Wikipedia:Reference desk/Archives/Science/2006 November 25

From Wikipedia, the free encyclopedia

You have new messages (last change).
Science desk
< November 24 << Oct | November | Dec >> November 26 >
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.


Contents


[edit] November 25

[edit] Taller people

In taller people, where is the extra height mostly evidenced? Is it the legs or is it evenly distributed over the whole body?--Light current 00:53, 25 November 2006 (UTC)

Evenly distributed I think Light current, unless there`s some underlying genetic problem. i.e. gigantism. For good 'evidence', just look at all those nicely proportioned 'healthy' professional basketball players! Not conclusive evidence, but, pretty good, I would think. Hope that helps a bit. Dave 172.144.28.171 03:33, 25 November 2006 (UTC)
Some people have long legs and short torsos. For other people it's the other way around. So your question really is if there is a correlation between height and the leg/torso length ratio. Right? DirkvdM 09:02, 25 November 2006 (UTC)

[edit] Defense mechanism

I don't know if this question is actually science, it's psychology in any case. My question, if you'll accept it, is this: When I meet a person and find out that he shares some interest with me, perhaps favorite band, movie or things like that, I tend to feel resentment to that person, rather than a connection and a "common cause". This seems to be some kind of defense mechanism but the behavior doesn't seem to fit in under any of those mentioned in Defense mechanism. Does anyone know if it does, or if there's any name for this behavior at all? Thanks. Jack Daw 01:14, 25 November 2006 (UTC)

Competitiveness? --24.147.86.187 02:08, 25 November 2006 (UTC)
Egocentricism? Grandeur? Jealousy? Just guessing. Dave 172.144.28.171 02:31, 25 November 2006 (UTC)
Well there could be several words to describe it ;) Jack Daw 03:36, 25 November 2006 (UTC)
Boredom? Projected self-hate? ☢ Ҡi∊ff⌇↯ 05:46, 25 November 2006 (UTC)
Do you real feel defensive if you find someone shares the same interest as you? This seems a bit bizzare to me. I mean obviously if two people find they're attracted to the same person or you both see a car you'd like to buy or whatever then yeah maybe but when someone likes the same band or movie as you? Nil Einne 05:59, 25 November 2006 (UTC)
I don't know if there's a special name for it. I suspect what you are after though is reference information or leads, some useful material to take away relating to it.
What I'd look at, that isn't mentioned above, is, do you have a need to feel "special", "unique", or possessive over things that interest you, or not wanting to share, so that others are infringing somehow on what feels like "your turf"? Or else, do you have some sense of fear or insecurity, that maybe you aren't as good or capable as you would like to be (or fear others will discover this somehow), so that others intruding on "your" fields or interests are somehow a threat, a worry they might take it away from you or you might not be able to keep up the appearance with others who are also involved? Thats a couple of places I'd be starting looking. Hope they help. FT2 (Talk | email) 06:14, 25 November 2006 (UTC)
Well I know I _want_ to feel a connection, but my mind won't let me, sort of. All you said is probably true, as well things stated by others. One pattern that emerges though is that when I've "trained" a person, i.e. I've introduced something to them and explained it (music, film, philosophy, politics etc) I don't feel any resentment. My guess is that I'm highly suspicious of other people's ability to reach a position in the "proper" way. Something like that. Jack Daw 14:31, 25 November 2006 (UTC)
That 'need to feel unique' option makes me think of "I was a punk before you were a punk". When being different in a certain way becomes mainstream it's no longer different. DirkvdM 09:07, 25 November 2006 (UTC)
My mind definitely works that way I can tell you, but not necessarily. Even a small group that shares a similar quality to myself can become "too mainstream" for me to handle, so to say. Jack Daw 14:31, 25 November 2006 (UTC)

This is, apparently, a pretty common behavior. It forms the root of the following well-known (well, well-known in computing circles at least) joke:

I asked my email-pal: "UNIX or Windoze?".
He replied "UNIX".
I said "Ah...me too!".

I asked my email-pal: "Linux or AIX?".
He said "Linux, of course".
I said "Me too".

