Wikipedia:Reference desk/Archives/Science/2007 August 7

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August 7

Speling queston

Wye are sew many wrods misplet in a forem four a dicshinery? I fell like im reeding the dairy of a desleksik sixyearold. Dew ewe supose its from texting? Butt if wee Hughes a spell checker, their ar knot sew many errers, rite? —The preceding unsigned comment was added by Milkbreath (talk • contribs) 00:06, August 7, 2007 (UTC)

Dis ain'd da dikshunery. 'S ovur heer. </joke> And yes, some people look at talk pages as informal and they forget that they need to be understood by everyone. Discussion should be in English, although informal language use is probably ok in most instances. -- Flyguy649 ^talk _contribs 00:13, 7 August 2007 (UTC)

And on a page like this, we want everyone to be welcome to ask questions, and putting up big signs that say "Post your question in perfect English or it will be either removed or ruthlessly edited depending on the mood of the person reading it" would not foster the appropriate atmosphere. (Although this is really the sort of question that should go to WT:RD.) Confusing Manifestation 01:26, 7 August 2007 (UTC)

Sometimes I mistype a word and I'm so lazy I can't even be bother to change it - nobody reads this anyway do they.87.102.43.16 09:20, 7 August 2007 (UTC)

Blood group and Vegetarianism

I saw on TV the other day a nutritionist recommend people with blood group A become vegetarians as they can't consume meat as well. Knowing how many dodgy 'nutritionists' exist (see "Dr" Gillian McKeith) I wondered if there was any truth in this. The guy agreed with a doctor that so called superfoods are more of a marketing ploy, so didn't seem all bad. Any ideas? Cyta 07:24, 7 August 2007 (UTC)

See Blood type diet. Dragons flight 09:39, 7 August 2007 (UTC)

No offense intended, but the Blood type diet is complete bullshit. 69.254.185.128 03:05, 8 August 2007 (UTC)

Yes I suspected as much! Cyta 12:13, 8 August 2007 (UTC)

Where is the brachialis?

(There should be a separate medical RD)

I'm trying to figure out which muscle is the brachialis but I get confused. Check out this picture from the brachialis article:

http://upload.wikimedia.org/wikipedia/commons/8/87/Brachialis.png

It looks like it's on the "inside" of the humerus bone, near the elbow area. Now look at this one:

http://upload.wikimedia.org/wikipedia/commons/d/de/Gray413.png

On this picture the brachialis appears to be on the "outside". So which is it? A naprapathy student I know claims that they're both, which seems really weird since there's no way that a muscle on the inside and outside of the humerus could possibly be connected - or could they? Take a look at these pictures of Schwarzenegger's well-developed arms and tell me which one is it:

1. http://www.mypix.se/VisaFullImage2.asp?id=JNJOKPFRMOPMF8&storlek=640 ("inside", "lower" humerus) 2. http://www.mypix.se/VisaFullImage2.asp?id=JNJOKPGNHMGQR0&storlek=640 ("outside", "middle" humerus)

I would truly appreciate it if someone could clear this out for me. Thank you in advance, Jack Daw 13:07, 7 August 2007 (UTC)

The brachialis is deep to (i.e. below) the biceps brachii (biceps) muscle, so in the first drawing, it is covered in part by the biceps. It arises from the anterior surface of the lower half of the humerus (see this image. At the superior part of its origin on the humerus, it is more lateral (outside), but for the most part it is right in the middle, which is why you can see it in both of the two pictures. -- Flyguy649 ^talk _contribs 13:17, 7 August 2007 (UTC)

The lads at the gym always told me that the brachialis pushes the bicep up when it becomes larger. To be able to do this it should be under the bicep like in the second Ahnold picture. PvT 13:21, 7 August 2007 (UTC)

Thanks, but I don't understand how to maneuvre the site. Jack Daw 15:29, 7 August 2007 (UTC)

At the Visible Human Project, they've sliced up a fellow like pastrami so you can see where each muscle goes. You could follow the brachialis from origin to insertion. See here or here. --TotoBaggins 14:24, 7 August 2007 (UTC)

I would only take important advice about your health from a licensed health worker

pale monarch

Are those butterflies that look just like monarchs but are kind of a pale yellow instead of orange still monarchs? thanks Gzuckier 14:09, 7 August 2007 (UTC)

Pictures on our Monarch butterfly page, and around the web, indicate that some of them are indeed pale yellow. See also Viceroy butterfly, though. --TotoBaggins 14:29, 7 August 2007 (UTC)

Thanks. my employer's firewall doesn't let me see the images. (^_^)Gzuckier 17:56, 7 August 2007 (UTC)

Weather book needed

Hi, this is a somewhat odd request, but my younger brother's birthday is coming, and I wanted to get him a Weather book (he wants to go into Meteorology). I'm looking for a large, preferable hardcover, with color illustrations, and medium to hard technical text that covers beyond the basics. He does read at a college level/above when it comes to science, so please do not suggest children's books, or intro books. Textbooks are fine. I'd appreciate any suggestions, thank you. :) Zidel333 14:23, 7 August 2007 (UTC)

Meteorology#Books_and_Publications would be a good starting point (you nearly answered your own question above) and Meteorology#External_links might have a list of their publications on their sites. Lanfear's Bane

I'm going to strongly recommend this book because I loved it - although I confess that it fulfills almost none of your criteria: "The Cloudspotter's Guide: The Science, History, and Culture of Clouds" by Gavin Pretor-Pinney - I recommend it because it's interesting and informative and NOT a content-free glossy coffee-table book. I have it in hardback - although I see only paperbacks of it now - it's small and has just a few small black and white illustrations - but if your brother is truly into weather, it's a great book. Amazon have a two-for-one deal with "The Book of Clouds" - which is a large, hardcover with color illustrations (and probably very little actual information)...get him both and between the two, you have all the bases covered. SteveBaker 15:51, 7 August 2007 (UTC)

