Wikipedia:Reference desk/Archives/Science/2014 May 15

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May 15

old steel bike frame compromised due to cold temperatures?

So I live in Minneapolis and I ride an old heavy steel framed Fuji road bike, probably from the 70's or 80's, kind of like this. I left it outside all through the winter, though under an awning so it wasn't covered in snow. It was one of our coldest winters ever, with windchills hitting -20F or worse for weeks. We'd have days when the high temp, not even the windchill, was like -7F. One of my extreme bike enthusiast friends told me that the frame is compromised simply from being that cold regardless of if it was actually exposed to snow/moisture. Is this true? NIRVANA2764 (talk) 13:50, 15 May 2014 (UTC)

Windchill doesn't matter. That's just a measure of how weather conditions "feel" to people. But either way, cold temperatures shouldn't have made a difference. Even if it was cooled below the ductile–brittle transition temperature, that's not a permanent change. Permanent changes in metals generally require high temperatures, not low ones. So as long as there was no load on it, it should be fine. Moisture could cause rust, but cold temperatures would slow rusting, and as long as the paint is intact, that should prevent rust as well. Mr.Z-man 14:36, 15 May 2014 (UTC)

Our article steel doesn't seem to mention it, but steel gets more brittle at low temperatures. See e.g. here [1] for a description. I agree with Z-man that there is no lasting degradation to the frame after being stored at cold temps. But it is possible that e.g. an accident that leaves the frame intact at 70F could crack the frame if it happened at a low enough temperature. SemanticMantis (talk) 14:44, 15 May 2014 (UTC)

So that impact would only damage it if it happened while the frame was very cold? We have sunny warm spring weather here now, but I'm worried about the frame being permanently delicate now that it simply has been very cold for months on end at one point. My friend told me that bumps which used to be fine could now buckle the frame. NIRVANA2764 (talk) 14:59, 15 May 2014 (UTC)

I'm sure it would not be difficult to subject the bike to a few test bumps or torsion without you actually riding it. I have no doubt your bike will be fine. Richard Avery (talk) 15:23, 15 May 2014 (UTC)

• The main issue is that steel shrinks significantly when it gets cold, and if different parts of the bike shrink by different amounts, you could get warping, and conceivably a cracked weld somewhere. But I don't think the risk is very high, given how robust steel bikes are, especially those heavy old Fujis (I rode one for years). If the wheels don't wobble when you spin them, and there is no feeling of vibration when you ride, and no visible damage, I wouldn't worry about it. Looie496 (talk) 16:02, 15 May 2014 (UTC)

• Agreed. I'd inspect all the welds for cracks. If you don't see any, it's probably fine. StuRat (talk) 16:20, 15 May 2014 (UTC)

The great and terrible thing about failure analysis is that on any individual unit, you only get one shot. I think your friend is 100% correct: the bicycle is compromised. That is a very specific word-choice: your friend does not say the bicycle is damaged - only that it is compromised. Statistically, there is a greater chance that it will become damaged. We don't know whether your specific bicycle is actually going to break due to brittle failure until it breaks! If (or when) it does break, we can't know whether it would have broken later - or if it would have withstood the same force - had it never been exposed to the cold.

What we can know is that in laboratory experiments, if we subject steel to cold (or any thermal cycle), then that steel is statistically more likely to yield or fracture. To what extent does this make your bicycle unsafe? Well, that's a very hard question. We'd need to have boatloads of statistics about the design and materials of the bike frame; we'd need data about the temperatures it had been exposed to; and so forth.

So what we can say - at the risk of using a weasel word - is that your bicycle is compromised. We suspect that it has been exposed to a condition that can adversely affect the structural integrity. We don't know how much it's affected. Presumably, we can't find any actual damage, and we won't go so far as to call the bicycle unsafe.

Entire factories are full of specialists who study this problem as it applies to mass production. These people include material science and engineering experts; reliability engineers, operations and supply chain experts, and so on. Not to discredit Richard Avery - but his approach is not really applying the scientific method. You can thump around the bike frame all you like, and you might still find that it is undamaged. But have you actually tested the null hypothesis? Of course not!

