Wikipedia:Reference desk/Archives/Science/2007 November 27

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November 27

Lighting yourself?

Continuing the thread about fire accelerants above, would it actually be possible to light yourself on fire by drinking gasoline and then swallowing a match or something? I am certainly not contemplating doing this, but I'm just wondering. bibliomaniac15 00:34, 27 November 2007 (UTC)

No, there is no oxygen (or at least not enough) —Preceding unsigned comment added by Shniken1 (talk • contribs) 01:08, 27 November 2007 (UTC)

If it was possible, then either they would've either done it on Jackass (or similar) by now, or someone would've done it whilst trying to get on Jackass (or similar) and we'd have read about it in the papers... :) --Kurt Shaped Box (talk) 01:16, 27 November 2007 (UTC)

Or Darwin Awards. --antilived^{T | C | G} 01:28, 27 November 2007 (UTC)

Since they can make fuel from pigs and chickens I guess they could make it out of us too. Its the third way between burial and classic cremation: get cremated in an internal combustion engine. "Help your children and become a galon of petrol". Keria (talk) 11:55, 27 November 2007 (UTC)

blah blah blah

OMG i can change the internet!

Rechargeable batteries

Why do rechargeable batteries have only 1.2 volts while other batteries have 1.5V? I'm referring to the common types: AA and AAA.

And I've heard that overcharging a rechargeable battery reduces its life. Is this actually true? Why is the life shortened? --Yanwen (talk) 03:21, 27 November 2007 (UTC)

The chemicals which make up the electrodes of a battery determine the open circuit voltage it produces. Alkaline batteries or Carboin Zinc have a higher voltage in each cell than rechargeable Nicad batteries because of the chemicals used for electrodes. Lead-acid batteries are rechargeable but have a higher voltage per cell than alkaline. Overcharging a battery is a bad idea because it can cause it to heat up and can cause the electrolyte to evaporate. Edison (talk) 03:37, 27 November 2007 (UTC)

You may also be interested in our article about nickel-cadmium batteries (i.e. rechargeable batteries). ›mysid (☎∆) 05:50, 27 November 2007 (UTC)

Overcharging can reduce the life of a rechargeable battery by driving water out of the cell, either directly as water vapor or as hydrogen and oxygen gases resulting from the electrolysis of the water within the cell. Most batteries contain a "recombination catalyst" that will burn small amounts of evolved hydrogen and oxygen back into water but serious overcharging will overcome the ability of the catalyst to cope with evolving gases.

Atlant (talk) 13:14, 27 November 2007 (UTC)

Actually, it depends on what kind of battery chemistry is being used - some of the rechargables have 1.3v, 1.4v or 1.5v. I used to mess around in the Lego robotics community - and the Lego computer runs off of 6 AA's to get 9v total - if you used NiCd rechargeables, you only got 7.2v and the computer couldn't run on so little. Since these things chewed through a set of disposable batteries in a couple of hours it was an expensive hobby. However, rechargeable Lithium batteries produced something like 1.4v and that was enough to run the computer. The subtleties of recharging them also depends on the chemistry of the battery. Some can be overcharged and need special rechargers that detect the fact that the battery is full and turn off - some cannot. Some batteries NEED to be fully discharged before you recharge them (NiCd's, certainly), others need to be kept fully charged as much as possible (Lead-Acid batteries like in your car), others don't care. With the wild profusion of battery types out there, you need to be careful that the 'rules' you are following are the right ones! SteveBaker (talk) 16:45, 27 November 2007 (UTC)

Endosteum: soft tissue?

Would the endostuem be considered, technically speaking, a soft tissue? Thanks. 75.42.209.73 (talk) 03:22, 27 November 2007 (UTC)

Yes. Its bascically mesenchymal cells in a collagen matrix that lines the cortical bone at the corticomedullary junction in long bones. Its function is to conduct nutrient blood vessels to the medullary surface of the cortical bone, and also contains undifferentiated osteoprogenitor cells that are recruited in Bone_healing. The article on endosteum is a bit light on detail, but you may find it helpful. Mattopaedia (talk) 13:05, 27 November 2007 (UTC)

Okay thanks that's what I thought! 75.42.209.73 (talk) 17:50, 27 November 2007 (UTC)

Cats, the hunting instinct, and feline psychology

My domestic cat brought a number of live mice into my home and I started putting the ones I rescued into a habitat so the cat would have mice around without letting them loose in the house. Now she spends a lot of time watching the mice, actually strongly resembling a human sitting in front of a television. (Feline reality TV! She's even gained weight with her new couch-potato lifestyle!) My question: Is the presence of mice giving the cat hours of lively entertainment, or is it horribly cruel to expose her to mice that she will never be able to catch? Thanks for any insight. Peter Grey (talk) 08:30, 27 November 2007 (UTC)