I asked him: "Emacs or vi".
He replied "Emacs".
I said "Me too. Small world."

I asked him: "GNU Emacs or XEmacs?",
and he said "GNU Emacs".
I said "oh, me too."

I asked him "GNU Emacs 19 or GNU Emacs 20"?
and he said "GNU Emacs 19".
I said "oh, me too."

I asked him, "GNU Emacs 19.29 or GNU Emacs 19.34",
and he replied "GNU Emacs 19.29".
I said "DIE YOU OBSOLETE NOGOOD SOCIALLY MALADJUSTED CELIBATE COMMIE FASCIST DORK!" , and never emailed him again.

Atlant 17:10, 27 November 2006 (UTC)

yes quite right - exclusivity means that you get what you want - when the unwashed masses get in on the action this mean that the lowest common denominator effect will begin to apply. And the usefulness/quality etc of the thing you liked/used will suffer. Your feelings are normal and based on real negative effects from popularisation of products - it's a natural reaction to the almost inevitable downward spiral in quality that comes from a mass audience (just my view..)87.102.20.219 17:34, 27 November 2006 (UTC)
For instance where can I buy a computer I can actually program????87.102.20.219 17:36, 27 November 2006 (UTC)

[edit] SpaceShip One

Is it possible for a SpaceShip One type craft(except quite larger) to go to the ISS and come back without having to use heat shields? Thank You.68.120.228.137 01:20, 25 November 2006 (UTC)

In a word, nope. SpaceShip One type craft achieve only a 'sub-orbital' flight...go straight up, come straight down. No 'great' speed achieved, to have to 'bleed-off' later. To 'capture' the ISS, a craft would have to accelerate to much higher velocities and then have to slow-down at a fast enough pace so as not to 'skip-off' the atmosphere. Heat shields are therefore necessary. As a side note: If a craft could carry enough fuel, it could 'climb' at a walking pace, and decend at the same pace, but that, of course, would not be a 'SpaceShip One' type craft. Dave 172.144.28.171 03:03, 25 November 2006 (UTC)

So It would have to be like an Ion Drive Craft or something with continuous exhaust?

No, an ion drive wouldn't do it either, ion drives are very-low-thrust drives for interplanetary travel, in order to get to orbit you would need a bigger rocket engine. You need to accelerate your craft to orbital velocity, something SpaceShipOne can't do. It reaches the altitude of low Earth orbit, but is not going fast enough to stay at that altitude, so within a few minutes will descend back into the Earth's atmosphere. — QuantumEleven 11:51, 25 November 2006 (UTC)

Thank You I believe I'm starting to understand physics more.

You're welcome, glad we could be of service! We have a rather technical article on astrodynamics which may be of interest to you, alternatively, look through the references and external links of said article for some more sources on calculating orbits. Our spacecraft propulsion article is also pretty good. — QuantumEleven 16:26, 25 November 2006 (UTC)

[edit] Question in chemistry

please say me what is the products when NH3 aquoes(NH4OH) reacts with MnO2,MnO3 ,FeO,Fe2O (Please note that others are in solid state) PLease say me whole the reactions possible in different temperateres


Hi! first you need to sort out your spelling and grammar a bit. "Please tell me what the products are when NH3 (aqueous NH4OH ) reacts with MnO2,MnO3 ,FeO or Fe2O".

I can't answer all your question but I can tell you than ammonia solution (also known as ammonium hydroxide or aqueous ammonia) will help to dissolve Fe0, MnO. It's ability to dissolve these compounds depends on forming ammine complexes of the metal ion. However the preparation history may affect the reactivity. Calcined FeO would be expected to be less reactive than FeO freshly prepared by dehydration of Fe(OH)2.

As for Fe2O do you mean Fe2O3?