If you want to know whether the cold has compromised the bicycle, you must conduct a proper controlled experiment. You need a statistically-valid population (say, many dozens or many thousands of bicycles). You need a test group and a control group. You need sterile laboratory conditions to isolate variables from the independent variable - the thermal cycle; and you need to conduct enough tests to determine time until failure on many bicycle frames (damage the bicycle until they break!) And then you need a statistician to tell you whether we can confidently say that the dependent variable ("damage") correlates to the thermal cycle.

And that's failure-analysis for a steel bicycle frame - a couple pieces of welded steel! Steel is a material whose properties are well-known; the common alloys haven't changed in decades and their thermal characteristics have entire ASME and ASTM handbooks encyclopedically detailing how and when they break.

My bicycle owner's manual, which I've of course read cover-to-cover, has an entire chapter on thermal properties of bicycles with complex parts including carbon fiber. Actually, high temperatures are the worse condition for my bike! If stored above 66.5°C, I'm afraid my bicycle falls "out of specification." I suspect exfoliation of the carbon-fiber from the aluminum becomes problematic. Long before we hit that temperature, the synthetic polymer "rubberized" grips also start to become irreparably melted. Around here, my bicycle rarely gets exposed to freezing conditions.

Now imagine if you mass-produce computers. Suppose, hypothetically, that your computer were mostly made out of metal and glass, but with lots of weird alloys - especially new, "non-hazardous metal" - plus silicon and plastic and fibers and flex circuits - and you want to know whether thermal cycles cause them to fracture. (Hey, people leave their metal-and-glass computers outside in the cold all the time - does that "compromise" the device?) Just imagine for a moment the complexity and the cost of building fully-functional computers, thermal-cycling some of them in hot ovens and ice-boxes for many weeks, and then dropping them on concrete by the thousands, just to see if they break. Only then can you safely assert that you know whether the mechanical parts are "compromised;" and you can confidently advertise an environmental requirement for operating- and non-operating temperatures.

Nimur (talk) 16:29, 15 May 2014 (UTC)

What an elaborate response! What my friend meant is, in layman's terms: it's trashed; don't ride it; permanently beyond repair now that it has at one point been so cold. But others have said that even if it got cold enough that it crossed the ductile–brittle transition temperature it would not be permanent change since there was no weight on it and it's warm now. So, Nimur... would you ride it? :) NIRVANA2764 (talk) 16:43, 15 May 2014 (UTC)

Sure, I'd ride it... but I wouldn't ramp it. Nimur (talk) 21:07, 15 May 2014 (UTC)

Indeed, what a lot of woffle from Nimur. But he is right in saying metalugy of the steels etc that bicylcles are made of is well understood. No permanent change in brittleness will occur. There is another aspect: Steel bicycle frames are made with brazed joints (similar to soldering). Any join involving dissimilar metals is subject to eventual failure if subjected to thermal cycling. The basic mathematical approach to predicting failure is called the Coffin-Manson relationship, after the names of two pioneering researchers. Coffin-Manson mathematics has been used to explain effectively "fatigue" failute in things ranging from aircraft airframes to power transistors. At the root of it is uneven thermal expansion. But if you do the calculation on a typical brazed jointed steel bicycle frame, you'd need 1000's of years of extreme weather to induce Coffin-Manson failure. 121.215.85.7 (talk) 16:56, 15 May 2014 (UTC)

As Nimur suggests, nobody here can assure you that the bike is just as safe to ride now as it was two years ago (or 10, or 20, etc). But consider: how old is the bike, and how many cold winters has it seen? What is the marginal change from just one cold winter? Personally, I'd ride it around town without a second thought. But maybe I wouldn't race it, or take a multi-day solo tour. For a point of comparison, I ride a ~1975 steel-frame Chicago Schwinn. It's seen plenty of temps that low over the past ~4 decades, and it still feels indestructible to me :) SemanticMantis (talk) 19:15, 15 May 2014 (UTC)