Kudos to you for not knocking the mice on the head or necking them when the cat brought them in - but is it really fair on/healthy for them in terms of stress to be placed on constant display in front of a fearsome (to them) predator many times their own size? --Kurt Shaped Box (talk) 08:42, 27 November 2007 (UTC)

I have heard (paraphrasing somewhat) that, while for a human being stalked by a carnivorous predator a hundred times their size would probably lead to post-traumatic stress disorder or worse, for animals like mice it would just be an average day. Plus I'm guessing a habitat with unlimited food, even with a cat nearby, is still preferable to being mauled to death. Peter Grey (talk) 12:17, 27 November 2007 (UTC)

If your cat was bringing in live mice for you and has stopped, she might be waiting for you to eat them or give one to her. If she's not desperately trying to open or get into the habitat, then she's probably not stressed about it. If she's stressed, she'll let you know (with piercing whines, for one). The mice may very well be under stress, but likely then they wouldn't be eating or drinking (I had a cat who had to live with a big dog for a couple months. She lost a lot of weight because she would only eat when the dog wasn't around, i.e. taken on walks). SamuelRiv (talk) 12:52, 27 November 2007 (UTC)

Still, it couldn't hurt to stick the mouse cage up on a shelf, table or something. You don't want a mess on the floor/massacre when the cat finally gets hungry, do you? --Kurt Shaped Box (talk) 17:25, 27 November 2007 (UTC)

Mice are hard-wired to feel fear when they smell cats, so it's possible that the mice in the habitat are suffereing from constant fear, unless they happen to be the genetically altered mice with no fear of cats. -- JSBillings 13:32, 27 November 2007 (UTC)

Don't worry about the cat. Cats are evil. They were created by Satan in mockery of the blessed Dog, who can be trained not to defecate in your house. Proofs of the cat's malignancy abound: cat scratch fever, fur balls, spraying, the infernal yowling when they copulate, that murderer's blank stare. They are often found in the company of witches, where their true nature as a mere receptacle for an otherwise incorporeal demon is revealed. Your "cat" will be content to gloat over your captive rodents and revel in their delicious terror at his presence. --Milkbreath (talk) 14:00, 27 November 2007 (UTC)

And a bunch of Animal lovers is hampering the efforts of Italians to rid the world of evil. Keria (talk) 16:20, 27 November 2007 (UTC)

Hence I don't want to inadvertently annoy my evil housemate. Peter Grey (talk) 17:12, 27 November 2007 (UTC)

That's why I prefer gulls to cats - gulls have honesty. Compare your average Herring Gull to your average HouseCat. The gull is every bit as loud, aggressive, raucous and cold-hearted as the cat (and - to bring up an old running joke, could probably equal it in a vs. battle) - but it never pretends to be anything different. --Kurt Shaped Box (talk) 17:54, 27 November 2007 (UTC)

You've never fed a gull? They can be very good at begging and acting nice if they learn it gets them fed. I remember one year my mother leaving out fish (leftovers from our cats — how's that for a tie-in?) for a young herring gull that had fallen out of its nest. For the rest of the year, until the weather got cold and the gulls flew south, we basically had a semi-tame pet gull. He (or she) learned to recognize my mom by sight, and would wait on the rooftops among the other gulls for her to come out. Then, if no other people or gulls were in sight, he'd glide down and land some distance away, all very quiet, and then walk up to my mom and stand there looking at her and giving her the "puppy eyes". Probably would've let us pet him if we'd wanted to. He may not have been physically as cute and cuddly as a cat, but he was most definitely on his best behavior towards my mother, even despite our efforts to convince him that there were other, more appropriate food sources for a gull. —Ilmari Karonen (talk) 19:13, 27 November 2007 (UTC)

I'd heard that cats watch you and decide that somehow you never seem to catch any mice. This elicits a behavior similar to how they train their kittens to hunt. They catch a mouse - deliberately not killing it and bring it to you so you can practice on it. If you don't succeed with live mice, they'll bring you ones they've wounded to slow them down so you'll have a chance to get some practice in. If all else fails, it's on to dead mice. If you pick up the dead mouse and chuck it out somewhere, the cat figures you've finally gotten the idea - so it's back to live and wounded ones. Yeah - dogs rule. They may be stupid - but at least they know it. They don't pretend to be smart like cats do. SteveBaker (talk) 18:46, 27 November 2007 (UTC)

So what does it say when my neighbor's cat decided to show up at my doorstep with half a mouse? (It was the back half, for what its worth.) Dragons flight (talk) 18:56, 27 November 2007 (UTC)