Just to further on Steve's comments... I have also enjoyed "Cloudspotter's Guide", but I must admit that the book kind of falls between camps. On the one hand, it's not a gorgeous coffee-table type book, but on the other it's also not an in-depth, scientific look at clouds. I agree that it is a good starting-off point, though. The website is in some ways better, since at least the pictures are large and in-colour. (Personal note: am I the only one who gets a little freaked out at this image?). Matt Deres 23:56, 9 August 2007 (UTC)

Clarification on Sun tanning

I'm worried I don't get enough sun, so I'm going to start lying in the sun once or twice a week - but I have some questions
(And yes, I've read Sun tanning)

The article says it is in fact the UltraViolet frequency of the sunrays that cause a) tanning, and b) production of Vitamin D.
I always thought ultraviolet was the enemy! I thought that's the reason we use suntan lotion! - which will actually prevent tanning and block production of Vitamin D.
But then later it recommends using suntan lotion when tanning! (How can you tan if you're blocking off the ultraviolet!)
Question 1: When tanning for 1-2 hours once a week, is suntan lotion necessary, or not? (assuming you want to get a tan and produce vitamin D?)
Next, it mentions that the suntanning booths at gyms and salons may be addictive because endorphins are released when the ultraviolet light helps produce Vitamin D.
Question 2: Do the tanning booths actually give off ultraviolet light? -- I figured they wouldn't for health reasons
Question 3: Would it be fair to say that the tanning booths are as good as, if not better than suntanning naturally in natural light?
Thanks in advance. Rfwoolf 14:44, 7 August 2007 (UTC)

Perhaps a look at tanning booth seeing as all your questions seem to be oriented towards tanning booths? Lanfear's Bane

The UV light is both what tans you and what produces the vitamin and what causes skin cancer and various eye problems. Suntan lotion (at least the 'sun-block' kind) blocks out some (but not all) of the UV - which reduces the amount of skin darkening - and the skin cancer risk - and cuts down on vitamin D production...pretty much the same result as if you didn't bother to lie in the sun in the first place! It's really unlikely that you are deficient in vitamin D - so why would you want all of the other health risks? Our article on Vitamin D says that unless you live in the Arctic: ...adequate amounts of vitamin D3 can be made in the skin only after ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen. In other words, you get plenty of Vitamin D when you take your trash out to the street twice a week! SteveBaker 16:00, 7 August 2007 (UTC)

Our article may say that, but when I've heard similar statements quoted from actual biologists it contained caveats. Basically, that 10 to 15 minutes a day was enough for a fair-skinned person in the middle of a summer's day in Britain. These things will vary by skin colour and where you live, as well as the time of day and time of year. Actually, looking at the article and where the 'only' is placed, it doesn't seem to say what you imply it does. I wonder if that's what the person who wrote the sentence intended. Skittle 09:39, 8 August 2007 (UTC)

"...in sunlight at sea level when the sun is more than 45° above the horizon, or when the UV index is greater than 3.[5] At this solar elevation, which occurs daily within the tropics, daily during the spring and summer seasons in temperate regions, and almost never within the arctic circles, adequate amounts of vitamin D3 can be made in the skin only after ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen." So in fact the article also states that this is only at certain times of day and year for many places, and later clarifies that those with darker skin need longer. Skittle 09:45, 8 August 2007 (UTC)

Actually there's serious current concern about vitamin D deficiency (not to the point of rickets, generally; a more "subclinical" sort of deficiency). Some studies seem to show that vitamin D is protective against cancer, including skin cancer. Some workers in the field suggest that many people are now not getting enough sun; others recommend supplements. Both of these ideas are controversial and I'm certainly not competent to say who's right, but I don't think you should liquidate the whole debate as casually as that. --Trovatore 16:49, 7 August 2007 (UTC)

It very much depends on two major factors: where you live (in terms of latitude) and what your skin tone is. If you are dark skinned and live at northern latitudes, then you may require more exposure to sunlight for optimal vitamin D production, then if you are pale skinned and live in southern latitudes. However, in most cases the exposure required is obtained by simply going about our daily business and eating a balanced diet. The not inconsiderable dangers of UV exposure balanced against its positive aspects is not something we could advise you on, you should probably speak to a health professional to get appropriate advice. Incidently, vitamin D (and hence sunlight) has recently been (re)found to be an effective anti-mycobacterial factor in the fight against tuberculosis. [1]

The OP is clearly concerned with a lack of Vitamin D - and you are correct in saying that there are some more extreme circumstances (eg Dark skinned people with indoor jobs who live in the extremes of latitude) when that might truly be a problem. But for most people, most of the time, the 'normal' amount of exposure to sunlight is more than enough. If you ARE getting enough Vitamin D then every extra hour you spend on a tanning bed or out in sunshine without a decent sunblock is increasing your skin cancer risk for no particular benefit. It follows that if you merely suspect that you are vitamin D deficient, then you should get tested for that rather than going out and lying unprotected in bright sunlight or on a tanning bed "just in case". As the Vitamin D article explains: Beyond the 15 minutes twice a week guideline: With longer exposure to UVB rays, an equilibrium is achieved in the skin, and the vitamin simply degrades as fast as it is generated. - so even if you are fighting some dread disease that would benefit from excessive levels of Vitamin D, you won't get that by lying out in the sun for longer. So forget such things as anti-mycobacterial factors in TB...extra sunshine just isn't going to do that for you. SteveBaker 18:03, 7 August 2007 (UTC)

The current debate is not just over black computer programmers living inside the Arctic Circle. Surveys of serum vitamin D have found quite a few people below the concentrations considered desirable. Of course, probably no one really knows what the truly optimum serum concentration of vitamin D is, but the concentrations found must be below the level where you'd be at equilibrium in bright sunlight, because one of the main explanations is that people have become diligent about using sunblock to protect their skin.

