Wikipedia:Reference desk/Archives/Science/2010 January 15

= January 15 =

Requirements for cloning
I've always been horrible at biology, so this is going to be a really nooby question. I'm wondering what is absolutely necessary in order to basically "create" a species from scratch; that is a species that is existent or has been, where you have access to genetic material.

I'm going to assume a process (that I presume doesn't exist, and won't for a very long time) whereas you can create full DNA strands from pure data, so this isn't really a realistic question, just a theoretical one. What kind of DNA would you absolutely need to produce a single specimen of a species; is just one kind enough, or are there multiple genomes? that you would have to figure out first. Also, does it matter what sequences you need if you are trying to make a male or female of the species?

Obviously I'm assuming here that the DNA created from data would be inserted into a living cell, which may not be possible, but I'd like to ignore that problem as well haha. Also, I'm assuming that you would only need one copy of (each?) data type to succeed, but I'm not sure if that's true.

Basically, I'm asking because lately I've heard a lot about different genomes and rDNA and mtDNA and I'm getting confused as to where the actual "core" of information, and the set of information which cannot be deduced from some sort of chemical process within eukaryotes is. Thanks in advance! 219.102.221.49 (talk) 02:08, 15 January 2010 (UTC)


 * A human genome, for perspective, consists of 3 billion DNA base pairs, each being one of four different types of nucleic acids. Each human cell has two copies of the genome, one from each parent, which in general may provide different allelles for the same gene.  In humans, the genomes are arranged in 23 chromosomes pairs.  I'm not sure what the longest DNA constructed from scratch is.  I don't think it is billions of base pairs, but I suspect 10 million might have already happened, so we aren't that far from being able to write a whole human genome from scratch.  Men and women have different sex chromosomes (one of the 23).  Inserting DNA into cells is possible, and at the heart of cloning efforts.  See also rDNA and mtDNA.  Dragons flight (talk) 02:22, 15 January 2010 (UTC)


 * I think the main part of my question was a bit unclear. I know generally how the cell is constructed and what the different kinds of DNA are, but I'm wondering which are absolutely and immediately necessary in the creation of a being. For example, if you had a data writeout of the base pairs for the 23 human chromosomes, and it was possible to construct the strands of DNA from scratch of that length and complexity, could you input just those created chromosomes into a cell and make it live, effectively cloning a human (though through an extremely inefficient means), or would you need to create copies of other types of DNA, perhaps some of the organelles for it to work? Plainly, is absolutely everything required to produce a human included in the 23 chromosomes? Is all the information required to produce an organism included in its chromosomes? 219.102.221.49 (talk) 06:33, 15 January 2010 (UTC)


 * Yes and no. In order to live the genome needs to be combined with a compatible set of cellular machinery.  In practice, this is quite general, but not open-ended.  So, for example, cells from organisms in the same family would probably be fine, but probably not cells from a different phylum.  The pre-existing machinery reads the DNA and starts producing the appropriate proteins to match the new genome.  Eventually the old cellular machinery is totally replaced, but that can't happen too quickly or the cell's behavior may go haywire (hence the need the need to start with something similar).  In general though, no other types of DNA have to be provided.  Dragons flight (talk) 09:46, 15 January 2010 (UTC)


 * Is the cellular machinery really that general ? I thought that somatic cell nuclear transfer had to involve a nucleus and ovum from the same species. Are you saying that it is possible to put a sheep's DNA into a cow's ovum and produce a sheep embryo, because both cows and sheep are bovids ? Gandalf61 (talk) 10:10, 15 January 2010 (UTC)


 * SCNT has a poor success rate (< 10%) even under the best of conditions, so one would ordinarily choose cells of the same species to maximize the odds. But no, that's not a strict requirement.  Work with endangered species has already produced clones where the egg donor was a different species than the DNA donor (harvesting eggs is an invasive and somewhat dangerous process, so you wouldn't want to subject a rare animal to that if a similar common animal would also work).  There haven't been enough experiments to tell exactly how similar the cell needs to be, but the core machinery for protein synthesis and DNA replication exists in all cells.  Hence we probably can fairly far in the genetic tree before secondary factors make it impossible.  Dragons flight (talk) 12:20, 15 January 2010 (UTC)
 * Additionally, we do know that there are viruses that can use their DNA in order to force cells to do work they wouldn't otherwise do—presumably this indicates some compatibility, or at least some flexibility. --Mr.98 (talk) 21:58, 15 January 2010 (UTC)
 * You might be interested in Mycoplasma laboratorium, also known as the Minimal Genome Project. Looie496 (talk) 19:02, 15 January 2010 (UTC)

