Wikipedia:Reference desk/Archives/Science/2007 August 20

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August 20

Cat Whiskers

Yo. I recently adopted a pair of kittens (approx. 8 weeks old), their mother was feral and the kittens were trapped and fostered. Anyways, one of the kittens I adopted along with a couple of the others that were available for adopting have really short, stunted whiskers; it kind of looks like they've been cut off or something. Any thoughts as to why this could be? Nutritional, maybe? Also, they will grow back in properly, yes? Thanks. 38.112.225.84 05:34, 20 August 2007 (UTC)

I'd look at them up close, do the ends taper off normally, or end abruptly ? If they end abruptly, they may have been cut or burned (they would look black at the end if singed). If they taper off, then I'd guess it's a protein deficiency. I'd expect them to grow back normally with a proper diet, in either case. If they don't, consult a vet. StuRat 11:04, 20 August 2007 (UTC)

Our larger cat used to chew off the whiskers of the smaller cat. I presume it was an aggressive act to establish a pecking order. After a while, this behavior stopped, but the pecking order was well established by then. Maybe your cats are exhibiting a similar behavior. Another possibility, as StuRat mentioned, is undernourishment or protein deficiency. Nimur 13:47, 20 August 2007 (UTC)

When and if the whiskers grow back the cat will have an important part of its sensory system back in action. Per Cat senses cats "see" with their whiskers to navigate in the dark and to tell where prey (or food or other nearby objects) are. They can sense nearby objects with them (perhaps by air currents). They are more functional than human whiskers. Edison 16:03, 20 August 2007 (UTC)

Hmmm, I'm going to have to go with some type of nutritional defeciency as the most likely answer I guess. Weird that some of the cats had these short whiskers and the others were normal. I remember reading some novel, can't remember the name, that referenced someone ridding themselves of cats by taking them some distance away and then cutting off their whiskers so they couldn't find their way back home. Just thought I'd share that. 38.112.225.84 07:12, 21 August 2007 (UTC)

Peeling

A question at the language desk led to the Hawaiian trouvaille "AKA'AKA'A", a word meaning "Skin peeling or falling off after either sunburn or heavy drinking". Now, this is supposedly from the book The Meaning of Tingo by Adam Jacot de Boinod, but I found it on several blogs - it's still possible that it was misquoted and then copied and mirrored. It's also entirely possible that the collector of this phrase has been had. But, assuming the translation is correct, what are they talking about? Does our skin peel off as a result from heavy drinking at all? ---Sluzzelin talk 07:14, 20 August 2007 (UTC)

Only if that causes you to fall asleep in the Sun, which may very well happen. StuRat 10:59, 20 August 2007 (UTC)

Skin can get rough from dehydration (from heavy drinking), but I wouldn't call it peeling. Of course, it could be a Samoan thing. Maybe they are prone to skin peeling when dehydrated. -- Kainaw^(what?) 16:11, 20 August 2007 (UTC)

Thank you for your replies. (I did think of indirect causation, Stu, but not the one you mentioned!) ---Sluzzelin talk 14:00, 22 August 2007 (UTC)

Hmm, which one did you think of ? StuRat 00:47, 24 August 2007 (UTC)

Stumbles and brawls, I guess. ---Sluzzelin talk 20:55, 25 August 2007 (UTC)

It seems to be most people are thinking of drinking alcoholic beverages, but who said anything about alcohol? When I was thinking about this I thought could this be an effect of kava perhaps. I then forgot about it for a few days but after coming across it again I checked and sure enough "Heavy consumption can produce effects on the skin, ranging from light, red bumps; to heavy, scaly ulcers. This is an allergic response to antigens that form when lactones in kava bind to skin proteins. The effects disappear if consumption stops or decreases". This is somewhat unclear since it says the effects disappear but I'm guessing excessive kava consumption can lead to peeling skin. Also supported by this "http://www.naturalproductsmarketplace.com/articles/0c1feat2.html" Nil Einne 14:21, 25 August 2007 (UTC)

Wow! Thanks a lot, Nil Einne! ---Sluzzelin talk 20:55, 25 August 2007 (UTC)

Cognitive Error.

Do we have an article on a certain memory phenomenon caused by looking at something for so long that you seem to forget how it works. For instance, while reading this thread on Doctor Who, I found myself asking "is that really how you spell who?". This kind of effect happens to me fairly often, where a common word looks to me like it is spelled incorrectly, it's often accompanied by a thought that it looks like a ridiculous way to spell such a word, and it takes a good amount of conscious thought to confirm to myself that the spelling is actually correct. Do we have an article on it? I have no idea where to start looking. Does anyone else suffer from the same effect? Has anyone else noticed the effect with something other than language? Capuchin 09:22, 20 August 2007 (UTC)

Jamais vu? ---Sluzzelin talk 09:34, 20 August 2007 (UTC)

From time to time I definitely experience the exact same thing you describe Capuchin. Weird. 38.112.225.84 09:38, 20 August 2007 (UTC)

Jamais vu is a start, but i've never really experienced it with anything except written text. Also it's not a feeling of thinking that i'm seeing a familiar situation for the first time, but more a feeling that the word is obviously wrong despite being able to conclude, with more thought than i would normally have to use to check spelling of a word, that it is indeed correct. It also doesn't seem to matter what the word is, both long complex words and short simple words are equally 'up' for being obviously wrong. Capuchin 09:53, 20 August 2007 (UTC)

I get exactly the same thing sometimes as well. 147.197.230.174 10:24, 20 August 2007 (UTC)

I'd bet this is related to how, when you repeat a word many times, it seems to lose it's meaning. StuRat 10:55, 20 August 2007 (UTC)

This happens to me quite a lot. I find that it's more likely to be with short, simple words. Maybe this could be something to do with it being longer since you learned to spell them. Presumably when you first learn to write you will not have any clear method of learning/remembering words, but as you get used to it you will come up with methods and patterns that help you to remember. Or I could be talking garbage. Does anyone here teach young children?