I live in a place where we get cold temperatures for months on end. Every winter people put their bikes into cold storage and bring them out again in the spring (around this time of year) and they have no problems. CBWeather, Talk, Seal meat for supper? 00:24, 16 May 2014 (UTC)

Just out of curiosity -- if people worry this much about bikes, why is it seemingly universal practice for states to leave bulldozers, road rollers, and such-like heavy duty equipment lying around in state parks, and even when they care enough to stockpile it in a secure lot they leave it out exposed to the elements? I mean, they don't even keep the snow and rain off them let alone anything else. I'd think if I had a $100k+ machine I'd garage it. Wnt (talk) 16:09, 16 May 2014 (UTC)

I think because of the expense of moving such things on the road. You need to rent special flat bed tow trucks that can lift them onto their bed, etc., and that's pricey. If you've been using it in that park until winter hit, and expect to use it again there next spring, it's cheaper to leave it on the job site. Presumably they are also built to withstand such weather. As far as theft goes, it would be rather difficult to hide and then sell such a stolen big rig. StuRat (talk) 16:30, 16 May 2014 (UTC)

Any bulldozer, grader, loader or any other heavy equipment that is going to be used during the winter will usually be kept inside. On the other hand things like dump trucks that are only used in the summer will be stored outside. For personal vehicles if you want to use it all winter and you don't have the space to build a shelter or you can't afford to heat one then it gets parked and plugged in on a daily basis. If you don't plan on using it till spring then it gets left outside. CBWeather, Talk, Seal meat for supper? 22:40, 16 May 2014 (UTC)

Bipedalism

Why back in dinosaurian times bipedalism in animals was more common and more widespread than now, when there are relatively few bipedal species (especially since small upper limbs of bipedal dinosaurs were of little use)? Brandmeister^talk

This is not true when you consider birds to be bipedal. They are modern dinosaurs. The reason that they are smaller is:

1) To allow them to fly (except for flightless birds, of course).

2) Because oxygen content in the air is less now, making breathing more difficult for huge land animals. (Whales get past this restriction because swimming is far more efficient than walking.) StuRat (talk) 16:15, 15 May 2014 (UTC)

Citing birds they way StruRat did is a nonsense. Birds are a later adaption, and their wings are adapted front legs/arms.

I note that most of the larger lizards around today are partially bipedal. When they want to go fast, the raise up their fronts so that the front legs are hanging free, raise their tails up for balance, and run on their back legs only. The back legs are bigger than the front legs, though the difference is nowhere as extreme as it was for certain types of dinasaur. A leg is not mechanically 100% efficient, having a certain level of energy loss mainly dependent on length and to a lesser extent on mass. So running on two legs is more energy efficient that running on four. Efficiency is not critical for mammals as their pressurised blood system, with 4-chambered hearts, allowing the presure to the limbs much higher than the pressure to the lungs, facilitates vastly better oxygen delivery to the muscles. Lizards can run pretty fast, but they tire extremely quickly due to low body temperature and a simplified low pressure blood system. Some large lizards can run as fast or faster than a man, but at max speed conk out after only 10 meters or so.

Running balanced on two legs also confers a significant manouverability advantage when negotiating complex terrain, as in dodging and going around rocks and plants. I've seen a dog chasing chickens that had had their wing feathers removed (so they could not escape over fences). They could not take off, but they could turn so fast the dog could not catch one, uselessly doing 4-paw slides and colliding with trees. But on open ground with no obstacles, those chickens would have been goners, as the dog has greater stamina.

I doubt that the very small front limbs of certain dinasours were completely useless. These dinosaurs persisted for millions of years, so evolution should have got rid completely of anything useless. When you look at some apparently useless feature on an animal, it's usually for sexual attraction or for courtship rituals/"dances".