If you can get your hands on a standard O or A level chemistry text (or the equivalent in your country) this should give you the answers to questions like this as well as explanations for and/or reasoning behind the observed behaviour. Good luck.83.100.138.7 15:32, 25 November 2006 (UTC)

Note: ammonia solution may not dissolve Feo, MnO.
Please do not double-post. Please do your own homework. --ColinFine 11:53, 26 November 2006 (UTC)

[edit] Shapes of the molecule

What is thestructure of the molecule H2OMufleeh 06:18, 25 November 2006 (UTC)2,Please indicate the angles between atoms

Well, you might start by reading water. It's in there. Good luck! – ClockworkSoul 06:32, 25 November 2006 (UTC)
Though Water (molecule) goes into more detail. GeeJo (t)⁄(c) • 13:48, 25 November 2006 (UTC)
Does the deadly compound oxygen dihydride deserve an article of its own? How about the organization dedicated to its regulation? [1] Clarityfiend 07:07, 25 November 2006 (UTC)
You mean this article? --Anon, 11:50 UTC, Nov. 25.

[edit] What population size is normal for humans?

What would be a 'normal' population size for an (sub)species the size of humans? So, say, deer or lions. Which raises a complicating aspect. Predators are fewer in numbers, and are we predators? Or rather, more relevant to the original issue, have we been predators during our evolution or is that more recent? This is about this question at the humanities ref desk. DirkvdM 07:41, 25 November 2006 (UTC)

That's a very difficult question to answer, mostly because of two variables: diet and technology. Since humans are omnivores, if the species choose to eat more meat then the number of humans that a given territory can support is less than than if the species chose to eat more vegetable matter (this has long been an argument of the vegetarian movement). Technology is the big one - I noticed you said "species the size of humans", that's unfortunately rather vague - but for humans, the population size supportable by a given territory is increased enormously through the use of technology, division of labour, agricultural techniques, etc.
If we consider a species the size of humans but which does not possess any technology (say, equivalent to primate or higher mammal level), even then the question is tricky, for it depends on the area in question. What is the vegetation? Climate? Number of other species competing for the same resources? And even if you know these numbers, a whole range of scenarios can be produced, trading off numbers of your species against numbers of other species occupying the same ecological niche. The word 'normal' is deceptive, there is no such thing as a 'normal' population size - population sizes are fluctuating constantly as some species out-compete others, climate and weather change, new species emerge and others die out etc. It never reaches an equilibrium for any length of time.
To answer your short final question, yes, early hominids were predators (much in the same way as chimps are today), although not apex predators, since individual humans are really rather wussy (not amazingly fast or strong, no five-inch claws that can disembowel your opponent, no huge teeth, not particularly big...) compared with apex predators such as lions or tigers. Humans became an apex predator with the advent of technology and communal existence - humans in a well-organised group are a force to be reckoned with, and technology (fire, stone tools, spears, assault rifles, supersonic bombers and nuclear ICBMs...) makes them virtually unstoppable. — QuantumEleven 16:23, 25 November 2006 (UTC)
Who are yoo calling wussy? :) DirkvdM 19:19, 25 November 2006 (UTC)
The original question really was about what population size humans would have had through most of their history, but I was trying to put this in perspective. I heard that a herd of animals of a million, such as wildebeest, is rather exceptional. But those are herd animals. I suppose through most of their history, humans lived in small bands in some corner of Africa. The human article mentions the theory that "during the Late Pleistocene, the human population was reduced to a small number of breeding pairs - no more than 10,000 and possibly as few as 1,000". So 'normal' would have been a lot more than that. Is somewhere between 100 000 and 1 000 000 a reasonable estimate? DirkvdM 19:19, 25 November 2006 (UTC)
I'd say "normal" would be a function of the carrying capacity of hunter-gatherer humans. Based on the link on the World population page, I suppose 5 million (the pre-agricultural human population) would probably be a good estimate. Guettarda 19:54, 25 November 2006 (UTC)
Thanks, good link (I could have found that). But it only goes back 12 000 years. That's (very) roughly 10% of mankind's history. So I suppose for most of the time there will have been less than a million humans. Would less than 100 000 be unlikely? DirkvdM 10:17, 26 November 2006 (UTC)