Anyway, I also find it happens mostly with unusually spelled/pronounced words, for example 'length'. 'Who' is another one, and all the words with ough in them. Probably if you forget how to spell, say, complete, your brain will notice the connection with compose, compost, complement, deplete, replete, etc. Bistromathic 11:48, 20 August 2007 (UTC)

Yes the English written language can seem pretty ridiculous at times. Can't we just spel al awer words phoneticaly? Yes, this happens to me ALL THE TIME. I thought I was the only one...67.70.29.35 00:24, 21 August 2007 (UTC)

Support group, anyone? 38.112.225.84 07:06, 21 August 2007 (UTC)

It happens to me too!! I speak three languages (read and write in two) and it only happens with English. Perhaps it does have something to do with the spelling rules (non-phonetic) in English. The other language I read and write with is Malay which is totally phonetic. I wonder if any French speakers out there have this issue.

Birth rates following wars

I was told at school many years ago that after a war the birth rate increased and more boys were born to replace those lost in the war. Is this true? Do statistics following wars prove this? If more boys are born, how does happen? Dianayork 09:45, 20 August 2007 (UTC)

I don't think there is more boys than girls after a war, other than the normal distribution. But it is unnecessary to replace those lost in a war as within a generation or two, the ratio of child-bearing age M/F will be restored to 50/50 because the birth rate is still 50/50. the only question is the size of the population. The skewed generation will die out leaving the correct ratio. --Tbeatty 10:02, 20 August 2007 (UTC)

(the statistics though? what do they say?)87.102.2.76 10:29, 20 August 2007 (UTC)

I believe that birth rates do often go up after major wars (such as the post WW2 baby boom in the US), but not to replace dead soldiers. The reason is that many people have "put their life on hold" while fighting the war, and afterwards want to "make up for lost time". Thus, a couple which would have had 3 kids during the course of the war will try to have them, instead, immediately after the war ends. I also doubt that any change in sex ratio occurs. StuRat 10:41, 20 August 2007 (UTC)

(the statistics though? what do they say?)87.102.2.76 11:50, 20 August 2007 (UTC)

Did you follow my link ? The baby boom article I linked to contains statistics (in graph form) on births in the US since 1934, which clearly demonstrates an increase in birth rates after WW2. StuRat 16:37, 20 August 2007 (UTC)

The question was about boys being born (assuming that more boys than girls die during wars) - at least that was how I read it...87.102.2.76 18:25, 20 August 2007 (UTC)

I took "the birth rate increased and more boys were born" to make two points: 1) The birth rate increased 2) More boys were born. I only addressed the first issue. StuRat 05:51, 21 August 2007 (UTC)

http://www.statistics.gov.uk/cci/nugget.asp?id=951 "Sharp peaks in the numbers of births occurred after both world wars"

http://www.actuaries.org.uk/files/pdf/library/JIA-084/0092-0096.pdf page 1 table 1 shows no blip in sex ratios post WW2. ?87.102.2.76 12:27, 20 August 2007 (UTC) There is a blip occuring during ww1/post ww1 is it significant though?87.102.2.76 12:27, 20 August 2007 (UTC)

From the source cited,

“ The sex-ratio does not, generally speaking, fluctuate wildly with time but only changes comparatively slowly. Table 1 gives the sex-ratio for live births in England and Wales over some 50 years of this century. The general impression is of a slow upward trend with periodic erratic fluctuations. This change may be due to the average age of the mother changing... ”

Now to answer your question definitively, one would need to establish whether the average age of mothers is definitely changing... and then, to establish a cause/effect relationship between the war and the average age of parenting...

I'm not a social scientist at all, so at best I can say that these cause/effect relationships are difficult to establish with certainty, especially on such a small blip. Nimur 14:06, 20 August 2007 (UTC)

I believe that this question over-estimates the number of men killed in war. I made a comment to a sociologist once about Russia practically losing a generation throughout the period of WWI and WWII. He corrected me by pointing out that while the number of men killed throughout that period was very high, it wasn't even close to half the men 18-35 in Russia at the time. I believe the U.S. lost a smaller percentage of men than Russia. I may be wrong about that also. -- Kainaw^(what?) 16:16, 20 August 2007 (UTC)

Even if far less than half, that's still rather significant in terms of demographics and population impact (it would be even more significant if they were women, however, as that would leave few women capable of childbirth). And yes, Russia had far more casualties than the US in WW2. StuRat 16:45, 20 August 2007 (UTC)

The US of course lost a smaller percentage of men than Russia. I've often heard the phrase 'the lost generation' refering to the young men who fought for Britain in WW1, but that wouldn't just be affected by the raw numbers. In Britain, because of the way people signed up and the way the army was arranged, whole villages would lose their men at once. Hence, many people's experience would be of huge losses. 86.141.89.213 18:17, 23 August 2007 (UTC)

I think that term refers to more than just death, also including "lost innocence". StuRat 00:44, 24 August 2007 (UTC)

But here's the thing - even if after the war, the ration of child bearing age women to men was 70/30. In two generations it would be 50/50 because of a complete turnover in the child bearing population. --Tbeatty 19:22, 20 August 2007 (UTC)

Plus a 2 week old boy isn't going to be much use to a 20something female widow..87.102.2.76 19:49, 20 August 2007 (UTC)

Thanks. I often wonder if the people that died in both world wars had lived and reproduced, what would be impact on the world population now. Including of course the holocaust victims. Dianayork 11:31, 21 August 2007 (UTC)

Trends across period 3 of the periodic table

Hello all. THis *is* a homework question, but it's a small part of a huge assingment, and i'm looking for links (not answers), as i have been unable to find information.

