Wikipedia:Reference desk/Archives/Science/2008 May 22

From Wikipedia, the free encyclopedia

< Wikipedia:Reference desk | Archives | Science

Science desk
< May 21	<< Apr \| May \| Jun >>	May 23 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

1 May 22

[edit] May 22

[edit] Bug identification

I found this little guy under a rock in the water. Does anybody know what it might be? Sorry about the blurry picture; it didn't like to stay put. Djk3 (talk) 00:58, 22 May 2008 (UTC)

Looks like a Dragon fly larvae. But that's a big ballpark. --71.236.23.111 (talk) 01:33, 22 May 2008 (UTC)

I think it's an earwig. Dragonfly larvae don't have such antennae AFAIK. If you want to be sure, dragonfly larvae have a very peculiar "mask" (labium) which can project forwards to catch prey; you can't see if it is present in the photo you posted, but this is how you can tell the dragonfly larva from anything else on this planet. Hope this helps. --Dr Dima (talk) 04:14, 22 May 2008 (UTC)

It wasn't an earwig. It was definitely some sort of water-dwelling thing. It was completely submerged, and when I lifted the rock out of the water, the thing went right back under water. Djk3 (talk) 05:43, 22 May 2008 (UTC)

It's a stonefly nymph [1], which despite its name is not a fly but a member of the order Plecoptera.--Eriastrum (talk) 21:19, 22 May 2008 (UTC)

Awesome, thanks! That's it. Djk3 (talk) 02:18, 23 May 2008 (UTC)

One of my favorite flies to try to tie. They're pretty amazing; some of them build little stone pebble fortresses around themselves. And the troutses just love 'em. --jpgordon^∇∆∇∆ 14:26, 24 May 2008 (UTC)

[edit] Local mean time

Is there a way to find out what is the correction for local mean time for a given locale or longitude? For instance, although Boston and Philadelphia are in the same time zone, local noon (when the sun is highest in the sky) will occur at different times because Philadelphia is maybe 200 miles west of Boston. In the days before time zones, there must have been charts or guides for travelers, no? Woodlore (talk) 01:26, 22 May 2008 (UTC)

Every 15 degrees of longitude equals a 1-hour difference. Every degree of longitude equals a 4-minute difference. And so on. So if you know the universal time (which is the time at zero degrees longitude, you can easily calculate the "local" time at any longitude. ~Amatulić (talk) 01:36, 22 May 2008 (UTC)

Perfect-- thanks amatulic Woodlore (talk) 01:45, 22 May 2008 (UTC)

See also Equation of time.--Shantavira|^{feed me} 06:33, 22 May 2008 (UTC)

The "equation of time" represents the difference between local mean time and local solar time. Woodlore asked about local mean time, for which Amatulic's answer is the complete one. --Anonymous, 20:30 UTC, May 22, 2008.

Ok, so in my example, disregarding the Equation of time: for Boston, at 71°W, local noon occurs at 11:44 AM; for Philadelphia at 75°W, it is 12:00; and for say, Louisville at 85.7°W, which really shouldn't be in the same time zone, but it is, local noon occurs at 12:43 PM. Have I got this right? Woodlore (talk) 11:43, 23 May 2008 (UTC)

Disregarding the definition of what exactly 12:00 means, your time differences look right to me. Franamax (talk) 06:22, 24 May 2008 (UTC)

In winter, you do. During daylight saving time, add an hour — 12:44, 1:00, and 1:43 PM. --Anon, 06:01 UTC, May 24, 2008.

[edit] Magnetic Moment

What is the magnetic moment of a single iron atom. Also, what is the spin? Thanks, *Max* (talk) 01:56, 22 May 2008 (UTC).

This question is very difficult to answer fully. The term symbol for the ground state of atomic iron is ⁵D₄, so the quantum numbers are S = 2, L = 2, and J = 4. (S is what's usually called "the spin", because it involves only the intrinsic spins of the electrons, but J is the total angular momentum.) By my calculations, that makes the Landé g-factor equal to 3/2, so the total magnetic moment is 4 * 3/2 = 6 Bohr magnetons. In SI units, that's $5.6 \times 10^{-23}$ J/T. However, this is only valid for a single iron atom that is isolated in a flat potential, i.e. a tenuous vapor of neutral iron atoms. If we're talking about a crystal of iron metal, the situation is totally different and you have to use high-powered condensed matter physics to work out things like the magnetic moment. In this case it's especially complicated because iron is a ferromagnet. —Keenan Pepper 03:10, 24 May 2008 (UTC)

Unfortunately, the reason I want to know about iron is because of it's ferromagnetic properties. Would the value of 6 Bohr magnetons be a good (order of magnitude) approximation? Would it be better than the value of 1 that I am currently using? What would the analogue of the Dirac equation or the Klein-Gordon equation for a spin-2 4 particle like iron be? Thanks *Max* (talk) 16:48, 24 May 2008 (UTC).