I'd guess it's either "here, I've saved the best part for you" or "here, I ate the best part, you can have the rest if you like", but, without firsthand knowledge of that particular cat's idiosyncratic dietary preferences, I can't really tell which. Or perhaps she was just halfway through her meal and taking a short break when you interrupted her. —Ilmari Karonen (talk) 19:19, 27 November 2007 (UTC)

I don't think it was accidental. A) My doorstep is not really a normal place for her to visit and B) She seemed very enthusiastic about delivering the half a mouse to me. Dragons flight (talk) 19:23, 27 November 2007 (UTC)

I think this cat has gotten to the point where it suspects you are an especially slow learner and you aren't really ready for an ENTIRE dead mouse - so perhaps you'd better start with a half of one and work your way up. SteveBaker (talk) 22:11, 27 November 2007 (UTC)

There seem to be different schools of thought on this behaviour, essentially coming down to a) the mouse is for the human and b) the mouse is for the cat, she just wants to get away from other cats while she toys with it. In this case, she isn't bringing me the mice - I've had to fight her for them. Peter Grey (talk) 07:40, 28 November 2007 (UTC)

There probably isn't a lot of research in this area. I'd guess that, as long as your cat is well fed, having a habitat for mice that the cat can watch is probably no more cruel than giving the cat toys that it can't eat. In other words, it's probably not a problem. I often see people trying to anthropomorphize animals by attributing human-like thinking to them, but they don't try to see if their hypothesis is correct or think about simpler explanations that would produce the same behavior. Don't overthink things. If your cat looks entertained, then it's probably entertained. If it looks stressed, then it's probably stressed. However, as long as your cat isn't starving, threatened, sick, injured, lacking sleep, or too hot/cold/wet/dirty, then it probably isn't under much stress. -- HiEv 20:33, 27 November 2007 (UTC)

The mice, on the other hand...may be nervous. SteveBaker (talk) 22:11, 27 November 2007 (UTC)

Who can say? Mice always look a little twitchy to me. And, for the dog lovers/cat haters who seem to have used this question as a dumping ground for their vile hatred towards nature's most perfect animal, I can only say this: Yes, a cat might shit inside your house, but even it, in contrast to a dog, is smart not to EAT cat shit. For all the tricks they can learn, even the smartest dog has struck me as being no smarter than a bug. Matt Deres (talk) 02:34, 28 November 2007 (UTC)

Besides that, my cat, indeed all cats I've ever owned have never shit inside my house at least not for long instead they do it outside and don't leave it all over the place for you to step on like dogs do... Nil Einne 12:00, 3 December 2007 (UTC)

This seems to be the right answer - I get to ask a vet and it's roughly the response I got. Peter Grey 23:48, 30 November 2007 (UTC)

acting out of character

Does anyone know in how many cases where someone has started acting selfish, self-centered and strange have refused to cooperate even with the police that something has gone wring with them physically internally. I am not refereeing to the brain purse but rather to things like some form of body cancer that has finally reached the stage that it is noticeably to the individual interfering with body functions or weakening the individual to the point of representing a clear threat of death where the individual does not know the cause but only that their life is threatened and at risk unless they do something even to the point of causing a public disturbance while refusing to cooperate in any way? The second part of my question is if the police were aware of this possibility - a feeling on the part of individual of a life threatening situation, the cause to them unknown, would the police act less violently toward the individual, especially to the extent of causing the individuals death? 71.100.0.58 (talk) 08:37, 27 November 2007 (UTC)

Hypochondria? Munchausen syndrome? ›mysid (☎∆) 12:26, 27 November 2007 (UTC)

We can't give professional advice. Seek medical help. --Sean 14:59, 27 November 2007 (UTC)

You are on an, "Every question someone asks that a doctor could answer is a request for medical advice." kick. If you are going to work the science desk I suggest you get off this kick. 71.100.0.196 (talk) 23:43, 27 November 2007 (UTC)

This topic was in the Canadian news yesterday [1], although specific to mental disorders. Conditions such as hypoglycemia and electrolyte imbalances (which themselves could be as a result of pancreatic beta-cell cancer or any variation of renal diseases, respectively) could cause changes in mental status. (EhJJ) 16:10, 27 November 2007 (UTC)

The second part of this question assumes that police normally act in a violent deadly manner because it asks if the normal violent deadly action would be changed. What is the basis for assuming that police normally act in a violent deadly manner? -- kainaw™ 16:13, 27 November 2007 (UTC)

Normally the police try to match, if not exceed, any potential level of violence with which they feel they may be faced. In the US it is common for the police to aim their weapons for their own protection on mere suspicion or "just in case" their subject has a gun.

