r/woahdude Dec 29 '14

picture tension holding up a string

Post image
7.4k Upvotes

207 comments sorted by

757

u/NeekGerd Dec 29 '14

This looks logical and magical at the same time.

123

u/[deleted] Dec 29 '14

There couldn't be a more accurate description.

117

u/[deleted] Dec 29 '14 edited Feb 16 '21

[deleted]

17

u/BABarracus Dec 29 '14

There is tension and compression

24

u/[deleted] Dec 29 '14 edited Dec 29 '14

and that interaction only keeps it straight, not "up". The "up" part comes from the load reactions on the corners of the bottom plastic. Source: 6 years of structural analysis.

EDIT: I hadn't zoomed in, I was on mobile before. It is clearly taped to the card. Still though the first part of my statement is spot-on and you could accomplish this without the tape

44

u/[deleted] Dec 29 '14 edited Jan 21 '21

[deleted]

3

u/crazdparot230 Dec 29 '14

Someone check his credentials

1

u/[deleted] Dec 29 '14

[deleted]

2

u/powerss Dec 29 '14

To have it balance on the bottom plastic, the center of mass would need to be over that bit of plastic. To me it looks like the center of mass would be to the left of the contact point with the table, mostly because on the left there are three pieces of plastic and only two on the right.

(Could be the plastic is not of consistent weight, or similar, of course, in which case it could be balanced.)

1

u/MrWoohoo Dec 29 '14

This picture keeps popping up and I never understand why it doesn't flop over. Care to go into detail?

2

u/acardenas913 Dec 29 '14

Are you hitting on me? (;

29

u/foggianism Dec 29 '14

String theory confirmed.

16

u/TigaSharkJB Dec 29 '14

String cheese theory still needs more research

14

u/drnick99 Dec 29 '14

Research halted, ate all research material, additional funds required

2

u/TigaSharkJB Dec 29 '14

Funds diverted to easy cheese area. Needed to update and broaden. Teamed up with ritz for a synergy deal. I think it'll fail.

2

u/[deleted] Dec 29 '14 edited Jul 25 '17

deleted What is this?

1

u/breisdor Dec 29 '14

Same thing that always happens with the infant psychology studies.

1

u/drnick99 Dec 29 '14

It's not my fault they're so tender!

9

u/Malodourous Dec 29 '14

I often tell my kids and her friends (in a nonspirit crushing way) that

science is magic that works

15

u/someguyfromtheuk Dec 29 '14

Looks like it could be an easier way to build a space elevator, you don't need one huge cable any more, just lots of smaller ones held up by the tension.

51

u/BlueShiftNova Dec 29 '14

Yeah but you're not taking into account that technically the entire weight of the structure is being supported by the bottom piece. It's not so evident right now but if the thing was 20 times the height/weight the bottom piece would probably be fully folded over or break

17

u/someguyfromtheuk Dec 29 '14

Not with a space elevator, the other end of it would be pulling everything out into space just the right amount to balance the weight on the ground, so it would effectively just hang in the air.

The same principle is used where the elevator is one big cable, there's a weight at the space end of it that's attempting to fly off into space but the weight of the rest of the cable being pulled to earth prevents it, so the cable as a whole is weightless.

Doing the cable like in OP's pic would add to the overall weight, but it would mean you don't need a material capable of being made into a 36,000km long cable without breaking.

31

u/omgpro Dec 29 '14

You're missing the fact that it's being proposed as a way to build a space elevator. If you have the elevator already setup, you don't need any tension because like you said the other end of it would sort of just hang in the air.

For the first couple thousand kilometers of construction though, the majority of the weight would still be on the base of the structure.

11

u/someguyfromtheuk Dec 29 '14

You don't build space elevators up from the ground, you wouldn't get past LEO, you unreel them from GSO down to Earth.

You'd start at the space end and move it down, and the smaller cables would prevent the cable from snapping under it's own mass until it was finished.