121.215.85.7 (talk) 16:35, 15 May 2014 (UTC)

While the question of why the bipedalism was ostensibly more common in animals in Mesozoic era than at present may not be answered in the strict sense, I believe the following factors should be considered. (1). Evolution does not produce perfect species, just "good enough" species capable of occupying an available ecological niche. It so happened, due to the mass extinction, that at the beginning of Paleogene many ecological niches became available; and the surviving land vertebrates were mostly small and nocturnal. A nocturnal biped is a rarity: there is no evolutionary benefit in tripping and falling. The available niches were therefore taken by quadrupeds. The quadrupeds diversified, became active at various time of day, and some of them (kangaroos, humans) did become bipedal. Flightless birds also occupied some of the available niches (see e.g. Cassowary, Ostrich, Moa, Aepyornis for extant or recently extinct examples). (2) Vegetation was quite diffferent in the Mesozoic than it is at present. It is possible that whatever suits velociraptor well wouldn't have suited a jaguar nearly as well, and vice-versa. (3) Bipedalism is not unique to birds, humans, and Mesozoic theropods. Even cockroaches are capable of bipedal locomotion when running fast to escape a threat. (4) The perception of the more common bipedalism in the Mesozoic may be rooted in human culture rather than in real fact. We are best acquainted with the largest terrestrial vertebrates. Indeed, they preserve the best, and draw the biggest crowds to museums and movie theaters. Vast majority of terrestrial species, however, are arthropods, molluscs, and small vertebrates. There are not too many bipeds among those, either then or now. A lot of the smaller Mesozoic animals haven't even left any fossils to work with. Hope this helps. Dr Dima (talk) 17:45, 15 May 2014 (UTC) NB. Velociraptor is actually a bad example: there wasn't too much vegetation where it used to live :) Dr Dima (talk) 18:06, 15 May 2014 (UTC)

• I question the premise of the OP. Per plurium interrogationum the OPs question posits a presumption we have not yet established as true. Do we know for certain that bipedalism was more common in the mesozoic era than at other times? I've seen no evidence that is even true. It may be, I am not saying that it is or isn't true, just that until we've established it as true, it makes no sense to say why it is true. --Jayron32 18:09, 15 May 2014 (UTC)
  • I may be actually wrong, it's just my impression. However, in terms of habitual, constant bipedalism it looks like back in the Mesozoic there were more terrestrial animals with such locomotion, than in modern times. My speculation after 121.215.85.7's reply is that at least partially bipedal manouverability proved to be superior to quadrupedal speed, such as in cheetahs. Brandmeister^talk 18:31, 15 May 2014 (UTC)
    • See, that's the problem. People have all kinds of impressions. Has there been any systematic quantification of the prevalence of terrestrial bipedalism across the eons? If not, then what are we basing this on? The fact that we've seen a lot of pictures of bipedal dinosaurs? Couldn't that just mean that the T-Rex is a popular dinosaur? Could it mean that our museums and artists tend to favor familiar forms, and that they tend to put more bipedal dinosaurs on display than others, merely because they generate more interest, being that humans are bipedal and thus tend to be more interested or attracted to bipedal dinosaurs? There's many ways to interpret your impression, and until we've established your impression as reliably enough confirmed, there's really no point in telling you why it is true; if in fact its truthfulness is an open question. It may be true, I haven't said it isn't. Just that it isn't worthwhile to develop a theory to explain why it is true, if it may turn out later to not be true. --Jayron32 00:54, 16 May 2014 (UTC)
      • Indeed. Given that in any ecosystem, herbivores necessarily outweigh carnivores (after all, carnivores need to eat something), and that triceratops, apatosaurus and stegosaurus species were all quadrupeds, this may simply be a wrong impression caused by the popularity of representations. --Stephan Schulz (talk) 05:55, 16 May 2014 (UTC)
        • What you say is common sense, but it is not always true that herbivores outweigh carnivores at a certain locale. See e.g. this (freely-accessible) paper [2], search for "pyramid". There is a whole section on 'inverted biomass pyramids', discussing how in some cases top predator biomass far exceeds herbivore biomass. When I heard Sandin present this work he had great photos of these shark-dominated waters. SemanticMantis (talk) 14:24, 16 May 2014 (UTC)
        • The relatively high prevalence of bipedalism among terrestrial vertebrates (except mammals) is probably because they can not run efficiently using all four limbs. This is related to the structure of their spines, which could only bend in the horizontal and not in the sagittal plane—good for swimming but not for running. So, the only option if you want to run fast was to use only one pair of limbs. On the other hand mammals acquired a number of adaptations that allowed them to effectively use all four limbs for running. This includes spines that bend in the sagittal plane. Ruslik_Zero 12:43, 16 May 2014 (UTC)