If the police tailor their actions to match the situation exactly and the situation is as described above then the police will escalate their reaction to be greater than the subject can overcome - including choke holds, placing too much weight on the subject's chest, tazerring the subject for too long or at too high a current setting, or not calling for medical help if the subject stops breathing or begins turning purple - all on their own assessment of being necessary to do their job and to protect their own lives while the subject may have been resisting at a level he felt necessary due to his own internal conditions to protect his life.

You Tube has a video example of this happening to an individual in an airport resulting in the individuals death by tazer. 71.100.0.196 (talk) 23:43, 27 November 2007 (UTC)

The most common cause for people to act out of character is mental illness, particularly bipolar affective disorder and other schizoaffective disorders. There are other causes as well, such as electrolyte disturbances, some cancers (this is rare though), and drugs. The other thing that often happens in these circumstances is the person loses insight, and so may not necessarily be aware of a need t o act in a certain way, or feel there is anything wrong with their behaviour. They may believe there is some threat to their life, but this may not be factual. As for the police, although IANAcop, I would expect them to only use reasonable force to preserve their own safety and the safety of any bystanders. It is a sad thing, but some people who are mentally ill do end up severely injured or dead as a result of an altercation during an acute phase of their illness, but suicide in the mentally ill is certainly a far bigger problem. It must be devastating for police officers to find they'd injured of killed a person whose actions were driven by mental illness. But that risk ultimately is a part of their job, which is a good reason to treat them with the utmost of respect, rather than criticising them for doing their job. Mattopaedia (talk) 05:38, 28 November 2007 (UTC)

I'm suggesting more in terms of life threatening illness generated paranoia (only it's not paranoia, but real) to the extent of causing total lack of cooperation and in fact opposition to anyone or anything versus the suicide-by-police due to mental illness syndrome. 71.100.0.196 (talk) 11:40, 28 November 2007 (UTC)

Building services

what are the environmental impact of the use and abuse of building services? —Preceding unsigned comment added by 81.199.59.84 (talk) 15:10, 27 November 2007 (UTC)

We don't normally do homework. Is this a homework question?

Atlant (talk) 16:44, 27 November 2007 (UTC)

This is a quite wide-ranging question that does sound like a homework essay so I am not going to give you anything more than a few bullet points to get you started:

Energy use (therefore carbon emissions) is the primary environmental cause for concern from building services

Heating, ventilation and air conditioning (HVAC) services are the primary use of energy in buildings. Natural ventilation is far better from an environmental perspective than mechanical ventilation. The fuel used for heating is also a consideration, generally coal is worse than oil which is worse than gas. Consider forms of renewable energy such as using photovoltaic panels to heat water, wind turbines or geothermal ground pumps. Combined Heat & Power also helps as it is more efficient than using fuel solely to produce heat.

Lighting is also a big user of energy. Natural lighting should be maximised in buildings where possible and energy efficient light fittings are preferred.

Refrigeration systems, for example cooling in air conditioning often contain gases that can contribute significantly to climate change. While CFCs (a major contributor to the depletion of the [[[ozone layer]]) have been all but phased out, their replacements are not perfect. Refrigerant gases should be treated with care and not allowed to escape to the air. Care must be taken when disposing of redundant refrigeration equipment, particularly older stuff.

Old electrical transformers contain Poly Chlorinated Biphenyls which are a major carcinogen.

Many older buildings (generally prior to the 1980s) may contain asbestos, particularly in heating plant and insulation to pipes.

Older heating systems often utilised underground oil storage tanks and these have a significant chance of leaking into the ground. Newer storage tanks for oil must be bunded, that is located in an enclosure that can trap the contents if the tank leaks.

Water usage is also key. Some cooling systems such as cooling towers can use a large amount of water.

Also consider wastewater disposal. It is better to have separate drains for foul and surface water as surface water can generally be returnerd straight to rivers while foul water has to be trated, which used energy. Where surface water is drained from car parks or roads, oil interceptors should be used to ensure water is not contaminated.