I have no idea. Why do you want to use a relativistic equation anyway? I would definitely start from the Schrödinger equation, not a relativistic equation like Dirac or Klein-Gordon. —Keenan Pepper 20:22, 24 May 2008 (UTC)

You're right, I don't need relativistic effects. I meant to ask for an analogue of the Schrödinger equation for spin-4 particles. Thanks for your help anyways. *Max* (talk) 21:48, 24 May 2008 (UTC).

[edit] i need help finding the name of a fish

it lives in brazil and i think it lives in lakes and rivers. if a man pees in the water the fish will swim up his penis. —Preceding unsigned comment added by 216.228.178.218 (talk • contribs) 14:19, 22 May 2008

You'd be thinking of the Candiru. Confusing Manifestation(Say hi!) 03:29, 22 May 2008 (UTC)

[edit] Truck Slipstream

This morning it so happened my sister was involved in an accident, when she lost control of her small rental car after being dragged into the slipstream of a passing tractor trailer in Tennessee. ( Miraculously, she walked away with only minor injuries despite her car being dragged along by the truck, flipping, and hitting a tree.) But in the course of her talking with people in the area, there seemed to be a consensus that this happened more frequently with 'fully loaded' trucks. I think the implication is that the weight of the truck somehow affects the strength of the slipstream. I'll admit I'm no graduate student in physics, but this doesn't make much sense to me. While a fully loaded truck would have more kinetic energy and momentum, I would think that the shape of the truck and its speed were the only factors affecting the slipstream, and while I could come up with something involving momentum and collision with air molecules, I don't really buy it. Any ideas? —Preceding unsigned comment added by 68.112.229.82 (talk) 05:01, 22 May 2008 (UTC)

The only way someone could even know a truck was "fully loaded" would be an open-bed trailer loaded with cargo. In that case, there would be much more turbulence than from an empty flat-bed trailer. A closed van would create the same air disturbance, no matter what was inside. However, I'm not a PhD either ;) Franamax (talk) 08:16, 22 May 2008 (UTC)

Your sister was affected by the same phenomena that racecar drivers and bikers use when drafting. -- JSBillings 12:25, 22 May 2008 (UTC)

How come there's never a physicist around when you need one? Our article "Sonic boom" mentions weight (in two places) as a factor in the strength of the boom. It does not, however, explain why weight matters. --Milkbreath (talk) 12:53, 22 May 2008 (UTC)

How much force does an aircraft have to exert on the surrounding air in order to maintain a constant altitude? How does that force vary with the weight of the aircraft? Now, how much force does a truck need to exert on the surrounding air to keep from losing altitude? Eureka.... TenOfAllTrades(talk) 13:39, 22 May 2008 (UTC)

Weight only matters in aircraft because it alters the wing-loading...but it's a much more complex matter than that. For a truck, weight is definitely irrelevent. Shape and speed are all that matters. 71.155.164.147 (talk) 13:47, 22 May 2008 (UTC)

Perhaps fully-loaded trucks ride lower to the ground and that has an effect? I don't buy it, either: the much simpler explanation is that people often "know" things without any evidence. --Sean 14:34, 22 May 2008 (UTC)

Most trucks use air suspension, so the ride height is constant. For a spring suspension, that's a possibility: if the unloaded ground clearance was 30" and loaded was 26", that's a 15% difference. If the calculation of the slipstream force depends on the ground clearance cubed (let's say), that becomes 50%. Just speculating on the numbers of course. Franamax (talk) 16:03, 22 May 2008 (UTC)

Yeah, but we never feel stupider than when we pooh-pooh an old wives tale that turns out to be true. About the sonic boom thing: So, momentum plays no part in the collision between a moving object and the air molecules it is pushing out of the way? --Milkbreath (talk) 15:07, 22 May 2008 (UTC)

Momentum does play a part, in that a more massive object will be slowed less by the wind resistance, but this just means that less engine power is required to overcome the wind. The cross-section and speed of the craft are what determines the intensity of the turbulence behind it. The reason mass matters in a sonic boom is a heavier craft will have a larger cross section because it has to fly at a different angle of attack to provide more lift. -- Mad031683 (talk) 16:19, 22 May 2008 (UTC)

No, I mean mass-times-velocity collision momentum between the truck and each air molecule.

