Wikipedia:Reference desk/Archives/Science/2008 June 21

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June 21

cheaper coffee - instant or ground?

shoo there, moved back to humanities here[1] for price factors and OP reasons Julia Rossi (talk) 10:37, 21 June 2008 (UTC)

Trig

Hello i have problems in remembaring trigonometrical ratio i know there is a table with the help of which can easily calculate any ratio for sin,cos and tan but i forget it in school times so please help me i will be very thankful —Preceding unsigned comment added by Usmanzia1 (talk • contribs) 00:54, 21 June 2008 (UTC)

I always just remebered the phrase "SOH-CAH-TOA" when I was in school. sin = opposite/hypotenuse; cos = adjacent/hypotenuse; tan = opposite/adjacent. I'd write it out each time, because I'm lousy at conceptualizing these things, and draw the little triangle (opposite is always the side that is directly opposite the angle you are looking at; hypotenuse is always the longest one; adjacent is the only other one left). Or is that not what you are looking for? --98.217.8.46 (talk) 01:31, 21 June 2008 (UTC)

A mnemonic I was taught in school goes: Some People Have (s=p/h) Curly Brown Hair (c=b/h) Till Painted Black (t=p/b), where s = sine, p = perpendicular, h = hypotenuse, c = cosine, b = base, t = tangent. No doubt there are lists of mnemonics somewhere.--Shantavira|^{feed me} 06:14, 21 June 2008 (UTC)

Alternatively, why remember complicated mnemonics when you can just look up the Wikipedia article Trigonometry#Overview. SpinningSpark 11:55, 21 June 2008 (UTC)

Nothing complicated about the mnemonics, but possibly best to pick (or invent) one that's memorable for you yourself. Look at the article Spinningspark linked to remind yourself of the actual ratios, then maybe invent your own mnemonic so you can remember :) (I would note that Shantavira's mnemonic only works when the triangle is lined up so that one side is horizontal and the other vertical, and the angle is opposite the vertical line. The method recommended by 98.217 and others which use the words 'opposite' and 'adjacent' work for any right-angled triangle) 79.66.20.219 (talk) 20:23, 21 June 2008 (UTC)

When the North American Indians taught trigonometry to the European colonists, they all said "SOH CAH TOA," and thus was learnt trig. Mac Davis (talk) 01:32, 22 June 2008 (UTC)

I've always felt that Sex On Holidays Can Advance Happiness To Outrageous Amplitudes, myself. Confusing Manifestation(Say hi!) 23:07, 22 June 2008 (UTC)

sunburn

Why does vinegar [distilled] totally relieve the pain (burn and sting) of sunburn? Adaptron (talk) 13:03, 21 June 2008 (UTC)

I've never heard of this effect, and I have no idea. I'm almost curious enough to try it out and see if it works, but that would involve my getting deliberately sunburned first, which is something I've been reluctant to do since adolescence. --arkuat (talk) 05:01, 23 June 2008 (UTC)

Normally stay out of sun to avoid injury. Following an accident local outdoor pool helped with no-load exercises. Sun screen reminders were not posted. Exposed for two to four hours. Used spray bottle to apply distilled vinegar as needed (almost constantly) in draft of a fan. Pain relieve is certain but redness still present going on third day. Have not blistered or started peeling (yet). Made big sign for local pool: "USE SUN SCREEN!" Adaptron (talk) 07:31, 23 June 2008 (UTC)

Vinegar stings in places where peeling has started. Adaptron (talk) 21:16, 23 June 2008 (UTC)

the stereotype about women being scared of bugs more than men

You see it all the time, when women are portrayed alot in pop culture as screaming at the sight of a spider and asking a man to kill it. Are more women than men scared of things like bugs, spiders, creepy crawlies? Is the stereotype justified in ANY way by psychology or any studies made to test its veracity? Even if the stereotype contains any grain of truth, I would have a hard time conceiving why there would be a gender difference evolutionarily speaking. (ie. It's true men are on average stronger than women by physical not like there would be a survival advantage or selection for women to be have a high incidence of phobia of creepy crawlies, because they are tiny and you don't need strength to kill/avoid them to save your life)