Ruslik obviously has never seen a lizard. When on all fours, their sideways swinging gait is generally quite pronounced. 121.221.156.103 (talk) 02:08, 17 May 2014 (UTC)

an illustration for the standard model of particle physics

Hi!

Could you please check this diagram for errors?

I double checked it, but i'm not a specialist in particle physics and i fear i got something wrong.

---

Mass:

   more than 80 GeV/c^2

   1-5 GeV/c^2

   90-110 MeV/c^2

   less than 16 MeV/c^2

   Massless

---

Spin (small blue circles in the middle):
empty circle: 0
full circle: 1
half-circle: 1/2

---

Charge (external circles):

   positive

   negative

full circle: 1 or -1 respectively
2/3 circle: 2/3 or -2/3 respectively
1/3 circle: 1/3 or -1/3 respectively

---

Participation in interactions:

  Weak force

  Electromagnetic force

  Strong force

Thanks!

P.S. I don't want to replace the standard diagram, this diagram is just an additional illustration.

Zhitelew (talk) 17:12, 15 May 2014 (UTC)

It's a really neat diagram, but it sure isn't the standard diagram. Did you create this diagram yourself or are you following a model from a reliable source?

Reputable publications all seem to use the same diagram - in other words, the standard diagram - to illustrate the standard model. I've never seen your new circular lay-out before - and I've read a lot of physics books - so I wonder if it really belongs in an encyclopedia article.

For example, you might find the diagrams in CERN's eduation resource website FermiLab's education resources page look awfully similar to the present diagrams we use in Wikipedia. It's probably best to stick to the schematic representation that real physicists are actually familiar with. Nimur (talk) 21:36, 15 May 2014 (UTC)

Hi, Nimur. Thanks for the answer!

I made this diagram myself, but there is nothing original in it. I just bended the "standard" table into a circle and replaced numbers with colors. The design of the diagram can be new, but all the science and data are from the same "standard" table. --Zhitelew (talk) 21:59, 15 May 2014 (UTC)

...Right, but what does it mean? Let me clarify: I know about the Standard Model, but let's imagine momentarily that I know nothing, and I'm learning it all from your chart. And, I apologize for nitpicking here... you've made a really nice picture and I can see that it took effort. It's quite artistic and very skillful. But, we're making an encyclopedia, not a graphics showcase... and I think there are important and problematic issues with your diagram as a physics-education tool.

See, I look at this chart, and I wonder why you've apparently plotted it in polar coordinates. I see that particles at larger radius have a larger area on the diagram. What does this represent? Are those particles larger? Are they more abundant? What does "area" represent in this chart? What does radial-distance from the origin represent? Are particles at the center of the diagram "inside", while particles at the outer rim or the diagram "outside" of composite particles?

The chart is circular. It "wraps around." What is the physical meaning of this? I'm going to start making inferences - physically incorrect ones! - "photons are close to tau mesons on the chart, so are they related?" ... And now, on account of a confusing diagram, I've embedded incorrect physics into my understanding of things.

So, you see, there is a reason why all the standard diagrams look the same. Consider, for example, the Periodic Table of the elements. It can be re-drawn in many ways;if you read into it, you'll see that many alternate diagrams do exist. But, except for a small number of special-purpose variants that are made for expert users, most of those charts just serve to confuse science-students.

