the drawing board... how about neutrally bouant monofilament at a near shore elevation of 0?

#### Greylandra

##### Active Member
Love how the thread was titled after being split. just straight up "NO it's not possible"... modern established science, in practice, at its finest. Does it really surprise that there's a growing host of plebs who question things, now, to such a degree that the shape of the world is back in question?

#### Auldy

##### Senior Member.
Does it really surprise that there's a growing host of plebs who question things, now, to such a degree that the shape of the world is back in question?

honestly, yes

#### Trailblazer

##### Moderator
Staff member
Love how the thread was titled after being split. just straight up "NO it's not possible"... modern established science, in practice, at its finest. Does it really surprise that there's a growing host of plebs who question things, now, to such a degree that the shape of the world is back in question?
It was labelled "No" after the discussion showed that no, it's not possible. Unless you have a magical weightless and infinitely strong rope then it is always going to sag far more than the Earth's curvature over a given distance.

#### Greylandra

##### Active Member
It was labelled "No" after the discussion showed that no, it's not possible. Unless you have a magical weightless and infinitely strong rope then it is always going to sag far more than the Earth's curvature over a given distance.
well let's replace "magic" with neutrally buoyant and place it in the water along its entire length. In a flat earth this rope or monofilament will remain fixed at its starting elevation along it's length. In a convex earth adding tension will cause the line to move lower into the water at its mid point.

#### Trailblazer

##### Moderator
Staff member
well let's replace "magic" with neutrally buoyant and place it in the water along its entire length. In a flat earth this rope or monofilament will remain fixed at its starting elevation along it's length. In a convex earth adding tension will cause the line to move lower into the water at its mid point.
Interesting idea. That might work. I wonder whether currents etc might complicate matters over a long enough distance to have a noticeable drop in the middle. You'd effectively be measuring the "bulge" height on the curve calculator, which is only 18 inches over 3 miles.

#### Mick West

Staff member
place it in the water along its entire length.

So how are you going to place three miles for line exactly one foot under the surface with zero tension?

Just slight currents would distort the line, and place significant tension on either end. Possibly more than gravity would out of the water.

You seem to be picking the hardest possible way of proving the Earth is round.

#### Trailblazer

##### Moderator
Staff member
So how are you going to place three miles for line exactly one foot under the surface with zero tension?
I thought the idea was to have it floating on the surface of the water and then tension it and see if it goes under the water in the middle. So it would need to be slightly buoyant. But yeah, currents would put a lot of tension on it.

#### Greylandra

##### Active Member
So how are you going to place three miles for line exactly one foot under the surface with zero tension?

Just slight currents would distort the line, and place significant tension on either end. Possibly more than gravity would out of the water.

You seem to be picking the hardest possible way of proving the Earth is round.
I'm trying to hone in on "definative"or" irrefutable" sorry if you find my "science a 10 year old can understand" "hard" ...and what's this "possibly" you speak of within 10 miles of my house there is a shallow, stagnant, body of water nearly 5 miles across... This is the opposite of "hard" Mick. If there does exist currents in the water applying pressure can we suggest that this would not change the fact that applying tension should always pull the center of line down on a round earth?

#### Mick West

Staff member
I'm trying to hone in on "definative"or" irrefutable" sorry if you find my "science a 10 year old can understand" "hard" ...and what's this "possibly" you speak of within 10 miles of my house there is a shallow, stagnant, body of water nearly 5 miles across... This is the opposite of "hard" Mick.

Go on then. I look forward to the results.

If there does exist currents in the water applying pressure can we suggest that this would not change the fact that applying tension should always pull the center of line down on a round earth?

It will pull it straight, pulling it into the chord position will be the LAST thing that happen, first you've got to counter the currents. I submit that even a very slow current would put more force on three miles of line than it would be able to hold. I'd be happy to proven wrong, as it would be a unique experiment.

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#### Kristian C

##### New Member
For the Wallace experiment. I would have thought that a preferbly frozen lake or so - to make it easier to get a fixed hight, Mount a tripod with a measured distance from a mark near the top - it should be 12 feet or so to avoid most refraction. Have 3 of these with the exact same distance from the mark to the ice (waterline).