I need information on a) the change in electorinic configuration and b) the change in net and core charge as you move across period 3 of the periodic table (from right to left).

Thanks for any help.Cuban Cigar 11:45, 20 August 2007 (UTC)

Period (periodic table) tells us that a period is a horizontal row, we even have an article Period 3 element.

Each of the elements in period 3 in the above link can be clicked on to link to the relevent article eg Sodium etc. The infomation you need should be in those articles (probably in the infobox on the right).

Ask again if you get stuck.87.102.2.76 11:55, 20 August 2007 (UTC)

Thanks a lot for the effort. However, i am looking specifically for the 'trends' across the 3rd period. The articles on the elements give information, but they say little on the trends.Cuban Cigar 12:06, 20 August 2007 (UTC)

If you make a list of for instance 'core charge vs column (group)' you'll be able to see any trends. Hint - in this case it increases - I leave the rest to you...87.102.2.76 12:30, 20 August 2007 (UTC)

Order: read Periodic trends!87.102.2.76 12:31, 20 August 2007 (UTC)

As mentioned, Periodic trends is the definitive article on the subject. I'm wondering if the title of that article should be renamed Periodic trends (chemistry) - as it stands, any recurring trend (such as an economic recession/boom cycle) could be called a "periodic trend." Nimur 13:56, 20 August 2007 (UTC)

I think that would only be neccessary when periodic trend (economics), periodic trend (history) articles actually exist!87.102.2.76 14:25, 20 August 2007 (UTC)

Added 'fix' to Periodic trends - a link to the disambig. page trends is that ok?87.102.2.76 15:28, 20 August 2007 (UTC)

Ha i managed to extract the information thanks to all who helped.Cuban Cigar 22:01, 20 August 2007 (UTC)

BIOLOGY

which is the Ovoviviparous roundworm? what type of egg is found in flat worms? how does cellulose digestion in ants carried out? which type non-chordates is bioluminescent? differences between nematocyst & trichocyst? interstitial cells in hydra are totipotent.give reasons?

This would not happen to be a homework set of questions would it? Have you read articles on roundworm, flatworm, termite, bioluminescence, nematocyst, trichocyst hydra (genus) (which is potentially immortal) or morphallaxis? Graeme Bartlett 13:44, 20 August 2007 (UTC)

Chemistry

Why is the SiH4 highly reactive so as to get easily hydrolyzed with aqueous alkali, while CH4 is nearly inert to it?

The usual explanation is that Si can expand it's octet whereas C can't - known as octet expansion - Si has 'available d orbitals'

4 is the maximum coordination number for c

Whereas Si can increase it's coordination number past four eg [SiH₄(OH)₂]^2- is possible (quite stable)

[SiH₄(OH)₂]^2- + 2H₂0 = 2H₂ + SiH₂(OH)₂ + 2OH^- and so on...

Look at the compounds of sulphur - you will see that stable entities such as SiF₆^2- are stable but have no parallel in carbon chemistry.87.102.2.76 15:43, 20 August 2007 (UTC)

chemistry

Bit confused with the term O_3 hole

Do you mean ozone hole or a Crystallographic defect in a oxygen containing lattice?87.102.2.76 15:50, 20 August 2007 (UTC)

Look at ozone hole. Flyguy649 ^talk _contribs 15:50, 20 August 2007 (UTC)

Per Flyguy; an underscore is sometimes used to indicate that the character that follows is meant to be subscripted. So O_3 → O₃ → trioxygen, usually called ozone. TenOfAllTrades(talk) 15:54, 20 August 2007 (UTC)

Petrochemicals

What is going to happen to the chemistry industry when we "run out of oil"? Where are we going to get all of our hydrocarbons from, especially ethene, the most commercial produced organic compound? From ethanol? --Russoc4 15:40, 20 August 2007 (UTC)

plants seem to be the probable source of carbon compounds when the oil and coal runs out.

There may be a major shift in the types of polymers produced when that happens - nowadays polyethene is common - because we can get ethene. In the future we may see a lot less of it and tend to use (if possible) 'starch' or cellulose based products if possible eg rayon.

It should still be possible to produce ethene from the cracking of vegetable oils.87.102.2.76 15:49, 20 August 2007 (UTC)

It's certainly a concern - and one that isn't mentioned enough. But I suspect (without proof) that the nature of supply and demand will mean that we won't ever literally "run out". It will be that the cost of crude oil will gradually increase as demand continues to rise but supply decreases - to the point where it's not economical to burn the stuff in car engines anymore and we are forced for cost reasons alone to switch to sustainable alternatives such as ethanol. What remains of the oil will probably last the chemical industry a long time. As an important feedstock for plastics and such, it's going to push up the price of some materials. As the stuff gets progressively rarer (and hence more costly), more and more parts of the industry will find alternative materials as a starting point - and what's left will become used in more and more specialised niches. There are precedents for this. Lots of industries used to be dependent on whale oil (and other whale products) - all adapted with the dramatic cutting of supply. SteveBaker 16:07, 20 August 2007 (UTC)