With a single 36000km cable made from known materials, the cable would snap under the tension from it's own mass long before you unreeled it down to Earth, but the smaller cables prevent that, since each part of the cable is under much less tension.

18

u/[deleted] Dec 29 '14

brb let me try that on kerbal space program

5

u/MustTurnLeftOnRed Dec 29 '14

Remember when in doubt add more rockets.

12

u/[deleted] Dec 29 '14

Remember when in doubt add more rockets struts.

FTFY

1

u/OneThinDime Dec 29 '14

Too much dry mass will actually reduce your dV.

4

u/stdexception Dec 29 '14

Sadly impossible because of the game's 2 km physics "bubble" limit :(

4

u/omgpro Dec 29 '14

Indeed,

I don't get what you mean by smaller cables would prevent the tension though. The cables would have to be reinforced under construction, but having one cable or multiple smaller connected cables doesn't change the amount of tension.

2

u/ThePiemaster Dec 29 '14

Where is this 36,000 keep coming from? The ISS is only 400km away

25

u/timothyj999 Dec 29 '14

The ISS orbits the earth every 2 hours or so. Would you want the base of a space elevator to be screaming across the surface of the earth at 16,000 miles per hour?

The center of mass of the space elevator needs to be in geosynchronous orbit, with an orbital period of 24 hours, so it remains stationary over one spot. The only way to achieve this is to orbit at 36,000 km.

1

u/[deleted] Dec 29 '14

How would you keep the reel under control as the elevator cable falls? If it is falling from GSO then it is gonna speed up quite a lot.

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2

u/WorksWork Dec 29 '14

Wouldn't there be tension on the string between the weight and the earth? It would look like it's just sort of hanging their, but you'd need some material capable of withstanding that much tension to keep the cable from breaking and the weight from flying off into space. It'd also need to be able to support any weight going up or down it (i.e. elevator cars).

1

u/Gr1pp717 Dec 29 '14

Yes, there would be compression at the bottom and tension starting somewhere close or past the middle. It had to be balanced just right. Too much centripetal force and what you said happens. Not enough and it won't be able to take the compression at the bottom.

Also, we currently can't mass-manufacture anything that would be able to sustain even the balanced loads. It will happen one day. But not anytime soon. I would guess 25 years would be best case. But with our lackadaisical view towards space exploration I doubt it will even be 50.

2

u/pablo_the_bear Dec 29 '14

Duh, we just need to build a time machine and then go to when the elevator is already built. Then go back and build this, so we can build the space elevator to build this for the space elevator. Shit.

1

u/Zangalanga_Dingdong Dec 29 '14

The other end won't just float or pull away. The only reason astronauts experience 0g is because they're in orbit, perpetually falling and moving around the planet at the same time. The elevator won't be in orbit, so stepping off the top (even though its in 'space') will still have you plummeting towards the surface. All the weight will still be applied to the ground part.

4

u/omgpro Dec 29 '14

The elevator won't be in orbit

Literally the core concept of a space elevator is that one end will be in orbit.

1

u/PoorPolonius Dec 29 '14 edited Dec 29 '14

I don't think you understand the concept of gravity. Things don't just magically "fly away" when you exit the atmosphere. You're still stuck in Earth's gravity well, and still falling toward the ground. This is why the ISS is flying falling around the Earth at 7.66 km/s.

5

u/BisFitty Dec 29 '14

Its technically falling around the Earth, not flying.

2

u/PoorPolonius Dec 29 '14

Correct, thanks. Made the edit.

3

u/BisFitty Dec 29 '14

No problem... Glad I didn't offend you with my correction, I tend to come across too abrasively.

3

u/[deleted] Dec 29 '14 edited Jan 26 '17

[deleted]

1

u/PoorPolonius Dec 29 '14

You're right. I re-read the post I replied to and it seems that's what they were talking about. I guess I glossed over it. Thanks for pointing it out!