74.14.117.135 (talk) 02:25, 21 June 2008 (UTC)

Well, I'm a man who is plenty creeped out by a centipede crawling on my leg, too. My first reaction is to get it off me, and my second reaction is to kill it. That last part is probably where the difference between men and women lies, the men want to kill those disgusting things while the women want someone else to kill it. This might just be a culturally learned trait, or it might have a genetic basis. If it is genetically based, I'd guess it goes back to the division of labor between men and women back in our hunter-gatherer past, where women did child rearing, gathering, weaving, preparing food, etc., and men did hunting and warfare. This would better equip men to handle dangerous animals. While most insects are harmless, a few are dangerous, and this probably explains why they creep us out. An exception is moths and butterflies. There aren't any poisonous moths or butterflies, so we don't fear them. StuRat (talk) 05:13, 21 June 2008 (UTC)

It all has to do with culture and conditioning. If you lived in the rainforest and ate tarantulas for lunch, you wouldn't be afraid of bugs at all, male or female. ScienceApe (talk) 06:39, 21 June 2008 (UTC)

I like bugs. Maybe it's a convention, a literary device, even a social device,to give the man a chance to impress and fulfil his protective role since there are no dragons to slay or handy mountains to climb. On the other hand, there is something disturbing about a little thing with excessive legs and a likely poisonous bite. Julia Rossi (talk) 09:54, 21 June 2008 (UTC)

I don't really know the answer, but I think the supposed difference in how much the two sexes fear creepy crawlies may be at least partly the result of gender roles. Girls may have been "taught" (explicitly or as a result of socialization) that it's OK to show their fear, whereas boys may have been "taught" to play the role of the protector and that they should not let their fear show. --71.162.233.193 (talk) 17:42, 21 June 2008 (UTC)

Spiders creep me out but other bugs don't, in fact I keep ants! JessicaN10248 18:59, 21 June 2008 (UTC)

Hmmm... So, I'm guessing this is pretty much cultural and not "evolutionary psychology" in any way (ie. If you explained that men are supposedly less scared for killing bugs because tribal hunts were done by men, and women were protected, it'd be a "just-so-story") 74.14.117.99 (talk) 21:25, 21 June 2008 (UTC)

Perhaps it is a culture-bound syndrome. I was scared a week ago from walking casually down the stairs only to notice a spider suddenly appear a foot away from me, hanging down from the ceiling. Bugs are good at being unpredictable and speedy. Mac Davis (talk) 01:30, 22 June 2008 (UTC)

Question about neutron bombs

According to the article, the neutrons are not radiated beyond the bomb's blast range because they are absorbed by air. So then how would the neutrons kill living beings? The living beings would have to be inside of the blast in order for the neutrons to reach them, but then they would be killed by the blast anyway. But then the article says, "The lethal range for tactical neutron bombs exceeds the lethal range for blast and heat even for unprotected troops". But how is this possible if the neutrons do not radiate beyond the blast range? ScienceApe (talk) 06:33, 21 June 2008 (UTC)

If I may be so bold... it is due to the number of neutrons. A neutron bomb is designed to release a far greater number of neutrons than a conventional nuclear bomb which greatly exceeds the number of neutrons the elements which make up the atmosphere can absorb. 71.100.3.84 (talk) 07:25, 21 June 2008 (UTC)

Actually, our article states that for a "high-yield bomb", the blast radius exceeds the direct radiation effects. The neutron bomb is a low-yield (well, comparatively) bomb. --Stephan Schulz (talk) 10:05, 21 June 2008 (UTC)

My guess is that after the air absorbs neutrons, it becomes radioactive and the radioactive air is what kills living beings. — DanielLC 14:54, 21 June 2008 (UTC)

Sorry, but your guess is wrong. It's indeed the initial neutron blast that is supposed to kill people. All the major components of air are low-weight atoms. It's not easy to turn them radioactive, especially not by bombarding them with neutrons. --Stephan Schulz (talk) 15:39, 21 June 2008 (UTC)

