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

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September 21

Birds noisy at night

It's that time of year when the birds begin to flock together before they head off south for the winter. I've noticed this year that during the night the smaller birds, Snow Bunting or Savannah Sparrow, have been much noisier than usual. I work night shifts so I'm often about during the evening and have not noticed this amount of chirping before. This is both in town and out of town. Any ideas why they would do this? CambridgeBayWeather Have a gorilla 00:02, 21 September 2008 (UTC)

BB gun --mboverload@ 01:08, 21 September 2008 (UTC)

Unlikely. Any kid wandering around here at night with a what could easily be mistaken for a firearm is going to get picked up very quickly. Anyway, BB's are not that common, now .22's are, but the RCMP would take a really dim view of someone doing that. That would only explain it in town, not out at the airport where I'm the only one around. CambridgeBayWeather Have a gorilla 06:22, 21 September 2008 (UTC)

No, if the birds are noisy just shoot them with a BB gun. --mboverload@ 06:28, 21 September 2008 (UTC)

Ahh, wouldn't work, too dark and the birds are too small. A shoutgun would be much better for that. Or I could just throw my cat at them. CambridgeBayWeather Have a gorilla 07:41, 21 September 2008 (UTC)

Hello CambridgeBayWeather, do you mean (i) they are noisier this year compared to previous years or (ii) noisier than the previous few months? Assuming (i) I would suggest that perhaps more birds survived the summer this year and so are simply noisier in their greater number. Total populations will rise and fall for various reasons which includes various abundance of food, see Population cycle. Assuming (ii) then I would imagine if it is the end of the summer they have done with their breeding and so simply have more time to be noisy (by defending their territory and other general communication) instead of searching for food constantly for themselves and their family which they would have been occupied doing in previous months. It is harder to forage for food in low light and so birds won't bother unless they have to. Also, since They'll be starting to get together in flocks ready for their migration (saftey in numbers) there are greater numbers in one place and are hence noisier. Another solution is that sound travels further at night time when there is likely to be a lot less human activity. Jdrewitt (talk) 14:34, 21 September 2008 (UTC)

It was number (i) that I was meaning and looks likley. It may have something to do with the increase in water levels. Over the past few years the ponds and such have been decreasing in size, U of A report. However, this year I noticed that most of them, in our area, were almost the same as usual and it's possible there was a larger number of insects and other foods available. Thanks. CambridgeBayWeather Have a gorilla 17:32, 21 September 2008 (UTC)

I read in the news a while back that birds are starting to sing more at night because they can't be heard over human noise during the day, especially in urban areas. Singing is something that birds need to do for various reasons, like announcing their presence to other birds to keep territory or attract mates and during the day they simply can't be heard. Another news story said that birds are starting to sing louder specifically in order to be heard over the noise of the daytime. If they are used to singing that loud all day, then I would assume they will do it in the evening too. In some cities of Europe birds have been known to break local laws against noise pollution! Also, light is an issue here, as there are more street lights and other human light, so birds are staying awake longer.--ChokinBako (talk) 21:30, 21 September 2008 (UTC)

That would make sense too. Although the amount of noise/light here has not really increased they would be bringing the behaviour from southern parts. One of the interesting differences in their actions over the last two years has been the "sentinel" bird. When, during the daytime, the cat goes out, one bird will sit on a high point and sing constantly. It seems to work because her ability to capture birds has decreased while the lemming kill count remains the same. CambridgeBayWeather Have a gorilla 08:29, 23 September 2008 (UTC)

How much does a 3.2 kilogram slug of tungsten cost?

Topic name says it all. ScienceApe (talk) 01:30, 21 September 2008 (UTC)

except why you want 3.2 kg, rather than asking for a bulk price per kg. Inquiring minds want to know! —Tamfang (talk) 04:27, 21 September 2008 (UTC)

Just comparing it to the cost of a cruise missile. A 3.2 kg slug of tungsten can do as much or more damage than a cruise missile when shot from a railgun. ScienceApe (talk) 15:21, 21 September 2008 (UTC)

Somewhere around $200 / kg. Dragons flight (talk) 04:49, 21 September 2008 (UTC)

Well from Google, [1] "A broad range of prices for finished tungsten products would be from $25 to $2500 per kilo, with the majority of products in the $75 to $300 per kilo area." And according to [2] the price at around the beginning of August was $245-$253/mtu (metric tonne unit check out the wikilink it does not mean 1 tonne of the metal but 10kg). In other words, anything from ~$80 upwards for 3.2kg. Obviously if you're only going to buy one 3.2kg slug you should be expect to be paying a lot more. On the other hand, if you're buying 10k of them it would be closer. P.S. All $ means US$ I believe Nil Einne (talk) 10:26, 21 September 2008 (UTC)

When I got a quote for tungsten it was AUD $70 per kilogram in kilogram quantity for powdered form, so your chunk would cost $224, however, if that was not a standard shape or size it would require plenty more cash to get it the way you want. Graeme Bartlett (talk) 21:08, 21 September 2008 (UTC)

iraQ PLEASE ASSIST

i have a rock association and my are roots in modern day nineveh..what is the answer to this brainy quiz.. —Preceding unsigned comment added by 196.1.26.35 (talk) 03:16, 21 September 2008 (UTC)

Not sure what you are asking here, but have you read our article on Nineveh? Plasticup ^T/C 16:46, 21 September 2008 (UTC)

Is this for a cryptic crossword? You may have to make an anagram from Nineveh. Graeme Bartlett (talk) 21:13, 21 September 2008 (UTC)

I doubt it. Wordsmith's anagram server failed to find any anagrams of "Nineveh". Plus it says "modern day" Nineveh...the nearest place to Nineveh is Mosul, Iraq - and neither Mosul, nor Mosul Iraq generated any interesting anagrams. However, Mosul is famous for production of Blue Marble...so I guess that's the most likely answer. SteveBaker (talk) 01:20, 22 September 2008 (UTC)

Petra? doesn't really fit though. Polypipe Wrangler (talk) 05:47, 22 September 2008 (UTC)

stable bleaching powder

what happens if MgO is above 1.5% in stable bleaching powder? —Preceding unsigned comment added by Mandyboy66 (talk • contribs) 06:33, 21 September 2008 (UTC)

I don't know about your "stable" bit, but MgO is insoluble in water, so you would ahve a white powder residue. It should not affect the chlorine bleaching mechanism, other than diluting it. Graeme Bartlett (talk) 21:30, 21 September 2008 (UTC)

Scientific meaning of 'Energy'

Finding it hard to discover an in depth exploration of the meaning of energy. any links, information would be greatly aprecciated. -- 118.82.177.151 (talk) 06:41, 21 September 2008 (UTC)

Energy should be your first point of call. Jdrewitt (talk) 08:01, 21 September 2008 (UTC)

Fixed sig. --antilived^{T | C | G} 09:35, 21 September 2008 (UTC)