[edit] Iron poisoning

In an above thread it was said that vitamin C helps in the absorption of iron and that too much iron can lead to iron poisoning. One of my favourite meals is spinach and black pudding. The former contains a lot of iron and I assume the same goes for the latter seeing as it's made of blood. To this I add the juice of half a lemon, which contains a lot of vitamin C. Am I now at risk of getting an overdose of iron or is that over the top? I assume I won't get poisoning, but can it be an unhealthy combination? Vitamin_C#Contraindications says something about it, but only for extreme cases. DirkvdM 08:53, 25 November 2006 (UTC)

    1. I'm not a doctor.
    2. I seriously doubt it, because from what I understand it's really, really difficult to OD on dietary iron unless you have a disorder that affects absorption. Do you? And even if, it takes a looooong time to build up the excess. I know when I was anemic (from giving blood), it took MONTHS of taking vast quantities of ferrous fumarate + all the correct vitamins to build my iron back up.
    3. I don't have it in front of me, but IIRC (might have read it here actually) spinach isn't that high in iron; the misconception stemmed from an historic decimal error. It might be high in Vitamin C tho. ;-)
    4. If you're really worried, you can always get a blood test. (Of YOUR blood, not your dinner).
--Anchoress 11:55, 25 November 2006 (UTC)
No need to worry, unless you are among the approx. 0.5% of northern europeans who are homozygous for the haemochromatosis gene. It is possible to get an iron overload by taking iron supplements unnecessarily, but not through an iron-rich diet, unless you are genetically predisposed. If was previously thought that african iron overload was caused by an iron-rich diet, but this turned out to be wrong - it too was caused by a genetic polymorphism.
It has been argued that increased iron levels may predispose to cardiovascular disease, see iron hypothesis, however, to my knowledge this still is controversial. If you are worried about this, ask your doctor to check your ferritin level and transferrin saturation. --Norwegian Blue talk 12:07, 25 November 2006 (UTC)
And to add this: Spinach actual is the subject of a rather famous incident of sloppiness in science: When the iron content was originally determined, the result was misprinted with the decimal point at the wrong position, and this lead to the claim that spinach is extraordinarily rich in iron and hence extermely healthy, which in turn led not only to a whole generation of children being annoyed by their mothers' insistence on eating spinach but also to Popeye the Sailor. The mistake was discovered and corrected only several decades later. (For references, see the spinach article.) Simon A. 22:38, 27 November 2006 (UTC)

[edit] Tasteless Thallium

I was following links after links, until i've reached Thallium.

As I was reading the article, I've read something strange: "The odorless and tasteless thallium sulfate was widely used in the past as a rat poison and ant killer."

Uh... If it is poisoning (very poisoning!), how do we know it is tasteless ? Did some 'crazy suicide scientist' taste some thallium sulfate, then wrote "It is tasteless. Goodbye cruel world" ?

--WendelScardua 12:09, 25 November 2006 (UTC)

I can't speak to thallium sulfate specifically, but there are a number of ways by which we might have learned about its taste. Chemists – and the alchemists who preceeded them – used to be very cavalier about exposure to, inhalation of, and consumption of the chemicals that they worked with. The artificial sweetener saccharin, for instance, was discovered accidentally by two chemists who didn't wash their hands thoroughly enough before eating dinner. Sir Humphry Davy made a regular practice of smelling all of the chemicals he worked with; this led to his discovery of nitrous oxide ('laughing gas').
In other words, the odour and taste (or lack thereof) may have been deliberately evaluated, or inadvertantly discovered through careless handling. Remember that 'the dose makes the poision'—in very small amounts, the compound wouldn't kill a researcher. I know one chemist who in the last few years has personally verified (not deliberately) that hydrogen cyanide has an odour of almonds and that arsine (arsenic hydride) in air smells faintly of garlic. TenOfAllTrades(talk) 13:32, 25 November 2006 (UTC)
I regard the smell of a chemical to be just as important as its color, physical state, texture, etc. I've done a distillation of a cyclohexane and toluene mixture and smelled the products to double check the results, knowing that toluene has a stronger smell. I find it to be quite useful while others warn against it. I also like the smell of vinegar, and have smelled lab grade acetic acid to compare it to store bought vinegar. I'll tell you, I won't be putting my nose that close again, but now I know what it's like. As far tasting chemicals, I'd be less inclined to do that, as here, I follow the rule never put anything in your mouth, even food, when working with chemicals. --Russoc4 17:35, 25 November 2006 (UTC)
IT seems pretty straightforward. When someone is poisoned, I suspect the first question is "Did you taste anything funny or different?". I suspect the spy who just died was asked that numerous times along with everything he had eaten in the last 3 days. --Tbeatty 21:55, 25 November 2006 (UTC)

[edit] orange

is there any word in the english language that rhymes with orange?