Set a laser to point from The mark at tripod A to Tripod C with tripod B in the middle along the way.

I would even think that even just a single mile in between each tripod would do.
If the distance is short enough a good laser SHOULD keep within a low dispersion enough to still show a result.

If Wallace was right - and the water would be curving, the marker on Tripod B would be over the lasers line as the laser shoot from A to C.

Ofcourse this should even be possible over the 'ol Bedford River

#### Clouds Givemethewillies

##### Senior Member
3 miles of 100lb
test line
Weightless test line is very hard to come by.

#### Spectrar Ghost

##### Senior Member.
Set a laser to point from The mark at tripod A to Tripod C with tripod B in the middle along the way.

No lazers! Lake Balaton has shown us this error.

#### Trailblazer

##### Moderator
Staff member
For the Wallace experiment. I would have thought that a preferbly frozen lake or so - to make it easier to get a fixed hight, Mount a tripod with a measured distance from a mark near the top - it should be 12 feet or so to avoid most refraction. Have 3 of these with the exact same distance from the mark to the ice (waterline).

Set a laser to point from The mark at tripod A to Tripod C with tripod B in the middle along the way.

The laser is just adding complication. Just use a decent surveyor's level set up at the same fixed height at mark A, and sight to mark C. The mark at B should be above the level of C. (And both should be slightly below the true horizontal.)

Example of view through the level (this is from a hill survey, and the pillar is a trig point about 4 feet tall, not all of which is visible, viewed over a distance of about a quarter of a mile)

With clear atmospheric conditions you should be able to see a good-sized marker from 3 miles away, I would have thought.

##### Senior Member
Weightless test line is very hard to come by.

you get it at the shop that sells stripped paint

#### Greylandra

##### Active Member
Weightless test line is very hard to come by.
Yes it is. You're the only one mentioning it. Neutrally buoyant, relative to freshwater, is another matter.

#### Trailblazer

##### Moderator
Staff member
Yes it is. You're the only one mentioning it. Neutrally buoyant, relative to freshwater, is another matter.
Indeed it is, but bringing water, with all its friction and unpredictable currents, into the equation just seems needlessly complicated.

Edit: BUT having said that, I think it would be an interesting experiment to try. If you have a suitable body of water near you then why not try to set it up? I strongly suspect you will find practical problems make it a more complicated task than you imagine.

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#### Whitebeard

##### Senior Member.
Edit: BUT having said that, I think it would be an interesting experiment to try. If you have a suitable body of water near you then why not try to set it up? I strongly suspect you will find practical problems make it a more complicated task than you imagine.
There is going to be a number of problems to account for.

Even the slightest breeze will disturb the surface causing ripples and waves. Air temperature will induce convectional disturbance to the top layer of the water. Any device to tension the line will also have to be bang on the surface, even a small deflection above or below the water level will skew the results. Check the moon phases, if there experiment takes place at the time of spring tides, (the time where the moons gravitational pull is greatest) the surface of a 3 mile wide body of water will be effected to some degree, this needs to be either avoided or accounted for in the final calculations.

Any others?

#### cloudspotter

##### Senior Member.
There is going to be a number of problems to account for.

Even the slightest breeze will disturb the surface causing ripples and waves. Air temperature will induce convectional disturbance to the top layer of the water. Any device to tension the line will also have to be bang on the surface, even a small deflection above or below the water level will skew the results. Check the moon phases, if there experiment takes place at the time of spring tides, (the time where the moons gravitational pull is greatest) the surface of a 3 mile wide body of water will be effected to some degree, this needs to be either avoided or accounted for in the final calculations.

Any others?

Ducks?

#### Rory

##### Senior Member.
Yes it is. You're the only one mentioning it. Neutrally buoyant, relative to freshwater, is another matter.
Can you post a link to the kind of line you have in mind?

#### txt29

##### Senior Member.
@Greylandra: 3 miles may not be enough. I suggest you take ~25,000 miles of the rope, run with straight until you either fall over the rim of the Flat Earth, or come back to your starting point. That should clear things up.

#### Greylandra

##### Active Member
Indeed it is, but bringing water, with all its friction and unpredictable currents, into the equation just seems needlessly complicated.