Stephan Schulz's answer is correct. Weapons can be 'tuned' for (somewhat) smaller blast and greater neutron yield, expanding the lethal radiation radius beyond the blast radius. While it is technically true that exposure to the intense radiation from a nuclear blast will make the air radioactive, this effect is slight, and the large majority of radioisotopes produced have short half-lives – less than a minute – and clear rapidly. (More dangerous is fallout—radioactive dust which settles after a nuclear blast; more fallout is generated when a bomb explodes close to the ground.) TenOfAllTrades(talk) 15:45, 21 June 2008 (UTC)

But the article says that the neutrons don't radiate beyond the blast range. But people would be killed within blast range anyway. Also the article said that people would be killed well beyond the blast range by the neutrons... Which contradicts the earlier statement that the neutrons don't radiate beyond the blast range. ScienceApe (talk) 17:16, 21 June 2008 (UTC)

The article does not say that. I think you are mislead by this sentence: "This is because neutrons are absorbed by air, so a high yielding neutron bomb would not be able to radiate neutrons beyond its blast range and so would have no destructive advantage over a normal hydrogen bomb". But, as the preceding sentence makes clear: "Neutron bombs have low yields compared with other nuclear weapons." --Stephan Schulz (talk) 17:31, 21 June 2008 (UTC)

To confuse things a bit further think of what happens to the air when a nuclear explosion occurs. The nuclear blast produces a dense "shell" of compressed air known as a pressure wave. This dense "shell" of compressed air absorbs neutrons so the less compressed or dense the shell the more neutrons that will not be absorbed. 71.100.1.215 (talk) 21:13, 21 June 2008 (UTC)

I'm not sure that's quite right. The pressure wave moves at the speed of sound and the neutrons move much faster than that, I believe. Also, the neutrons are generated more or less instantaneously, so they would always be moving in advance of the air density fluctuations. Franamax (talk) 04:06, 22 June 2008 (UTC)

When I said air what I really meant was the elements of which the air is composed and not air as a gas. The wave front or "shell," which is made up of those elements, can travel much faster than the speed of sound if the gaseous elements of which the air is composed are compressed sufficiently to change their phase into a liquid or solid at speeds higher than the speed of sound. 71.100.1.215 (talk) 23:21, 22 June 2008 (UTC)

I should check my references before commenting. From Arsenal by K. Tsipis, 1983: "The immediate result...completed in less than a millionth of a second...a few metres in diameter...the fireball", followed by a description of the fireball propagation by electromagnetic radiation, presumably starting somewhere around the speed of light in air, then "When the fireball's temperature is reduced to about 300,000 deg C., the speed with which it grows...equal to the speed of sound in air", and this apparently comes about when the fireball is some hundreds of metres in diameter. However, "At this point...a shock wave develops at the outer surface of the fireball" which does indeed travel much faster. For a 2 megaton device at 1 mile distance, the peak overpressure is around 67 psi, and by the graph, the shockfront velocity is around 2500-3000 ft/sec. I know I'm mixing up the unit systems, but hey, tell it to the skeleton, the shock wave is way more than supersonic in air, you're right, it's sonic in the medium it creates for itself. (At 1000 ft, ~6900 psi, and 23,000 fps!) However Tsipis also notes "Certain fusion weapons, commonly called neutron bombs, do not have the U238 mantle, thus allowing fast, lethal neutrons to escape", and this is in that first millionth of a second. Looking at our article on fast neutrons, I see a speed of 14,000 km/sec, but for fusion reactions, 52,000 km/sec. It seems to me that this is fast enough to escape the fireball while it's still in the fireball phase, before the breakaway point when the supersonic blast wave begins the density effects that might affect absorption. Until breakaway, the fireball is building by ionization and movement of the fissile and weapon materials, none of those will particularly change the rate of neutron absorption. As to how fast normal air absorbs fast neutrons, mentioned elsewhere, I don't have that figure, but it seems to me that the cross-section becomes smaller as the energy increases, so collisions become less likely. They did design these weapons for a reason, so I personally wouldn't stand out in the open field and say "don't worry, the air will protect me" :) Franamax (talk) 08:21, 23 June 2008 (UTC)