Cats and plastic garbage bags
Anyone who is owned by cats or knows someone that is owned by them, knows that cats hate the sound of plastic garbage bags. Can anyone explain this phenomenon? Thanks. Viriditas (talk) 04:34, 15 January 2010 (UTC)
 * That's news to me and I have four cats. Can you supply some sort of source for the observance of this "phenomenon"?  In fact, the cabinet that we throw our plastic grocery bags into is the one of our cats favorite places to get into.  I know you said garbage and not grocery but they don't sound that much different.  Dismas |(talk) 05:04, 15 January 2010 (UTC)
 * I can confirm that at least some cats enjoy playing with grocery bags. APL (talk) 06:03, 15 January 2010 (UTC)


 * I can attest that in my house (4 cats) the phrase "the cat's out of the bag" and the accompanying implication that it's impossible to get it back in (undo something) seems preposterous. Our cats LOVE plastic bags and immediately enter any they're offered, which they then joyously tear to shreds.218.25.32.210 (talk) 07:48, 15 January 2010 (UTC)


 * Funny; I have three cats, and not one has ever reacted to the sound of a plastic garbage bag. Someguy1221 (talk) 07:57, 15 January 2010 (UTC)

Responding to the above: Plastic garbage bags are not plastic grocery bags, nor do cats love or play with plastic garbage bags as they are generally compressed before usage in rolls or sheets. A good image of what I'm talking about can be found here and after seeing this image, it becomes clear why cats can't play with them. I wasn't aware there could possibly be any ambiguity in the words I chose, but evidently the words "plastic garbage bag" means something different to various people here, and I now see that I'm probably using American English. Anecdotal reports of typical house cats running feverishly from the sound of plastic garbage bags being torn off rolls and opened (it is generally a loud sound) are numerous and can be found all over the place. There are thousands, perhaps tens or hundreds of thousands of comments like this:


 * "She is a typical cat - attitude et al. However, every time we put a new garbage bag in the bin, she freaks out and runs - and she reacts the same way with plastic bags."
 * "My cat is scared of many things. How can I help him? He is very frightened of: 1. Thunderstorms 2. Airplanes/any loud noises 3. Plastic bags..."
 * "Our cats are afraid of their own shadows. They hate the rustle of plastic bags, where our previous cat came running when he heard the noise (he liked to lick plastic bags ... )"
 * "I have one cat who likes to be vaccuumed (gently), and another who is terrified of plastic bags..."

I think you get the idea. Obviously, the noise of the bag can scare some cats, but I've noticed this myself with so many different cats, that I'm curious about the sound of the plastic bag unfurling and why they would be afraid of it. Does the sound cause them pain? Viriditas (talk) 09:51, 15 January 2010 (UTC)


 * My cats don't like the sound of the ripping perforations,(note I didn't say "scared of") but once the bag is opened they will quite happily play with, explore, and even eat the bag! You may as well ask, why are all humans scared of spiders? This is quite obviously not the case. --TammyMoet (talk) 10:45, 15 January 2010 (UTC)


 * The third example seems to be enough to disprove the "all cats are afraid" assertion. And the plural of anecdote is not data.  As far as terminology, I think our British friends use Bin liner.  -- LarryMac  | Talk  13:54, 15 January 2010 (UTC)

Here's another the OR-into-felines thread. My cat is oblivious to all sorts of noises around the house and even backfires from the road outside. But a firework bang overhead prompts a desperate run for cover. I conclude that direction, and possibly ultrasonic sound that I can't hear, are decisive for the cat. Do plastic garbage bags produce ultrasound? Cuddlyable3 (talk) 11:24, 15 January 2010 (UTC)


 * Unfortunately for scientists, cats are inscrutable.--Shantavira|feed me 11:28, 15 January 2010 (UTC)


 * If you catch my catastrophic catechresis, cats categorise scientists as scrutable, shevelled and/or gruntled. Cuddlyable3 (talk) 12:23, 15 January 2010 (UTC)
 * manufacturaplastikosaphobia ?  Kittybrewster   &#9742;  12:40, 15 January 2010 (UTC)