But then, you're assuming it will continue to be more economical to continue to produce all these products from the small remaining oil supplies. But if we move away from oil for energy, it seems to me so will a lot of the industries which use oil as a cheap 'chemical' source. For some, it may still be the most economical for others probably not so much. The comments about the types of plastics in particular is a significant one. One area of particular significance of course is the current reliance on artificial fertilisers for much of our agricultural produce including biofuels (along with the large amounts of oil used in other ways in the product of biofuels such as transport, tractors etc) Nil Einne 13:44, 25 August 2007 (UTC)

Also, expect plastic recycling to become far more prevalent as the product becomes more expensive. StuRat 16:31, 20 August 2007 (UTC)

Most hydrocarbons can be synthesized from coal; see for example coal gasification. Crude oil can also be generated from organic waste by thermal depolymerization. --Carnildo 23:07, 21 August 2007 (UTC)

Eagle Project

I am currently a Life Scout in The Boy Scouts of America and am currently thinking of things to do for my Eagle Project. I want to do something to help the enviroment. I was leaning towards planting trees in a city park or school. WhAt I want to know is what kind of tree would be most beneficial. I live in North East Texas near DFW. Or if someoen could point me to a website that deals with this kidn of thign that would be great. Also, when I do this project, I will need to raise money and if I have any money left over I need to donate it to an organization. I want to donate it to an organization that deals with this sort of thing. Thank you very much. schyler 15:53, 20 August 2007 (UTC)

I would definitely concentrate on native Texas species - they'll survive best without lots of careful treatment afterwards. As for funding, you might try to hook up with companies who are trying to be 'carbon neutral' - they realise that they are pumping CO₂ into the atmosphere (bad for the greenhouse effect and global warming) - and some of them are starting to try to offset that by paying people to plant trees on their behalf. Trees eat up about their own weight in CO₂ and pump it back out as oxygen - so if a company pushes out a hundred tons of CO₂ per year, they would (presumably) be interested in getting enough trees planted each year to compensate (ie enough to grow into a hundred tons of trees). Really big businesses would probably only do this sort of thing through a very organised company or whatever - but I bet you could find some small businesses in your area, figure out how much CO₂ they are putting out in a year (or causing to be put out because of electricity they use or something) - and approach them with the idea that they could offset this nasty behavior by planting trees. I bet that if you approached a small-ish sized business with a well-thought out proposal - and made them some posters they could stick up saying "We are now carbon-neutral!" (or whatever) - then they'd hand over the price of some baby trees and whatever you need to get them planted. You can turn this into a project including: science (coming up with the carbon numbers), art (drawing the posters), marketting (putting your plan to the businesses) and some outdoorsy stuff (planting and tending for the trees). SteveBaker 16:16, 20 August 2007 (UTC)

Just as an aside, it is not entirely clear that carbon offsetting by planting trees is quite as simple as all that. It sounds nice and green but the actual science of carbon sinks is a bit more complex, I gather... --24.147.86.187 20:44, 20 August 2007 (UTC)

Well, yes - sure. But we're talking about a boy scout activity here - I think we can allow a measure of approximation. SteveBaker 00:13, 21 August 2007 (UTC)

The National Arbor Day Foundation sounds like a natural choice for the charitable donation, to me. StuRat 16:25, 20 August 2007 (UTC)

Utah Mine Disaster

I guess that I am more comfortable placing this question in the Science (as opposed to the Miscellaneous) Help Desk. I certainly know nothing about mines or mining. So, in simple layman's terms, why is is it that "they" can't find those six miners in Utah? Specifically, I wonder the following (probably naive) questions. (1) Why is it not simply a matter of re-tracing their (the six miners) steps? (2) Is there no technology available and/or industry practice/convention followed whereby outsiders would be able to tell the location of trapped miners? Or whereby trapped miners are able to relay that location information to the outside? And (3) Are there no methods/means of communication (cell phones, walkie-talkies, emitting beeps, GPS, etc.) that are used in such instances? I mean ... mining has been around forever ... and this is certainly not the first time miners have been trapped. To me (an outsider, unfamiliar with the industry), it seems like they are reinventing the wheel, as if no miner in the history of the world has ever been trapped before? What is the logical explanation to all this? Thanks. (Joseph A. Spadaro 17:05, 20 August 2007 (UTC))

I'm not a mining engineer, but will do my best to address some of your questions. (1) Re-tracing steps. This can be virtually impossible following a collapse - as well as clearing débris from the access levels & shafts, safety work (eg. shoring up the roof) must be done at the same time, to protect the rescuers. Also, more than one level may have been affected by the collapse - imagine a multi-storey buiding collapsing, one cannot simply go to, say, the 2nd storey, as the collapse will have destroyed access routes, and jumbled the different levels together. (2 &3) Mines in the developed world are likely to employ a variety of communication techniques underground, however, radio is largely ineffective through rock, cell-phones & GPS do not work at all underground, and physical connexions (telephone) are likely to be destroyed in a collapse. Infra-red imaging may be of some use, as may radar techniques to identify potential voids (open spaces, which may have survivors in them). Any survivors would be likely to attempt to communicate their location by making noise (eg, banging on structures which could conduct sound) and they may have bleeper devices, however, they are likely to be injured, exhausted, and suffering the effects of thirst, hunger, and heat. They would also be aware that banging around in unstable ground could precipitate further collapse. Sadly, mining remains an inherently dangerous occupation, and those who benefit us all by their delvings are all too often killed in their efforts. DuncanHill 17:27, 20 August 2007 (UTC)

Short versions are

1. Retracing steps would involve going through unstable recently-caved-in rock, possibly the worst mine-related material to work with. Remember, the rescue effort was shut down because rescue workers were killed in a related cave-in.
2. Not with certainty. Rescue efforts are based upon knowing the general areas in which the miners are located and where the most survivable areas are, coupled with best-guesses as to the extent of cave-ins. That leads into...
3. Not really. Rock does an excellent job of attenuating electronic signals, particularly the weak ones that miners could have transmitters for. A high-powered signal from the surface might reach the miners; a return signal is unlikely to reach the surface. Sound, however, is a relatively common signal, though it requires that miners have the ability to strike something appropriate both hard enough to be heard and long enough to be located.