...nooo, but some of that SPF 15,000,000,000,000,000,000,000,000,000...,000 sunscreen might work. ;-] Adaptron (talk) 20:46, 23 June 2008 (UTC)

I'm not sure that air is dense enough to stop neutrons immediately. Usually when you want shielding against neutron radiation you use something that is dense and full of light atoms, like paraffin. Air is full of light atoms but is not dense. Air is not, by itself, a shield against neutron radiation, though I guess after a certain limit they'd probably eventually hit oxygen molecules and slow down. --98.217.8.46 (talk) 05:14, 22 June 2008 (UTC)

how is sugar used to treat battlefield wounds

Im trying to find out how using Osmotic Pressure,sugar is used to treat battlefield wounds,I herd that it dates back to the napoleonic war. Can someone give me some details please. —Preceding unsigned comment added by Frostytsnowman (talk • contribs) 11:27, 21 June 2008 (UTC)

This article on honey explains how the osmotic pressure acts as an antimicrobial agent. There are plenty of references in the article (which I havn't looked up myself) which seem to indicate that this was a treatment for wounds long before the Napoleonic wars. SpinningSpark 12:17, 21 June 2008 (UTC)

Skin effect of jewelry

What component of cheap jewelry causes a bruised coloring to the skin around where it's worn? What's the chemistry involved? —Preceding unsigned comment added by 67.241.181.205 (talk) 15:15, 21 June 2008 (UTC)

probably non-noble metals eg metals that are not gold/platinum etc.

Nickel and copper are common metals in cheap jewelry - reaction with perspiration (water) in sweat etc causes nickel/copper salts to be produced which are green/blue in colour

eg see http://jewelry.about.com/od/jewelrymetals/a/skin_reactions.htm87.102.86.73 (talk) 15:20, 21 June 2008 (UTC)

Thanks everyone. -- 67.241.181.205 (talk) 15:52, 21 June 2008 (UTC)

Simple Demonstrations to Show the Faultyness of Human Memory?

Hello,

I work as a teacher and I often try and explain to students how poor their memory, but they fail to believe me. Does anyone happen to know any simple (the simpler the better) experiments or demos that can be used to quickly show just how fault human memory can be?

Thanks for any help,

--91.106.26.7 (talk) 15:21, 21 June 2008 (UTC)

A simple example to show the weakness of memory would be to tell the students to remember a three digit number (not an obvious one to remember like 123), then read them(/get them to read) a chapter from an unrelated book. Then ask them to write down the number... I would almost certainly forgotten - though this only shows the brains inability to remember non-essential information.87.102.86.73 (talk) 15:26, 21 June 2008 (UTC)

You could get some people to suddenly come into the classroom and do something unusual (have a big row, say), and then ask the children to answer a few questions about the event. A few simple things like "What were they rowing about?", and then more subtle things like "What colour was X's shirt?", and then, if you want to get really clever, something like "What colour was Y's cardigan?" when Y wasn't wearing a cardigan. After asking them that question and giving them some time to try and "remember", a lot of people will insist they saw Y wearing a cardigan. --Tango (talk) 15:32, 21 June 2008 (UTC)

Yeah, I've had this done in class before. It's a classic psychological experiment, sometimes called the "eyewitness game". --98.217.8.46 (talk) 16:24, 21 June 2008 (UTC)

I seem to remember our teachers doing something like this, where someone burst into assembly, whipped out a banana and appeared to threaten a teacher, then ran away. Possibly in poor taste... Anyway, many students were convinced they'd seen a gun, and none could accurately describe the person. 79.66.20.219 (talk) 20:16, 21 June 2008 (UTC)

This Trick or some variation on it, could be done in real life. APL (talk) 20:08, 21 June 2008 (UTC)