 * I haven't noticed anything particular with cats, but I have noticed many times that rats are very easily startled by the sound of paper tearing. I speculate that a sudden ambush attack by a predator often produces a similar sound. Looie496 (talk) 17:13, 15 January 2010 (UTC)


 * It might be the noise - but I'd bet it was the smell of the plasticizer or some kind of release agent or something. SteveBaker (talk) 18:55, 15 January 2010 (UTC)


 * I was quite clear that I knew the difference between garbage and grocery bags. And I again ask for some reliable source that points this out.  You've supplied four links to what is essentially original research.  It's selection bias.  You also mention the part about opening the bag which is a loud sound.  Many creatures great and small are startled by loud sounds including humans.  I have a human friend and a dog who both hate gun shots.  Furthermore, I can see a range of reactions to loud sounds from the cats in my house.  For example, a dog's bark.  One cat we have runs under the bed even when she's on a separate floor from the barking dog.  Meanwhile, the other cats generally either don't react at all or just wake up and look around wondering what all the excitement is about.  And you yourself prove your own conclusion to be wrong with your third quote.  It says "our previous cat came running when he heard the noise (he liked to lick plastic bags ... )".  So right there you have at least one cat that liked the bags.  Dismas |(talk) 04:04, 16 January 2010 (UTC)
 * There is simply no comparison between grocery and garbage bags here, since the noise comes from unrolling the bag and opening it with a flick of the wrist.  This has nothing to do with OR (that term does not even apply on refdesk) or selection bias; It's a well-known phenomenon in most cats.  My question has to do with why they are scared of the sound, not whether cats are afraid of it.  And, it doesn't have to be loud for cats to have an extreme reaction to it.  According to your own comments, you haven't heard of it and didn't see the difference between grocery and garbage bags, so you probably aren't aware of the issue in the first place, nor have you ever witnessed it, apparently. Viriditas (talk) 09:01, 16 January 2010 (UTC)


 * Ok, Viriditas, look... Counting above, it looks like you have the opinions of no less than 16 cats that plastic bags, garbage or grocery or otherwise, are not scary. But with regard to the links you posted above of anecdotes...seriously? Dude, are you going to listen to us, or just read posts from random people on the internet? Someguy1221 (talk) 09:08, 16 January 2010 (UTC)
 * There's literally tens of thousands of reports about this, and people aren't making them up. I've witnessed it myself in at least half a dozen cats over the years. The sound is certainly scary to some cats, and my question is why.  I fail to see how you've answered my question, so if you have nothing to add, simply ignore me.  I see nothing wrong with addressing the anecdotes of cat owners about their pets.  It's called observation, and for our purposes, there's not a thing wrong with it.  This isn't a scientific journal, this is a refdesk. Viriditas (talk) 09:15, 16 January 2010 (UTC)


 * I'm sorry, Viriditas. That was meant to be a joke (aka we are all random people on the internet). Someguy1221 (talk) 22:08, 16 January 2010 (UTC)


 * The trouble with this claim of yours is that selection bias is rife here. Nobody - and I mean NOBODY wrote about how their cats totally ignored any and all things their owners did with plastic bags of any kind.  Why would they?  They also didn't write about how their cat completely ignores all use of the word "Nuclear" on the radio.  People don't write about non-events.  So we may well have about a billion cats who's reactions to plastic bags were not mentioned - and (by your count) a mere few tens of thousands of cats who freaked out in this way.  That's so statistically insignificant that we really can't draw any conclusions on that basis.  The only way to make a statistical claim is to do a proper double-blind statistical study...and you haven't done that.  Anecdotes are not data.
 * Furthermore - I'm 100% certain that you have NOT read "tens of thousands" of reports about this. What you REALLY mean is that you typed some kind of search terms into Google and counted the number of hits you got back.  However, as any experienced web searcher will tell you - that count doesn't tell you much about what the reports actually contain.  Perhaps the ones that come up on the first few pages of most appropriate hits were about this - but the 23,456th report is almost certainly about something completely different that merely happens to contain the terms you typed in several paragraphs apart and totally unrelated to the question at hand.  So your claim of many reports is quite utterly valueless - even bogus.