Personally I'm not willing to give up sunblock because I don't want my skin to age quickly. I'd rather take oral supplements, which is what I did when I lived in Canada. Oral supplements are controversial because overdose is possible -- but apparently it's not really very likely unless you go very seriously over the recommended dosages. --Trovatore 18:19, 7 August 2007 (UTC)

We should probably mention Seasonal affective disorder here too - this condition is to do with Seratonin - not Vitamin D - but it's also caused by a lack of sunlight. It is generally treated with bright light - but the light doesn't need to contain any UV component - so you wouldn't use a tanning bed or advise sunbathing. SteveBaker 18:10, 7 August 2007 (UTC)

Water in the human body

That the human body is approximately sixty to seventy percent water is well-known or at least widely accepted. But who calculated this in the first place?

thanks,

db

I was wondering the same thing not long ago. I can think of all sorts of comical ways to calculate it (weight a man, squeeze all the liquids out, weigh him again), but I don't know where they came up with that first. Maybe I'll hunt around, my blind guess would be 19th century physiological literature, but maybe 18th century. Probably not a whole lot earlier, but I could be wrong. --24.147.86.187 13:28, 8 August 2007 (UTC)

My guess is that they figured out how much water is in the various organs and structures of the body and averaged (or something) the results. I still like 24.147.86.187's idea :)69.205.180.123 16:38, 8 August 2007 (UTC)

Weigh the body - dehydrate it - weigh it again. Since Egyptian mummies are dehydrated - it's possible that the Egyptians first knew this...although they also pulled out some of the internal organs which would have to be accounted for - so maybe not. But since most mammals are going to have broadly similar proportions of water - you could get the numbers for (say) a Pig - and you'd be in the right ballpark. SteveBaker 20:38, 8 August 2007 (UTC)

Weigh it while floating? 68.39.174.238 02:05, 10 August 2007 (UTC)

I think that the weighing of the body after being dehydrated could be how it was calculated. And also the amount of water in most cells, because the whole body is made up of cells that can give a rough percentage. Cory Nelkin 21:27, 11 August 2007 (UTC)Cory Nelkin

Alcohol from beans

Passing on a question from my wife..."Is there any reason why we dont have an alcohol made of fermented beans? Princy fermented some beans the other day and they smelled of alcohol so it got her wondering if bean brew had been done before. a quick google search rendered no bean alcohol." ike9898 17:16, 7 August 2007 (UTC)

I don't have a good reference for this, but my guess is, since beans aren't very sugary, they're not commonly used to try to produce alcohol. I'm not saying it couldn't be done, but this may explain why it's not a popular choice. Friday (talk) 17:48, 7 August 2007 (UTC)

Yeah - I was thinking that too - but then I recalled that alcohol is routinely made from potato and rice - both of which are really starchy and have no sugar worth mentioning. SteveBaker 18:54, 7 August 2007 (UTC)

I probably shouldn't say sugary. In terms of food, people think of starches and sugars as being fairly different, but my layman's understanding is that chemically, a starch is mostly just a large sugar. Ethanol_fermentation makes it sound like starches are easily fermented into ethanol. Now that I look, starch says that edible beans are starchy too. So I suppose I have no guess why beans wouldn't work. The suggestion that maybe cheaper things are used instead seems sensible to me. Friday (talk) 19:13, 7 August 2007 (UTC)

See mashing - the starch (from potato whatever) is polymeric sugar, and is easily broken down by boiling etc.87.102.75.182 19:49, 7 August 2007 (UTC)

Are you sure about that? That certainly isn't what the article you linked to says. In beer brewing, the starch is broken down by enzymes in the malt. ike9898 21:33, 7 August 2007 (UTC)

For "boiling etc" you can replace with "heating + enzymes" if you wish.87.102.76.73 10:14, 8 August 2007 (UTC)

Since someone raised this issue again, I'm going to clarify further about 8 months later. Bear in mind that beans contain a fair amount of protein, from which it is much more difficult to produce sugar from. They also tend to contain a large amount of dietary fibre which also has a similar problem. They also tend to be quite oily. Taking a look at Common bean, it doesn't look like the amount of sugar or starch (as Friday said, these are basically the same thing) is going to be particularly good for producing alcohol. Compare this to refined rice or potato for example which are basically just sugar/stach. In conclusion while perhaps not the only reason, the fact that beans in general contain a very low amount of starch/sugar is probably a significant factor. Bear in mind as well it depends on availability and taste. I think most societies has at least one starch/sugar source be it rice, potato, wheat, barley, tapioca, kumara, whatever. If you're going to be producing alcohol, your more likely to produce the cheaper raw material, which probably has a better tasting product and which has a much higher starch/sugar content then the more expensive raw material with a potentially worse tasting final product and which has a rather low starch/sugar content. Nil Einne (talk) 08:15, 4 May 2008 (UTC)

soy sauce is fermented, but that's not what you were asking - in general things that are fermented have a high carbohydrate/sugar content - potatos, sugar etc. Beans have this - however it is possible that the high amount of protein/amino acid in beans might interfere with the fermentation? - causing unpleasent substances to be formed or just a foul taste?

Bear in mind it's not just soy sauce. Quite a number of products are made from fermented beans. tempeh, some sorts of [[|tofu|taufoo]], fermented black beans. Soya beans in particular are often fermented... None of this answers the question of course Nil Einne 00:03, 10 August 2007 (UTC)

More likely is that beans are just too high value to be considered for fermentation - they are relatively expensive compared to beet/corn.87.102.75.182 18:00, 7 August 2007 (UTC)

I can definently see how they might not be a good feedstock for fuel ethanol, but I would think that a culture that uses a lot of beans (Mexico?) would have a bean liquor if there wasn't some sort of problem with it. ike9898 18:55, 7 August 2007 (UTC)

Maybe it would just taste awful? 151.152.101.44 20:02, 7 August 2007 (UTC)

OK - I think maybe I know the answer - although I'm no chemist. I'm pretty sure a chemist will either confirm this or shoot my idea down in flames! When I do a Google search on 'soybean alcohol' - almost every hit is for papers talking about 'soybean alcohol dehydrogenase' - and they all say that beans in general and soybeans in particular are rich in the stuff. Our article on Alcohol dehydrogenase says that they are enzymes that facilitate the interconversion between alcohols and aldehydes or ketones. So I wonder whether the dehydrogenase in the beans is decomposing the alcohol as fast as it forms? This might explain why I got exactly zero hits talking about brewing alcohol from beans. Is there a chemist in the house? SteveBaker 22:34, 8 August 2007 (UTC)

There's a biochemist, I hope I'll do. If this was the problem, boiling would easily kill the dehydrogenase activity. Aaadddaaammm 01:11, 9 August 2007 (UTC)

Darn! Well it was worth a try! Many thanks! SteveBaker 15:14, 9 August 2007 (UTC)

Anybody have additional answers on this? As a random web surfer, I'm rather curious...