You may be interested in this NYTimes article, which notes the problems with #1 and the lack of proven success with locating miners via sound. Consider also that it's not "reinventing the wheel" when the wheel in question has never been adequately invented to begin with. — Lomn 17:30, 20 August 2007 (UTC)

A widely known way to save lives after cave-ins is to have regularly spaced "safe areas" where miners can go in a cave-in, which have air, water, food, and a hard-wired communication line to the outside world. Why don't they have them ? Because they are expensive. Why don't government safety organizations like the US Mine Safety and Health Administration force mines to have them ? Because many, perhaps most, "safety" organizations in the US have been subverted from their original purpose of protecting people from businesses to their new purpose of protecting businesses from people (who might win lawsuits, had the safety organization not given the business it's seal of approval). StuRat 17:51, 20 August 2007 (UTC)

Supporting StuRat's point, note that Richard Stickler, the current administrator of the US Mine Safety and Health Administration only gained his job through a recess appointment by George W. Bush. His appointment was strongly opposed by both the United Mine Workers union and the United States Senate, even though the Senate was then in Republican hands and ought to have been sympathetic to a Bush appointee.

Many of the "regulatory" agencies in the United States no longer actively regulate the industries they were meant to oversee.

Atlant 18:11, 20 August 2007 (UTC)

Hmmmmmmmmmm. There is no feasibility to use, say, those scent-smelling dogs ...? The kind that sniff drugs or find criminals on the loose? (Joseph A. Spadaro 18:53, 20 August 2007 (UTC))

I haven't heard of them being used, but they may have possibilities. However, mines may have a lot of strong smells in them already, and I doubt there are many dogs which can sniff out a man covered in coal-dust buried under tens of thousands of tons of coal. DuncanHill 19:05, 20 August 2007 (UTC)

The problem with search dogs is that someone would need to take them down close to where the miners are, and others would need to clear the way of rubble and shore up the mine supports, and that would risk the lives of those people, just as earlier rescue workers were killed by a subsequent cave-in. StuRat 05:44, 21 August 2007 (UTC)

I have found a fascinating paper on-line here [1] which discusses various factors affecting survival after mine accidents, and looks at such issues as air-supply, "safe havens", etc. DuncanHill 23:11, 20 August 2007 (UTC)

Another relevant article is here, which notes a few more of the problems with using existing technologies, including a link to government tests in which no technology examined was able to communicate through 300 feet of earth.

Tension in a string tied between two supports

Imagine a situation very similar to a suspension bridge. A string is tied between two rigid supports and the length of the string is more than the actual distance between the supports. Now, tying a weight and allowing it to hang down would exert wht all forces ??? I think one would be the tension but does the support also exert some force such as compression ???

Please enlighten.

The string would be under tension only, but each support would be under compression (from the weight of the support itself plus the half the weight of the string and mass supported by the string) and also under bending and shear (from half the weight of the string and mass supported by the string). StuRat 17:37, 20 August 2007 (UTC)

Precisely. See suspension bridge.--Shantavira|^{feed me} 17:38, 20 August 2007 (UTC)

Also, if the string is attached off-center to each support, then each support would undergo torsion (from half the weight of the string and mass supported by the string). StuRat 18:00, 20 August 2007 (UTC)

MPG: reality versus EPA ratings

This is more a technology question than a science question, but here goes. Anyone have info on how cars tend to perform in real life, mileage-wise, versus EPA estimates? I'd always been under the impression that the estimates are optimistic. I know the EPA estimates have been revised for 2008 (and possible a few times before that?) to be more accurate. I have a 07 model (which, in my understanding, would be rated a couple mpg lower with the '08 method) and it consistently gets better than advertised mileage. It's rated at 20 city, 28 highway, and we very regularly get 31-32 highway, and 22ish city. I did get 28 (mostly) highway once, with several passengers and their stuff in the car. This is with fairly brisk acceleration, whenever there is enough open road to allow such a thing. Did we get lucky with this car? Is it all down to driving habits? I've noticed that if you don't realize how soon you can upshift (at surprisingly low rpm for a 4banger) your city mileage quickly goes to hell. Have the estimates perhaps already gotten more conservative? Any idea how common it is to get better than expected mileage? Friday (talk) 18:33, 20 August 2007 (UTC)

I am a strong believer in driving habits. I had a 1994 Saturn SC1 that I sold last weekend. I regularly got 35-40mpg. I now have a 1997 Toyota Corolla. I regularly get 35ish mpg. I know people with the same vehicles that get less (even half) what I get. However, they do not drive the speed limit. They do not accelerate slowly. Instead, they speed and jackrabbit start from every stop. -- Kainaw^(what?) 18:37, 20 August 2007 (UTC)