 * Your personal observation of many cats that have this problem is also lacking any kind of scientific rigor. Suppose, just for one moment, that you had ONE cat who is the only cat in all of history to be afraid of unrolling bags.  You see this and are surprised by it - so the next time a different cat is nearby as you unroll the bags, you pay very careful attention to the cat - and lo and behold, it runs away!  You do this a dozen times - same result every time!!! Surely you've discovered something here?  Well, maybe not - maybe all but the first cat are freaked out by the threatening way you fixate your attention on them and run off every time you do that even though they don't give a damn about the bags?  So, I'm sorry - but your anecdotal information in favor of your hypothesis is actually not very convincing at all.  On the other hand, we have evidence of a dozen or more cats who we're told don't give a damn about these bags...how does that fit into your hypothesis?  It's not so easy to explain away is it?  So THIS evidence is pretty significant.  It says that at least a significant sample of cats are not afraid.  You only have really conclusive evidence of one cat that you personally know for sure is scared - and a random scattering of junk from the web.


 * So - please step down from your high horse and listen to what the experts here are telling you. SteveBaker (talk) 17:07, 16 January 2010 (UTC)
 * No that isn't correct at all. I very clearly said that "I've witnessed it myself in at least half a dozen cats over the years" so I have no idea why you say that I "only have really conclusive evidence of one cat that you personally know for sure is scared." This is the pattern in this discussion.  I say one thing, someone says that I say something else.  I'm not on any high horse, and I see no animal behavior experts in this discussion nor has anyone addressed my question other than to say "I have a cat and he's not scared" so, there isn't anyone to listen to on the subject, as my question hasn't been addressed, nor have any "experts" (Wikipedia, cough, cough) addressed it.  The reading comprehension level here is close to zero. Viriditas (talk) 00:27, 17 January 2010 (UTC)
 * Before you start flinging around accusations of poor reading comprehension - I suggest you exercise some reading comprehension of your own. Please carefully re-read what I wrote.  You categorically do not have evidence of 12 cats responding to this phenomenon - you might (maybe) have evidence that ONE cat responded to the bags and eleven more who merely responded to your curiosity on the subject.  That's not the same thing as 12 cats who responded to the bags.  That's why proper evidence requires a double-blind experiment.  Let me remind you of how you started this thread.  You said "Anyone who is owned by cats or knows someone that is owned by them, knows that cats hate the sound of plastic garbage bags." - but we came up with a whole lot of people/cats who do NOT respond in the way you describe...just one is enough to destroy your hypothesis...so it's busted.  Worse still (if you had read my yet earlier post), any reaction you've observed may well be to the smell of the chemicals that were trapped between the folds of the plastic - you have ZERO proof that this is a sound-related phenomenon at all.  So please stop insulting us and carefully read what we're telling you. SteveBaker (talk) 01:16, 17 January 2010 (UTC)
 * I strongly disagree with your assessment. I did not find the responses from people who disagreed persuasive.  It sounds like they never experimented with the plastic garbage bag sound I described and admitted they had never heard of it.  It has absolutely nothing to do with the smell, (cats often freak out in other parts of the house or outside when the bag is opened inside) and everything to do with the sound.  Nothing mentioned in the comments above "destroyed my hypothesis", but rather demonstrated that people will respond to anything without having familiarity with the topic.  Since you and others do not recognize the problem I describe, I fail to see how you think it has been addressed.  Some cats are scared or distressed by the sound of some plastic garbage bags.  Ask anyone who has worked with feral or house cats and they will report this as a fact.  Why this is the case is my concern.  Claiming that the concern is false or imaginary is not a satisfactory answer.  It's a real feline phobia and it is well known.  Why this happens or why the sound causes this reaction in cats has not yet been determined.  As an experiment, I just got off my computer chair and headed to the kitchen.  With my cat seated approximately eight feet away, I grabbed the roll of plastic "bin bags" in full view of the cat.  This did not deter him, and he didn't even blink.  Then, I slowly tore a bag off the roll, trying to do it quietly.  Nothing happened.  At this point, I slowly separated the bag, and lightly flicked my wrist, opening it with a soft sound.  At this point, the cat freaked out, and ran out of the room.  It's the same reaction every time, and it has to do with the sound of the plastic.  My vet and other experts I trust, say that some cats are more high-strung than others, and the new "trend" is to give these types of cats anti-anxiety medications. I'm not planning on doing that, but that is the typical response from the experts.  Treat the problem with medication rather than try and figure out what causes it. Viriditas (talk) 01:36, 17 January 2010 (UTC)
 * You have obviously pre-decided what the answer must be on the basis of hearsay and anecdote (as an earlier poster pointed out: The plural of "anecdote" is not "data"). I'm sorry you don't like what we're telling you here - but you're stuck with it - that is the answer, whether you happen to like it or not.  Your grasp of scientific methodology is clearly inadequate to the task of understanding what we're trying to tell you.  I think this thread is over. SteveBaker (talk) 13:08, 17 January 2010 (UTC)