  • No. Many have tried, but all thier "solutions", like "door hinge", are only assonances, not exact rhymes. - Nunh-huh 14:12, 25 November 2006 (UTC)
Don't forget to use the language page next time Wikipedia:Reference_desk/Language.
  • Blorenge (the place) rhymes with orange. ny156uk 16:13, 25 November 2006 (UTC)
  • If you say both in a French accent, I suppose blancmange might work. GeeJo (t)⁄(c) • 16:19, 25 November 2006 (UTC)
Incidentally, the band Jets to Brazil released an album called "Orange Rhyming Dictionary" (the Wikipedia page for this album claims that the lack of rhymes for orange is a "misconception" but doesn't back it up) and on a song called "Business", Eminem makes a valiant effort to rhyme orange with 'hinge' and 'syringe' but only by transfering the accent on 'orange' from the first syllable to the second.Wolfgangus 20:29, 25 November 2006 (UTC)
  • ny156uk is correct about Blorenge and while we're at it, there's also two words that rhyme with purple. I think one of them was curple. (Source is Stephen Fry on his quiz QI). - Mgm|(talk) 22:20, 25 November 2006 (UTC)
The Blorenge thing is covered in a clip on YouTube, just search for QI and orange. - Mgm|(talk) 22:21, 25 November 2006 (UTC)
Are those supposed to rhyme with orange? I've never heard someone say or-aynge or o-range in my life. It's usually pronounced ornj. Black Carrot 06:57, 26 November 2006 (UTC)
  • flange - Keria 09:46, 26 November 2006 (UTC)
  • Syringe and scavenge. To BlackCarrot, most of us are going by the "or-inj" or "or-enj" pronunciation I think. X [Mac Davis] (DESK|How's my driving?) 16:19, 26 November 2006 (UTC)
See the problem is that people are pronouncing orange as orringe. Now if thats the case then other rhymes come to mind: cringe, hinge, singe, tinge, whinge, minge, fringe,--Light current 14:35, 27 November 2006 (UTC)
  • There's a japanese band caled Orange Range, maybe for them these words rhyme (as for me, i don't speak english, so i can't tell what rhymes or not ^^;; ) WendelScardua 17:09, 5 December 2006 (UTC)

[edit] wood beetles

Is there such a thing as "wood beetles?" 14:18, 25 November 2006 (UTC)14:18, 25 November 2006 (UTC)14:18, 25 November 2006 (UTC)~And is there any way of getting rid of them?

A number of species in longhorn beetle family (Cerambycidae) are known to damage wooden furniture and structures. The larvae dwell in wood, boring "holes" (more like tunnels) as they go. Some can survive in a long-dead wood (no small feat if you consider how little nutrients and moisture it contains). Some beetles in superfamily Bostrichoidea are quite good at damaging wood, too. A Death watch beetle is a rather famous one. Actually, there is even a Woodboring beetles page on Wiki! As for getting rid of them - I suggest contacting a professional. You need something that either penetrates wood or cuts off the air supply to the larvae. --Dementios

[edit] What's the difference between a pigment and a dye?

Please answer in 1 paragraph. (Its for my grade 9 science project and I need to know please. I will cite this page on my project (im not gonna plagiarize) :-) thanx. --Storkian 00:19, 24 November 2006 (UTC)

Retrieved from "http://en.wikipedia.org/wiki/Talk:Dye"

I appreciate your honesty - but if you had looked at the first section on the page pigment you would have found:

"A distinction is usually made between a pigment, which is insoluble in the vehicle, and a dye, which is either a liquid, or is soluble in its vehicle. A colorant can be both a pigment and a dye depending on the vehicle it is used in. In some cases, a pigment can be manufactured from a dye by precipitating a soluble dye with a metallic salt. The resulting pigment is called a lake pigment."