Nobel prize winner Richard Feynmann gave a very clear introduction to the concept of energy in his Lectures on Physics - I think it is Volume I Chapter IV in the full set of lectures, and it is reprinted in the (much shorter) book Six Easy Pieces. Gandalf61 (talk) 11:14, 22 September 2008 (UTC)

Lab test overkill

In "studies" why do they give animals a 1,000x normal dose of some additive (making it like 10% of the diet) and are then *shocked* when the animal gets messed up? Is there a legitimate scientific reason for this or is to feed the culture of fear? I mean, seriously, wackos use these nonsense studies with completely non-realworld conditions to support their (false)beleifs. Why do "scientists" do this?--mboverload@ 07:23, 21 September 2008 (UTC)

I think you may be confused between the shock stories that journalists write compared to the inquisitive mind of a scientist. A scientist does any experiment to see if what he thinks will happen matches what will happen. You may find Pharmacology and Scientific method interesting. - Phydaux (talk) 10:18, 21 September 2008 (UTC)

I expect they test a wide range levels, from so small they're almost certain it will have no affect to so large they're almost certain it will. They're more interested in the levels inbetween, but it's important to test the extremes in order to be able to draw proper conclusions (otherwise you'll find out the dangerous level is "somewhere less than x" or "somewhere greater than x", but won't know precisely where it is). As Phydaux says, it's only the journalists that are shocked and take everything out of context, the scientists know how to draw proper conclusions from their experiments. --Tango (talk) 11:31, 21 September 2008 (UTC)

See therapeutic index. --Arcadian (talk) 14:28, 21 September 2008 (UTC)

Thank you for the answers everyone. --mboverload@ 18:25, 21 September 2008 (UTC)

You may be talking about the LD50 test. This is the dosage of some substance which causes 50% of the recipients to die. In some legal juristictions it may be required to determine the LD50 amount for a drug or food additive by animal testing. For substances that are in fact completely harmless - the dosage required to kill 50% of the test animals may be exceedingly large - and 1000x the normal dose is by no means impossible. Fortunately, this ridiculous test is no longer a requirement in most places...check out our article to get more details. SteveBaker (talk) 20:12, 21 September 2008 (UTC)

I think what he's referring to more specifically is the testing that has been behind warnings about things like aspartame, which causes cancer in mice at huge levels, which led to questions about its safety in humans. In this case I'm not sure the scientists were just trying to figure out how much was toxic, per se, and more to the point, the question was not whether a similar amount would be toxic in humans, but whether small, tiny amounts would somehow probabilistically affect risk factors, for example. It's the sort of thing that makes you ask, "what non-standard chemical could you pump into rats in massive amounts and not find is statistically carcinogenic", which is I think what the OP is asking. I think in general is that the answer probably is in line with the needs to establish toxicity levels of any new chemical, and in the process finding side-effects at lower-than-toxic doses. Of course the extrapolation to humans from mice models etc. is not a simple thing. --98.217.8.46 (talk) 21:57, 21 September 2008 (UTC)

Part of some approval processes for a chemical (drug, pesticide, food additive, whatever) requires an analysis of the toxicity of the material. It's crazy, but some approvals really do require an actual "how much is toxic", not just "it's not toxic at 10000x what is an even remotely possible dose, so don't worry about it". DMacks (talk) 00:26, 22 September 2008 (UTC)

When testing is done with very large doses, it's about determining carcinogenicity (whether it causes cancer), not toxicity (whether it'll "mess you up"). The theory behind this is that a substance either is carcinogenic or it isn't. If it isn't, it may mess you up in some other way, but it won't mess with the genes in your cells. On the other hand, if it is carcinogenic, it only needs to mess up one cell to start a cancer -- so even a tiny amount could cause your death, although a large amount would be more likely to. Hence the fuss about carcinogens: the more we can eliminate exposure to carcinogens and replace them with non-carcinogenic substances, the fewer people will get cancer.

The idea of the experiments is that you apply say 1,000 times a normal quantity to 100 rats. If none of them get cancer, then that's pretty good proof that the stuff is not carcinogenic. But if 5 out of 100 do, that's pretty good proof that it is. You could alternatively do the experiment by giving a normal quantity to 100,000 rats and again maybe 5 of them would get cancer for this reason. But this is inferior for two reasons. First, using an unnecessarily large number of animal subjects is inhumane and expensive. And second, if you start with 100,000 rats, some of them will get cancer for other reasons, so it's harder to "read" the results of the experiment. Hence the use of megadoses.

It is sometimes argued that some substances may for some reason be carcinogenic only in megadose quantities, in which case a positive result of the megadose experiment would be misleading. Or that some substances giving a positive result may be carcinogenic to such a low degree that banning them is not warranted. I am not a biochemist, this is not biochemical advice, and I'm certainly not saying that these arguments are either right or wrong. I am saying that the argument "megadoses are toxic and therefore don't prove anything" is wrong.

--Anonymous, 02:26 UTC, September 22, 2008.

Einstein refrigerator

How does it really work? How can it apparently reduce entropy with no energy input? If you link a Stirling engine won't you have your very own perpetual motion? --antilived^{T | C | G} 10:18, 21 September 2008 (UTC)

I haven't really looked at the design/article but immedietly "requires only a heat source to operate". How exactly does requiring a heat source to work become "no energy input"? Nil Einne (talk) 10:31, 21 September 2008 (UTC)

Hmm seems like I've skimmed too much in the operations section to see the "heat source". Thanks. --antilived^{T | C | G} 10:44, 21 September 2008 (UTC)

I just had a google and I see there still are kerosene operated fridges for sale. I thought they'd gone out ages ago! Sounds a strange idea cooling down by lighting a fire. Dmcq (talk) 10:51, 21 September 2008 (UTC)

People also use propane-powered refrigerators for caravans - and for places where the electrical supply is intermittant. Just type "propane refrigerator" into Google and you'll find a bazillion of them. SteveBaker (talk) 20:08, 21 September 2008 (UTC)

Children listening to older sisters, learning right from wrong, and all that

Why do younger children tend to listen to older siblings - or do they? - when it comes to rules, etc.? Would this be different in a child who has not consistently been taught right from wrong by the parent(s), unless said older sibling has acted to teach that?

The reason for my question is this. I've spoken to numerous child psychologists and/or professors in that fieldwho have confirmed my suspicions concerning the TV series Full House. That while the youngest girl could have gone without punishment from an adult till almost age four (timeout or removed privileges, which they called punishment)) she could not have been anywhere near as well behaved and in control as she was before, at school or int he home, without someone enforcing consequences for right and wrong to teach her. And, that as oftenhappens in real life, the oldest sister could well have done so behind the scenes, in the time we don't see the family.

There is a spot in that episode where Michelle hasn't been punished till almost age 4 where D.J., the oldest sister, tells Michelle, the younest, to do something, and she obeys perfectly. When someone tried to use this as an example of how D.J. would have been listened to, another person said, "Well, children just naturally listen to their older sisters."