You might enjoy reading the Junk Charts blog. The authors tear apart a variety of infographics that they find on the internet. Artistic creators can draw lots of neat-looking charts - and nowadays, it's very popular to design an exciting-looking infographic diagram - but what do the axes mean? Does the diagram convey information in a straightforward, accurate way that is easy to interpret? Does your diagram? Or, quoting Mr. Fung more directly:

• What practical question are you trying to answer?
• What does the scientific data say?
• What does your chart say?

So: how are the particles of the standard model related? Does your chart answer this question?

These are tough questions, but if you want an honest and very brief answer, "no." (It is my opinion that) your chart is not the best way to represent the standard model in an encyclopedia article. The standard diagram - as boring as it may seem - has been around for a while, and it's best to stick to that layout, unless you find a reliable physics education source that makes a convincing case otherwise. Nimur (talk) 04:10, 16 May 2014 (UTC)

OP isn't suggesting replacement of extant figures. I take your points, but I think this figure is quite nice. Of course I would personally never think the areas represent anything, but that can be explained in the legend to head off confusion. I actually think the colors and pie chart insets for spin and charge make those pieces of info much more easy to grasp at a glance. That is something that this new chart "says" much more clearly than the ones you linked. So, provided there are no factual errors (which I assume you'd have mentioned), I see no reason why this can't be used to supplement other, more standard graphics in our articles. I also don't think this is WP:OR, insofar as nothing is original except for layout. We aren't publishing a paper book, (WP:Notpaper), and there is no limitation on how many figures can be used to express concepts. I don't share your fear of the graph leading to non-physical notions, but again, a good legend will go a long way in preventing that. SemanticMantis (talk) 15:22, 16 May 2014 (UTC)

I have to agree with Nimur. What is this trying to show? For example reading this graph in the top column you have the Higgs with the Z⁰followed by the neutinos (why no anti neutrinos, they haven't been confirmed as Majorana particle yet) working away from the centre of the circle. Okay they all only weak force and are neutral but they are fundamentally different particles. The neutrinos are seperated from the other leptons, why? From this graph it doesn't look as if the charged leptons and the neutrinos are part of the same family but the neutrinos are asociated with the Higgs. There is nothing fundamentally wrong with graph (besides saying for sure the neutrino is not a Dirac particle like all the fermions) but it can lead people to make the wrong connections.Dja1979 (talk) 19:53, 16 May 2014 (UTC)

Thanks for the critics! I didn't add antineutrinos because (as far as i know) the existence of antineutrinos is not confirmed yet.

In the Standard Model antineutrinos exist and they have been shown to be different to neutrinos (sorry I don't have the paper).The MINOS experiment was able to produce a beam of neutrinos and then by flipping the horn currents produce a beam of antineutrinos. Nuclear reactors only produce antineutrinos so expriments like Daya Bay only see antineutrinos never neutrinos. T2K and NOvA are using the differences between neutrinos and antineutrinos to find the value of the CP violating phase. So we do know that antineutrinos exist.Dja1979 (talk) 23:09, 18 May 2014 (UTC)

Agree. The diagram should better display borders between particles with different spin. This should help against possible wrong connections and accentuate the right ones.

I probably should mark the empty slots with other color. These white spaces only indicate the absence of the particles with corresponding properties, not borders between groups of particles.

By the way, aren't neutrinos fundamentally different from other leptons? Yes, they have the same spin as other leptons, but they have all these unique wired properties like oscillations, extremely low mass, only week interacting etc. Shouldn't we indicate this somehow? --Zhitelew (talk) 20:48, 16 May 2014 (UTC)