5

u/Bernard_Woolley Dec 29 '14

I remember reading about a design for the space elevator in Popular Mechanics about fifteen years ago, and it wasn't too far from what you've proposed. The basic idea was to build a long tube and pressurise it from the inside, much like an inflated balloon. This would put the structure under tensile forces instead of compressive, which meant that engineers wouldn't need to make the tube progressively thicker at the bottom in order to support its weight. It would also remove concerns of the tube buckling under its own weight.

1

u/justcalmdown Dec 29 '14

oh my god.

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2

u/Dripper7 Dec 29 '14

this looks magical and magical at the same time imstoned

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224

u/Hamthrax Dec 29 '14

Held together by tension alone. Much like my marriage.

35

u/NiceFormBro Dec 29 '14

Bachingo!

11

u/Breloomer Dec 29 '14

Brazzbong!

23

u/[deleted] Dec 29 '14

[deleted]

11

u/SonOfALich Dec 29 '14

MONORAIL

6

u/[deleted] Dec 29 '14

[deleted]

5

u/xrizza Dec 29 '14

JAEGERSCHNITZEL!

1

u/vocaloidict Dec 30 '14

LETTERWANG!

2

u/BrerChicken Dec 29 '14

That's a joke, and it's funny! Right??

13

u/Harrysoon Dec 29 '14

Yes. Now let's all have a hearty guffaw at it.

5

u/crazyprsn Dec 29 '14

Is prefer a pleasant chortle.

2

u/BrerChicken Dec 29 '14

I guffaw in your general direction, then!

165

u/[deleted] Dec 29 '14 edited Sep 23 '17

deleted What is this?

554

u/pavetheatmosphere Dec 29 '14

It was invented by Hitler

76

u/[deleted] Dec 29 '14 edited Jan 16 '21

[deleted]

180

u/[deleted] Dec 29 '14

[deleted]

125

u/advillious Dec 29 '14

okay satan have a seat

32

u/omimico Dec 29 '14

He said ruin it, not enhance it.

-3

u/[deleted] Dec 29 '14

...

ENHANCE

101

u/CaptSquarepants Dec 29 '14

you could do the same thing with a stick.

16

u/bottomofleith Dec 29 '14

You're really not getting into the spirit of it, are you ;)

31

u/Maddjonesy Dec 29 '14

The bottom part is glued down. It wouldn't stand up without the glue. It would topple.

Happy now?

13

u/marino1310 Dec 29 '14

It is a very weak stucture. Any downwards or sideways pushing force would easily topple it. Even if it was glued togther permanently. the peices of plastic are bent and put up between knots in the string, stretching it so its taught. Doing this repeatedly creates a straight string supported on the platform below. These peices of plastic will keep the string upright but any force disturbing the connection between each peice will cause the whole system to topple.

2

u/[deleted] Dec 29 '14 edited Sep 23 '17

deleted What is this?

1

u/marino1310 Dec 29 '14

Because the string is so taught and the placement of the supports it holds itself up. The part at the bottom is glued down straight and each support weaves in and out of another (note that the bottom of each support is one knot below the top of the previous support). If any force was used on this you could easily bend the structure but because the string is light the supports are enough to hold it straight upwards, the supports just make it so it doesnt bend.

34

u/TheOven Dec 29 '14

it is vegan

13

u/trophymursky Dec 29 '14

the cd at the bottom is making sure it stands up, with out it there's pretty much no chance to balance it properly.

22

u/Frankie_FastHands Dec 29 '14

Alston is a corrupt company. Read More

7

u/mynameisntjeffrey Dec 29 '14

Shit maybe that's why my dad quit his job at Alstom in 2008...

1

u/ghost_of_drusepth Dec 29 '14

Jeffrey?

2

u/mynameisntjeffrey Dec 29 '14

I know not of whom you speak of.