So, is that true? And, if so, would they naturally listen to an older sister if they hadn't been taught to obey rules normally? It seems that the oldest sibling (which will happen where parents don't discipline, from what I've been told) has to be the one teaching for that part of the child to take hold that tells them to obey rules, especially by almost age four!209.244.187.155 (talk) 11:00, 21 September 2008 (UTC)

Just a comment, not quite an answer to your question: there are much better ways of establishing a cooperative relationship with a child than by punishing the child. See for example Jesper Juuls work.--Lova Falk (talk) 13:24, 21 September 2008 (UTC)

I agree entirely. We almost never punished my son - a sharp word was all we ever required to stop a problem from developing just long enough to explain to him why it was a bad idea. I can only recall one time he ever got into serious trouble and he was so very aware of what he'd done wrong that no punishment was required...rather, he needed to be reassured that he was forgiven and that we still trusted him. He graduated high school a year early and is now doing very well in college. He has a fine sense of moral integrity - I don't have to worry about him doing stupid stuff. The trouble with punishment is that it requires escalation - if you punish with a timeout, then is a timeout enough the next time it happens? What about the time after that? Better to explain WHY this behavior is bad and bring your kids up to be intelligent enough to listen and understand. I haven't been watching Full House though - I have no clue how believable it is. Extrapolating from real life to fiction and vice-versa is a really bad idea. SteveBaker (talk) 01:10, 22 September 2008 (UTC)

Please, go on the "Full House" boards on www.tv.com and explain this in the threads about "stupid stuff Michelle did and got away with" and stuff like that. Some of these people need to learn this! (www.sitcomsonline.com isn't much better.) Or leave your own thread begun; some of the poeple just don't understand that just becasue a child does something wrong doens't mean they need punished. (Though if the posters got punished themselves as children, are they more likely to expect others to be? Probably.) —Preceding unsigned comment added by 209.244.187.155 (talk) 12:04, 24 September 2008 (UTC)

The Vena Cava

if water were poured into the vena cava, through which vessel would it emerge from the heart? —Preceding unsigned comment added by 82.28.243.9 (talk) 12:52, 21 September 2008 (UTC)

Have a look at this diagram. The venae cavae enter at 3 and 11 and from there its out to the lungs via the pulmonary artery (number 5). Fribbler (talk) 12:58, 21 September 2008 (UTC)

Anatomy lectures transcription

Dear Wikipedians:

Right now I'm taking an anatomy lecture with an overwhelming amount of information delivered each lecture. I have recorded each lecture but find that I don't have enough time to sit down and listen through each one of them. So I am wondering if there are transcription services out there affordable to students that will do the job for me?

Thanks in advance.

74.12.199.113 (talk) 13:56, 21 September 2008 (UTC)

As you wait for more quality replies, please check this link. You could also try sweatshops like Amazon.com's Mechanical Turk HTH, Thank you. Kushal (talk) 16:23, 21 September 2008 (UTC)

As a teacher in that sphere, I suggest you talk to your professor. My guess is that they would not want you to focus so closely on the words said, but the concepts emphasized and synthesized. Anatomy requires a certain amount of rote memorization, so it is worth reviewing terms prior to lecture, then it might be easier to follow along. If your learning style is not compatible with the way the course is being taught, the faculty are often willing to make reasonable accommodations. The goal of teaching is for the student to learn, and part of that is learning about one's learning style. --Scray (talk) 20:09, 21 September 2008 (UTC)

There are a number of programs on the market that will convert text to speech automatically (see list here). I haven't tried any myself, but would bet that they'd have the same problem any cheap transcript service would have: horrible misspellings - but they'll likely be cheaper than getting transcripts made. Convert your lectures to mp3 and listen while on the bus or going to sleep.

It's a little off-topic, but if you're having trouble with human anatomy, might I suggest one of the human anatomy colouring books on the market. Sounds silly, I know, but they help immensely and they're just as detailed and in depth as you'd want them. Twenty years later and my ability to rhyme off almost every bone and major muscle still surprises me. Thisis the one I used so long ago. Matt Deres (talk) 16:40, 22 September 2008 (UTC)

I read the OP as if having not enough time to listen to all the talking but prefer a written transcription (not translation) which he/she can do faster and in her/his own time, skipping known facts and concentrating on new ones. My approach to that task was that there were always some students who, from their own approach to learning, had to write down what the teacher said. Copy their scripts and reward them by explaining things they could not understand, being busy writing down the words. 93.132.148.11 (talk) 18:48, 22 September 2008 (UTC)

Measuring angles

I have a photo taken by a Nikon D40x at a focal length of 18 mm, with a rectilinear lens. How do I accurately measure the angle between two objects in the photo? --Bowlhover (talk) 15:29, 21 September 2008 (UTC)

I think you would need to know the distance to the objects - a given separation in the photo would correspond to a greater angle if the objects are closer. --Tango (talk) 17:20, 21 September 2008 (UTC)

Why would that be the case? Anyhow, all the objects can be assumed to be at infinite distance. --Bowlhover (talk) 17:23, 21 September 2008 (UTC)

Actually, I'm doubting myself now. However, if they're at infinite distance, doesn't that mean there is no angle between them? The rays of light would be parallel, that's why it's often convenient to assume infinite distance. --Tango (talk) 17:59, 21 September 2008 (UTC)

Perhaps the question is how measure an angle drawn on the surface of the photograph? Franamax (talk) 18:05, 21 September 2008 (UTC)

In which case, this would be a problem in orthophotogrammetry and you could look at the lens distortion article. It recommends software to undistort the image, plus there's an external page about correcting distortion. Franamax (talk) 18:09, 21 September 2008 (UTC)

I assumed he meant the angle subtended at the camera by the line joining the two objects. If we're talking about lines in the photo, then it's another matter entirely, and those links should help. --Tango (talk) 18:20, 21 September 2008 (UTC)

The focal length is the distance at which the image is focussed - you can relate it to the field of view if you know the size of the film (or the digital sensor). Knowing that, it's just a matter of trig. Hence, for 35mm film (in 'landscape' orientation), an 18mm lens has a horizontal field of view of:

2xarctan((35mm/2)/18mm) = 88.4 degrees.

For different film sizes - or in portrait orientation...do the math. For digital cameras, I suspect they label the lenses as would be appropriate for 35mm film...but perhaps not.

SteveBaker (talk) 00:57, 22 September 2008 (UTC)

What I meant is this: suppose there are two lines that stretch out to infinity, each one joining an object to my camera's lens. What is the angle between these two lines? The distance of the objects should not matter; if an object on one of the lines is moved along the line, its position in the picture doesn't change.

Steve: I think I know my camera's field of view, but how do I calculate the angle between two objects that do not stretch across the entire FOV? --Bowlhover (talk) 01:27, 22 September 2008 (UTC)

Well, we calculated your camera's field of view to be 88.4 degrees with a 35mm film. You can use the same approach with objects that are not at the edges of the photo.