The truck continues to exert enough force on the ground to keep it moving at a (effectively) constant velocity. So in essence momentum isn't conserved in this problem (unless we want to include the rest of the planet in our closed system). Because of that and the fact that the truck's mass is huge compared to an air molecule's, I think it is best to approach the problem in a way that doesn't depend on the truck's momentum. Think of the air molecule as a small mass colliding with a solid wall. Does the wall's mass/momentum matter? --Prestidigitator (talk) 20:07, 22 May 2008 (UTC)

Yeah, I wouldn't look for weight to be a factor either, but different trailers would be a factor, and weight would vary with them also. Surrounding wind conditions could definitely be a factor though, and this would easily account for why this effect is sometimes worse than others. Friday (talk) 15:13, 22 May 2008 (UTC)

Are these types of accidents common? I drive a medium-size car, but I've never experienced a slipstream anywhere close to being strong enough to drag me out of a lane. It's hard to imagine how driving a car even half the weight of mine would make much difference. And if the slipstream from a truck could be strong enough to drag a small car, wouldn't anyone riding a bicycle along a highway be blown around like a feather by passing trucks? --Allen (talk) 19:43, 22 May 2008 (UTC)

I drive one of the smallest cars in North America and I don't generally have problems, but you do need to be aware and ready to react. If it's very windy and there are large trucks around, there can be some large buffets as the truck passes. Of course, it's usually me passing the truck, so I'm prepared ;) Franamax (talk) 19:50, 22 May 2008 (UTC)

Interesting. It still makes me wonder about bikes... are they safe because they lack big impermeable surfaces? --Allen (talk) 19:58, 22 May 2008 (UTC)

No, I've heard stories of people being strongly affected/pulled into trucks on bikes and especially motorbikes. No accidents but enough to seriously frighten people. I guess it's worse for motorbikes because they're much more likely to encounter trucks and they're also likely to be a lot faster which I presume (can't be bothered thinking of the physics of it) would make it a lot more of a problem when they hit a slipstream. These stories are from Australia and NZ, I presume it's worse in the US given that trucks tend to be larger and more common in the US Nil Einne (talk) 22:45, 28 May 2008 (UTC)

My parents tow a travel trailer around, and passing trucks can be a tricky proposition. The large side area gives the Bernoulli effect plenty to work on when passing a truck going the same direction, and when passing a truck going the opposite direction, the bow wave can cause the trailer to fishtail. --Carnildo (talk) 22:56, 22 May 2008 (UTC)

Hmm. Tennessee, "fully loaded" and slipstream? Was it a coal truck? Those trucks have the big box trailers but the top is open, so coal can be dumped in. They also (nowadays) have a canvas that gets pulled over the coal when full, due to regulations. When the truck is empty, they typically have the canvas pulled up so that the empty trailer is exposed, which means air is getting pulled into the trailer and circulated there. Full trucks, because of the tarp on top, cause the air to pass overtop, just like a normal tractor-trailer. That probably does make a difference in how other cars can draft with the trucks, but the big thing is that loaded coal trucks are much harder to drive than the empty ones. Likely, what happened was a combination of the air turbulence coming off the truck combined with the truck veering a little too close is what caused the accident. Living in Kentucky, I'm all too familiar with the way air off those trucks can either blow you aside or pull you close, and even experienced truck drivers can sometimes get out of their lane on windy/rainy days. — The Hand That Feeds You:^Bite 23:54, 22 May 2008 (UTC)

Loaded trucks have a greater inertia than unloaded ones; so they move less when hit by a gust of wind. Also they shake less in response to wind gusts and when passing other facing trucks. The leaning and shaking of an empty truck as it passes (or experiences a wind gust) may well lessen the wind speeds around it. Polypipe Wrangler (talk) 21:42, 24 May 2008 (UTC)

[edit] Fleas

How long does an adult flea, which has had a blood meal, live ? (ie. If there are adult fleas in my house, how long do I need to vacate the house before they die of starvation ?)

How long does a newly hatched flea live without a blood meal ? (eg. if my house is vacated for a week, then I visit to jump about and make vibrations to cause any unhatched fleas to hatch, how long to I need to remain absent to cause the new hatched fleas to die die of starvation ?)

How long does it take to drown a flea ? (ie. could clothing be submerged in water for,say, 2 hours to drown fleas and ensure their removal ?)

Signed:Jennylindmac (talk) 08:01, 22 May 2008 (UTC)

Ugh, fleas. Don't scratch the bites. If the flea has had a blood meal, it will be in position to lay eggs. According to this, the adult can live two months to a year without a meal. According to the same link, the flea can develop to adulthood inside the pupa and survive for months as long as they don't emerge. Running your clothes through a normal wash and dry should take care of any adults and eggs on the clothing.