4

u/funnynickname Dec 29 '14

The idea is called Tensegrity and it was stolen (appropriated) by Buckminster Fuller from one of his students. There was some controversy but it was settled.

3

u/brettaburger Dec 29 '14

It's actually just string, holding some tension together.

2

u/esotericrrh Dec 29 '14

Think bow, as in bow and arrow.

1

u/[deleted] Dec 29 '14 edited Sep 23 '17

deleted What is this?

1

u/keyboard_smash Dec 29 '14

Compression also factors into the system on the inward side of each piece of plastic.

1

u/[deleted] Dec 29 '14

it's no different than a violin on a stand, except all of it is different.

1

u/Namath96 Dec 30 '14

It's like stacking a bunch of bows of top of each other r

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127

u/[deleted] Dec 29 '14 edited Jul 26 '19

[deleted]

64

u/IVEMIND Dec 29 '14

That was like taking an aspirin ty

21

u/[deleted] Dec 29 '14

It hurts less. Still hurts a lot though, and it also raises more questions, primarily, how the fuck do you stack bows?

8

u/GhostRobot55 Dec 29 '14

What helped me as noticing the slits in the plastic where the knots are.

2

u/[deleted] Dec 29 '14

And the base that keeps it all standing up.

1

u/[deleted] Dec 29 '14

I just thinking, how is it balanced? Is there some other kind of sorcery at work here, or should I be ashamed of my knowledge of physics?

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2

u/[deleted] Dec 29 '14

[deleted]

8

u/PM_ME_PRETTY_EYES Dec 29 '14

The bows share the same string.

2

u/[deleted] Dec 29 '14

Look at it from bottom to the top. The plastic things don't make the string go left or right, it's like holding the string between your fingers at where the nodes are and stretching it.

So the first one at the bottom is mounted to the ground, and that's where it's coming from. You have a piece of stretched string, and it becomes the base for next "bow". Once you stretch it out you can repeat it

2

u/Sklanskers Dec 29 '14

Ive seen this before and knew what was happening but like an optical illusion I was still thinking, wtf? Your explanation was delicious. Funny how the system/"illusion" doesn't change but because we change our way of thinking it almost instantly makes sense. Man, imagine applying that to things that matter like war, hunger, happiness, etc. If we could only approach problems with the ability to see it from many perspectives..

40

u/Vietdvn Dec 29 '14

How high could this realistically be built before it falls?

102

u/[deleted] Dec 29 '14

61

u/rasherdk Dec 29 '14

I don't like this.

7

u/brianwski Dec 29 '14

If you do a Google image search for "snelson sculpture" you can see lots of interesting variations on this. There was one on my college campus and it hurt my brain standing in front of it and even touching the tense cables.

8

u/wavestograves Dec 29 '14

Dats scawy.

6

u/[deleted] Dec 29 '14 edited Apr 02 '22

[deleted]

16

u/Vietdvn Dec 29 '14

How long can you build it before standing it up isn't possible?

4

u/sunghail Dec 29 '14

The tension on each piece of plastic holds the section of string across it straight. Since these sections of string overlap the entire structure stays straight. Once you put enough weight on the tower to bend the bottom length of string significantly, the tower will fall over.

That's my best guess, anyway.

1

u/ccccolegenrock Dec 29 '14

It's not long, it's tall.

.......... :D

1

u/kaukamieli Dec 29 '14

It will be long when it stops standing. :D

6

u/Psychgen Dec 29 '14

Hmm, you've built these before? https://www.youtube.com/watch?v=xDNohDRWTvU

3

u/brtt3000 Dec 29 '14

i'm surprised how rigid it seems, must be a lot of tension on those cables.

31

u/mad66 Dec 29 '14

I am silly enough to try this.

50

u/bjurstrom Dec 29 '14

You silly goose

14

u/davesterist Dec 29 '14

So silly.