I would say no. Only weak interating is stated by the fact that they have colour charge 0 like all leptons and their electric charge is 0, gravity isn't included in the Standard model so left of this only leaves Weak charge I don't think this needs more explanation (any more than up quarks and down quarks are different, so needing explanation). Oscillations in the charged leptons hasn't been observed yet but it could happen. For example the quarks mix to a lesser extent, so not unique to the neutrino. Low mass; we don't know what generates the mass so it may be important, it may not be, I would leave it for the time being. Dja1979 (talk) 23:09, 18 May 2014 (UTC)

spiral periodic table

• This might also be a good question for the Mathematics desk since what you have here is a rectangle transformed into a cylinder looked at from a polar prjection (I may have the terms slightly off.) This works fine if the opposite edges joined to form a cirle actually can be so joined--you can do this with a periodic table with some jiggering. You can't do it with a normal chessboard howver, since pieces aren't allowed to move diagonally acrost the right and left edges in the standard game. μηδείς (talk) 20:07, 16 May 2014 (UTC)

Engineering disciplines

Is there a huge difference between different engineering disciplines other than what they're engineering? For example civil engineers engineer civil infrastructure and aerospace engineers engineer aircraft but do they use the same principles? 82.40.46.182 (talk) 22:38, 15 May 2014 (UTC)

No, there isn't a huge difference in disciplines. At my university the big divide was between civil and all the rest, and in the second year the electricals started to specialise away from the rest. Civil is a bit odd as they often design to code, whereas most disciplines design for function. As such I would expect a mechanical engineer to happily work in aerospace, I think that might be more of a stretch for a civil engineer. If you see a mechie in a civil firm he is likely to be working either on the mechanical systems (lifts, HVAC,plumbing) or as a structural engineer, as frankly the civil guys seem a bit flaky on structural analysis. FWIW I was more or less in the mechanical stream, yet my career includes fairly big lumps of electrical and signal processing. University is NOT about teaching you to do a job, it is about giving you the basic tools and the confidence to be able to teach yourself. As such, if you haven't covered the design of power amps during uni, you know at least enough to find the right book and learn from it (to pick an example that came up for me). For that matter I've worked with engineers who did maths or physics at uni, they taught themselves what they hadn't picked up at uni. Greglocock (talk) 23:40, 15 May 2014 (UTC)

On a day-to-day basis engineers usually work with approximations and simplifications that apply in their field or sub-field, even though these approximations and simplifications are not true in general. An example for electrical engineers would be Kirchhoff's circuit laws. Jc3s5h (talk) 23:53, 15 May 2014 (UTC)

Kirchoff's circuit laws are conservation laws which when properly applied to lumped components are exact, not approximate. 84.209.89.214 (talk) 01:55, 16 May 2014 (UTC)

But the real world is not made up of lumped components. Jc3s5h (talk) 02:18, 16 May 2014 (UTC)

• On the contrary, I find that, other than some superficial similarities, the practices and workings of various engineering fields to be quite different. I'm not sure that the training and/or job requirements of a civil engineer, a chemical engineer, and a biomedical engineer are all that similar, excepting that they all are engineering fields; more like each other than they would be to other jobs like say a school teacher, a chef, or an economist; but otherwise I'm not sure many job skills from one of those fields would transfer well to the other. Someone designing a prosthesis would have a hard time working out the fluid dynamics and heat transfer problems a chemical engineer needs to face, and neither would necessarily be able to do the work necessary to design an automobile from first principles, without being fully retrained for the others job. Certain broad concepts, such as the mathematics background and basic physics principles, may cross over, but I'm not sure much more than that. --Jayron32 00:39, 16 May 2014 (UTC)

Curious. Are you an engineer? Greglocock (talk) 01:54, 16 May 2014 (UTC)

Civil engineering tends to be more about managing people and less on the technical side than say electronics engineering, but there is always a large component of working with other people. All also have to work safely within set constraints, be a bit practical, and be conscientious about keeping to schedule and documenting things. And it seems all have to at least occasionally work long hard and unsocial hours. It is a career for people who want to make something useful in the world. Dmcq (talk) 11:19, 16 May 2014 (UTC)

A military perspective. Mechanical engineers build weapons. Civil engineers build targets. HiLo48 (talk) 01:52, 17 May 2014 (UTC)