I went through a bad experience with fleas (I now know why they call them "flea-bag motels") that got in my bedroom at home. Washing, vacuuming and putting down powder would work for about three days, then I got bitten again. Eventually, moving and leaving the bed unslept in for three months solved the problem. Hopefully your experience will be better! Franamax (talk) 08:30, 22 May 2008 (UTC)

A lot depends on the species of flea as well because fleas are "preferential" about who they'll feed from. So, for cat fleas on an "indoor cat", for example, you can eventually eliminate them by combing your cat every day (or more often) with a flea comb, flushing all the captured adult fleas down the toilet, and vacuuming every day to eliminate from the floors as many of the eggs and immature fleas as you can. Meantime, the fleas probably won't be bothering you so much because they'll be busy bothering your cat.

Atlant (talk) 12:00, 22 May 2008 (UTC)

You want a bad experience? We had a mother cat leave a litter of kittens in the bushes out front when I was a teenager. I had to get them out, and they were coated in fleas. Stupid me wore shorts, and my legs were covered in the things. Had to hose myself off and run straight to the shower after that. Kittens wound up going to the vet and were so anemic the vet said they'd have died in a couple days if we hadn't brought them in. — The Hand That Feeds You:^Bite 00:04, 23 May 2008 (UTC)

With fleas being able to live up to a year without a meal, you would have to leave your home unoccupied for a very long time to be sure of getting rid of fleas. The apartment I lived in had a flea problem once. I used flea powder on the carpet and upholstery (twice), washed all affected clothing and bed linen, and treated my cats with Nitenpyram (Capstar). That Capstar stuff is amazing. 152.16.59.190 (talk) 04:03, 23 May 2008 (UTC)

I've found flea bombs work wonders Nil Einne (talk) 22:47, 28 May 2008 (UTC)

[edit] RTI International

RTI International is

The second largest independent nonprofit research organization in the United States....

– RTI International

Which is the first?68.148.164.166 (talk) 10:08, 22 May 2008 (UTC)

[2]--71.236.23.111 (talk) 13:08, 22 May 2008 (UTC)

Off the top of my head, MITRE has 6,700 staff. -- Coneslayer (talk) 19:14, 23 May 2008 (UTC)

SRI International. MITRE is not considered independent for these purposes, I think, because it is an FFRDC. Nimur (talk) 06:23, 26 May 2008 (UTC)

[edit] explaining science to kids

Can anyone help me explain to my 5 year old daughter why it's still daylight when we send her to bed? Obviously this is not because we send her to bed in the afternoon - her bed time is 7.30/8.00pm, it's just light in the summer and dark in the winter.

thanks spiggy 83.104.131.135 (talk) 10:15, 22 May 2008 (UTC)

Got a globe and a torch ? Turn the lights off and give her a visual demonstration of time zones and axial tilt. Oh - hang on - you'll have to wait until it's dark ... Gandalf61 (talk) 10:39, 22 May 2008 (UTC)

Gandalf, thanks for the links. However, I can barely get my brain round the concepts outlined there - I don't expect my 5 year old to be able to. I have a globe, and a torch. I get that I can use those to explain day and night on opposite sides of the world. But how do I explain shorter days in the winter/longer summer days? thanks 83.104.131.135 (talk) 10:51, 22 May 2008 (UTC)

There is a clearer explanation and a diagram here. So here's an idea for visualising what is happening. Find the location of your home on the globe and put a line/rubber band/piece of string right around the globe at your latitude - at a constant distance from the equator. Then show how more than half of this line is lit up when your hemisphere is tilted towards the torch/sun (when it is summer in your hemisphere). And less than half of this line is lit up when your hemisphere is tilted away the torch/sun (when it is winter in your hemisphere). So days are longer than nights in summer, and vice versa in winter. Mid-way between summer and winter, at the equinoxes, there is a point where exactly half the line is lit - so day and night have the same length.Gandalf61 (talk) 11:22, 22 May 2008 (UTC)

Take the globe and place a table-lamp (with no lampshade) in the middle of the room. Turn off all the other lights. Put a "You are here" dot onto the globe where you live...a sticker or something. Now, hold the globe at the same height as the table-lamp bulb - and tilt it so that the imaginary line between the north and south pole is not quite vertical - the real world is tilted about 14 degrees...you don't have to be exact! Now you can walk around the table lamp to represent the earth orbiting the sun - each lap around the room is a year. You can spin the globe to show a day going by and watch your "You are here" sticker go through day/night cycles. As you walk around the tablelamp, it's VERY important how you hold the globe. Assuming you live in the northern hemisphere, during the "summer" the north pole should be closest to the lamp and the south pole furthest away...keep that tilt so that in the "winter" (when you are on the opposite side of the table lamp) the north pole is furthest away from the lamp. If you get that right then it will be possible to show that in summer, the lamp illuminates your "You are here" dot for more of the daily rotation than it does in winter. You may need to slightly exaggerate the amount of axial tilt to make that obvious. 71.155.164.147 (talk) 13:39, 22 May 2008 (UTC)

And then of course in many places they use daylight saving time to shift some of that extra summer sunlight from the early morning when most people are asleep into the evening when they are up, so increasing the effect on daylight vs. bedtime. --Anonymous, 20:35 UTC, May 22, 2008.