Let's first consider two objects that lie on a straight, horizontal line that goes through the center of the photo...that's the simplest case. Suppose you were measuring the positions of the objects on the original 35mm film negative rather than on a print made from it. The angle between a line shooting out through the center of the photo and a line shooting out towards your object is arctan(position in millimeters/18mm) - you can do that calculation for both objects and you'll know the angle between them (it's the sum of those two angles if they're on opposite sides of the center of the photo - or the difference between them if they are on the same side).

But you probably don't want to do this on the original photo - you want to do it on either a print or an uncropped digital image (if it's been cropped - you're doomed!). Now, you don't have a 35mm image - you have a 2048 pixel image or an 8"x10" print or something. Well, that's OK - you just need to scale the distances of your two objects by a factor of 35mm/imageWidth (where 'imageWidth' can be in inches or pixels or whatever you like).

That's all very well if the two objects lie on a horizontal line through the center of the image. If the image is rectilinear (it should be) then the same calculation works even if the line between your objects isn't horizontal. But if the line between your objects doesn't run through the center of the image - then things get much more complicated. For a narrow-angle (telephoto) lens, you can just not bother and approximate it as arctan(( distanceBetweenObjects x 35mm ) / ( imageSize x 18mm )) ... but for wide angle lenses (or if you need a LOT of precision) - then that's not good enough.

Sadly, it's getting late and I don't have the time to figure the math for that case. What I'd probably do would be to project use the (X,Y) position of the object in the photo to generate a horizontal and vertical angle relative to the centerline of the camera - then use that to generate a 3D (X,Y,Z) coordinate at some arbitary distance from the camera, then normalize the resulting 3-space vectors, then use a vector cross-product followed by an arc-cosine to figure out the angle between those two vectors. If this means something to you - then you're good to go...if not...I'm sorry, I don't to elementary 3D geometry this late at night!

SteveBaker (talk) 02:33, 22 September 2008 (UTC)

psychology type I and type II error

I was wondering if you could help me with the definition of type I and type II errors and my college teachers disagree with the wikipedia page and many other internet pages. Many Thanks —Preceding unsigned comment added by 86.140.106.119 (talk) 16:18, 21 September 2008 (UTC)

A Type I error is a false positive. In statistics, it occurs when the null hypothesis is rejected although it is actually true. A practical example this would be your fire alarm going off when there is no fire.

A Type II error is a false negative. In statistics, it occurs when the null hypothesis is not rejected even though it is false. A practical example of this would be your fire alarm no going off while your house burns down. Plasticup ^T/C 16:40, 21 September 2008 (UTC)

Whose idea was it to call them "Type I" and "Type II" and not just "false positive" and "false negative". The latter are far easier to understand... --Tango (talk) 17:21, 21 September 2008 (UTC)

...and to remember. OP, what do your teachers say the definitions are? --Allen (talk) 17:47, 21 September 2008 (UTC)

Oscillating systems, periodic time and maximum acceleration

I'm trying a homework question, not looking for an answer but for some guidance.

The question is: "A spring with a k-value of 220Nm-1 is attached to a mass of 0.20kg which is then displaced by 30mm and allowed to oscillate. Calculate the maximum acceleration of the mass."

Presumably I need to use this equation: a=-(2π (f²))X

My question is, how do I work out X in this equation? I can work out the frequency from first using T=2π(square root m/k) then 1/T, but can't find out X.

—Cyclonenim (talk · contribs · email) 16:54, 21 September 2008 (UTC)

do you know what X represents? Wanderer57 (talk) 16:57, 21 September 2008 (UTC)

I should have made note somewhere, but I can't remember where. In a previous question it represented amplitude, so presumably it's the same here. —Cyclonenim (talk · contribs · email) 17:01, 21 September 2008 (UTC)

Simple harmonic motion should be helpful. Dragons flight (talk) 18:30, 21 September 2008 (UTC)

It would indeed be useful at the next stage up from where I am, but most of those equations have been simplified for 'A' level physics :) I think it'd probably be better for me to check with my teacher tomorrow. Thanks anyway. —Cyclonenim (talk · contribs · email) 19:11, 21 September 2008 (UTC)

X is the displacement, which you have the initial displacement in your original question, but you will have to decide what displacement gives the largest acceleration. Graeme Bartlett (talk) 22:14, 21 September 2008 (UTC)

snake venom how does it travel through the body

i was told by a nurse that snake venom does not travel through your blood it travels through your limphatic system is this true and what is the diference —Preceding unsigned comment added by R611 (talk • contribs) 17:07, 21 September 2008 (UTC)

The nurse would be half correct since lymph vessels are different to blood vessels, but lymph generally drains back into the blood stream. Those two articles linked above should give you your answer on differences too. —Cyclonenim (talk · contribs · email) 17:18, 21 September 2008 (UTC)

The articles linked go into more detail, but in general, some of the blood plasma is intentionally forced out of the blood vessels to help feed & moisturize surrounding tissue (interstitial fluid). This fluid is collected by the lymph vessels, and eventually makes it's way back to the circulatory system via the thoracic duct and the right lymphatic duct. If the snake's fangs inject directly into a blood vessel (like an IV needle), the venom will travel through the bloodstream. However, it's more likely that the snake will miss a vessel and inject the venom into the interstitial space, causing it to be transported by the lymph system. -- 128.104.112.147 (talk) 22:40, 21 September 2008 (UTC)

Indefinitely orbiting a singularity inside of the event horizon of a black hole

Is this possible? Super massive black holes can have extremely large event horizons, so there's definitely room for orbit. So is it possible to orbit a singularity inside of an event horizon, without ever touching the singularity, just in a constant state of freefall? ScienceApe (talk) 18:50, 21 September 2008 (UTC)

if the universe is closed, then we are all doing this all the time. -Arch dude (talk) 19:14, 21 September 2008 (UTC)u

You can't even orbit a black hole at up to 1.5 times the radius, see Photon sphere. It is possible for a super-massive black hole that a pair of orbiting bodies cold continue orbiting each other for a while after they pass the event horizon before they are destroyed, they couldn't orbit the singularity though. Dmcq (talk) 19:55, 21 September 2008 (UTC)

Just as we can't stop ourselves travelling forward in time, once you're inside the event horizon, you can't stop yourself travelling towards the singularity. Whatever you do, you will hit the singularity within a finite amount of time. --Tango (talk) 20:07, 21 September 2008 (UTC)

Sure, but if you have a forward velocity, you would be in orbit, hence a perpetual state of freefall like the international space station in orbit around Earth. The concept should be the same, even inside of an event horizon, unless there's something else stopping that from happening. Tidal forces aren't strong close to the edge of the event horizon of a super massive black hole. ScienceApe (talk) 20:31, 21 September 2008 (UTC)

Orbital velocity within 1.5 Schwarzschild radii of the singularity is greater than the speed of light, so it's impossible to orbit. --Tango (talk) 20:53, 21 September 2008 (UTC)

Even if the event horizon is massive? The event horizon at Q0906+6930 is stated to be 1000s of times the volume of our solar system. ScienceApe (talk) 21:58, 21 September 2008 (UTC)