Sounds reasonable, but the odd thing in my case is that I do speed and start quickly compared to most other cars on the road (many of whom appear to be asleep at the wheel.) I've noticed that mpg tends to be higher when average speed is higher (according to the car's mileage/trip computer). I have always chalked this up to less time spent stopped, though. I would rather change lanes to get around stopped cars than stop myself. Time spent idling and not moving seems to kill the mpg pretty quickly. Friday (talk) 18:47, 20 August 2007 (UTC)

As I noted, I drive the speed limit. I rarely stop/idle. Traffic lights tend to be set to the speed limit. So, I continually see the same thing. Light turns green. The guy next to me floors it. Two blocks later, I pull up next to him at the next light just as it turns green. He floors it. Two blocks later, I pull up next to him at the next light just as it turns green... Also, driving 65 on the highway (speed limit on our highway) means that I rarely have to slow down. People behind me who have a desire to do 80 have to slow down and go around me. So, all in all, idling isn't an issue. -- Kainaw^(what?) 22:33, 20 August 2007 (UTC)

Oh come on - get real. Yes, a lot of people say that - but they conveniently forget that the guy who accellerated hard from the lights will (maybe one time in ten) squeak through the next light when you get stuck there - or make the oddly timed filter arrow on a turn - or be at the front of the line of traffic and therefore be able to do a 'right on red' when you get stuck behind a car that's going straight on. That can easily save him a couple of minutes each time it happens. Sure it makes a nice story ("Oh I drive so carefully but I still get there just as fast") - but let's be honest here: it's bullshit. Simple mathematics and a dose of statistics will show that. Even if you stick to the speed limit, drag racing style starts and lethally dangerous lane changing will get you there faster. Driving slowly and carefully (laudable though it is) can only allow you to break even with the guy who's going nuts in the best of all possible circumstances. Obviously we must consider the law and safety issues in driving reasonably - but the argument that driving fast doesn't get you there sooner is just wishful thinking. This is the science desk - not religion. SteveBaker 23:18, 20 August 2007 (UTC)

A lot depends on the car - and a lot depends on how you drive it. It's well known that hybrids don't get anything like as good milage (by maybe a factor of two!) compared to the EPA ratings because by luck, the EPA test conditions are a very good match for what the hybrids can manage. For most cars, you can reach the EPA number if you drive them carefully. A few years ago, I had a car (a MINI) that was claimed to be able to do 35mpg. I was getting 28mpg. But I knew why that was - and I decided to find out whether I could actually manage 35mpg. So I filled up the tank, turned off the A/C checked my tyre pressures and drove very gently - trying to keep the revs between 2000 and 3000 rpm by never stomping on the gas, not going over 60mph and shifting gears (it's a stick shift) much sooner than I normally would - keeping a close eye on the tachometer. I also used cruise control whenever possible to avoid the little variations in speed that also eat gasoline. It took me two weeks to run through that tank of gas - the most boring two weeks of driving I've ever done! But when I filled it up (noting carefully how much was needed to fill the tank and dividing by the milage on the tripmeter) - I was astounded to discover that even doing a mixture of town and freeway driving, I was getting close to 42mpg! 42mpg is a LOT more than the EPA estimated (35mpg) and VASTLY more than my usual 28mpg. So for that car (at least) the EPA numbers are too optimistic for a 'typical' driver (well, OK I am a bit lead-footed) - but quite pessimistic for a really, insanely fanatically careful driver! On the other hand, my daily commute went up from 25 minutes to 35 minutes each way. Over two weeks, I spent 200 minutes longer in traffic and saved $15 in gas! However, that's less than $5 per hour. Do I really want to pay myself minimum wage for being stuck on the freeway? Hell no! So now I'm even more lead-footed than I was before! SteveBaker 23:02, 20 August 2007 (UTC)

Steve, supporting your story, last summer I did a lot of carefully-studied research on my 1996 Dodge Grand Caravan (FWD with the 3.3L engine). Normally, driving "with traffic" (so about 75 MPH tops), but taking no special steps to either conserve or consume gasoline, I reliably get about 23 MPG on my commute (mostly highway, some stop-and-go traffic on said highways). With maximum care (say a 52 MPH top speed, use of cruise control, minimal braking, etc.), I was able to get a maximum of 29 MPG. But not only did I consume a lot of extra wall-clock time, psychologically, the ride seemed to take forever because it was a very high-stress way to drive as I tried to fit in among the going-75-MPH traffic. This summer, I'm driving "with traffic".

By the way, at least for this Dodge Grand Caravan, the old canard about "Air Conditioning is more efficient than driving with the windows open" turned out to be complete bullshit. The highest MPG run was done with the windows open; every run with the A/C on was at least 4 MPG lower than a corrseponding run with the A/C off. Windows up or down seemed to make no discernable difference.

Atlant 12:23, 22 August 2007 (UTC)

Mythbusters tested the A/C versus windows-open thing - the result was that it depended critically on your speed (although I forget what numbers they came up with - it doesn't matter because the critical speed must depend on the kind of car, the weather conditions and your precise A/C settings). Here in Texas, opening the windows just makes matters worse anyway because once the air temp gets over body temp, blowing more of the stuff at you doesn't cool you off. But the critical speed thing should be no surprise because drag is a proportional-to-the-cube-of-the-velocity effect - where as A/C cost is irrespective of velocity. So if opening the window changes the drag on the car at all - you'd expect there to be a cross-over speed - above which A/C is better and beneath which you're better off with the windows down. I did my experiment with the windows up AND the A/C turned off in order to be sure I was doing the optimum thing. But you're certainly right about the psychological thing. It's not worth the mental anguish (particularly on a stick-shift car) to save so little money. The only reason to do it would be for "saving the planet" reasons - and I already feel that by buying a 42mpg car and a house with foot-thick walls with an insulation 'R' value three times higher than is required by law, spending more on electricity to get the 'green' stuff, avoiding food with excessive packaging and processing...I'm entitled to a bit of lead-footed driving! SteveBaker 16:47, 22 August 2007 (UTC)