This should more than answer your question.83.100.138.7 15:48, 25 November 2006 (UTC)

Also from dye (first two paragraphs)

"A dye can generally be described as a colored substance that has an affinity to the substrate to which it is being applied. ... In contrast with a dye, a pigment generally is insoluble, and has no affinity for the substrate."

Giving you all the info you need...83.100.138.7 15:50, 25 November 2006 (UTC)

[edit] Endangered bacteria, algae or similar

Does some bacteria, algae or similar organism can become endangered?Mr.K. 19:37, 25 November 2006 (UTC)

Smallpox is endangered, existing only in a couple of locked laboratory freezers. Poliovirus was endangered-- almost eradicated until Muslim clerics in Asia and Africa decided not enough of their children were suffering enough, and resisted the immunization campaign in its final phase. Pox be upon him. alteripse 21:56, 25 November 2006 (UTC)
Organisms continually go extinct, or adapt to the changing environment into a new creature. This brings up the Ship of Theseus problem. See natural selection X [Mac Davis] (DESK|How's my driving?) 08:40, 26 November 2006 (UTC)
Bacteria have a name of being indistructible, but that's probably because under extreme condiditions some bacteria will probably survive. But most others won't. There are millions of species of bacteria (check the link) and many are probably highly specialised in a specific environment. If that environment disappears (at that location on Earth, for example through climate change) then they will die out. But since they have a short life cycle they evolve fast and another bacterium one will soon take it's place. My guess is bacteria actually experience the highest rate of extinction of all life-forms, despite their reputation. DirkvdM 10:24, 26 November 2006 (UTC)
Climate change happens on a extremely slow scale, with regards to bacteria. Unless you mean "climate" as in local conditions. X [Mac Davis] (DESK|How's my driving?) 16:16, 26 November 2006 (UTC)
To avoid another off-topic heated discussion, even the present and projected climate change of several degrees over a few decades are probably still on too large a scale for bacteria to worry about. Then again, if there is no surrounding area they can move (and evolve) into then they're still screwed, but I suppose that won't happen too often. Relatively speaking, that is. But since there are millions of species there probably are a few that have specialised too much in too different a surrounding environment. DirkvdM 20:01, 26 November 2006 (UTC)

[edit] Engine Idling

This is a multi-part question on the topic of engine idling as it relates to engine wear and the environment.

1. Warmup: Many people think (and sometimes swear that experts have told them) that a normal car's engine should be warmed up for several minutes before driving. I have seen it stated in many places, and agree that it makes more sense to drive the car as soon as it is started (or running smoothly) (avoiding high revs) because it will warm up more quickly under load, thus getting past the higher friction of a cold engine more quickly. But I can't really convince those who believe otherwise because I have been unable to find any proof, just opinions, in my web searches. What I want to know is: has anyone actually tested these two philosophies and compared them? I suppose it would mean that both ways should be tried, then the moving parts of the engine examined under a microscope to determine the amount of wear. Or maybe there is a simpler way. Can anyone cite such a study?

2. Stop time: I have read that it is best for the engine (and the environment) to turn off an engine if your car is going to be stopped more than 30 seconds. Has any research been done to prove this? Admittedly it probably isn't a good idea at a red light, but if you are off the road waiting for someone or something it should apply.