 * There's a 2009 article in the New York Post about the phenomenon, but I doubt the conclusion reached by the author is true. Also, the author talks about the plastic grocery-type bags, not the bin liners. Viriditas (talk) 09:06, 16 January 2010 (UTC)


 * Cats' ears (and brains) are attuned to the rustle that a mouse makes (especially amongst dry leaves), so the rustle of a plastic bag is likely to sound louder to them than it does to us. Most animals (including humans) have a natural reflex to run away from a loud sound that we don't understand, but this refex reaction is easily modified by behaviour learned from the reaction of others and from experience.  Do these facts help to explain the variations in the reactions of cats to high density polythene?    D b f i r s   21:27, 17 January 2010 (UTC)


 * Plastic bags are "opened" by humans by moving them in such a way as to force air into the opening. This is especially true of bags fresh off of a roll of unused "garbage" type bags. But even "used" grocery-type bags can be opened fully using the same type of motion. This motion causes the rapid opening of the bag. It is similar to the way a parachute opens. It takes place rapidly. I think the rapidity of the moving material, in either case, can reasonably be expected to startle. I think it has a visual and an auditory component to it. In the case of the opening of a bag by a human, there is also the close association between the rapid hand movement and the concomitant sound and motion. The bag can seem to expand in size very rapidly. It does not seem surprising that this could be startling to any creature. Bus stop (talk) 22:06, 17 January 2010 (UTC)

Hydrogen, Oxygen, and Nitrogen
Does pure hydrogen only exist as molecues of two atoms? Does pure oxygen only exist as molecues of two or three atoms? Does pure nitrogen only exist as molecues of two atoms?

Bowei Huang 1 (talk) 05:52, 15 January 2010 (UTC)


 * Have a look at ozone and trihydrogen (very unstable), and there is also octaazacubane N8 and Tetranitrogen N4. At extremely high temperatures the elements can be monatomic, and at extreme pressures nitrogen can form other allotropes, and even more extreme pressures all molecules form metals: eg Metallic hydrogen.  Graeme Bartlett (talk) 06:14, 15 January 2010 (UTC)
 * In other words, all of those elements can exist in other forms under unusual (non-Earth-Atmosphere) conditions. Under standard temperature and pressure, the conventional two-atom molecular form is by and large the most common, orders of magnitude more stable than any other configuration.  Nimur (talk) 06:20, 15 January 2010 (UTC)

Cheap hurricane and earthquake protection?
Supposing nylon or metal guy wires like the ones supporting tents and radio masts were retro-fitted into or around normally weak buildings? Would this be an affordable form of hurricane/earthquake protection? For example, could a large nylon sheet deeply pegged to the ground at all corners, given sufficient warning of a hurricane, keep the roof on?Trevor Loughlin (talk) 14:29, 15 January 2010 (UTC)
 * While it would be better then nothing, we really do not know how much better without knowing things like soil conditions, building materials, building size, shape etc. Chances are good that it would be only a minor improvement for hurricanes.  For an earthquake, these would help even less because the method of failure is very different, and in many earthquakes, that soil is going to act like a liquid and your stakes are going to move.  Googlemeister (talk) 15:11, 15 January 2010 (UTC)
 * Regarding Googlemeister's comments on soils in an earthquake, see Soil liquefaction. -- Jayron  32  15:46, 15 January 2010 (UTC)
 * In an earthquake the guy wires could pull the building down rather than support it. 78.149.116.255 (talk) 12:17, 16 January 2010 (UTC)

Gas furnace ignitor
In a typical gas furnace, there are several burners but only one (electric) ignitor. How does the ignitor light all the burners? —Preceding unsigned comment added by 173.49.10.145 (talk) 16:22, 15 January 2010 (UTC)


 * It would seem likely that if the burners were in a line, that the igniter would light the first one, that would light the next burner or jet, and so forth along the line. If there were sufficient 'un-lit' gas the igniter could easily light them all simultaneously. If you mean totally seperate 'bar' or ring burners the same idea still applies--220.101.28.25 (talk) 17:04, 15 January 2010 (UTC)Bold text