Even if your kid doesn't understand it all now, she will at least learn that science can be fun, mysterious things can be explained, and her dad is the smartest man in the world. --Sean 14:44, 22 May 2008 (UTC)

thanks guys. 83.104.131.135 (talk) 15:01, 22 May 2008 (UTC)

Or her mom. Zain Ebrahim (talk)14:55, 22 May 2008 (UTC)

and girls 83.104.131.135 (talk) 15:01, 22 May 2008 (UTC)

Perhaps you should let her stay up late one night (until it is dark) then in the morning, asker if she is tired. Voila! —Preceding unsigned comment added by 79.76.202.222 (talk) 02:54, 24 May 2008 (UTC)

I can tell you aren't a parent! Jeez - make one mistake like that and you're doomed! She'll swear she's not sleepy even the forth or fifth time you had to wake her up to give her supper. Then, every time you try to put her to bed in daylight she can say "Well, I wasn't tired so I can stay up until it gets dark this time." and you have an argument on your hands...noooo - don't go there. Trust me. Get out the globe and the table lamp and do only experiments where you KNOW the outcome in advance! 70.116.10.189 (talk) 03:03, 24 May 2008 (UTC)

[edit] ARUN S BAGH QUES ABOUT THING

WHAT IS THE NAME OF THAT THING USED IN SPORTS ON WHICH FIRST SECOND THIRD POSITION WINNERS STAND ? —Preceding unsigned comment added by 59.95.159.68 (talk) 10:33, 22 May 2008 (UTC)

a podium? 83.104.131.135 (talk) 10:37, 22 May 2008 (UTC)

Didn't we have this question on one of the desks recently, as in the last week?--Fribbler (talk) 11:54, 22 May 2008 (UTC)

Possibly last fortnight, but yes. --Tango (talk) 12:32, 22 May 2008 (UTC)

Here Algebraist 12:55, 22 May 2008 (UTC)

CAPS LOCK IS CRUISE CONTROL FOR COOL...BUT EVEN WITH CRUISE CONTROL YOU STILL HAVE TO STEER Ziggy Saw dust 00:22, 23 May 2008 (UTC)

[edit] Nuclear Bomb

Say a Nuclear Bomb was set off and 80% of the human population was dead. Say that some hardy plants and some other forms of animals and bugs survived as well. What characteristics would the humans have to have to survive to say the age 70 during this time? --Vincebosma (talk) 13:14, 22 May 2008 (UTC)

They'd have to have had their 69th birthday party 51 weeks ago. 71.155.164.147 (talk) 13:25, 22 May 2008 (UTC)

Well one nuclear bomb wouldn't take out 80% of the human population. If you are going to have a real scientific discussion of this you need to set the parameters more realistically about how people died.

Let's say it was a full nuclear exchange. Lots of people died either from direct blast/heat/fire effects, and lots more died later from drifting fallout.

Let's assume the population who survived were mostly those who did not get hit directly by the weapons but were instead subjected to fallout. The biggest problem for long-term survival in that sort of situation would be that most of the ground would be salted with radioactive fission products. That means that any food grown from the ground would have a high uptake of radioactive products as well. Which means that eating them would likely deposit many of said products into your bones, blood, etc., leading to cancer.

So if I were to hypothesize about their survivors, I'd say they had an alternative food supply, or had the infrastructure or means to filter out the upper layer of topsoil.

That's just one approach. If this is for sci-fi you can say they had an "increased resistance to radiation" but that's just hand waving. --98.217.8.46 (talk) 13:52, 22 May 2008 (UTC)

I can't imagine that even a cobalt bomb would kill all life in the oceans, though I've never seen calculations. I imagine that eating things from the deep, low on the food chain (to avoid biomagnification), would be a reasonable attempt to avoid contamination. --Sean 14:55, 22 May 2008 (UTC)

Your best bet is probably if your survivors were a tribe of subsitence farmers or hunter gatherers on some remote island in the Pacific or some out of the way place. If by some miraculous coincidences they survived the fallout scenario of 98's objection and the Nuclear winter didn't affect their place. Getting agriculture going from scratch is a lot harder than people think. We're not just talking one harvest or back yard size additions to what you buy at the supermarket. Even if your survivors had studied the subject in detail that would not guarantee success. (see Biosphere 2) Fungi could be grown underground as a food source, which might let them evade soil contamination. But your survivor would have to have had an established mushroom culture, might face nutritional deficiencies and would probably get tired of mushrooms very soon. Society wise an established unit like a tribe has a better chance of not having it's members go on a murdering rampage out of sheer despair. Survivors from a high tech culture depend on a social structure that would also have been wiped out, like law-enforcement, penal code, prisons. Moral dilemmas we usually only have to deal with theoretically come knocking at the door. Experience has shown that some individuals react to the trauma of having their social rug removed from under them by taking up arms and limiting their chances for survival even further by eliminating others who might be able to lend a hand. An established tribe would not face any of these problems. Just a couple of thoughts. --71.236.23.111 (talk) 16:20, 22 May 2008 (UTC)