This is only scratching the surface but hopefully it will inspire you to come up with some more ideas. Let me know if you have any specific questions. GaryReggae (talk) 22:53, 27 November 2007 (UTC)

Gadget Show phone comparison

Last night's Gadget Show featured a comparison of three multimedia phones. To compare the music capabilities of the devices, identical MP3 files were loaded onto the phones, then each phone was connected in turn to a sound desk in a music studio and the track was played through the studio's speakers. Since the link between the phones and the sound desk was presumably digital, I expected there to be no difference at all in the quality of the playback - it seemed it should be just like plugging three different makes of USB flash drive into your laptop. Indeed, I failed to see what the point of the test was. Yet the testers claimed to notice differences in the quality of the sound depending on which phone the track was "played" on. What am I missing here ? Gandalf61 (talk) —Preceding comment was added at 15:12, 27 November 2007 (UTC)

Why do you presume that the connection from the phone to the sound deck was digital? My guess would be that it was analog, but I did not see the show. -- Coneslayer (talk) 15:27, 27 November 2007 (UTC)

Good point. Because they were using a fancy sound desk, I assumed that the connection would be something more sophisticated than a 3.5mm jack plug - but if was just an analogue link, the whole test makes a lot more sense. Gandalf61 (talk) 13:38, 28 November 2007 (UTC)

The available output of the phone would be the limiting factor; they could have had the super-whiz-bangiest desk in the universe, but I'd be surprised to find a mobile phone with a digital output. --LarryMac | Talk 20:12, 28 November 2007 (UTC)

Why do amps kill you, but volts don't?

Like when being hit with an electroshock weapon. Why is it that a large number of amps can kill you, but a large amount of volts do not? 64.236.121.129 (talk) 15:56, 27 November 2007 (UTC)

I usually simplify electrical stuff to water and plumbing. I feel this helps people understand it - even though it is not a perfect analogy. Voltage is roughly equivalent to water pressure while amperage is roughly equivalent to the amount of water that is flowing. I can take a squirt gun and hit you with high pressure water, but not hurt you at all because there is very little water flowing. Alternately, I can hit you with 500 gallons of water at very low pressure and you'd definitely feel it. So, you can see that water pressure can be felt, but it is the quantity of water that is required to cause damage. Similarly, high voltage can be felt, but is high current that kills. -- kainaw™ 16:08, 27 November 2007 (UTC)

Regarding the analogy you and others have used: I know you admitted the analogy is not perfect, but I should point out that small streams of very high pressure water can cut through titanium. See the water jet cutter article. Can very high voltage with low amperage do damage in the same way? -- HiEv 20:56, 27 November 2007 (UTC)

That's more or less the kind of explanation I was going to attempt. All I can think of to add is that we have articles on electric current and voltage which also explain the difference, altho not necessarily specifically in the context of injuries they cause. Oh, it looks like Electric_shock is the article most relevant. Friday (talk) 16:11, 27 November 2007 (UTC)

Yes - the electric shock article also covers what kind of physical damage high electrical current can cause - which I didn't mention in any way. -- kainaw™ 16:15, 27 November 2007 (UTC)

(Darn - beaten to it by an edit conflict!)

The Hydraulic analogy often helps here: Voltage is like the pressure of the water, Amps (current) is like the amount of water flowing. Ohms (resistance) has to do with the diameter of the hole or pipe through which the water is flowing (small pipe - lots of resistance, big pipe - less resistance). Ohms law says V=IxR (V=Voltage volts, I=Current in amps, R=Resistance in ohms). In water-analogy terms, more pressure (voltage) comes about when there is a lot of resistance to the flow or when a lot of water is flowing.

When a pipe bursts, it's the volume of water that causes the damage to your basement (When you touch the bare wire it's the Amps that kill you). But even if the pressure in the pipe is huge - if it's squirting out through a tiny pinhole - it doesn't bother you much because not much water comes out. (If the voltage is high, then so long as the resistance is high, you don't get many amps). But if the pressure in the pipe is high and there is a HUGE hole (so not much resistance), then lots of water is going to flow and you're in trouble. (If the voltage is high and the resistance is low then the current is high and you're in trouble). So voltage does matter. The other part of the analogy is that if whatever is pumping the water has a limited capacity - so even if there is a big hole in your water pipe, if there isn't much pressure then not much water ends up in your basement (So if the power supply is a little 1.5v AAA battery, then even if the resistance is low, not much current will flow and you'll be OK).

The pressure of water can be high (like inside a coke can that you just shook up), and the resistance can be low (like you suddenly pulled the tab on the can) but because there is only 8 ounces of liquid in there - the resulting high current won't flow for very long. This is like one of those static electricity demonstrations where there is a million volts (lots of pressure!) built up in a nice shiney dome - and as you touch it, a spark ionises the air (making a low resistance path) and you get a very short, sharp 'zap' of current - then it's all discharged (the coke can is now empty).