3. Diesel: Do the above two issues also apply to diesel engines? Specifically, I would love to have a study to cite whenever a truck driver leaves his engine running right outside the door of my workplace. (In some circumstances like refrigeration or powered lifts I can see it, but many trucks don't have these devices.)--Benbrilling 07:01, 26 November 2006 (UTC)

If I was really interested in scientific backing, I would do some Power Googling. Otherwise, off the head of physics-type person, cars should be warmed up while driving gently, saves a lot of fuel. If its up here in Canada during the winter, you save a lot by having a block heater. The stopping of the engine for more than 30 seconds is just a fuel saver. That's the break-point on the starter energy. Diesel usually needs to keep running if it is extremely cold, because they are hard to start. But I assume most truckers are addicted to the fumes. :) --Zeizmic 20:30, 25 November 2006 (UTC)
Very good question, and I too hope that some actual evidence is uncovered. Like you, I belive that it's best to begin driving immediately upon starting one's car, albeit at a moderate pace, rather than let the car sit and "warm up" for an extended period of time. The mechanism at work dates to the days of the electric choke, long before fuel injection was commonplace. The electric choke served to enrichen the fuel mixture while the engine was cold, and so keep the engine running. The drawback was that to keep the engine running, the fuel mixture had to be very rich, and a very rich fuel mixture would also tend to wash the lubricating oil film off of the cylinder walls, and so increase wear between the piston rings and the cylinder. Therefore one would want to reduce the time

that the choke is engaged, and so reduce the time that the fuel mixture is enrichened.

The best way to do that is to make the engine perform work and heat up more rapidly than if it was just idling. However, as you've noticed, that concept seems lost on a lot of people. Perhaps the answer is to ask your friends: If I let the engine idle it will take X minutes to "warm up" to operating temperature. During that time, the fuel mixture is being enrichened, and the upper cylinder walls are not being lubricated properly. However, if I begin driving the car, it will take fewer than X minutes to warm up, and so the time the upper cylinder walls are not properly lubricated is accordingly reduced. Which situation is worse for the engine? A protracted period with insufficient lubrication, or a shorter period with insufficient lubrication? 192.168.1.1 10:30pm, 25 November 2-zero-zero-six (PST)
This line of reasoning may very well be useful, but there's a twist to it: an engine will be running faster (in terms of RPM) when the car is actually being driven, so your "shorter period" may actually correspond to just as many (or more) engine cycles. Now, whether it's time or cycles or both that damage the engine is another concern... I'm just saying that it's not as simple/obvious as it seems. --Tardis 17:42, 27 November 2006 (UTC)

[edit] Lockwashers: which when?

The two most common lockwashers, split and star, are used in many applications. But are there any commonly accepted engineering guidelines of which type to use in which application? Or are they effectively interchangeable?--Benbrilling 06:57, 26 November 2006 (UTC)

The split type is usually referred to as a spring washer. As to the comparative efficacy of the two types, I'm not too sure.--Light current 23:54, 25 November 2006 (UTC)
Here http://everything2.com/index.pl?node=Lock%20washer has more info than wikipedia does.. Shame.
Well why dont you add it? 8-)--Light current 00:35, 26 November 2006 (UTC)
Star washers are used for electrical connections usually with a bit of metal hanging off them to crimp a wire to (usually an earth connection). Otherwise no real idea..83.100.138.7 00:20, 26 November 2006 (UTC)
(Don't forget Castellated nut - having a similar purpose)
Yes I would concur that star washers are better for ensuring a good electrical connection because they bite thro any oxide on the opposing surafces. Spring washers OTOH may be better(or not) for resisting loosening. But what about the general term: shakeproof washers?--Light current 01:14, 26 November 2006 (UTC)
True, they will bite through oxide (if any: a tight fit will often seal out moisture), but another consideration, if large currents are to be conducted, is the contact surface area, which would be significantly larger with a split washer. Have you noticed that many terminal strips come with screws with split washers? Also, I've only seen split washers on large circuit breakers and contactors.--Benbrilling 03:18, 28 November 2006 (UTC)
Split lock washers have at least one advantage over star lock washers: You can easily tell when they're fully compressed, both visually (they're squashed flat) and through the rapid rise in torque that occurs. They can also be a lot less-marring to the surface and the bolt. (Wave washers and Bellevilles are even less-marring, of course, and share some of the "indicating" advantages of split-lock washers.) But as 83.100.138.7 mentioned, if you're looking for a solid electrical connection, those star washers (with their surface-up-chewing teeth) have it all over the other kinds of washers.
Atlant 17:18, 27 November 2006 (UTC)
Agreed. But I dont know the advantages of 'wavy' washers over split types. Do you? (and they look to be more expensive.)

