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Geek Culture / String Tension Questions

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Dark Java Dude 64
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Posted: 24th Aug 2011 04:50 Edited at: 24th Aug 2011 05:02
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Hello! So i was wondering, let's say you have a section of string that weighs one pound. Im guessing that if the only force on the string is the force exerted by gravity, you would need to tension the string up to one pound of force to make the string completely straight. Is this true??

Now the reason i am asking this rather random question, is for a very strange reason indeed! In essence, im making a 6000 foot long zip-line made of fishing line for small objects to roll down it! This 'zip-line' would extend between my house and my friends house which is on a hill. His house is 500 feet higher than mine and just over 6000 feet away, according to Google Earth. There are no trees, hills, or other objects blocking a straight path between his house and I's; i can see his house from mine, and vice verse. He and i currently have no idea how we are going to actually get the line between his and I's house, so if any of you have an idea, please tell me!! We have thought of ideas like RC planes and helicopters, and even a strategically placed and aimed model rocket with a lot of stages! However, we have figured none of these will exactly work well. Thanks for taking any time you do to answer this very strange inquiry of mine!

In all seriousness, answers are appreciated!

Irrigation of the land with seawater desalinated by fusion power is ancient. It's called rain.
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Neuro Fuzzy
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Posted: 24th Aug 2011 07:48
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no, you would need an infinite amount of force to make a 1 pound rope completely straight!


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BMacZero
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Posted: 24th Aug 2011 17:20 Edited at: 24th Aug 2011 17:20
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I read the title and wondered what new and exciting definition of "tension" allowed it to be applied to a sequence of characters .

Now, I wasn't able to find any stats on how much fishing line weights, but keep in mind that 6000 feet is more than a mile, and it's quite possible that the line will not be able to support its own weight at that length, much less the weight of another object. In fact, with that much line if you put enough tension on it to make it nearly straight it would almost certainly break. Sag is fine.

I like the RC helicopter idea for getting it up there, seems like fun to me .

http://brianmacintosh.com
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bitJericho
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Posted: 24th Aug 2011 17:31 Edited at: 24th Aug 2011 17:49
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I'm reading online and it seems like 6000 feet is probably going to break your budget, of course, I can really only find info on lines capable of hauling humans...

That said, you could instead try to setup a wifi network between the two houses!

http://www.turnpoint.net/wireless/cantennahowto.html

Oh you could also checkout:

http://www.notebookreview.com/default.asp?newsID=2859

I know it's not what you're looking for, but if you can't zip line crap between the houses, at least you can fileshare!


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Dark Java Dude 64
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Posted: 25th Aug 2011 00:38 Edited at: 25th Aug 2011 00:43
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Quote: "no, you would need an infinite amount of force to make a 1 pound rope completely straight!"
Now wouldnt this mean that a very small string, like 1 foot long, would need infinite tension as well? If so, then how am i able to make a 1 foot long string completely straight without infinite force?

Quote: "Now, I wasn't able to find any stats on how much fishing line weights, but keep in mind that 6000 feet is more than a mile, and it's quite possible that the line will not be able to support its own weight at that length, much less the weight of another object. In fact, with that much line if you put enough tension on it to make it nearly straight it would almost certainly break. Sag is fine."
Well, the real i will get it 2800 yards of 40 pound line, and the whole thing is only 2 pounds and 70 dollars!! Not bad--i though it would be well over ten pounds and well over 100 dollars!

Quote: "I like the RC helicopter idea for getting it up there, seems like fun to me"
So far that seems like the best method to me as well!

Quote: "I know it's not what you're looking for, but if you can't zip line crap between the houses, at least you can fileshare!"
^^Lol this sentence made me LOL.^^

But i want to zip crap between houses!!! This string will go over people's houses, but at most points, the string will be about 50 to 200 feet above the houses so people wont be able to see the string. This means that i can send a UFO with flashing lights and strange sounds down the line at night, and people would likely think it was real!! Ok, maybe they wouldnt but it would grab their attention i imagine! Or maybe i could send down one a ancient bird!

Irrigation of the land with seawater desalinated by fusion power is ancient. It's called rain.
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Code eater
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Posted: 25th Aug 2011 01:19
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Quote: ""no, you would need an infinite amount of force to make a 1 pound rope completely straight!"
"

Quote: "Now wouldnt this mean that a very small string, like 1 foot long, would need infinite tension as well? If so, then how am i able to make a 1 foot long string completely straight without infinite force"


I think he was being kind of pedantic. To get it COMPLETELY straight you would need infinate force therefore you will neve get it COMPLETELY straight... But it is possible to get it straight enough to run something down...