Frozen Water Picture

How exactly would you go about taking a picture like this http://en.wikipedia.org/wiki/Image:Michael_Melgar_LiquidArt_resize_droplet.jpg ? I know you need a very fast shutter speed, but what setup is best?

Thanks, --Fadders 19:45, 7 August 2007 (UTC)

Could be done with a strobe, too. I'll leave the rest for the more qualified. Flyguy649 ^talk _contribs 19:56, 7 August 2007 (UTC)

Looking at the creators talk page - someone has already asked - strobe flash seems like a likely explanation.87.102.75.182 19:58, 7 August 2007 (UTC) (note the shutter speed is 2sec - suggesting a flash..87.102.75.182 19:59, 7 August 2007 (UTC)

While I'm here High speed photography and also Flash (photography)87.102.75.182 20:00, 7 August 2007 (UTC)

Or even try http://www.doctormelgar.com/gallery/ and read http://www.doctormelgar.com/gallery/the_technique.htm.

I'd go with a low shutter speed (several seconds or longer), a dark room, and a bright strobe (a camera flash should be bright enough and fast enough). Since the only source of light is the strobe, it doesn't matter that the shutter is open for a long time, and the longer shutter speed makes the setup simpler. With a digital camera, I'd just take a series of photos and hope I got one with the drop in the right place; with a film camera, I'd use an infrared sensor and light placed to detect a falling drop of water and trigger the flash. --Carnildo 00:03, 8 August 2007 (UTC)

There's some discussion threads at Flickr on this topic, like this one. Pfly 19:27, 10 August 2007 (UTC)

International Space Hygene

How do astronauts shower on the ISS? 151.152.101.44 20:24, 7 August 2007 (UTC)

There is a full-length, sealed shower cabinet that they use. Water is removed by a suction device. Angus Lepper^{(T, C, D)} 21:14, 7 August 2007 (UTC)

And of course, weightless water can still be forced out of a nozzle. --Bowlhover 22:34, 7 August 2007 (UTC)

I remember reading somewhere that in the shower, they only need about a gallon of water. Since it's weightless, they just grab a blob of water and use it. I believe it's located in the Zvezda module, although I can't find a picture. Afterwards, the water is reclaimed. BTW, I believe the astronauts on the space shuttle have to do without showering during their trips. Ew. --Bennybp 02:00, 8 August 2007 (UTC)

They use sponge baths, to the best of my knowledge. Angus Lepper^{(T, C, D)} 14:01, 8 August 2007 (UTC)

Is it really a problem tho? Given the environment they're in, it would seem they wouldn't get that dirty Nil Einne 23:28, 9 August 2007 (UTC)

If you really want to be grossed out, there is a whole exhibit on space toilets at the Smithsonian. --24.147.86.187 01:42, 9 August 2007 (UTC)

Temporary fix to glassware

Any recommendations on what can be used to temporarily hold together broken glassware? The piece in question does not contain liquid but it has hot air flowing through it (~80C)(it's one of these; the part that is broken is the inlet). My only two ideas so far are crazy glue, or this sort of fancy duct tape I've seen at Home Depot - shiny silver, heat resistant and ten times as expensive. Your hints, please! ike9898 21:15, 7 August 2007 (UTC)

How much pressure do you need to contain? How critical to its function (and your safety) is the absence of any leak? How badly broken is it (crack vs piece broken off vs holes where the original glass no longer exists, etc)? How long does this fix need to last? How big is this thing? I've used epoxy on glass that gets heated (can't remember exact temp). Tygon or other plastic or rubber materials may soften but not melt, you could use them as a sealing layer against the glass, held in place with duct tape or string. How about going to the other extreme, with a torch and reassembling the glassware:) DMacks 21:32, 7 August 2007 (UTC)

Have you seen the website http://www.thistothat.com/ ? It recommends Loctite 349 for your particular problem, and it gives some other suggestions too. Hope that helps a little. TreeKittens 04:46, 8 August 2007 (UTC)

I'd try silicone sealent- the sort that comes in a gun - they are generally known for their temp resitance - not necessarily the strongest bond though - you might want to reinforce it with a splint and tape.87.102.76.73 10:23, 8 August 2007 (UTC)

Just as an example something like the products here http://www.workshopsupplies.co.uk/en-gb/dept_440.html - you can get this stuff cheaper..87.102.76.73 10:29, 8 August 2007 (UTC) Even the cheapest silicones are serviceable upto 100C87.102.76.73 10:30, 8 August 2007 (UTC)

Bernoulli Principle

When an aircraft is on the runway and about to take off, when does the Bernoulli Principle come into effect? My assumption is that the aircraft needs to travel fast enough for the effect to work and pitching the nose up brings it into effect along with the help of the thrust which the engine creates. But can anyone provide more details about this. Thanks in advance.Tbo 157 21:28, 7 August 2007 (UTC)

The Bernoulli principle applies as soon as air is moving over the wing. Sufficient lift is attained at different speeds for different aircraft. Another concept worth looking into is that of the Angle of Attack (angle of the wings to the airflow): as it increases, lift increases up until the point at which the aircraft will stall — where lift suddenly drops off (in terms of what this would actually feel like: the aircraft will slow down, and begin to be buffeted as the airflow is dirtied; the nose will begin to drop (also, a rather loud horn or clacker will be sounding in the cockpit to warn of the stall). During takeoff and approach stages of flights, flaps are deployed which increase lift and drag (useful to reduce speed on approach — a greater area and sometimes different type of flap is deployed on landing; around something like 10-15 degrees on takeoff, around 20-25 or more on landing), enabling the aircraft to maintain the same lift with a lower pitch (which is helpful for takeoff and landing where your pitch is, for obvious reasons, much lower). Angus Lepper^{(T, C, D)} 21:22, 7 August 2007 (UTC)