That's right you can't orbit, you can only fall. With a lot of sideways velocity, you may be able to hit the singularity on a curve, but it cannot be avoided or orbited. Graeme Bartlett (talk) 22:18, 21 September 2008 (UTC)

Does the above also apply to rotating black holes, or are we just talking about the Schwarzschild metric here? Algebraist 10:45, 22 September 2008 (UTC)

Rotating black holes change the distances of the last stable orbits, but once you are inside the event horizon you are guanteed to hit the singularity and no orbit is possible regardless of whether the hole is rotating. Dragons flight (talk) 11:16, 22 September 2008 (UTC)

Thanks. Algebraist 14:49, 22 September 2008 (UTC)

I read somewhere that all paths inside black hole lead to singularity. So if you try harder not to fall, we will fall faster. Is this correct? Two particles entering even horizon at different speeds will fall inside with same speed or different? manya (talk) 07:13, 22 September 2008 (UTC)

All possible trajectories hit the singularity in finite time but some take longer than others (as measured by proper time). Assumming you had a means of propulsion you could steer yourself towards a slower fall. Dragons flight (talk) 11:16, 22 September 2008 (UTC)

Actually manya is right, if you thrust you actually hit the singularity sooner. The longest proper time comes from following a geodesic. (For a non-charged, non-rotating black hole, anyway, I don't know about more complicated cases.) --Tango (talk) 13:24, 22 September 2008 (UTC)

If something BIG is orbiting something even BIGGER then you sure don't have a stationary BH with an unaltered Schwarzschild metric, you'll have angular momentum. 93.132.148.11 (talk) 18:28, 22 September 2008 (UTC)

Yes, most of the maths is done using "test objects" of negligible mass, if the object has significant mass it does change things and I haven't seen the more complicated maths myself, but I believe the same end result applies. --Tango (talk) 18:31, 22 September 2008 (UTC)

I haven't seen it either but I hope someone else here has. Uh, now we are doing discussion on the reference desk --- or is it just a superposition of partially answering and posing new questions? And what would be the difference? 93.132.148.11 (talk) 19:03, 22 September 2008 (UTC)

That is often reported, but is simply not true. See: [3]. The only traveler who can't benefit from firing rockets is one who crossed the event horizon with negligible velocity. In other words, the geodesic starting at rest at the event horizon takes maximal time. Dragons flight (talk) 19:18, 22 September 2008 (UTC)

Right, but for "negligible velocity" read "moving at the speed of light." The maximum is when you're at rest with respect to Eddington-Finkelstein coordinates at the event horizon, but because of the way the light cones are tilted that's actually light speed. The maximum isn't exactly achievable, but you can get arbitrarily close. -- BenRG (talk) 21:48, 22 September 2008 (UTC)

Now that you mention it, that assumption was included in the homework question when I did it (actually I failed to do it, but that's not the point!How I managed to get 82% in the GR exam, I'll never know...). I shouldn't trust my memory so much... --Tango (talk) 22:31, 22 September 2008 (UTC)

The earth itself has a Schwarzshild radius, very small near the center. So all matter should be drawn in to that. It isn't. The reason, as I understand, is that there is a lot of mass outside the radius, pulling back. All analysis on traveling in a Schwarzschild metric assumes that very nearly all the mass is centered (and non-rotating) at a single point in the center and that there is no large scale mass around. Being inside the Schwarzsild radius and obeying a Schwarzschild metric is a very different thing. 93.132.148.11 (talk) 20:10, 22 September 2008 (UTC)

When we talk about the Schwarzchild radius of an object that isn't a black hole we mean the radius it would need to be shrunk down to in order to turn into a black hole. Of course, all matter is drawn towards the centre of the Earth, since that's the centre of gravity of the Earth. The Schwarzchild metric is a "vacuum solution" to Einstein's equations, it's a solution in which there is no matter, there is just a singularity at the centre which behaves as though it has mass. --Tango (talk) 21:46, 22 September 2008 (UTC)

In a rotating/charged black hole described by the Kerr-Newman geometry the singularity is timelike and you can avoid it indefinitely if you accelerate. I don't know whether there are stable freefall orbits (probably not). -- BenRG (talk) 21:48, 22 September 2008 (UTC)

People said that the photon sphere is the closest to a black hole where you can orbit. Is this taking into account that light falls twice as fast as massive particles? — DanielLC 23:19, 22 September 2008 (UTC)

Light doesn't fall twice as fast as massive particles, it falls at the same rate. I've heard that before on this desk and can't remember where it comes from - there is a situation in which light seems to fall twice as fast, but I don't recall the details. In the normal sense, however, it falls at the same rate. --Tango (talk) 23:51, 22 September 2008 (UTC)

Probably it comes from the fact that the deflection of starlight around the sun predicted by general relativity is exactly twice the prediction of a Newtonian corpuscular theory. But that's a difference between Newtonian and Einsteinian physics, not between light and massive particles. -- BenRG (talk) 14:23, 23 September 2008 (UTC)

Why don't quartrbacks get the types of injuries pitchers do?

I heard a doctor on Sporting News Radio's pregame today say pro football quarterbacks get mostly contact-related injuries, whereas baseball pitchers, whose shoulder and elbow injuries are more usage-related. (And you rarely ever heard of a QB with a bad elbow.)

At first, that made sense - QBs throw hard only 20-30 times a game (a little dump or screen pass wouldn't seem to exert much force ont he arm), and then only once a week in game conditions. However, as I thought about it, this would be like being a relief pitcher, and the amount of repetitions in practice mean they're really doing that every day, if not more. And, they certainly have to put soe zip on the ball to get it downfield.

Is it the fact baseball pitchers throw more than just a fastball, which is what the NFL pass amounts to? I've read that the other pitches cause a lot of wear on the arm, but also that overhand throwing itself (like both positions do) isn't that natural a motion. (Hmmm, come to the think of it, the baseball catcher usually doesn't get arm injuries, so that might be it.) Or, is it that there are so few starting quarterbacks compared to baseball pitchers that we just don't notice it unless we follow every single college team, as well as the NFL?Somebody or his brother (talk) 19:10, 21 September 2008 (UTC)

Um, this is wildly outside of my bailiwick, but don't football quarterbacks have 300-pound men determined to hurt them? --Sean 00:24, 22 September 2008 (UTC)