A lot of girls and boys make a big deal of picking what they are going to wear in the morning for school (if there aren't wearing uniforms). Pick a few to come up to the front of the class and blind fold them. Ask them about things they are wearing, like what color shirt. Remembering myself from middle school—I could never remember what I ate for breakfast that day. There's another idea. Simple real-world things like that work better than artificial things. Mac Davis (talk) 23:03, 21 June 2008 (UTC)

I recently had a doctor's visit where I had to do a simple memory test. It starts out with your name, where you are and the current date. Then the doctor asks me to repeat three words, each one as he says them. (So, he says "apple" and I repeat "apple" to him.) Then I'm asked to spell another word backwards. Finally, he asked me to tell him which three words he had me repeat earlier to him.

I got one. Most people get two, and it's rare for someone to get all three. — The Hand That Feeds You:^Bite 12:36, 22 June 2008 (UTC)

Charles Ludlam, on his death-bed, was asked three basic questions as a mental status test: What year is it, what day of the week, and who were the president and vice-president of the United States. Unable to speak, Ludlam took a pen and wrote in response on a pad of paper, "I'm sorry. I have not yet read the Times this morning.". I really like that answer. - Nunh-huh 15:17, 22 June 2008 (UTC)

The simplest example of faulty memory is the set of sentences wherein pragmatic implication causes listeners to remember "The hungry python caught the mouse" as "The hungry python ate the mouse" and "The angry rioter threw a rock at the window" as "The angry rioter threw a rock through the window." [2].

This might have more to do with vision and perception than actual memory, but here's an amusing test where they ask you to watch a video and count how many basketball players wearing white shirts pass the ball. You watch it and count them, then they ask you if you saw any animals or things that look like animals in the video. Almost all watchers failed to see/remember the guy in a gorilla suit walking around in the video. :) --Sean 14:28, 23 June 2008 (UTC)

That video deals with attention, but I gotta say it's been my favorite psych experiment ever since I first saw it a few years back. --Shaggorama (talk) 07:08, 24 June 2008 (UTC)

Blood types

Moved from WP:HD Can a parent with A+ and the other parent with O+ have a child with A- Thank you for your assistance. —Preceding unsigned comment added by 24.17.150.22 (talk) 20:05, 21 June 2008 (UTC)

The short answer is yes. According to the article on ABO blood group system, a parent with A blood and a parent with O blood will have either A or O children, so as far as the ABO type is concerned, it is possible. The article on the Rhesus blood group system says that the R type is determined by a single gene with 2 alleles. The R+ version is dominant. It is possible that two parents would have one of each allele and the child get the negative one from each parent. This is better described in the article on genotype.Gjmulhol (talk) 20:46, 21 June 2008 (UTC)

sports drinks

Why does Lucozade Sport/Powerade make me want to pee more than say orange squash or water? —Preceding unsigned comment added by 86.144.125.17 (talk) 20:49, 21 June 2008 (UTC)

Those kinds of drinks have high levels of glucose in them. If your body cannot product enough insulin your blood sugar level will be very high, and the kidneys will be unable to diffuse sugar back into the bloodstream after ultrafiltration, meaning you have no choice but to pee it out. JessicaN10248 21:13, 21 June 2008 (UTC)

um that doesn't sound good (not being able to make insulin) but I only drink sports drinks during exercise. —Preceding unsigned comment added by 86.144.125.17 (talk) 21:44, 21 June 2008 (UTC)

I rather doubt that explanation: Lucozade has about 100 calories in 8 oz, and is marketed as "low-cal"; if it's causing osmotic diuresis in someone by virtue of its sugar content, that person is probably diabetic. More likely explanation: Lucozade energy drink contains caffeine, a diuretic. And both Powerade and Lucozade contain more electrolytes than water, which could possibly cause a diuresis. Or: you're drinking the Powerade right before you'd have to pee anyway... - Nunh-huh 02:24, 22 June 2008 (UTC)

Another guess, many people drink energy drinks while exercising. However a lot of people have the tendency to drink too much Nil Einne (talk) 11:30, 22 June 2008 (UTC)