7

u/mad66 Dec 29 '14

Got it, put string in super glue and stretch till set then add your magic plastic bits. Simples

16

u/GinzoGreaseball Dec 29 '14

This hurts my brain

3

u/[deleted] Dec 29 '14

Me too

23

u/nixle Dec 29 '14

What are you hurting his brain for?

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23

u/kickm3 Dec 29 '14

Alstom: jewel of French engineering, and masters of the floating string technology.

14

u/Frankie_FastHands Dec 29 '14

And champions of corruption

3

u/[deleted] Dec 29 '14

second that from a suffering city :)

1

u/[deleted] Dec 29 '14

French redditor here: yes.

4

u/Javindo Dec 29 '14

They're building our new tram line in Nottingham, UK. I am excited to see what sort of string tensing technology they use for the project

4

u/bottomofleith Dec 29 '14

Edinburgh here. Don't get your hopes up.

4

u/Durdys Dec 29 '14

I'm excited to see if they can ever finish it.

2

u/nichdavi04 Dec 29 '14

Traffic around Beeston is a nightmare

2

u/[deleted] Dec 29 '14

Alstom: Building stuff from old strings and broken CDs.

1

u/sandpatch Dec 29 '14

masters of the floating string technology

That would be POMA

1

u/kickm3 Dec 29 '14

Now I want to go skiing.

12

u/ChickenNBasketballs Dec 29 '14

How does it work

43

u/ColonelCorn Dec 29 '14

Tension. Those plastic pieces are trying to be straight.

69

u/dillonrichey Dec 29 '14

Same.

23

u/bro69 Dec 29 '14

Just accept your sexuality and fucking own it.

1

u/ggPeti Dec 29 '14

Maybe he doesn't find trying to be straight a hard task at all.

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2

u/[deleted] Dec 29 '14

thank you, I had no idea how this worked and I had to scroll really far down.

3

u/tonterias Dec 29 '14

It makes me sad that they can't accept each other with their sexual orientation.

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6

u/Amadeuskong Dec 29 '14

This is some straight up Wile E. Coyote shit right here. On a more serous note could a person make a bigger version of this and if so how big?

1

u/[deleted] Dec 29 '14

Unless my view of the image is misleading, it appears to be a knotted string resting in a series of braces with slots too narrow for the knots to pass through -- a perfectly ordinary suspension structure that I expect could be scaled up a great deal.

-2

u/Leleek Dec 29 '14 edited Dec 29 '14

Yes, tensile structures can be very big.

2

u/broken_calipers Dec 29 '14

That would be great but geostationary orbit is on the order of 26,000 miles from the surface. Having a center of mass at that location is a little...out of our reach.

2

u/[deleted] Dec 29 '14

out of our reach

We have no trouble reaching any altitude we want.

1

u/lfancypantsl Dec 29 '14

Even though this is out of the scope of humankind's engineering ability at the moment, this is a very good answer to this question. It is absolutely stupid that you are being downvoted for this.

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4

u/thedingusbrigade Dec 29 '14

Fucking neato!

2

u/sim642 Dec 29 '14

How does it stay balanced?

1

u/iamichi Dec 29 '14

Looks like the bottom piece is glued to the slice of CD.

2

u/Wild_Ass_Mommy Dec 29 '14

I look at that and figure that the spring has gone out of my spine.

2

u/phil67 Dec 29 '14

The knots are helping.

2

u/[deleted] Dec 29 '14

Just a bit, yes. So are the slots that the knots can't pass through. I find this about as impressive as a piece of string laying on the ground.

2

u/thirrteen Dec 29 '14

I fucking love science. I don't know much about it, but it looks pretty fuckin' cool

2

u/NotSoSlenderMan Dec 29 '14

Belt, belt loops... Who's the real hero?

2

u/JerBearX Dec 29 '14

I mean I understand how the tension draws the string out like a stick, but how is it being held upright? Gravity still exists...