There is a huge difference though - the throw of a pitcher has his fingers moving through the air between 80 and 100mph, propelling just 5 ounces - and is expected to do it 100 times or more in a single game - and to twist the ball in a variety of weird and unpredictable ways as he does so. The quarterback has to throw a 15 ounce ball - but only at 45mph, only 20 times a game and always with the exact same spiral move. Remember that kinetic energy is proportional to mass times the square of the speed. At three times the mass but only half the speed - the quarterback doesn't have to impart as much energy to the ball as the pitcher...but the energy imparted to the ball is negligable compared to the energy imparted to the guy's hand and forearm - which is going to have comparable mass in the two sports - making the baseball pitch require four times as much kinetic energy as the quarterback. So: baseball requires four times more energy, twice the speed and five times the number of throws...it's not hard to see how there would be a huge difference in usage-related injuries. SteveBaker (talk) 00:42, 22 September 2008 (UTC)

thanks - wow, quarterbacks only throw about 45 MPH? I always pictured it as much closer to the speed pitchers throw at - 80-100 MPH. the weird twists of the arm match my thoughts about the types of pitches. Relievers usually only throw 20-30 pitches a game, but maybe that's all that QBs throw in practice, too, in the days between games. (The kinetic energy is stuff I'll have to look at when I have more time - definitely been too long since high school physics. :-)Somebody or his brother (talk) 01:10, 22 September 2008 (UTC)

"Only" 45 mph?! That's pretty fast. But football doesn't demand a fast throw - it has to be accurate and go a long distance and it has to anticipate where the catcher will be when it gets there - but you WANT the guy you're throwing it to to be able to catch it! The pitcher has to deceive the batter - he doesn't want him to be able to hit it - and hence speed is a key factor.

45 mph is about 66 feet per second. If you throw a ball upward at 45° at that angle, the horizontal and vertical component of its velocity will each be 66/sqrt(2) = 46.67 feet per second. For convenience say 48 ft/s. By symmetry, when the ball returns to the same distance above ground to be caught, the vertical component of its velocity will now be 48 ft/s the other way. To change speed by 48+48 = 96 ft/s under a gravitational acceleration of 32 ft/s² takes 96/32 = 3 seconds, during which the horizontal component of 48 ft/s will carry the ball 48 yards (since 1 yard = 3 feet). (Hey, look at that -- a physics calculation that isn't easier in metric!)

Now of course this calculation not only adjusts the numbers slightly for convenience, it also ignores air fraction; but I don't think the effects of air friction on a football at that speed will be all that large. And then of course a quarterback will normally throw the ball at an angle lower than 45° so that it gets to the receiver faster, and this reduces the horizontal distance it will travel -- but that fits with the fact that most passes are thrown over distances shorter than 40 yards. So for several reasons the calculation is only approximately applicable. But I think it's still sufficient to show that a speed of 45 mph is in, if I may use the expression, the right ballpark. Note also that a quarterback's typical arm motion when throwing is a lot shorter than a pitcher's, indicating that a lower speed is reached. --Anonymous, 04:02 UTC, September 23, 2008.

The difference between practice and the real game is that if your arm hurts in practice, you take a break and stick an ice-pack on it. If that happens in the game, you keep going. So injuries ought to be less serious in practice. All you need to know about kinetic energy is that E=1/2 m v². (E=energy, m=mass, v=velocity)...if you double the velocity, you QUADRUPLE the energy. The mass is not so important - and in any case, the muscle effort is not so much the effort to get the 5oz/14oz ball up to that speed - it's mostly the effort to get your hand and forearm (10lbs?) to go at that speed. Since that is a similar mass in the two sports, the mass of the ball is pretty irrelevent and the v² thing is what makes the baseball player have to push with four times the force in order to get four times the energy - and that's what injures cartilage, ligaments, bone and muscle. Having to twist the ball in weird ways as you do it probably doesn't help! SteveBaker

(talk) 02:09, 22 September 2008 (UTC)

I think Steve is right on the money here, but would lie to add a couple more thoughts. When a QB is throwing the ball, the amount of precision required is not that great; he tries to get the distance correct and aims for the general area where he's expecting the receiver to go, but there really isn't a whole lot of time to really line up the throw. A baseball pitcher, on the hand (heh) lives on his ability to aim the ball to within a few inches and he needs to try to hit that target every time. He won't, but that's what he's going for. I imagine the stress imparted on an arm that has all its muscles tightly locked would be much worse than an arm that's throwing while "loose". Matt Deres (talk) 16:53, 22 September 2008 (UTC)

"Microscopic Black Holes"

Much has been said about the possibility that the LHC may create black holes, amongst other things. When this has come up, most people refute it by saying the chance is very slim, and even if they were created, they would be microscopic and would fizzle out very quickly. Since a black hole is a singularity, or at least starts out as one, would that not mean that they are ALL microscopic to begin with?--ChokinBako (talk) 21:14, 21 September 2008 (UTC)

They usually start out as large stars, several times the size of our own, and contract down to a singularity. So it's pretty much exactly the opposite of microscopic origin. :) Arakunem^Talk 21:17, 21 September 2008 (UTC)

Well, all black holes do start out microscopic in some sense; the event horizon "forms" at one or more points inside a collapsing star and then grows. I don't know how Hawking radiation figures into it, but presumably the growth is fast enough to outweigh the evaporation. I have some misgivings about saying that, though, because event horizon dynamics is a subtle thing and Hawking radiation even more so. I think I understand event horizons classically but I don't grok Hawking radiation at all (and I'm not sure anyone does). -- BenRG (talk) 14:25, 22 September 2008 (UTC)

The singularity itself is infinitesimal (within our current framework, anyway). What people usually mean when they talk about the "size" of a black hole is the Schwarzchild radius, that is, the distance from the singularity to the event horizon. --Tango (talk) 21:32, 21 September 2008 (UTC)

Actually there's no such thing as the distance from the singularity to the event horizon of a Schwarzschild black hole—the singularity is "in the future." The Schwarzschild radius is the "reduced circumference," that is, the circumference of a great circle of the event horizon divided by 2π (or, equivalently, sqrt(A/4π) where A is the area of the event horizon). Unlike the distance to the center, this is something that one could imagine directly measuring in principle. -- BenRG (talk) 14:25, 22 September 2008 (UTC)

True, I over-simplified it. It's what the radius would be under Newtonian approximations (with the speed of light limit tacked on), in the actual GR case it's more complicated, as you say. --Tango (talk) 15:41, 22 September 2008 (UTC)

As far as I know a "standard" hole has lots and lots of mass (giving it the large event horizon due to the large gravitational field) whereas a microscopic black hole would have very little mass and thus a tiny event horizon (smaller than the gaps between atoms even) 212.219.8.231 (talk) 08:37, 22 September 2008 (UTC)

Correct. --Tango (talk) 13:25, 22 September 2008 (UTC)

Solstice/equinox dates

Why does the June solstice sometimes fall on the 21st and sometimes the 20th? Similarly why does the December solstice sometimes fall on the 21st and sometimes the 22nd? The equinoxes behave similarly. Are leap days responsible for keeping these dates consistent over the years? Why the inconsistency? Thanks. - Meersan (talk) 21:32, 21 September 2008 (UTC)

The inconsistency is because there isn't a whole number of days in a year, so the days get out of synch with the equinoxes, and leap days are needed to correct it. See leap year for more information. --Tango (talk) 21:46, 21 September 2008 (UTC)

Because of the overall drift due to the leap year cycle and the Gregorian correction cycle. The image at left shows this graphically (from the article winter solstice.) In addition, the solstice and equinox proper aren't really days, but a single instant in time. From the equinox article: "An equinox in astronomy is the moment in time (not a whole day) when the centre of the Sun can be observed to be directly above the Earth's equator." (The solstices happen at the North/South extremes of the sun's movement.) Which date this moment falls on will depend on when in the cycle you are, as well as which timezone you're in. (In one year, the solstice could fall late at night on Jun 20 for people in the US, but early in the morning of Jun 21 for people in Europe.) -- 128.104.112.147 (talk) 22:29, 21 September 2008 (UTC)

For that matter, since the world's extreme time zones (-11 in e.g. Samoa and +14 in the Line Islands of Kiribati) are 25 hours apart, the same soltice or equinox could occur on three different dates. --Anon, 02:34 UTC, September 22, 2008.

