Spider Silk Can Halt a Train | Hacker News Reader

Spider Silk Can Halt a Train

news.discovery.com

54 pointsgeeknik23 comments

Former vice president Gore spoke at Google a couple of weeks ago (promoting his new book). One of the research projects he mentioned was "spider-goats", goats that are genetically engineered to secrete spider silk along with their milk.

Some details in a news article here: http://www.guardian.co.uk/science/2012/jan/14/synthetic-biol...

Given the value of the silk (and presumably the difficulty in mass-farming spiders), this seems like an attractive idea -- as long as the scientists do the math right and don't end up with spiders the size of goats or something.

Look on the bright side, we'll have a new sport: Spider Goat Jousting.

Sounds like an unacceptable risk to me

Exact line used in criticism of vaccines, air-travel and in-vitro fertilization.

All new technology carries unacceptable risk... until they don't. But that's why science needs a constant feedback loop to improve understanding and safety. We can't make safe what we don't understand.

He was making a joke about the risk of goat-sized spiders.

I don't think drawing attention to the fact the comment wasn't short sighted, merely inane will gather much more sympathy for the poster.

It might be interesting to introduce you people to the concept of humor.

the joke here is that there are no jokes. that's what makes it funny.

Having the silk liquid along with the milk is not enough to produce the solid silk. Spiders physical action in turning that liquid to solid is indeed another important part of that. Probably they should produce 8 legged spider goats!

The article is a bit misleading in that it states that a spiders web could stop the train. The paper is clearer in this respect. Of course it should say the fictional web in Spiderman could stop the train, if it were made of the material of the actual spiders web. They assume a thread diameter of 5mm, as opposed to probably about .1mm in a real spiders web.

My take on Spider-Man stopping the train was that the first several anchor points failed as anchor points in the web/anchor/train system (they underwent systemic collapse due to loads past their design tolerances). Therefore, Spidey increased the number of anchor points to more even distribute the load.

http://what-if.xkcd.com/18/

So can AK-47s.

  | air rifle fires [...] at a muzzle velocity of
  | 100 meters per second

  | The GE Genesis Series I locomotive [...] travels at   
  | around 45 meters per second

  | If you bounce a single BB off the front of the
  | locomotive [...] you slow it down by about a foot
  | per day

Why is everything in meters per second, then we jump to using feet all of the sudden? Isn't this just asking for conversion errors? :P

> Why is everything in meters per second, then we jump to using feet all of the sudden?

Metric is easier to do calculations in, while imperial is used for the "layman terms". The intended audience is mainly american, and feet are more familiar to them than meters.

But that's precisely the sort of practice that causes conversion errors. Non-metric units should only ever be used in addition to the metric ones, in parentheses, if at all.

If you're trying to stop a train with a BB gun conversion errors are not going to be your primary worry.

It's more poetic than "30 cm per day" or "a third of a metre per day".

  | We were surprised to find out that the webbing
  | was portrayed accurately.

They are forgetting that in the movie the strands of web were not all connected together. They had Spiderman at their center, holding on to them. It would seem that his body and/or his grip on the web strands would be the weakest link in trying to resist the force of a train.

There's also some issues with conservation of mass.

Poor Peter would at least be thirsty after all that web shooting, if not wildly hungry.

Anything can halt a train, if you put a lot of it in one place.

This is related to biomimicry (using nature as the inspiration for design). If you're interested in learning more, I helped start a local group: http://bayareabiomimicry.org/

- Ryan

What about the materials and structure of a train car - can they sustain instantaneous force required to stop a speeding train? RRRIP! Oops, maybe not.

They mention 300kN in the article, and in the design of trains that isn't a lot at all. For example, the AAR [1] standards require a railway vehicle to take up to 1.8x 1560kN longitudinal force - that is, the force imparted down the length of the train through the couplers in to the body structure - without causing bulk yield [2] of the body material. A second design requirement is for the body structure to take 4450kN 'collision' force without exceeding the ultimate strength of the body structure material.

Other design criteria include, for example, crash protection of the driver's cabin if it's a locomotive where the drivers sit at the very front, so that part's often very strong and rigid as it needs to preserve a 'survivability space' for the drivers.

For passenger cars, the body structure tends to have a lot of strength against longitudinal loads in order to combat the phenomenon of climbing. That is, in a railway collision with passenger cars, as the vehicles ride in to one another, there is the tendency for one to pop up/down and try to 'ride up/down' on top of/under the one in front. [3]

This was demonstrated rather tragically in a particular accident (I can't find its name, sorry) where old wooden passenger vehicles did this. Their comparatively strong underframe simply sliced through the comparatively weak cabins like horizontal blades and caused huge fatalities. This is because old passenger cars used to basically be flat-top wooden vehicles with a cabin placed on top, so the body structure was very strong compared to the weak cabin. Since then, passenger vehicles must be specifically designed not to climb up on one another and do that.

So really, in the sense of railway design, 300kN is minimal, especially when placed longitudinally down the length of the vehicle structure. They are far weaker against lateral collision so I guess if you ever want to cause a huge railway accident, hit a train side-on rather than end-on.

[1]: Not the standards themselves, as they're not publically available - https://www.aar.org/Pages/Home.aspx

[2]: By 'bulk yield' I mean yielding over a significant portion of the structure. This is a legacy of the AAR standards originally being targeted towards hand calculations, where you couldn't easily inspect every particular section of every particular beam but rather you calculated it as a whole. With the advent of finite element analysis you can now do that, so it's permissible to see slight yield-levels of stress in certain small parts so long as the overall section as a whole remains under it.

[3]: This will give a brief example of anti-climbers on rail vehicles: http://www.oleo.co.uk/products/rail/anti-climbers

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