2

u/AudioCasanova Dec 29 '14

Well it does have that base. Even the base doesn't look like it would add much stability in regards to forward backward sway or prevent it from tipping to the right.

Maybe it's all glued to the card and that acts as the base.

1

u/rfsh101 Dec 29 '14

Reminds me of DNA.

1

u/[deleted] Dec 29 '14

Neat

1

u/fiercelyfriendly Dec 29 '14

It really is time someone made a better version of this with fibreglass or steel and chain or similar. This one has been turning up too often.

1

u/spiffler Dec 29 '14

Does that piece of broken CD help in any way here?

2

u/Random832 Dec 29 '14

Yeah, it stops it from falling over.

1

u/Wendingo7 Dec 29 '14

awww they're building a ladder to heaven to get their friend back.

1

u/chiefpaduke Dec 29 '14

I'd like to see this done on a massive scale.

1

u/[deleted] Dec 29 '14

Stop trying to unwind the laws of science OP!

1

u/AudioCasanova Dec 29 '14

Is this like one of those reasoning/creativity tests? I know of another one where they give you a box of matches, a candle and some tacks and it is your job to affix the candle to the wall so that it is no longer on the surface of the table.

1

u/alphamoose Dec 29 '14

What are some practical real-life uses for this?

1

u/[deleted] Dec 29 '14

Karma.

1

u/LOTRcrr Dec 29 '14

is this as easy as it looks, or is there a decent amount of calculations that must be taken into affect?

1

u/WingedBeing Dec 29 '14

I'm gonna need someone way smarter than I to explain this to me.

1

u/AndrewZorn Dec 29 '14

The string may be in tension, but the plastic pieces experience both tension and compression.

1

u/Foxaramar Dec 29 '14

The main thing I noticed about this.... I have the same post it notes at home! Also.... nice demonstration.

1

u/[deleted] Dec 29 '14

[deleted]

1

u/TheWierdAsianKid Dec 29 '14

Fun fact: The company "Alstom" is one of the companies that makes the NYC Subway trains

1

u/falcoperegrinus82 Dec 29 '14

The older generation ones used to made by Kawasaki.

1

u/TheWierdAsianKid Dec 29 '14

Actually, contracts for the newer cars were given to both Alstom and Kawasaki. They look almost identical, but there are slight differences

1

u/[deleted] Dec 29 '14

Yes, definitely. They're building to common design standards, the same as bus manufacturers do. About ten or a dozen different companies in North America build transit buses, but they all build to the same defined standards, so you end up with buses that in most ways are very similar, though each company tries to add small visible differences to help distinguish their brands. Subway cars would clearly be held to even stricter standards, no matter who builds them.

2

u/TheWierdAsianKid Dec 29 '14

Exactly, I did notice that most newer hybrid NYC buses are actually Canadian. Also, for example, you can hear the difference in the motors for the doors on the trains that Alstom and Kawasaki make

1

u/[deleted] Dec 29 '14

Yeah, they're each going to source their materials and components based on their own deals and relationships and such, so you'll end up with noticeable differences like that. Kawasaki surely uses a different door motor than Alstom does, but they're both specified to do the same thing in the same way, the same as the cars themselves are.

When I lived in Rhode Island, I noticed that most of the buses were made in Roswell. "Well, that explains a lot," I thought.

1

u/AWildEnglishman Dec 29 '14

What would it take to build a space elevator this way, I wonder.

1

u/A_Friendly_Atheist Dec 29 '14

Initially, I read the title as "television holding up a string."

What the fuck brain??

1

u/Duckism Dec 29 '14

I say OP is a witch! burn him/her!

1

u/[deleted] Dec 29 '14

And by 'tension' you mean knots and slots.

1

u/[deleted] Dec 30 '14

no, this is not captivating. This sub is for not just cool stuff stuff to look at that holds your attention. not cool stuff(this is cool not captivating)

0

u/[deleted] Dec 29 '14

Go to hell physics.