Right. The real point of a sports drink is not to give you more energy, but to keep hydrated. Just like you shouldn't guzzle a large glass of water while/just after exercising, you shouldn't drink an entire sports drink at once. Small sips as you go along are the key. The sugar and sodium in Powerade and Gatorade keep you thirsty, so you keep sipping at them and stay hydrated. "Energy drinks," on the other hand, are of no real use for sports or exercising, as they're primarily about putting lots of caffeine and sugar into your body so you feel like you have more energy. — The Hand That Feeds You:^Bite 12:47, 22 June 2008 (UTC)

Uh....HUGE edit conflict. It's my understanding that the purpose of the electrolytes in power drinks (like sugar and sodium) is the same reason that it's actually pretty unusual that they make the OP wanna pee. I don't know about Lucozade (in fact, this post was the first I've heard of it) but gatorade and powerade have the same osmolarity as blood because of their electrolyte concentrations. When you drink them, they rapidly increase the volume of fluid in your body without diluting you, so normally you can go without peeing for longer than if you drank the same quantity of water. In fact, when I took the MCAT my test prep company advised everyone to drink gatorade instead of water or coffee so we could sit longer without getting distracted by the bathroom. If the sugar and sodium were there to keep you thirsty, then your thirst would be a sign that you weren't properly hydrated. --Shaggorama (talk) 02:39, 25 June 2008 (UTC)

alcohol based vinegar

Will all alcohols become vinegar if oxidized by fermentation and if so what organisms will ferment methanol and isopropyl alcohols? 71.100.1.215 (talk) 21:32, 21 June 2008 (UTC)

The alcohol dehydrogenase enzyme in the human liver oxidizes ethanol to acetic acid and methanol to formic acid, although the latter reaction is slower. I'm not sure, however, if the corresponding enzymes in the acetic acid bacteria that produce vinegar also work on methanol too. Isopropyl alcohol, being a secondary alcohol, cannot be similarly oxidized into a carboxylic acid; the closest you can get is acetone.

Heat transfer through different mediums

Right, lets imagine you make a cup of tea, bring it into your room and leave it until it's cold. Now unless I am mistaken heat loves nothing better than to try to spread itself equally. So why is it that when I put my tongue in the air for instance, it doesn't feel as cold as the tea which should have cooled down to around the same temperature? Jimothyjim (talk) 23:39, 21 June 2008 (UTC)

• In fact heat loves nothing better than to try and burn me... -Benbread (talk) 23:41, 21 June 2008 (UTC)
• Water (and tea) has a much higher specific heat capacity than air. So cold tea will transport heat away from your body much more efficiently than air. For very similar reasons, metal usually feels cold, while wood feels warm. --Stephan Schulz (talk) 23:44, 21 June 2008 (UTC)

Indeed. Bring back wooden toilet seats!--Shantavira|^{feed me} 06:58, 22 June 2008 (UTC)

Isn't it not just the specific heat capacity but also how much of a conductor or insulator the substance is? Metal is an excellent heat conductor. Air or wood not so much. While water (or tea) are not as good as metal in general but as liquids, they make excellent contact with your skin. Nil Einne (talk)

Quite. While heat capacity can be important in the limiting case – how cool will the system be at equilibrium? – when we look at how cool bulk material feels then we're asking a question about heat conduction. Actually, in fluids like air, water, and tea the picture is even more complicated, because we also have to worry about fluid flow: convection. Our article on heat transfer links to a number of useful articles.

Boiling it down to a short answer, though, water (or tea) has a high heat capacity compared to air, so a small volume can absorb a significant amount of heat without warming appreciably. Both water (or tea) and air can move freely past your tongue, providing a constantly-replenished supply of cool fluid. The one that will feel cooler, then, is the one that extracts heat from your tongue most efficiently: in this case, the tea. (Its much-higher density than air helps it here.) This is, incidentally, one of the reasons why modern automobile engines virtually all employ water-based cooling systems rather than relying on the simpler but less-effective air cooling of their predecessors. TenOfAllTrades(talk) 14:00, 22 June 2008 (UTC)