[edit] Effect of Flat Circular Shapes Falling onto a Flat Surface

What effects are involved when a circular flat object falls through the air onto a flat surface?

Breaking apart a 3.5" floppy disc to destroy it for security reasons I happened to flip the internal plastic disk through the air as a kind of frisby. I noticed that it floated down to the ground at a constant rate and without tumbling but then 'appeared' to speed up just before it hit the ground and contacted with the flat ground surface very emphatically with all edges immediately in contact. I'm assuming that there is some physical effect of a falling object / air pressure above / air being forced out below etc? I would be fascinated to understand a little of the physics involved and whether we make use of this effect for anything?

In case it is important and you don't have ready access to plastic disc out of a floppy disc I'll describe it. It's a stiff plastic disc with a metal central hub. When falling through the air after being dropped (not thrown) the plastic doesn't deform in any way.

I too have experience here. I think the brown/black surround acts as some sort of airbrake/psuedo parachute on falling. No idea about the speed up - I'll pay more attention next time. As for the slap on landing - the parachute effect causes the edges to be forced up - when the disc stops the flexible outer part can flap back down giving the emphatic landing you describe.83.100.138.7 00:28, 26 November 2006 (UTC)
Perhaps as it appreaches the ground, air speeds under the disc increase due to bernoulli's law? This might permit it to travel faster where certain conditions of pressure are being met. - Rainwarrior 06:43, 26 November 2006 (UTC)
That's what I thought of, assuming you gave the disc a spin, as you would a frisbee. This would cause an airflow from the centre to the edges. Air flow means 'underpressure' (is that the right word?). Initially that would work both up and down. But as it approaches the ground there will be less and less air there to replenish the air that flows out, so there will be more underpressure at the bottom and the disc will get sucked to the ground. <smug>Sounds plausible, doesn't it?</smug> DirkvdM 10:33, 26 November 2006 (UTC)
Not convinced/87.102.12.129 13:47, 26 November 2006 (UTC)
<looking down the nose>Well, you come up with something better then.</looking down the nose> DirkvdM 20:04, 26 November 2006 (UTC)
Seriously - there would be air pressure under the disk due to it moving down - the same way any moving object gets air resistance - underpressure - don't know - just doesn't make any sense to me.83.100.250.53 20:17, 26 November 2006 (UTC)
See ground effect -Ravedave (help name my baby) 05:27, 27 November 2006 (UTC)
That's different. The airplane moves, so there is a constant influx of air, that the wing pushes down, to create overpressure, lifting the plane. I suppose the disc-effect here will be strongest if it goes down pretty much vertically when it approaches the ground. If it were to still move forward, the 'vacuum' under the cd would be filled in by the air of the new position it moves to and the effect I described would be annulled. DirkvdM 07:25, 27 November 2006 (UTC)
Quuery:The 'vacuum' or low pressure area would be above the disc moving down, not below, right?87.102.20.219 20:22, 27 November 2006 (UTC)
Therre is underpressure on both sides, due to the air being spun towards the edges. This is due to the movement of the air (bernoulli's law). This air gets replaced by air flowing in. But, and this is my theory, when the disk approaches the ground, there is no air there to flow in, so now we get na absence of air creating an even stronger underpressure. DirkvdM 05:44, 28 November 2006 (UTC)
for air to be pushed to the edges (as far as I know the discs not spinning nor is the air) there must be 'overpressure' under the disk. As the disc falls the air under the disc is squashed - causing it to be pushed out around the edges. I can't explain any speed up.83.100.158.227 14:17, 28 November 2006 (UTC)
Ah, but I said "assuming you gave the disc a spin, as you would a frisbee" because that is what he suggested in the second sentence. Failing that, you're right. DirkvdM 19:49, 28 November 2006 (UTC)
Retrieved from "http://en.wikipedia.org../../../r/e/f/Wikipedia%7EReference_desk_Archives_Science_2006_November_25_43bf.html"