If pots and pans were "if"s and "and"s there would be no work for programmer's hands...
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Benjamin
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Posted: 25th Aug 2011 01:36
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Pretty sure this is not legal.



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Dark Java Dude 64
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Posted: 25th Aug 2011 02:49 Edited at: 25th Aug 2011 04:42
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Pretty sure this is legal.

IF you owned all the air above your property up to space, then it would be illegal for planes to fly over your property. But planes do, and you only own the land on your property here in America, so there should be no problem having a string in the air. However, in the case some one legal comes knocking on my door asking me to take it down, i would be more than happy to oblige!

Also, i found that the total surface area of the string would be around 38 feet square. We get 60 mile an hour gusts here in the winter sometimes, so i am afraid that could break the string. So i tried to find how much force that would put on the string, but i cant find the drag coefficient of the string! However i know it MIGHT be 1.7 So if anyone's got the coefficient, please tell meh!

@Code eater Sorry, i just now saw your post!!

Irrigation of the land with seawater desalinated by fusion power is ancient. It's called rain.
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BMacZero
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Posted: 25th Aug 2011 07:13 Edited at: 25th Aug 2011 07:14
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Two pounds is quite light, but as Neuro Fuzzy hinted at, it actually takes quite a lot of force to straighten out a line.

If the two ends differ in elevation by 500 feet and 6000 feet in distance, the minimum angle of "sag", if you will, you could have would be arcsin(500/6000), or 4.78 degrees. If it is any deeper than this, the line will dip below the downhill attachment point and the load could get stuck.

I did some scribbles for you and the tension in the line is going to need to be at least T = weight / sin(theta) to keep the line at this angle. This is 12 times the total weight in your case. So if you want to send a one-pound load down your two-pound line, it better be rated to at least 36 pounds, nevermind the wind you just brought up.

http://brianmacintosh.com
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Dark Java Dude 64
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Posted: 26th Aug 2011 01:18 Edited at: 26th Aug 2011 01:19
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Oh wow, thank you! Good points! So that means the max load i could put on this would be only around 1.34 pounds, not much... But good to know!

Quote: "nevermind the wind you just brought up."
So you mean the wind wont matter?

Irrigation of the land with seawater desalinated by fusion power is ancient. It's called rain.
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BMacZero
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Posted: 26th Aug 2011 03:30
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No, I mean you'll probably have to take that into account as well.

It also occured to me that there might be a bit of elasticity in the string, which would need to be allowed for as well. Not positive how to compensate for those two things, though.

I love physics .

http://brianmacintosh.com
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Dark Java Dude 64
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Posted: 26th Aug 2011 03:44
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Lol!! Yep, physics are awesome! They essentially determine everything that happens in the universe!

Irrigation of the land with seawater desalinated by fusion power is ancient. It's called rain.
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bitJericho
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Posted: 26th Aug 2011 19:49
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I dunno, I think an aereal vehicle is different from a wire. If the wire fails and causes damage, you would probably be directly responsible. Also, if there are legal requirements or something, you could be fined. If your wire causes injury or property damage, you could be sued!

Anyway, just be careful


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Neuro Fuzzy
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Posted: 26th Aug 2011 20:14
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I think an RC helicopter wouldn't work well at all. They do horrible when it comes to wind! An RC plane would work if you were super skilled, but they're hard to fly. It would be awesome to set up landing strips in your back yard though!

Maybe you could set up a small wooden channel on the ground, through which you could drive an RC car or something? That would be more intrusive than a wire, but probably less likely to damage anything.


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Dark Java Dude 64
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Posted: 27th Aug 2011 05:31
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@The Forum President Haha great points!!!! Dang, you are really quite correct! That's a deal breaker right there, i really appreciate you pointing that out!!

@Fuzzy Brain Cell (or at least i think that is what your forum name implies) The wooden channel would go over private property!!




So, i think ill have to stick to smaller 'zip lines' in my back yard, which is 5 acres so i got a lot of space to play with, and as a bonus, i have a very nice hill right to the north of my house, only 20 feet away. On top of that, im going on 6 zip lines tomorrow, should be a lot of fun! Two of them will be the largest in Colorado.

Irrigation of the land with seawater desalinated by fusion power is ancient. It's called rain.
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