SteveBaker (talk) 16:19, 27 November 2007 (UTC)

I see, thank you. How do Watts fit in? Is there a water analogy for it too? 64.236.121.129 (talk) 16:38, 27 November 2007 (UTC)

Watts represent power, so there are still water analogies. A huge river (high current) can be flowing by you at quite a low pressure (voltage) yet still represent a large amount of mechanical power. A fire nozzle or water cannon, spraying a relatively small volume of water (low current) but at very high pressure (high voltage) can also represent a large amount of mechanical power. But a very large volume of water that's just sitting there with no pressure (zero volts) isn't doing any work (right now) nor is a tank of water at very high pressure with no outlet (zero current).

Atlant (talk) 16:48, 27 November 2007 (UTC)

(edit conflict) "Voltage" is nothing. It is "potential difference", that's all. Nothing happens. Some electrons over there want to get over here, and how bad they want to is what we call voltage. It's when the electrons actually move that the party begins. That's current. Current generates heat and disrupts the body's electical stuff, the heart's most importantly because that can kill you quick.

It does seem counterintuitive that 5,000 volts can leave you unharmed and 300 volts can kill you, but the truth is that the harmless kind of 5,000 volts is not really 5,000 volts at all. A power supply, be it a circuit or transformer or battery, can only provide so much current all at once, not infinite current. As soon as you exceed its capacity, its voltage goes down. A supply rated at 5,000 volts at one milliamp will only stay at 5,000 volts if you draw one milliamp or less, and will fall in voltage as necessary to maintain that maximum level of current if you try to draw more. Or smoke, pop, and melt. Or blow the fuse. On the other hand, if you get across 5,000 volts from one of those power company transformers that looks like a refrigerator, we're talking closed casket.

Another thing to bear in mind is that the human body has a fixed resistance, and that will dictate the maximum current that can be drawn at a given voltage. This means that no matter how many 12-volt batteries you strap together in parallel, they can't hurt you if you get across them with your hands, even if their current capacity is a zillion amps. At the body's 50,000 ohms, you get 240 microamps, period. With dry hands, one hand on each pole, it takes about 300 volts at 100+ milliamps to have a good chance of stopping your clock. Wet hands or something like taser darts bring the lethal voltage way down, because the resistance is less and the lethal current of about 100 milliamps can be more easily produced. So in this respect you can say that it is the voltage that kills you.

When I said that "nothing happens" with voltage, that was for voltages we're likely to encounter in our everyday lives. Something like lightning is a bit different. Electrical current creates a field in its vicinity (you can feel the effects of a field by holding a hairy arm near the front of a TV screen). If the field is strong enough and sudden enough it will make the electrons in your body move violently all by itself. People get knocked out or even killed by near misses of lightning all the time. --Milkbreath (talk) 17:00, 27 November 2007 (UTC)

So if you dump water or salt water on someone, it will decrease his electrical resistance, and thus increase the amount of amps he recieves? Even if he is shot by the same exact electroshock weapon? 64.236.121.129 (talk) 17:37, 27 November 2007 (UTC)

Yes. Of course, if it's the kind that sticks barbs into your flesh, it won't matter how wet or dry you are. But the cattle-prod kind will be more effective on a salt-water soaked suspect because that will negate the insulating effect of any clothing in the way. Bear in mind that these weapons are pulsed, that is, they provide current in many very, very quick bursts, which is a different ball game from a constant current. We can take a lot more current in little doses. Also, the current mostly runs between the contacts, and so doesn't get to the heart or brain so much, meaning that such weapons can run a higher voltage than a person could take right across the chest. --Milkbreath (talk) 17:56, 27 November 2007 (UTC)

What if it's an electrolaser? 64.236.121.129 (talk) 18:58, 27 November 2007 (UTC)

Then it's insult to injury. Once the holes are burned clean through you, you'll welcome the anaesthetizing effects of the electricity. --Milkbreath (talk) 19:29, 27 November 2007 (UTC)

Big Idea of Particles, Mass Conservation

Hi im afraid that i have three q.that i would like to ask. I would firstly like to know, what is the big idea of particles? I h ave searched in books and on the internet and i have so far found nothing that can help me. I would also like to know as to how mass is conserved in a reaction between an antacid tablet and the hydrochloric acid in ones' stomach. I would finally also like to know about a particle diagram.

Thank you for your help in advance.

P.S. Please try to explain this in simple terms.