Ignoring the problems above, one of the biggest problems is that very few people are likely to survive to such an age without the advanced medical care and access to food we have nowadays, which is likely to disappear. Even if your survivors are remote subsitence farmers or hunter gathers as suggested above, they're probably not generally living to 70 already and this isn't going to change with the bomb Nil Einne (talk) 22:54, 28 May 2008 (UTC)

[edit] oil shortage.

apparenlty oil will run out in 40 years and I guess that petrol will be too expensive before that happens.

So are we looking at a global shift in transport and work patterns?

Are electric cars going to be the norm in my lifetime? —Preceding unsigned comment added by 78.144.138.155 (talk) 14:49, 22 May 2008 (UTC)

Oil has been going to run out in 40 years for at least the last 40 years... It will run out, or at least get too expensive, at some point, though. Electric cars are a possibility, but I expect biodiesel and similar fuels are more likely. Electric cars just move the power generation back a stage to the power station - quite a few of those are oil powered as well, so without a massive increase in renewable electricity generation the price of electricity will also increase substantially (I'm sure we'll get that massive increase eventually, but probably not until after the prices go up - no real incentive until then). --Tango (talk) 15:07, 22 May 2008 (UTC)

The Dodo

Oil will never "run out". It's not like there's one big reservoir in the ground and when it's gone, it's gone. There are myriad reservoirs, each holding oil with varying difficulties of extraction. But as we exhaust more and more of the "easy" oil and therefore need to extract the more and more "difficult" oil, the price will rise, pretty much inexorably for a while. Liquid oil alternatives like oil shale and tar sands also fall under this general rubric. You might want to read our article about the "peak oil" theory. And then there are paradigm-shifting events like the likely onset of commercialized nuclear fusion power sometime mid-century; that may remove many of the current markets for liquid fuels, substantially reducing the demand for oil. See our ITER article for a possible timeline. Another, much-more-grim paradigm shift might be a massive die-off as a result of Oil War III or starvation as a result of the rise in oil prices leading to Mad Max-like scenarios.

Atlant (talk) 15:41, 22 May 2008 (UTC)

Be aware, of course, that people have been expecting nuclear fusion right around the corner for over 60 years. Each success is met with new difficulties. And in any event, it will never be as cheap as the optimists have hoped. So we'll see how that turns out. I doubt it will be paradigm shifting in any case—at best it looks like it will be low-emissions form of centralized electricity generation. That's well within the same paradigm. --98.217.8.46 (talk) 16:19, 22 May 2008 (UTC)

There will be a point, though, where it takes more energy to extract the oil than the oil will provide. Then we have essentially run out. Djk3 (talk) 17:08, 22 May 2008 (UTC)

Right. Peak oil is more about when oil will no longer be an effective source of energy, than an actual "zero oil" state. — The Hand That Feeds You:^Bite 00:07, 23 May 2008 (UTC)

Surely you mean Peak oil is more about when oil will no longer be an effective source of cheap energy, than an actual "zero oil" state. 202.168.50.40 (talk) 03:17, 23 May 2008 (UTC)

It's not just about being cheap, it's also about the difficulty of getting to the oil, and the extra refining necessary as we start to use lower and lower quality oil. At a certain point, it's just no longer worth it in time, effort and (yes) cost. — The Hand That Feeds You:^Bite 03:23, 23 May 2008 (UTC)

Time and effort are usually measured in terms of cost when you're talking about big business. As it gets more difficult to extract and refine, the cost will increase which will limit demand and will presumably mean we will never actually run out completely. Demand may drop to 0, though. --Tango (talk) 12:42, 23 May 2008 (UTC)

But if it costs more energy to extract then you get out of it, then no amount of time or effort is worth it to extract the petroleum, at least as a source of energy. Of course, improvements to technology has changed that. BTW, peak oil isn't about zero oil OR when oil will no longer be an effective s ource of cheap energy. Peak oil is the hypothetical state when we can no longer increase our level of production of oil in response to increasing demand. For the reasons outlined above, it's arguably a bit of a pointless concept but there you go... Nil Einne (talk) 22:56, 28 May 2008 (UTC)

[edit] Watermelon seeds

Seeds are surely very nutritious. Would it be much better for you if you eat your watermelon seeds? Pound for pound, would it be better to eat seeded watermelons with seeds than seedless watermelons and then seeded watermelons without the seeds?