The EPA just revised their mileage estimating routine to make it more in line with reality.Gzuckier 14:16, 21 August 2007 (UTC)

My girlfriend insists that she uses a tank of gas about every 300 miles. I drove the same car, went up to 330ish miles and still had a quarter tank. I'm pretty sure it's just the way you drive. --Wirbelwindヴィルヴェルヴィント (talk) 16:41, 21 August 2007 (UTC)

She probably refills the car BEFORE the little red light comes on - you wait for it to come on and THEN refill it. It's a guy thing (my wife says that that I think the 'E' on the bottom end of the gas gauge stands for "Enough (just)"). That difference in when you judge the car to have 'used a tankful' is more than enough to account for a gallon of gas - which could easily be 30 miles difference. You can't use the gas gauge to do exact measurements. You have to fill the tank all the way to the top - zero the trip-meter - drive for a couple of hundred miles - then refill the tank all the way to the top again. Now you know (from the second gas pump reading) how much gas you used - and from the trip meter, how many miles you drove. But saying X number of miles 'per tankful' is probably meaningless. SteveBaker 19:53, 21 August 2007 (UTC)

Actually, that's not true either. In my 7-8 years of driving, I've seen the red light once. I used to get bitched at by my parents if I have less than 1/8 of a tank. --Wirbelwindヴィルヴェルヴィント (talk) 18:18, 22 August 2007 (UTC)

Either way - there is still no guarantee whatever that what you think of as a 'tankful' is the same as your g/f thinks it is. If your judgement on when to refill is just 10% different, that's enough to account for your 10% milage difference. I'm not saying that this proves that you aren't driving more carefully than she is - merely that you don't know this for a fact without doing a more careful experiment. Fuel gauges on cars are notoriously inaccurate and (importantly) non-linear. They rely on float valves and they read differently on a slope or when accelerating or when the temperature changes or...lots of things. When you have a gauge marked with three tick-marks, it doesn't mean that they relate to 3/4, 1/2 and 1/4 full even if they are evenly spaced down the gauge. My car takes an eternity to get from full to (seemingly) 3/4 full - but then drops very rapidly to the empty mark. I've tried to measure this effect accurately - but it's a bit of a pain to do well because you have to keep refilling the car when the tank is almost full anyway. SteveBaker 18:45, 22 August 2007 (UTC)

See United States Environmental Protection Agency#Fuel economy testing and results for details. Apparently, the EPA testing simulates unrealistically slow travel, amongst other things. As noted by others, they are revising their testing procedure. --136.186.1.191 07:26, 22 August 2007 (UTC)

birds

I have a 1st grde question I need to know if the hummingbird is the bird that has the fastest wing flaps. I think I am right but need to be sure. Thank You.22:34, 20 August 2007 (UTC)63.3.15.1≥ MDS

Yes. According to The Bird Almanac: A Guide to Essential Facts and Figures of the World's Birds. ISBN 1-55297-925-3., the Amethyst Woodstar and Horned Sungem hummingbirds both have maximum wing beat rates of 90 per second. -- MarcoTolo 22:43, 20 August 2007 (UTC)

Yes - they do. But there is a lot of difference between the biggest hummingbirds and the smallest ones. According to our article on hummingbirds, the Giant Hummingbird's wings beat 8–10 beats per second, the wings of medium sized hummingbirds beat about 20–25 beats per second and the smallest beat 70 beats per second. There might be some other kinds of birds that could manage 10 beats per second and be faster than the giant hummingbird - but nothing can come close to the speed of the little ones. To get a feel for how amazingly fast that is, your fingers are about as long as a hummingbirds' wing. See how many times you can 'flap' a finger up and down in 30 seconds. SteveBaker 22:49, 20 August 2007 (UTC)

And note your fingers won't make a humming noise. This is where the name 'hummingbird' comes from. A frequency over 30 Hz will produce an audible sound. But this makes me wonder - at what frequency does a mosquito flap its wings then? Judging by the pitch that should be in the thousands. Is that possible? DirkvdM 18:38, 21 August 2007 (UTC)

According to this ref, mosquito wing cycle rates are in the ballpark of 350–550 Hz (odd, I would have pegged them higher, too). Here is an interesting paper on how insect muscles can move so much faster than those of vertebrates. -- MarcoTolo 19:50, 21 August 2007 (UTC)

As far as audible noise, the flaps-per-second establishes the fundamental frequency, but harmonics due to other vibrations could possibly form the dominant audible tones. These could easily be in the kilohertz, as complex standing waves might be set up on the actual wing surface due to dynamic tensions of the flapping. Nimur 05:32, 22 August 2007 (UTC)

Speed limit "c"?