I believe mass is conserved as long as it is converted into another form. Either another form of matter, or into energy. 64.236.121.129 (talk) 16:42, 27 November 2007 (UTC)

That's a pretty general question. What do you mean by particle--are you asking about the physics concept of subatomic particles, or about something else? Also, mass is not conserved--conservation of mass is a historical theory which, like Newton's physics, is close enough in most situations. In the same way that Newtonian physics start to fail obviously at high velocities and tiny scales, mass becomes very obviously not conserved in nuclear reactions. What is conserved is energy; a bit of mass is converted into energy, released as heat and light. What you're talking about seems to be stoichiometry--does that article help at all? And can you provide an example of what you mean by a "particle diagram"? grendel|khan 17:18, 27 November 2007 (UTC)

Let's be careful not to confuse the OP with teeny-tiny details here. Mass IS conserved to a truly spectacular degree of precision through almost all 'everyday' events. Utterly, vanishingly tiny amounts of mass are interchanged with energy in rather obscure ways relating to relativity and other stuff - but if we are talking about normal, mundane, day-to-day stuff like antacid pills in your stomach - then it's accurate to say that mass is conserved. This is a valuable principle that one should not toss out in ones zeal to be modern and utterly correct. In a chemical reaction - whatever atoms you started with are the atoms you have left at the end. None appear from nowhere or vanish abruptly...unless you are looking inside a particle accellerator or a nuclear weapon or something much more bizarre. As far as 'classical' physics and chemistry is concerned, mass is conserved. SteveBaker (talk) 18:26, 27 November 2007 (UTC)

When antacid is mixed with acid, you get a chemical reaction that produces some salt, some water and maybe some carbon dioxide or something - but no mass is lost. The mass of the antacid plus the mass of the acid is PRECISELY equal to the total mass of the byproducts you are left with at the end. The atoms that were present in the antacid and the acid merely rearranged themselves. Sodium bicarbonate (a common antacid) is NaHCO3 which means that each molecule contains one sodium atom (Na), one hydrogen (H), one carbon (C) and three oxygen (O). The acid in your stomach is hydrochloric acid (HCl) with one hydrogen (H) and one chlorine (Cl) atom. When an HCl molecule meets an NaHCO3, you get CO2 + H2O + NaCl - which is Carbon dioxide, water and common table salt. No more acid, no more antacid - just salty water and a small (but hopefully polite) <burp>! But at the end, you still have one sodium, two hydrogens, one carbon, three oxygen and one chlorine atom...they just rearranged themselves. Nothing was lost or gained in the process. SteveBaker (talk) 18:17, 27 November 2007 (UTC)

If you take a sealed, air tight, container and put acid and antacid (a base) in it but not mixed, and weigh it, then mix them and allow them to react and then weight them again, the weights will be the same. That is concervation of mass. It's all still there just rearranged. (Note: this assumes the containter doesn't explode or something because of gas pressure, that could be dangerous). RJFJR (talk) 19:08, 27 November 2007 (UTC)

Inability to Scream

Is there a medical term for someone who has the inability to scream? I am not referring to any dreams nor any type of sleep or awakenings. --WonderFran (talk) 17:42, 27 November 2007 (UTC)

That seems like a rather unlikely condition - can this person talk? Talk loudly? Shout? Shout loudly and incoherently? Shout "Aaaaaaarrrrggghhhhhhh" with steadily increasing pitch? 'Cos if so, they are screaming. It's hard to imagine any kind of condition that would strike selectively at one part of that process. SteveBaker (talk) 18:08, 27 November 2007 (UTC)

Spasmodic dysphonia can inhibit certain vocalizations while not affecting others. As I recall, Scott Adams was able to give prepared speeches, yet unable to speak conversationally. I don't know about an inability to scream, specifically. -- Coneslayer (talk) 18:20, 27 November 2007 (UTC)

Actually, it is me. I have no problem speaking in normal tones. I am in a girl in my late 20's but I have an unusually high pitch, soft voice. My mother had the same thing, too. The problem is that no matter what I try to do, I cannot sound my age. When I speak, people assume that I am much younger or dim witted and it's hard for me to get respect. My dentist had mentioned that the roof of my mouth was unusual but I don't know if that affects it. All my life, I cannot scream at all. It's wierd. I remember my teachers in elementary school trying to get me to scream for a school play and I couldn't. I tried to scream lot's of times, even tried to scream into a pillow and I cannot scream at all. It almost sounds like I am exhaling really loud. --WonderFran (talk) 18:24, 27 November 2007 (UTC)

This seems as though it would be general dysphonia, not spasmodic. There is no ICD9 or ICD10 code for an inability to scream. It is classified as dysphonia-unspecified. As a rule, we do not diagnose your specific problem or offer treatment. Dysphonia is merely the medical term for a voice disorder - not a diagnoses of the reason for the disorder. If you are concerned about this, seek advice from a medical professional. -- kainaw™ 18:32, 27 November 2007 (UTC)

Correction - I have just been told by an ENT surgeon that it is adductor spasmodic dysphonia and that it is not very rare. -- kainaw™ 18:36, 27 November 2007 (UTC)