I guess if all else being equal, seedless watermelons may store a little more "seed" nutrient in the meat than seeded watermelons. However, you don't get the seed-only nutrients, such as watermelon seed oil from the meat. You probably get a little more sugar and maybe some vitamins from the meat of the seedless ones. -- Toytoy (talk) 17:03, 22 May 2008 (UTC)

I don't have specific answers to your questions, but I do want to point out some perhaps unfounded assumptions you are making when asking them (which may affect the validity of answers, etc.). "Seeds are surely very nutritious."^{[citation needed]}. There are surely chemicals in there, but how do you know that it's mostly useful as human nutrients (and also that it is not balanced by other toxins)? "seedless watermelons may store a little more "seed" nutrient in the meat than seeded watermelons."^{[citation needed]} Do we know that seedless fruits the same as seedy ones except that the "seed contents" are dispersed, or is the "seed stuff" itself completely absent? DMacks (talk) 18:11, 22 May 2008 (UTC)

Watermelon seeds do indeed seem to contain some nutrients. I'd watch out for the 4.7% Arginine if you're a guy or are pregnant. If you'd plan to eat more than about 12kg in a day, Tyrosine might also become a problem :-). People with Phenylketonuria should stay away from watermelon seeds because they contain Phenylalanine. Don't know at what dosage the 1.5 % Alanine might become a problem for people with high blood pressure. Glutamic acid, Lycopene, Methionine, Phosphorus ,Serine, Stearic acidand Threonine don't seem to be causing any problem and are actually good for you. Watermelon seeds act as a diuretic, so drink lots of water and keep a bathroom close by. One source said there was a suspicion watermelon seeds might cause liver damage, but gave no specifics. --71.236.23.111 (talk) 21:02, 22 May 2008 (UTC)

Note that there appears to be little evidence, from the article, that arginine is actually like to cause any problems for most men and definitely not at such a low concentration (I suspect other things will become a problem long before the arginine does if you really eat that many seeds) Nil Einne (talk) 23:58, 23 May 2008 (UTC)

Note that unless you actually chew the seeds your not likely to get much of the nutrition Nil Einne (talk) 23:54, 23 May 2008 (UTC)

Careful now folks. Some seeds are actually toxic, such as apple seeds. It is believed that consumption of toxic seeds resulted in the death of Christopher McCandless. Of course, wild plants are surely more dangerous in general than domesticated. --Shaggorama (talk) 06:43, 24 May 2008 (UTC)

Hmm... Cooked watermelon seeds are sold in the Philippines as a light snack. I haven't heard any news here that it has an adverse effect on your health.--Lenticel ^(talk) 07:14, 24 May 2008 (UTC)

But they are used in folk medicine to induce abortion. (No research evidence I know of, though).--Lisa4edit (talk) 08:13, 25 May 2008 (UTC)

I haven't heard that property yet but then again there are a lot of folk "menstrual cycle inducers" sold here. Maybe the chemical that induces miscarriage is destroyed as the seeds that are sold in the market are usually served roasted.--Lenticel ^(talk) 12:11, 25 May 2008 (UTC)

[edit] Riding a Bike

So I noticed on my way in to work today how difficult it is to keep my balance on a bicycle while it is stopped at a light, and was wondering why this is? 142.33.70.60 (talk) 17:14, 22 May 2008 (UTC)

As luck would have it, we have an entire article on the subject: Bicycle and motorcycle dynamics. In particular, the Balance - Forward Speed section. --Tango (talk) 17:48, 22 May 2008 (UTC)

[edit] Animals and earthquake

There are many reports tha animals may be able to sense a coming earthquake. I am not going to argue over this. I just wonder why couldn't us sense earthquakes if many other animals could?

Then, how about animals from areas with very few earthquakes? Do they have any earthquake-sensing instincts? How about the birds? How about the freshwater/saltwater fish? There's an old Japanese saying that catfish can sense the coming earthquake. How about other catfish species around the world?

Can anyone induce animals' earthquake symptoms in a lab? Maybe if you expose pandas in some crazy magnetic field ... I don't think I can buy a panda in a pet shop and do the experiment by myself. -- Toytoy (talk) 17:14, 22 May 2008 (UTC)

The ability of animals to sense earthquakes has been long speculated. However, it's by no means scientifically accepted. Per this National Geographic article (which provides an excellent overview), "the United States Geological Survey, a government agency that provides scientific information about the Earth, says a reproducible connection between a specific behavior and the occurrence of a quake has never been made." As such, very little of your follow-up questions can be answered. Since the behavior can't be reproduced and no one can establish what the active mechanism actually is, there's no way to state whether certain animals can detect earthquakes, and no such experiments have been successfully defined. — Lomn 17:58, 22 May 2008 (UTC)

