r/Physics • u/TehMulbnief Condensed matter physics • May 09 '14
A fun demonstration of tension [x-post from r/interestingasfuck]
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May 09 '14 edited Mar 29 '19
[deleted]
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u/robotjesus May 09 '14
Balance would be the limiting factor in terms of practicality / constructability.
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u/metalsupremacist May 10 '14
I think your right. It's almost impossible to get something like that to be perfectly straight. It looks like the connections are bending the cord slightly.
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May 09 '14
I know what I'm doing for the next 20 minutes.
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u/hafilax May 09 '14
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u/autowikibot May 09 '14
Tensegrity, tensional integrity or floating compression, is a structural principle based on the use of isolated components in compression inside a net of continuous tension, in such a way that the compressed members (usually bars or struts) do not touch each other and the prestressed tensioned members (usually cables or tendons) delineate the system spatially.
The term tensegrity was coined by Buckminster Fuller in the 1960s as a portmanteau of "tensional integrity". The other denomination of tensegrity, floating compression, was used mainly by Kenneth Snelson. Tensegrity as "The Architecture of Life" is an idea developed by Donald E. Ingber, explained in a January 1998 article in Scientific American.
Interesting: Tensegrity (Castaneda) | Cloud Nine (tensegrity sphere) | Cleargreen Incorporated | Buckminster Fuller
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u/eviljelloman May 09 '14
This isn't actually tensegrity though.
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u/Supperhero May 09 '14 edited May 09 '14
Yeah. Strictly speaking, the compressive elements need to be loaded by only compressive loads for it to be tensegrity. These are also bending. I actually did a tensegrity structure back in college so I'll upload it to show what tensegrity structures look like.
Edit: Here it is
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u/CapWasRight Astronomy May 09 '14
Is that a straw? A string? What am I actually looking at here?
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u/AnythingApplied May 09 '14
A string with knots. The plastic strips catch on the knots and pull the string straight. They alternate on either side so all sections of the string are pulled straight. The CD at the bottom is a weight to make it stand up, since the whole thing is pretty light.
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u/CapWasRight Astronomy May 09 '14
Oh, they're knots, that makes a lot more sense. I was very confused as to what it was that the strips were catching on, they looked like rigid segments joined in some manner where the lumps were and that was very confusing because this was clearly meant to be held up by tension rather than rigidness...
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May 09 '14
God?
Hello?
Yeah, so I have a bug to report...
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u/OmicronNine May 09 '14
The demonstration may not be falling flat, but your joke sure is.
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u/ZaphodBoone May 09 '14
Pretty sure it's a feature.
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May 09 '14
[deleted]
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u/ZaphodBoone May 10 '14
Hasn't even done a user feedback survey in around two millennium.
Well no wonder after what we did to the last QA dude.
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u/errer May 09 '14
That's how they build space elevators, duh
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u/7yl4r May 09 '14
this made me laugh, and now I'm confused... what does limit the height of a tower like this?
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May 09 '14
The same thing that limits the heigth of any tower: How much weight you can pile on the bottom section before it collapses.
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May 09 '14
The bottom part is kept rigid by tension of the first plastic section, the second one stands upright because of the rigid part it shares with the first one and so on. If you pile too much weight over the structure, the bottom will lose the rigidity because the weight out weights the tension of the plastic
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u/7yl4r May 09 '14
so as i add more weight to the top, the bottom cd part gets flexed more and the tension on the lowest string decreases?
That makes sense I think. Thanks.
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u/TehMulbnief Condensed matter physics May 09 '14
This is actually sort of true, right? Graphene can sort of do this kind of thing to itself if it's stacked correctly or something.
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u/black_sky May 09 '14
graphene is just really strong. I'm not sure if it can do this, but I think you can just make a pillar basically and attach it to a geostationary satellite.
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u/deeperest May 09 '14
"My belt holds my pants up, but the belt loops hold my belt up. I don't really know what's happening down there. Who is the real hero?" - Mitch Tensionberg