 * A source of ignition "very close" to a fuel is enough to light it. Gas is...a gas, so gas from burner B quickly spreads to the flame on burner A, which lights B, and so on. DMacks (talk) 17:05, 15 January 2010 (UTC)

Building construction standards in earthquake-prone areas
In earthquake-prone areas, how strong an earthquake are buildings required to be able to withstand? I expect the answer to vary a lot depending on the jurisdiction, but would like to know how different governments balance the tradeoff between cost and safety. —Preceding unsigned comment added by 173.49.10.145 (talk) 16:54, 15 January 2010 (UTC)
 * See earthquake engineering. Looie496 (talk) 17:05, 15 January 2010 (UTC)

water liquid temps
Is there any way to get water to remain liquid at the temperature of -20F (lowering the freezing point by at least 52F)? Preferably a method that is not corrosive, like adding salt would be? 65.121.141.34 (talk) 17:09, 15 January 2010 (UTC)
 * Supercooling. Staecker (talk) 17:13, 15 January 2010 (UTC)
 * That would require extremely pure water would it not? Since the smallest speck of dust would start the seed crystal reaction and freeze everything up?  65.121.141.34 (talk) 17:20, 15 January 2010 (UTC)
 * Yes it would. And a fancy bottle to hold it in. Depending on your needs and equipment, this may not be the easiest way to do it. But it's the first (and only) that comes to my mind. Staecker (talk) 17:22, 15 January 2010 (UTC)
 * Antifreeze. Dauto (talk) 17:36, 15 January 2010 (UTC)
 * I considered that, but car antifreeze is usually something like 25% or more of the solution, at which point you don't really have water anymore, but diluted antifreeze. I am mostly looking for solutions of 99% or higher water content.  65.121.141.34 (talk) 17:56, 15 January 2010 (UTC)
 * You can do it by increasing the pressure by thousands of atmospheres. — DanielLC 18:10, 15 January 2010 (UTC)
 * I don't think you can. -20F is about -29C.  This suggests that even at high pressures, the melting point of water can only be brought down to -20 C or so. Buddy431 (talk) 18:27, 15 January 2010 (UTC)
 * I guess Dauto beat me to it. Buddy431 (talk) 18:28, 15 January 2010 (UTC)


 * Not quite. The minimun temperature for the freezing point will be about -10F at a pressure around 200 Megapascals. Dauto (talk) 18:18, 15 January 2010 (UTC)


 * The answer is no, not for macroscopic amounts of a nearly pure substance. Maybe if you elaborated on why you want that then we could suggest and alternative.  Dragons flight (talk) 18:29, 15 January 2010 (UTC)


 * Freezing-point depression doesn't require salt. Any solute would do, since the amount the freezing point depresses depends only on the concentration of the solute.  Just pick something that isn't corrosive.  --Bowlhover (talk) 01:54, 16 January 2010 (UTC)
 * But you still need like 15 moles of solute per liter of water. At that point, so matter what the solvent solute is, you aren't working with mostly pure water. Buddy431 (talk) 02:11, 16 January 2010 (UTC)
 * A 48% (by weight) propylene glycol solution will give a freezing point of -20F. 50/50 water/glycerol solutions are commonly used in biology to preserve proteins. --Atemperman (talk) 03:57, 19 January 2010 (UTC)

Stress on a shelf bracket
How can I calculate the maximum horizontal stress or tension on a shelf bracket that has the shape of a right-angled triangle? The bracket is X metres horizontally, Y metres vertically, and has a weight of Z kilogrammes half way along the horizontal surface. Assuming (for simplicity) that there is a fulcrum at the lower angle of the triangle that stops the bracket from moving down but would allow it to rotate, what would be the horizontal force at the right angle? Not a homework question, I would just like to estimate if a simple wood-screw (or two) will be enough to safely fix the bracket to a vertical surface. I suppose it would be like an L-shaped lever. Thanks. 84.13.50.207 (talk) 17:53, 15 January 2010 (UTC)


 * If I've understood the geometry correctly, then, by taking moments about the fulcrum, one obtains the result that the horizontal force is ZX/2Y kilogrammes. One should always allow a factor of 3 or more as a safety margin, and remember that the fixing into the wall is usually the weak point, rather than the strength of the screw.   D b f i r s   18:33, 15 January 2010 (UTC)

Thanks, although I thought the answer would be in newtons rather than kilogrammes. 84.13.50.207 (talk) 18:59, 15 January 2010 (UTC)