This is a little off-topic, but I found it neat: we can't sense coming earthquakes, but our laptop computers connected to the internet can, via the Quake Catcher Network. Franamax (talk) 18:44, 22 May 2008 (UTC)

Animals have lots of useful abilities that humans don't have. Elephants and other animals can hear infrasound. Bees can see infrared. Bats and dolphins have echolocation. Some animals are able to sense magnetic fields. If it weren't a trade off for hands and arms wings might be nice to have. As Lomn said we can't reproduce the effect, so we don't know what trait, if any, it is that we are missing out on. You could catch or buy a catfish, but just warn us before you create an earthquake to study their reaction :-) --71.236.23.111 (talk) 22:07, 22 May 2008 (UTC)

Just a nit: Bees see into the ultraviolet, not infrared. Pit vipers, on the other hand...

Atlant (talk) 13:51, 23 May 2008 (UTC)

Oops. Talk about "the other end of the spectrum". I guess one of my gears got stuck on the "infra...". Thanks for supplying the viper. (Eeek, snakes!) --71.236.23.111 (talk) 14:41, 23 May 2008 (UTC)

[edit] Long-Life Milk

What is added to the milk to make its life longer? Is it more healthy than normal milk? —Preceding unsigned comment added by 217.44.210.227 (talk) 19:47, 22 May 2008 (UTC)

I don't think anything is added; I think it's just ultrapasteurized. But I could be wrong. --Allen (talk) 19:54, 22 May 2008 (UTC)

Ultra-high-temperature processing has quite a lot of information, including nutritional details. --Tango (talk) 20:20, 22 May 2008 (UTC)

You might be looking for ESL milk. Check in Pasteurization. The description hidden in the text isn't great and we don't seem to have a page. One of the steps that can be used is Microfiltration. (NB. That abbreviation is also used for English as a Second Language.)--71.236.23.111 (talk) 20:38, 22 May 2008 (UTC)

ESL is the same as/similar to UHT (Ultra heat treatment/ultra high temperature processing - as mentioned above) nay? Fribbler (talk) 22:41, 22 May 2008 (UTC)

Similar, yes, same no. The Europeans distinguish 3 types: pasturized, ESL and UHT. Pasturized ("fresh"} has a shelf life of only about 5-6 days, ESL 15-20 or even 40 days under ideal cooling conditions (constantly at 5 deg. C). Both need to be kept refrigerated. UHT keeps between 3 to 6 months and doesn't require refrigeration. I tried to narrow down the differences, but some of the sources I found seem to contradict each other. Since the milk we buy in the US keeps longer than 5-6 days something seems to be different in treating it, here (We just bought a gallon that's labeled with an expiration date in 10 days).--71.236.23.111 (talk) 04:32, 23 May 2008 (UTC)

It seems that in the US there are (at least) three types of processing too. Ordinary pasteurized milk has the shortest shelf life, which seems to be somewhat longer than 5 or 6 days. Organic milk, kept refrigerated and sold in cartons, typically has a shelf life of about a month (based on my recollection). UHT processed milk, kept unrefrigerated and sold in "juice box" packages, has a shelf life measured in months. --72.78.237.229 (talk) 13:47, 23 May 2008 (UTC)

[edit] Multivalent Ionic Charges

Hello. How can a multivalent element's ionic charge change during a chemical reaction for example (my guess) 2Cu₂O + 4H₂SO_4(aq) → 4CuSO₄ + 4H₂↑ + O₂↑? Thanks in advance. --Mayfare (talk) 20:15, 22 May 2008 (UTC)

Sounds like a simple case of redox. DMacks (talk) 21:23, 22 May 2008 (UTC)

[edit] Weird growth on agar plate

I grew e coli on an LB agar plate. When I checked for growth, I thought I got some colonies (only 3 white spots), but what looked like colonies were actually beneath the agar surface touching the bottom of the plate. What are those? —Preceding unsigned comment added by 128.163.224.198 (talk) 21:46, 22 May 2008 (UTC)

The simplest explanation would simply be air bubbles left over after pouring the agar. They usually masquerade as colonies. Wisdom89 _{(_T / ^C)} 22:38, 22 May 2008 (UTC)

And another explanation: contaminant microbe colonies growing inside the agar (fellows who fell into the agar after it cooled and before it was poured). Or detritus. Woodlore (talk) 10:38, 23 May 2008 (UTC)

If in doubt, don't wonder what it is, just toss it. However, if it's a reeeeeeeally important dish, then you're on your own ;) Sjschen (talk) 06:27, 26 May 2008 (UTC)

Good thing Fleming didn't have that attitude.Woodlore (talk) 11:42, 27 May 2008 (UTC)