Thanks for the reply. Im aware that heavier aircrafts need to achieve a higher speed in order to get the Bernoulli Principle into effect and that it is when the velocity of air is higher above the wing. However I am asking when this happpens exactly.Tbo 157 21:28, 7 August 2007 (UTC)

It isn't just heavier aircraft that need to achieve a higher speed; it also depends on the aerodynamics of the aircraft. What I'm saying is that the Bernoulli principle doesn't suddenly come into effect — the wing is designed such that it will produce lift whenever any air is flowing over it. The strength of the lift generated by the wing increases with the speed of the airflow and with the angle of attack. When the lift is greater than the weight of the aircraft, the aircraft will take off. Angus Lepper^{(T, C, D)} 21:35, 7 August 2007 (UTC)

Again, thanks very much for the helpful info. I would also like to know how this works for fighter jets, in particlular harriers, which are much more maneuverable and can even reverse while in flight. I am presuming that there is a separate effect for this. Tbo 157 21:48, 7 August 2007 (UTC)

(De-indent for readability) The principle is much the same for fighter jets in general. However, the thrust-to-weight ratio of an F-15 far exceeds that of, say, a Boeing 767 — hence it can accelerate faster (also, no care need be taken for passengers, so high-G braking can also take place). Although, an aircraft carrier's flight deck is still too short, hence the need for special procedures (including the use of a steam powered catapult) to launch aircraft from carriers.

Also, aircraft such as the Harrier and F-35 are slightly different: whilst the Bernoulli principle applies without change during normal flight, it isn't related in any way to their aerobatic abilities.

In fact, the solution is quite 'simple' (from a high-level point of view; from an engineering point of view, it's a nightmare). They have engine(s) (the Harrier has two, the F-35 one) which can use an extreme form of thrust vectoring. Basically they can direct the engine's exhaust downwards, allowing them to hover. However, this is difficult: the Harrier is limited to 90 seconds in a hover because of the fuel requirements and extreme temperatures (no fast moving air to cool the outlets) involved. Angus Lepper^{(T, C, D)} 23:29, 7 August 2007 (UTC)

Argh! There is so much nonsense talked about how the Bernoulli principle makes airplanes fly. You see endless textbooks and articles that show the air taking a longer path over the curved top of the wing than the straight part beneath - and that resulting in decreased pressure above the wing - and hence lift - from the Bernoulli effect. Hence the old explanation that Bernoulli effect is what makes airplanes fly. Bullshit!...or more correctly: "mostly bullshit"...someone needs to set the record straight. Note that the Bernoulli principle doesn't explain the following three things:

• Some aerobatic aircraft have 'symmetrical' chord wings that have the same curvature top and bottom - hence the air travels the same distance top and bottom, no Bernoulli effect here - yet these airplanes fly very nicely!
• Many aircraft with the more common asymmetric wing cross-sections can fly for extended periods upside-down. If the Bernoulli principle was what gave them all of their lift then they'd be sucked violently towards the ground - and they aren't!
• I've seen model aircraft built with rectangular cross-section wings(!) that also managed to fly (although not very nicely). A friend of mine who is an R/C plane enthusiast once took a solid block of foam polystyrene - painted it to look like a brick - and put a motor and control surfaces onto it. The 'flying brick' did fly...kinda...well, to be most charitable we should probably say: "it exhibited lift"!

The fact is that Bernoulli's principle does provide some lift - especially when cruising along at high speed in straight/level flight. But it's not the primary mechanism. What generates the most lift (expecially on take-off) is the angle of attack of the wing to the airflow which diverts the airflow downwards. If the wing was just a dead flat sheet, it would still generate lift if placed at an angle to the airflow. The main reason for curving the top of the wing is to improve the stall speed at high angles of attack associated with low airspeeds.

Now, I hear a lot of people complaining! They are recalling science classes at school - pretty illustrated pictures of wing cross-sections and numerous animations on TV documentaries that said quite the opposite of what I'm saying. Well, OK - scepticism is good. But hey - this is the science desk - you don't have to take my word for it - you can do an experiment! You don't need a wind tunnel and a bazillion dollar research budget. Prove it to yourself next time you are riding as passenger in a car at moderate speed. Wind down the window, hold a paperback book outside and tilt it up and down in the airflow. Notice that whilst it's not curved in any way, it still generates a lot of lift when you tilt it up into the airflow...you can clearly feel that. Now, hold it parallel to the airflow with the spine facing into the wind and push on the topmost pages so that the top surface of the book is upwardly curved and the bottom is dead flat. What little lift you are now feeling is due to Bernoulli's effect. You now have a very good feel for just how important the Bernoulli effect actually is (or, in this case, isn't).

So to answer the OP, the answer is that you don't need the Bernoulli effect at all. But in any case, the effect (such as it is) happens at any speed providing that the wing isn't stalled.

SteveBaker 14:03, 8 August 2007 (UTC)

Steve, while angle of attack is very important like you've mentioned. Do not under-estimate the effect of Berniulli. What you described about acrobatic planes and fighter jets are indeed true. However, that's only because their flight charistics are built for manuverbility. (Same thing with RC). When stability and efficiency are concerned, like for most general aviation planes, the effect of berniulli on lift is much greater. For example, bernoulli allows the plane to fly leveled (as opposed to constantly banking one way or another) without any manual input. It all depends on the purpose of the aircraft. I'm a private piolt and experienced RC builder.