This idea has been a nuisance since I first thought of it. I know there must be something really simple and elementary that I’m over looking here so be kind in your responses. The scenario is as follows. Suppose we have a sequence of satellites (planets) each traveling in the same (forward) direction. Each satellite travels at a velocity of 50,000 km/s (say) relative to the satellite before it in the sequence. The first is at rest and the 6th and last one is therefore traveling at 250,000km/s relative to the first (or use any speeds and the appropriate number of planets, the question is the same). Then suppose we have a space ship taking off from the 6th satellite reaching a speed of 60,000km/s (say). Shouldn’t this be impossible as its relative speed to the first satellite is greater than c? However, as far as I know it is perfectly possible to create an object that can accelerate to such speeds (theoretically) relative to earth. Why can’t earth be the 6th planet? How would the space ship “know” whether its motion is being compared to that of the 1st or 6th planet or any other satellite?67.70.29.35 23:54, 20 August 2007 (UTC)

Speeds don't add. If A is going at speed u with respect to B's rest frame, and B is going at speed v with respect to C's rest frame, then A is going at speed $(u+v)/(1+(uv/c^{2}))$ with respect to C's rest frame. This is smaller than $u+v$ and never exceeds c provided u and v don't. This formula is sometimes confusingly called "the velocity addition formula" even though it's not an addition. It's better called "the velocity transformation formula." It looks like Wikipedia's article is currently under velocity-addition formula, unfortunately. -- BenRG 00:56, 21 August 2007 (UTC)

Well, there are two things to consider.

• Firstly, there are no 'absolute' velocities - the word "relativity" in "Einsteins theory of relativity" means that you can just choose to decide which of your satellites and space ships is considered to be 'stationary' and choose to measure speeds relative to whatever you decided to pretend is stationary - what's more, the rules of physics and outcomes to all experiments are identical no matter which thing you choose to be stationary. This doesn't seem that weird to most people. If you've sat in a train with another train next to you - when the other train starts moving forwards, you get a really powerful feeling that you're moving backwards and that the other train is stationary.
• Secondly (and this is the weird part), we humans are used to a nice simple world where you can say if one object (object 'A') is moving away from me at speed X and it launches another object (object 'B'( at speed Y (relative to A) - then I should see B moving at a speed (X+Y). That simple arithmetic is really close to the truth at 'normal' speeds (like anything under a million miles an hour). But sadly, the universe doesn't actually work like that. From the point of A, it did indeed launch B at speed Y - but because A is moving away from me at anything like the speed of light, distances and times as measured by A seem to be 'wrong' to me - which means that as far as I'm concerned, A's measurement of B's speed is also 'wrong' - so instead of B's speed seeming to me to be (X+Y), it's X plus a bit less than Y. That 'wrongness' gets worse and worse the faster A moves away from me - and (by an amazing cosmic conspiracy), the result is that the speed of B NEVER seems to be faster than light - no matter what speed A is moving and no matter how fast A launches B. Weird - but true.

So, in your case, you're assuming you can just add those speeds together from the perspective of you standing off to the side of all of this complicated stuff. But as soon as these things start moving fast, their time and space distortions start to mess things up - and all of that always makes sure that nothing goes faster than light. It doesn't matter that A launches B which launches C which launches D, E, F - all we care about is that if 'F' is zipping away from me at a good fraction of the speed of light - then when it launches it's satellite, it's view of time and space will be so messed up that from the standpoint of someone watching all of this, the speed of the satellite will ALWAYS be less than 'c'. SteveBaker 01:06, 21 August 2007 (UTC)

Here's the kicker, everything else is modified to keep two fundamental principles: 1) the speed of light is constant in all frames and 2) energy is conserved. That means mass, lengths, time and frequency of light all change depending on the frame of reference. --Tbeatty 05:40, 21 August 2007 (UTC)

The way I've alwasys looked at this problem is that, we assumed that the time is constant through out the world, and we can measure the time from the other side of the world instantaneous. This assumption is the cause of all the confusion. Think about this scenerio: You and I are standing next to each other, both of us are holding a very accurated watch and have the exact same time. I start to walk away and point my wacth at your direction so you can tell the time on my watch. After I walked 5 meters, you look at both watch and see exactly one second had passed on both watches, you then say I moved with speed 5 m/s. This is what we experience in our world. There is one important factor we ignored so far is that, how is it that you can see my watch from 5 meters away? Simple, light travelled from my watch to yours, in exactly 5/c seconds (distance over speed, make sure it makes sense). If both our watches read the SAME TIME, then how is it after signal from my watch after 5/c seconds still the same as yours? The only logical interpretation is that my clock must have gone a little bit slow, and reads (c/5) second slower. Put this in cosmic scale, you will see relativity does make sense.192.53.187.183 14:44, 21 August 2007 (UTC)

No, no, no! That's not it at all! That's far too mundane! The world is wierder than that. Even if you accurately take into account the amount of time it took the light to get from him to you (which you must) - there is still a tiny discrepancy due to your relative speeds. Suppose your fast moving friend with the watch starts off a long way away from you and rushes past you at enormous speed. Just as he passes you, he sticks his watch right in front of your face - an inch from your nose. When you read it, it STILL won't agree with the time on your watch. It has nothing to do with the distance between you - it's only to do with your relative speeds. Time passes at a different rate for your fast moving buddy than it does for you. Lengths, masses and all kinds of other things you might measure are distorted by virtue of his speed. How does your explanation cover the fact that the other guys watch weighs more when he's running away at high speed? Worse still, your explanation only accounts for 5/c worth of disrepancy between the two watches - if he's moving at 99.99999% of 'c', his watch will read differently by a thousand years! (OK - I made that up - I can't be bothered to calculate it - but it's a hell of a lot!) SteveBaker 20:08, 21 August 2007 (UTC)

You've started on the twin paradox, but missed it by that much. If your buddy walked away from you and went all the way around the world to where you stood so that your distances were exactly the same as when you started, your watches would still mismatch because of your relative velocity. --Tbeatty 06:23, 23 August 2007 (UTC)