Edit: BUT having said that, I think it would be an interesting experiment to try. If you have a suitable body of water near you then why not try to set it up? I strongly suspect you will find practical problems make it a more complicated task than you imagine.
You know this is why I love you guys at MB. Around here its considered "complicated" to take standard 100lb test line which is nearly neutrally buoyant ,as it is, and place a length of it into a body of water while stretching it out. (Not directed solely at you)... when considering the experiment can we at least agree that on a round earth: no matter the forces involved the only possibility is for the mid point of the line to move away from the surface in a downward direction. Current and any other lateral forces, upto the point of snapping the line, will add to this relative vertical downward motion in direct proportion? (With resistance forces like friction adding lag to the effect)...the only other possible results would be( flat model) the line stays at or near its depth, on average over time considering the other forces or it attempts, and likely fails, to break the surface tension at the mid point (concave model)...But why even set this up? There is no amount of testing that someone of my credentials can do to prove this to anyone other then myself. Lol, read the closed minded comments just on this thread...this experiment is so simple, so repeatable and so conclusive, the mind here is repelled. Consider how, off the cuff, the admin here answered the question postulated in the title of this thread with a "[no]".

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#### Greylandra

##### Active Member
There is going to be a number of problems to account for.

Even the slightest breeze will disturb the surface causing ripples and waves. Air temperature will induce convectional disturbance to the top layer of the water. Any device to tension the line will also have to be bang on the surface, even a small deflection above or below the water level will skew the results. Check the moon phases, if there experiment takes place at the time of spring tides, (the time where the moons gravitational pull is greatest) the surface of a 3 mile wide body of water will be effected to some degree, this needs to be either avoided or accounted for in the final calculations.

Any others?
At the surface I'd be contending with the strongest possible unwanted forces and conditions Especially the surface tension of the water. I belive the best possible location is a few inches below the surface at the points of tension.

#### Auldy

##### Senior Member.
when considering the experiment can we at least agree that on a round earth: no matter the forces involved the only possibility is for the mid point of the line to move away from the surface in a downward direction

Can you clarify this point for me @Greylandra (or anyone else). How can the line be moving away from the surface in a downward direction? Assuming the line is suspended above the water, it moving downwards is getting closer to the surface, not away, right?

#### Bfahome

##### Member
So let's say you have your near-neutrally-buoyant line pulled as tight as it will allow under a stagnant body of water over a distance of a few miles.

How do you confirm that the line is indeed straight?

#### Greylandra

##### Active Member
Can you clarify this point for me @Greylandra (or anyone else). How can the line be moving away from the surface in a downward direction? Assuming the line is suspended above the water, it moving downwards is getting closer to the surface, not away, right?
Sorry. [ ...]... 3 miles of neutrally bouant, 100lb monofilament stretched taught a few inches below the water line at opposing shores.

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#### Greylandra

##### Active Member
So let's say you have your near-neutrally-buoyant line pulled as tight as it will allow under a stagnant body of water over a distance of a few miles.

How do you confirm that the line is indeed straight?
It wont be. However in a round earth it will, in all cases move further from the surface as any tension is applied. The "straighter" we attempt to pull it the more the curve of the earth should be shown at the mid point.

#### txt29

##### Senior Member.
Although in theory it sounds like an easy experiment, as others wrote, in practice it would be rather difficult. At three miles, the height of the Earth curvature in the middle is some 45 centimeters (around a foot and a half). Now you would need a perfectly flat water surface with no waves and no currents. But not only that. You would have to exclude that no garbage, fishing lines or nets, dirt, sediments, water plants, fish/plankton, or gas bubbles impact the buoyancy of your line over all the length. You would have to exclude any boat traffic in the proximity. You would have to account for the influence of the tide, atmospheric pressure difference, wind, water temperature, depth, sun exposure, evaporation rate, and vertical currents - all of that can have quite important impact on irregularities of the flatness of water body surface (look up for example the term Atmospehric tide in WikiPedia). And even if you eliminated or accounted for all of those named effects, and measured the expected dip of ~45cm in the middle, the Flat Earth supporters would still come with some easy explanation - like for example that an Illuminati diver pulled your line to the bottom, so you would have to have cameras all over the 3 miles to prove the opposite.

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