Voice

i would like to know if the voice is louder in the light or when its dark? thanks 845 eli

Neither. The sound is entirely unrelated to the lighting conditions. There may be a psychological effect whereby it is perceived to be louder in the dark because you rely on senses other than your eyesight, but this will be subjective. Angus Lepper^{(T, C, D)} 21:35, 7 August 2007 (UTC)

but from where do you know that cause it seemes like the dark is more louder even if there is noise in the backround just as it is in the light? thanks in advance 845 eli

Sound is transmitted by compression waves moving through a medium such as air; your eardrum vibrates when these waves hit it, and these vibrations are converted to a meaningful form by your brain (I can't say how, biology never really grabbed me). 'Light' is the visible portion of the electromagnetic spectrum, transmitted by photons (which are tiny packets of energy with fascinating properties which aren't worth going into at the level of this discussion). There is virtually no interaction between the two (except in highly contrived and primarily theoretical scenarios). Because light is a part of the electromagnetic spectrum, an analogue to your question would be why your voice isn't affected by how close you stand to a radio mast, a mobile phone or a hot object (all of these emit eletromagnetic radiation). Angus Lepper^{(T, C, D)} 23:35, 7 August 2007 (UTC)

Could also be a false perception. A dark place in the middle of the day will be enclosed and far away from light sources. This sorta implies an acoustically isolated place, which in turn means any little sound will probably be audible due to less background noise. — Kieff | Talk 00:31, 8 August 2007 (UTC)

You could also be paying more attention to sounds in the dark than you do in the light, or this is just an example of the faults non-blind testing. Someguy1221 01:29, 8 August 2007 (UTC)

It is generally colder at night, which would cause the air to be more dense, which might transmit sound better. --Mdwyer 05:20, 8 August 2007 (UTC)

Only by a few percent, unless the temperature drops several hundred degrees at night where this guy lives ;-) Someguy1221 05:28, 8 August 2007 (UTC)

Less ambient noise at night (not in all circumstances of course). Might give the impression of something being louder. Lanfear's Bane

It looks like the general consensus is, it is subjective. Darkness or light has no effect on sound, right?69.205.180.123 16:42, 8 August 2007 (UTC)

Correct. Someguy1221 17:41, 8 August 2007 (UTC)

So you are saying photons have no effect on matter? Light will increase the temperature of the air and the speed of sound in air is dependent on the temperature. So there will be some very very small effect, but nothing anywhere near big enough for a human to detect.--Dacium 04:11, 9 August 2007 (UTC)

Well, of course 'photons' have an effect - sunlight warms things up - duh! Weather is complicated though - and it's not the case that night is always colder than day. But we already explained that the effect of changing the air temperature is going to make a very tiny difference - not enough to be noticable. Humidity also plays a part. But by far the best answer is that it's generally quieter at night - so your voice simply seems louder. SteveBaker 15:11, 9 August 2007 (UTC)

The light and dark itself I don't believe has any effect, it is the state of the medium which the sound is traveling Like the molecules that make up the air we breath being cold or hot. Sound traveling much further in water. Cory Nelkin 21:22, 11 August 2007 (UTC)Cory Nelkin

Tappan Zee bridge clearance

what is the Tappan Zee bridge in new york usa "lowest" Clearance above the water?

I'm not 100% sure what you're asking. Tappan Zee Bridge says that it's highest point is 42m above the water - the lowest would presumably be at the very ends of the span when the clearance (presumably) drops to zero where the bridge meets the ground? Are you perhaps asking what the center span clearance is at high tide or something? SteveBaker 13:25, 8 August 2007 (UTC)

I'm going to guess "Clearance" is the lowest point of it which hangs over the navigable channel. 68.39.174.238 02:07, 10 August 2007 (UTC)

Human and animal sperm

What home remedies and commercial ointments would one find as an ingredient either human or animal sperm? Clem 23:16, 7 August 2007 (UTC)

I dunno, but there was an episode of Nip/Tuck I think where they made a face cream from human sperm. Aaadddaaammm 00:49, 8 August 2007 (UTC)

Hair gel. Raul654 00:51, 8 August 2007 (UTC)

Simply brilliant. Delmlsfan 00:45, 9 August 2007 (UTC)

Hair gel? DMacks 03:06, 8 August 2007 (UTC)

You might find the Premarin article to be enlightening... Ew. --Mdwyer 05:17, 8 August 2007 (UTC)

Possibility of landing on a neutron star

Could you land on a neutron star, if the star was spinning so fast that the centripetal force throwing you from the surface matched the gravitational pull? Of course tidal forces come into play, but you could always use (very) short astronauts for the research.Myles325a 23:43, 7 August 2007 (UTC)

Um, not so much land as crash, I think. --Trovatore 23:47, 7 August 2007 (UTC)

Then be compressed into a film approximately one atom thick on the surface of the star... :) --Kurt Shaped Box 23:50, 7 August 2007 (UTC)

Im not going to work it out, but I would think the required angular velocity would be extremely high -- so high that you would have difficulty landing on it. You might get some nice friction burns though!--SpectrumAnalyser 00:07, 8 August 2007 (UTC)

I have to correct one misunderstanding here. Centripetal force never pushes you out, it pulls you in. In the case of your circular motion as you stand on the surface of a spinning planet (for instance, going around the Earth once per day), gravity provides the centripetal force. What you're thinking of is centrifugal force. Even though you may have heard that centrifugal force is a "fictitious force," it's perfectly real in a rotating coordinate system. [2]

If the neutron star were spinning so fast that centrifugal force balanced gravity, the outer part of the star would be in orbit! The additional force of the star's own pressure would push it apart, and it would blow off mass. --Reuben 00:19, 8 August 2007 (UTC)

Myles325a 01:31, 8 August 2007 (UTC) questioner back here. Well, nothing so far says anything as to why this is impossible. So what if the outer layers of the neutron star are "in orbit"? As for being "crashing" and "turning into a film" I wish people would READ questions before answering stuff that wasn't asked. The whole point of the question was whether you could cheat the huge gravity of such a place, if it were negated by centrifugal (not centripital) forces. Myles325a 01:31, 8 August 2007 (UTC)

In all practicality, you'd be squished; the centripetal force of something spinning hundreds or thousands of times a second, with a radius of several miles, still won't be enough to stop that. There is also the problem that the surface of a neutron star is a gas. There is also the problem that the magnetic field on the surface could be strong enough to seperate the diamagnetic and paramagnetic atoms from whatever just landed on it, if I recall correctly. Someguy1221 01:43, 8 August 2007 (UTC)

THe magnetic field is so strong that atoms have their electrons distorted into a needle shape, long and thin. Life processes could not withstand that even for a microbe sized nanobot. The short answer to the question is no. GB 06:05, 8 August 2007 (UTC)

You asked if it's possible. People told you reasons why it's not possible. What's the problem? A neutron star like you describe would fly apart. You couldn't land there because there wouldn't be a there to land on. --Reuben 06:11, 8 August 2007 (UTC)