 * No doubt you are looking at the "Design for a wood shelf bracket" and sketch on 12 January 2010. Dbfirs gives an expression for the force acting away from the wall at the inner top edge of the shelf. However a woodscrew cannot be placed there and the screw will instead be W meters below the surface of the shelf. The force tending to pull the screw out of the wall is ZX/(2(Y-W)) kilogrammes. There is also a downward force Z kilogrammes on the screw. (You are correct that the forces should be expressed in Newtons. Multiply the kilogrammes by 9.80665 to obtain Newtons.) The safety margin that Dbfirs advises is definitely needed to allow for items being dropped on to the shelf, or even items being wedged in under a shelf above as often happens with books in crowded library shelves.Cuddlyable3 (talk) 23:54, 15 January 2010 (UTC)


 * A student visited a fellow student in his apartment which he saw was crowded with stacks of books so that there was hardly any living space. "Why don't you put your books neatly on shelves like in the public library?" he asked. His friend replied "Oh, do they give away the shelves too?". Cuddlyable3 (talk) 23:54, 15 January 2010 (UTC)


 * I considered converting to Newtons, but since the OP gave the weight in Kilograms-force, I responded in the same units. If you live in Stockholm, multiply by 9.818, or by 9.781 in Singapore, or by 1.625 if you put up shelves on the Moon (assuming the weight is actually a mass in Kg).  The method of fixing into the wall is crucial.  A friend of an acquaintance last week came down to breakfast to find a new 50-inch plasma TV smashed to pieces on the floor because the wall-fixings were defective!    D b f i r s   00:25, 16 January 2010 (UTC)


 * ZXg/2Y N is indeed the horizontal component of the force at the top of the bracket, where g is the acceleration due to gravity. But if the only fixing is at the top of the bracket (in other word, the force at the bottom of the bracket is normal to the wall i.e. horizontal) then this fixing also has to provide a vertical force of Zg N to support the weight of the Z kg mass. The total force at the top of the bracket is therefore


 * $$Zg \sqrt{\frac{X^2}{4Y^2}+1}$$


 * This ignores friction between the bracket and its support. In practice, friction will introduce a small vertical component which will reduce the total force at the fixing, so this is a worst case. Note that we have also ignored the weight of the bracket - we might be tempted to make Y as large as possible to minimise the force at the fixing, but eventually the weight of the bracket would become significant. Gandalf61 (talk) 09:35, 16 January 2010 (UTC)

minibeasts
What are the top ten most deadly minibeasts in the world? —Preceding unsigned comment added by Jay Dale (talk • contribs) 22:49, 15 January 2010 (UTC)


 * I don't know if you'll get a top-ten, but the Guiness Book of Records says the most poisonous spider is Brazilian wandering spider, and apparently the most poisonous insect is the Maricopa Harvester Ant. -- Finlay McWalter • Talk 22:53, 15 January 2010 (UTC)


 * You might also be interested in the List of venomous animals article (it doesn't order them by poisonousness, or distinguish minibeasts from the non-mini, but it's fun nevertheless). -- Finlay McWalter • Talk 23:00, 15 January 2010 (UTC)


 * But really, if you're looking for the coolest poison, you have to go to the slow loris. A mother licks poison onto her kids before she goes out. So it's like if your mum covered you and your sister in poison before she went to Tescos to buy dinner. That way, if a lion ate your sister in the meantime, it would be sickened by the poison, and you'd still be alive to help your mum do the washing up when she gets back. -- Finlay McWalter • Talk 23:12, 15 January 2010 (UTC)


 * Remember there are also amphibians that are extremely poisonous, for example the poison dart frog. ~ A H  1 (TCU) 03:26, 16 January 2010 (UTC)


 * Depending on definition of minibeast (for example do you include flatworms as minibeasts since they are animals?) and I'm surprised no one has said it, but perhaps mosquitos are the most deadly of all based on numbers of human deaths they contribute to every year. Of course the mosquiotes themselves don't kill people Nil Einne (talk) 12:19, 16 January 2010 (UTC)


 * You can check out the Irukandji jellyfish.  DRosenbach  ( Talk 06:03, 17 January 2010 (UTC)


 * Don't forget about the box jellyfish. ~ A H  1 (TCU) 21:18, 17 January 2010 (UTC)


 * Or the Blue ringed octopus. 220.101.28.25 (talk) 14:11, 18 January 2010 (UTC)