Gamma spectroscopy

The Gamma spectroscopy article does not make clear whether Gamma ray detection is accomplished by metal or ceramic (such as aluminum or a mineral) prism refraction. Assuming metal prism refraction can be used to detect various wavelengths (energies) of Gamma rays to what extent can Gamma rays be concentrated using a lens made from the working prism material? 71.100.15.15 (talk) 21:47, 21 September 2008 (UTC)

You will need a high electron density, materials like aluminium will be quite transparent to gamma rays, stuff like tungsten or lead will have a bigger impact. Graeme Bartlett (talk) 22:22, 21 September 2008 (UTC)

Neither. Gamma ray spectrometers don't use prisms. Similarly, gamma ray telescopes don't use lenses. Refraction, the physical process underlying lenses, largely does not work effectively at gamma energies. Dragons flight (talk) 22:28, 21 September 2008 (UTC)

In fact the article explains how gamma rays are detected, by Scintillation dectectors, more information here Jdrewitt (talk) 08:29, 22 September 2008 (UTC)

Exploding barrels

Is there any substance commonly stored in barrels that will explode when shot, as in many video games and movies? Mythbusters proved propane tanks (from Casino Royale) busted, but I'm curious if there's any materials that will do it in real life. Call of Duty 2 also has barrels of benzene which explode when shot, can bullets ignite a barrel of benzene as well? 67.169.56.8 (talk) 22:54, 21 September 2008 (UTC)

Very unlikely. Kinetic energy alone could never do it to benzene. Their needs to be a spark to ignite most flammable materials. I seem to remember on that Mythbusters episode, they did mention near the end that the only hope they would have would be a spark resulting from the contact with the bullet and the metal of the propane tank.--ChokinBako (talk) 00:04, 22 September 2008 (UTC)

The cause of exploding barrels in video games is lazy video game designers - not interesting chemistry. Having said that, I would imagine that Acetone peroxide, Nitroglycerin or (depending on how it's prepared) Nitrocellulose would explode if you shot them. But the trouble is that it would take some kind of maniac to use a 50 gallon barrel to store something so unstable that a good hard knock would set it off! Also, it's hard to imagine something that would explode so easily yet would produce such a tiny explosion in 50 gallon quantities. Think about it - in most games, you can safely be in the same room as the exploding barrel and suffer no harm...anything you could imagine that would actually explode would level half a block if you blew up a 50 gallon drum of the stuff! For future reference, you can measure the lazyness of game designers using the "Time to First Crate or Barrel" test - it's quite infallible. SteveBaker (talk) 00:19, 22 September 2008 (UTC)

That site makes a fair point about the contents of crates. When was the last time you saw a large crate in the real world that contained precisely *one* medikit/box of shotgun shells/whatever - and nothing else? --Kurt Shaped Box (talk) 00:46, 22 September 2008 (UTC)

Well, nowadays, I think a crate is likely to carry one piece of large, delicate equipment. The only actual wooden crates I've ever dealt with were of this purpose-built sort. Anything else would be shoved in cardboard boxes and shrink-wrapped right on the pallet. APL (talk) 02:20, 22 September 2008 (UTC)

(after ec)That's one of the things that always shatters the illusion for me in that type of game - the bad guys seem to have some sort of fetish for stockpiling drums of toxic waste/fuel in unlikely areas of their bases (instead of say, keeping them all in one place for reasons of safety and simplicity), sometimes even to the extent that they block the corridors and doorways.

That, and the way that you have to traipse all around the map looking for a key or switch to open a door, instead of being able to shoot the lock out with your shotgun (you always have a shotgun in these situations), or blow it down with a rocket. --Kurt Shaped Box (talk) 00:33, 22 September 2008 (UTC)

I think that's why there is so much interest in "open city" games these days. In the past, it was necessary to 'partition' the game into regions that were not trivial to move between in order to limit the amount of 'stuff' you had to have loaded into the console's memory - and also to ensure that the player would continuously find new areas to explore as the game progressed in order to keep it interesting. Now that game machines are fast enough and have enough memory to allow data to be streamed in from the game disk as you play - and now that we have DVD-ROM and BluRay, we can make worlds that are so large that it'll take you enough hours to explore it fully to avoid the need to 'ration' content artificially. In some cases, you still want to limit player access to some areas so that he doesn't encounter the serious challenges before he's progressed through the easier stuff...but at least now that's a design decision rather than a technological limitation.

Before that was technologically possible, game designers had to continually come up with inventive new ways to block off the entrances to certain areas until the player had progressed far enough. Hence the need to find keys, find a weapon to kill the guardian monster, find the magic word to say to open the door, collect enough stars, etc.

But crates and barrels are a failure of imagination. Just what kinds of things would there be in this improbably large enemy facility? It's tough to come up with objects that are inert enough to not need lots of programming and are cheap enough to keep polygon budgets within reason - hence crates and barrels are the last refuge of the designer who has run out of ideas and the first refuge of the ones who didn't have imagination to start with. It's not just game designers either - look at Hollywood Action movies - the "Time to first Crate" metric applies there too!

The reason they explode is that sometimes you need the player to move the crate/barrel out of the way - or to open it and take out the medikit inside - but with a limited physics engine and a really terrible interface into the game (a gamepad for example), it's hard to give the player the controls needed to do that properly. Worse still, if the player can move boxes around in a natural manner, it can be tough to design obstacles that the player can't shortcut around/over by building piles of crates and climbing over them. So you end up making the crates immovable and let him blow them up to get them out of the way or to get stuff out from inside of them.

It sucks...but that's what you get when nobody can be bothered to think of something better.

SteveBaker (talk) 01:46, 22 September 2008 (UTC)

(going off on a tangent) I'll tell you one thing that sucks more. The 'picking up this object turns out all the lights and causes several monsters to spawn right behind you and immediately attack' trick. It's usually pretty obvious when it's going to happen, it doesn't make you jump after the first time and it's basically just a cheap method of taking health points off the player so that the game appears more difficult. Doom 3 was probably the worst game I've ever played for that. --Kurt Shaped Box (talk) 02:07, 22 September 2008 (UTC)

Yes - but there has to be something that triggers surprise attacks. The player taking some arbitary action (like touching that control panel) is one - a simple timer is another - a random number generator is a third. Random numbers and timers tend to be tough to control to keep the game balanced. We don't want to let unskilled players get through the area simply by being careless and not looking around enough so they get out before the timer goes off. But the act of grabbing some article that's necessary to you to proceed is a way to ensure you're at the right point in the "story" for that attack to happen.