He also doesn't seem to have noticed the literary allusion, in spite of the heavy clue in the edit summary... --Trovatore 06:18, 8 August 2007 (UTC)

That amount of spin would probably not build up. At least, I assume the spin is a result of the star 'crashing in on itself', like a figure skater spinning and then pulling in his arms. So the centrifugal force of the spin can not exceed the gravitational pull that causes it. But it would also be much smaller I assume, unless (almost) all the energy from the collapse is transferred into spin. Don't know if that could be the case. DirkvdM 06:32, 8 August 2007 (UTC)

We need to put some numbers to this - because OP clearly doesn't understand the magnitude of the problem. According to Neutron star they typically have a radius of 10 to 20km and spin between 700 times per second down to a couple of times per second. They weigh between 1.35 and 2.1 times the mass of our sun - which is between 2.6x10³⁰ and 4.2x10³⁰kg. So gravity at the surface is somewhere between 86,700,000,000g and 140,000,000,000g. That's 140 BILLION times bigger than at the surface of the earth. Mmmm'k - so how about centrifugal force? 1400 radians/second at 20km is a centrifugal force of 3,920,000,000 g - which is pretty impressive - but at the other extreme, 6 radians/second at 10km is a rather pathetic 3,600 g. So very the best case for our poor astronaut is that centrifugal force is going to reduce the effects of gravity by about 1 percent. Sadly not enough to avoid splatting into the surface at an impressive fraction of the speed of light and then getting squashed into a suprisingly thin layer of neutron-soup a dozen nanoseconds later. SteveBaker 14:48, 8 August 2007 (UTC)

Nice calcs. thanks I was too lazy to do it myself.--SpectrumAnalyser 14:56, 8 August 2007 (UTC)

tides would tear you apart. (i dunno if tides is the right description; the shear caused by the difference in orbital velocity over 6 or so feet of human height) Gzuckier 15:48, 8 August 2007 (UTC)

I think what Gzuckier is saying is, if you were going fast enough so that centrifugal force equals gravitational force, each half the object would be pulled in opposite directions with the same force that the neutron star's gravitational field has in the first place. The force involved here may come close to ripping protons apart in defiance of the nuclear strong force. Even a science fiction solution, such as the SIF in Star Trek's advanced U.S.S. Enterprise E would probably not be able to withstand the incredible power of this interaction.69.205.180.123 16:55, 8 August 2007 (UTC)

OP Myles325a back here. Yeah, that’s right, I’m the sort of wacky kook who not only asks questions but wants to comment on answers, mark and rank them, add codicils and addenda, and pick fights with respondents. Next week I’m getting a life, but right now…

1. Someguy1221 asserts neutron star “is a gas”. Really? One that weighs millions of times more than lead? Heavy sort of gas that. And besides, what does that have to do with the price of eggs in China?

2. nanobot. Tells us all that electrons in neutron star turn into a bed of pine needles and can scratch you. Hurties. I thought that, as the name suggests, neutron matter (neutronium) pretty much by definition had its electrons either ejected or crammed into protons to make neutrons.

The nanobot approach has the advantage that a very tiny robot could be built to withstand 1000g or more, and is much more resistant to tidal disruption. On a neutron star the neutronium can only exist under immense pressure. Such a star will have a crust with less pressure on the surface of more normal kinds of matter. In this there will be protons and electrons. An ultra intense magnetic field will make a moving electron move in a very tiny circle much smaller than an atom, but along the field line it is not constrained, so the atom will be pinched into a long thin shape like a needle. So even if I call it normal matter, is is very different to anything we are familiar with. Graeme Bartlett 11:29, 10 August 2007 (UTC)

3. Reuben. Yeah, people have told me that the neutron star “would fly apart”. So what? Maybe I don’t believe those people. Maybe I think some people are just talking out their ass. Tell me, Reuben, just how fast does a neutron star have to be rotating before it starts being going doing whirly-turds?

That's because you haven't bothered to understand the answers you've been given. The surface of the neutron star will fly apart when it's rotating so quickly that centrifugal force balances out gravity, which is, after all, what you proposed in your scenario. --Reuben 07:14, 9 August 2007 (UTC)

4. Trovatore. This ones got me. No, gotta admit, didn’t catch literary allusion. What is this - some kind of uber-geek ref to Captain Kirk or summink?

The Restaurant at the End of the Universe. --Trovatore 00:26, 9 August 2007 (UTC)

5. DirkvdM. Now this is more like it. Here’s a guy who starts thinking about how angular momentum works, and how rotation speed would be related to mass to begin with. I’m with you on this one, even if haven’t got the maths. Agree with you tho that if figure skater rotates faster as she pulls her arms in, then she could never rotate fast enough to have said arms fly off her body. Probably. Not sure about this. But in any case, my astronaut trying to explore neutron star is a thought experiment, and we could imagine that it was sped up by some exterior mechanism.

6. SteveBaker Thanks mate, you done the hard yards, you get the kudos, and the kewpie doll to boot. I do however have a grasp on the problem, in a sort of amateur way, as the foregoing will attest. You said though centrifugal effects might “…reduce the effects of gravity by about 1 percent.” Actually, that’s a HELL of a lot, I thought. And this is in a normally rotating star. What about one that was artificially sped up? Rem, guys, this is about what could happen in theory, not what might not be practicable for many centuries.

7. Gzuckier. I mention tides in my question. That’s why I make the allusion to short astronauts. If tides are a problem, then perhaps nanobot explorers might be the way to go.

All in all, no one has said, “Hey, never thought of that, made me think. Yeah, that Myles, he is one wise guy. Centrifugal force. Hmmm…come to think of it, it SHOULD have SOME mitigating effect against gravity. Wonder if it could work…”Myles325a 00:23, 9 August 2007 (UTC)

Well, no - you DIDN'T read all the answers - or at least not well enough to understand them. So the kewpie doll is tossed out the window and we're rolling up our sleeves to try to explain this again.

If (and it's a great big IF with capitals, italics and boldface) the neutron star was spinning fast enough so that centrifugal force equalled gravity at the surface and therefore (you fondly imagine) someone could conceivably land on it - then let's think about what happens. The neutron star material is under phenomenal pressure - a hundred billion g's in fact. Gravity gets stronger as you get closer to the star - centrifugal force gets bigger as you get further from it. This means that only AT the surface - precisely at the surface - do the two forces (hypothetically) cancel out. It's like a zero-g orbit at ground level. But that's a razor-edge kind of a thing - given the insane g-forces and the insane speeds, being even a teeny-tiny fraction of a micro-meter further away from that ideal distance and you're being flung off into space or if you are a tiny fraction too close, you'll be squished into neutron soup.

But at that precise distance, when everything is in balance at the exact surface of the star - the neutrons are not under any pressure anymore - they aren't going to stay as neutron-soup - they are going to very abruptly - indeed EXPLOSIVELY turn back into normal matter - so the first millimeter or so (I'm guessing) of the material would evaporate and spin off into space at spectacular speeds. This would continue to happen until enough material had spun off that the surface gravitation of the star was enough to keep it as a neutron soup. So it follows that if by some magical means a neutron star could spin that fast, it would evaporate down to a smaller size - at which point surface gravitation is once again a few billion g's more than centrifugal force. It follows then that you can NEVER have a surface that's survivable to humans because if it were survivable to humans, it would not be survivable to neutron-soup.

In your enthusiasm to dismiss other people's answers, you should slow down and think carefully about what they said.

Incidentally - if you are interested in neutron stars and what might happen to people who visit them - read the EXCELLENT sci-fi book "Dragon's Egg" and (if you enjoy it) it's sequel "Starquake" - both by Robert L. Forward who was an exceedingly well renowed physicist (who worked on some of the coolest stuff) and who describes Dragon's Egg as "A textbook on neutron star physics disguised as a novel". It's a good story too. SteveBaker 15:02, 9 August 2007 (UTC)

(OP Myles325 responds) Ok Steve Baker, becoz you actually seem to know a bit about what you are talking about, and have made the effort to pen a detailed answer, I am prepared to accept the insane agony of being patronised by you. Don’t you admit that it is a refreshing change to have someone who actually TALKS BACK to respondents, and wrestles with their ideas? And I think you are too harsh in saying that I simply have no idea of just how improbable the whole scenario of landing on a neutron star is, and that I have ignored the answers given (despite my unique policy of assessing [nearly] each and every answer given.) My original query was intended as speculation, not a “GEE WHIZZ let’s all go and land on a neutron star” comic book notion. You will find that I am not as scientifically illiterate as you suppose. For example, I will beg to differ on an important point in your otherwise impressive narrative on what happens to neutronium in the very space where gravity and centrifugal forces cancel out. First though let me preface by saying that I did not “ignore” what you wrote earlier. I gave you a kewpie doll, which you have hurled back at me. Your latest answer provides a lot more detail than did your earlier response. Had you included that material initially, I would have assayed it then, as I am doing now.

Suppose we, for the moment, relocate our thought experiment to more familiar and hospitable surroundings – planet Earth. If the Earth were sped up slowly to the point where centrifugal forces cancelled out gravity, then would a human, on the surface, be flung into space? No they wouldn’t. Now sit on MY knee and I’ll tell YOU why, for a change. At that exact speed, a human would only JUST be launched into orbit. The launch would be so weak that in a matter of moments, the human would be back on the ground, only to launched once again. It would be a bit like walking on the Moon, except with a much lower gravity. Your feet would leave the planet; you would float a bit, and then land once again, only to be GENTLY lifted off again. You would not be FLUNG off into space, as you suppose. That would require much greater speeds. Now if we transfer back to the neutron star, we find, to use your analysis, that the neutronium at the surface is constantly being launched into space, but only by the weakest margin. It is not FLUNG into space. This could mean that in moves only by nanometres outwards, and then back again. Could such a situation allow for some exterior entity to conduct research. I am hopeful, and putting your name down for that mission: The Spaghetti Ligeti.

A crucial point is the behaviour of neutronium. You imply that it only has the properties it has as long as it is confined by enormous pressures and gravity. But is this the case? Your knowledge would be superior to mine. I had thought that once it was created, it would be stable, or semi-stable, like other heavy elements created by nucleosynthesis. Neutrons are unstable, but they can exist for millions of years without change, and they are the combination of a proton and an electron. Would a teaspoon of neutronium OUTSIDE of its native star, simply explode, or sublimate into a gas? Perhaps not. Perhaps it would remain neutronium, in which case your scenario of neutronium disintegrating upon its release from gravity would be wrong. Oh, and thank you for those book refs. Sound v. interesting. Of course, they seem to posit entities landing on or somehow interacting with neutron stars. Are the authors of such also scientifically obtuse? Perhaps you should write them and explain how wrong they got it. (They prob don't do this here, but here goes (;-)> Myles325a 02:10, 10 August 2007 (UTC)

On the topic of no one thought of that, Hal Clement did, and had a novel called Mission of Gravity where a massive planet spins so fast that humans can only survive near the equator. Graeme Bartlett 11:35, 10 August 2007 (UTC)

In Dragon's Egg the humans are in orbit around the star (not a simple matter as it turns out) - they don't land on it. The story mostly takes place amongst very peculiar life forms living on the star itself. But I won't spoil the plot for you. The author was a very well renowned physicist - most of what he writes about is entirely possible. I believe there is an appendix where he explains the few liberties he took with reality for the sake of the plot. SteveBaker 12:16, 10 August 2007 (UTC

It is a interesting question, but not plausible. Cory Nelkin 21:16, 11 August 2007 (UTC) Cory Nelkin

Will definitely have to get hold of those books. I have a vested interest. I was bequeathed a piece of neutronium by my grandfather. About the size of a grain of rice. Still have it, in the original snuff box he kept it in. But it’s the very devil for weight, no question! It took 3 guys to carry snuff box and contents in. I tried to taste it once, and it almost pulled my tongue out. (Tastes a little like copper). I keep it in the shed, away from the house, so as to minimise gravitational effects. Myles325a 01:46, 13 August 2007 (UTC)