I kinda object to your complaint about "a cheap method of taking health points" though - I'm reminded of a quote from one of the designers I used to work with who points out that we can very easily make one bullet kill you, make the enemies fire 60 shots per second with 100% perfect accuracy, we can make them have perfect information about where you are and what weapons you have - we can make them move infinitely fast, teleport through walls, ignore gravity or any other laws of physics and we can make them immortal - we can design the level with perfect places for them to hide and no place for you to go than into the jaws of death. The only reason you survive for any amount of time in the game is because the game designer wants you to have fun.

Remember that - HE WANTS YOU TO HAVE FUN - that's his job - that's what he gets paid to do - that's what he dedicates his entire working life to doing. He may not always succeed in that - but that's his goal. He doesn't arbitarily take damage points for his own amusement - he's doing it because (rightly or wrongly) he believes you'll have more fun if he does. So, if he needs you to be challenged more in order to keep you interested in playing for longer - or to get your heart racing - or to achieve some goal that temporarily pisses you off in order that your ultimate feeling of achievement will be higher - then he has to find a way to do that. He can either provide much harder monsters - or he can take you down a notch or two by wearing you down with a bunch of lesser monsters or by not giving you enough ammunition or by not providing health packs as often as you'd like. But at least realise that he's doing that for your ultimate personal benefit. He's on your side - he wants you to finish the game - and he wants you to win...but not so easily that you race through the game in a couple of hours and feel unfulfilled. But it's really impossible to give you the "high" of passing a difficult area without giving you a "low" to contrast it against. Producing a continual stream of ever increasing "highs" is impossible. Movie makers call this "the story arc" and there a lots of learned papers on what the shape of that arc should be.

SteveBaker (talk) 03:14, 22 September 2008 (UTC)

All that said there is still a difference between a well designed game where the challenges are all organically derived from the core mechanic, premise, and story, and an irritating game where the challenges are arbitrary and random.

Basically everything you said could be restated to defend the design of any game, no matter how horrible. I'll concede that you have superior knowledge here, but unless your side of the software industry is radically different than the side I'm familiar with, won't the designer have even more important goals like, "Finish this game before we go bankrupt"? I know I've had to make compromises our software that, while the customers have every right to complain, we wouldn't have finished it if the cuts and shortcuts hadn't been made. I'm purely theorizing here, but It seems to me that if faced with a level whose difficulty was significantly lower than expected, faced with looming deadlines, a designer might decide to add in additional challenges more or less at random as opposed to giving the level the serious overhaul it needs.

(further onto a tangent) What about games where the barrels and crates are always sitting right next to the enemies so you can go through most of the game and never get into real combat. Just sneak around the corners and secret passages, killing all the baddies by sniping barrels. Quake 2 comes to mind. -- kainaw™ 02:11, 22 September 2008 (UTC)

Some players like "stealth" games - where you can sneak past enemies rather than killing them - and there is a trend to provide MULTIPLE ways to finish each section because that pleases everyone and it gives super-skilled players the additional tactical element of deciding which of those multiple ways are most appropriate to use in any given situation...that rewards skill - which is always a good thing. So it's certainly legitimate to provide ways to pass a level by sneaking around rather than just mindlessly gunning down everything in your path. The business of barrels exploding and killing people nearby is just another way to ferret out an enemy who's hiding behind cover...as a one-time trick, it's pretty neat - but if you over-use it than we're back to game designers with insufficient imagination. If you ever play the Midway game "Stranglehold" - you can deal with enemy in cover in all sorts of creative ways - shooting out the chain holding up one end of a heavy light fitting so it swings down and side-swipes him for example. Again, this is clever - but can be over-done - at which point your shoot-em-up game turns into a puzzle game where the object is to find which way the game designer wants you to kill the bad guy on THIS game level.

SteveBaker (talk) 03:15, 22 September 2008 (UTC)

As this is not the Entertainment desk, let me point out that it certainly is true that there have been massive explosions in real life due to too-large amounts of explosive substances being stored in close proximity. As I understand it, the main hazard is that the shockwave from one detonation may be sufficient to detonate the next container, resulting in what amounts to a single massive explosion of the whole lot. In the Halifax explosion, during WW1, an accidental fire set off an entire shipload of explosive chemicals (and one of them, benzol, was indeed in barrels). Warships destroyed in battle by the explosion of their own munitions have included the HMS Hood and a number of ships at the Battle of Jutland. A more recent example, involving fireworks rather than military chemicals, that I just happened to see a TV show about was the Enschede fireworks disaster in the Netherlands. --Anonymous, 02:44 UTC, September 22, 2008.

Another recent example is ammonium perchlorate, stored in barrels, going off in PEPCON disaster. --Dr Dima (talk) 05:48, 22 September 2008 (UTC)

There is no question that a barrel of something inflammable could explode if ignited correctly. Black Tom is my favorite ammunition dump explosion. Even a relatively stable substance like dried milk powder or flour or sawdust can be made to explode if you set it off just right...but the question here is whether you could set it off by shooting a barrel of the stuff with a bullet. A substance that will explode from the addition of a small amount of kinetic energy alone must be extremely unstable to start with. It has to be much less stable than (say) dynamite or any other modern high explosive. Substances that explode spontaneously if you merely hit them (like nitroglyerin) are strongly avoided by military and commercial organisations for precisely that reason. As I said before, something that unstable would not be stored in barrels and just stacked up in piles around a building! Barrels of sawdust (or dynamite) could be made to explode if something else exploded next to them - but that's a LONG way from exploding due to a simple rifle bullet hitting their barrels - which is what our OP is asking about. SteveBaker (talk) 12:02, 22 September 2008 (UTC)

I am surprised no one mentioned picric acid which was stored by the military in barrels and is shock sensitive. It was stored wet (and safer) but old dry (and more dangerous) bottles continue to turn up. Rmhermen (talk) 00:00, 23 September 2008 (UTC)

Suggestion : What about old dynamite that has 'sweat' out enough nitroglycerin to ignite the rest? Does that happen outside of the movies? And could that be set off by a bullet? APL (talk) 00:47, 23 September 2008 (UTC)

Yet another tangent : Shooting a hole in a barrel of gasoline could certainly be a dangerous thing to do. With fluid simulations getting better and better, I look forward to the day when we get games with realistic exploding barrels which don't explode immediately but instead leak some of their extremely volatile and improperly stored fuel out onto the floor where it spreads out until it reaches [some very hot thing, also improperly stored] and blows the whole thing up. That'll be great. APL (talk) 03:25, 23 September 2008 (UTC)