Argh! You blew it. Now we know it's you - this is a medical diagnosis question and we aren't allowed to answer it. If it bothers you - see a doctor. But - did you ever wonder: perhaps your 'exhaling really loud' is sound so high in pitch that you can't hear it? SteveBaker (talk) 18:37, 27 November 2007 (UTC)

How long do you think it will take for someone to delete this whole thread even though no diagnoses were given? -- kainaw™ 18:42, 27 November 2007 (UTC)

You guys are funny! I was looking for a medical term, not a medical help. The only reason why I gave more info was because I wanted to give Steve Baker a better unerstanding of what I was referring to. --WonderFran (talk) 18:49, 27 November 2007 (UTC)

Well, I'm still curious. So indulge me - let me ask some questions - without diagnosing anything. You can shout - right? Can you shout the word "Aaaaaaarrrrrggggggggghhhhhhh!"? If not, what words can you shout? But if so, can you just gradually increase the pitch and volume of your voice? If so, then at this point, I think we have what I would call a scream - but if you can't do that then at some curious point in this process, there was something you were unable to do - some kind of threshold. I can't get my head around where that point is exactly. SteveBaker (talk) 22:03, 27 November 2007 (UTC)

This is a touchy subject because some editors are far too sensitive to the whole "medical advice" issue and some are happy to hand out medical advice without any expertise in the area at all. Everyone else is stuck in the middle between some editors blanking threads and others diagnosing and prescribing treatment. -- kainawBPG7WY 18:52, 27 November 2007 (UTC)

Seriously, she's just asking for a term. Don't be a rules nazi. 64.236.121.129 (talk) 21:17, 27 November 2007 (UTC)

Stop gratuitously insulting people (or is "Nazi" a term of endearment to you?). Kainaw was speculating that other people would think she had violated the rules, and would therefore delete this thread. Seeing as how Kainaw provided a very useful response, it is clear that he or she does not personally believe that a rules violation occurred. -- Coneslayer (talk) 21:57, 27 November 2007 (UTC)

Voice Immodulation Syndrome? :) shoy (^words _words) 23:41, 27 November 2007 (UTC)

Make sure you dont have The Tingler inside you! [2] ARRRRGGHHH! —Preceding unsigned comment added by TreeSmiler (talk • contribs) 02:48, 28 November 2007 (UTC)

By asking for a diagnosis, how can this question be anything but asking for medical advice? 199.76.152.229 (talk) 04:41, 28 November 2007 (UTC)

It is far too common for editors here to have a complete misunderstanding of what a "diagnosis" is. This person asked for the medical term for a physical property. This is no different than asking for the medical term for an ear ache or the medical term for a broken toe. It is not a diagnosis. If, however, she said she couldn't scream and asked what was causing it, it would be a request for a diagnosis. Of course, a person can present a diagnosis without asking for one. She could have said that she was in a car accident and asked if that could lead to an inability to scream. Again, it is not a request for a diagnosis, it is a question about the possibility of one event causing another - similar to asking if I can get liver damage from drinking too much alcohol. I hope that it will be possible for editors to eventually understand what is and what is not a diagnosis. -- kainaw™ 13:08, 28 November 2007 (UTC)

This is just to answer Steve Baker's question. I can shout but not that loud and sometimes it feels very straining to do so. Butwhat came to mind that men in general do not have the ability to do a high pitch scream like some women can, especially in horror films. I don't know if this helps, but I also have a horrible singing voice. Its sounds like cats drowning or mating or something.... :) --WonderFran (talk) 17:45, 28 November 2007 (UTC)

That didn't stop Yoko Ono from singing (sorry - couldn't help it). If you believe that this is purely physical and you have no health problems, you could work with a voice coach. They specifically handle this sort of problem. -- kainaw™ 18:56, 28 November 2007 (UTC)

Can both of you have your discussion about the Desk's policies on the talk page, and leave the Desk for answering questions? TenOfAllTrades(talk) 19:45, 28 November 2007 (UTC)

I wouldn't be sure that most woman can scream in a high pitch just because they seem to do in horror movies. It might be just a pre-recorded effect by some other actrees, like the Wilhelm scream. – b_jonas 16:23, 29 November 2007 (UTC)

What happened to the Michael Pursinger page?

Awhile ago Wikipedia had an excellent page on Dr. Michael Pursinger, a scientist who researches how electromagnetic fields affect the human brain. I'd like to know why this page was taken off Wikipedia; Dr. Pursinger's work is at the cutting edge of psychological research and so it definitely merits to be put back online. ````M.P.

Michael Pursinger does not seem to have been deleted. Is it spelled correctly? RJFJR (talk) 19:01, 27 November 2007 (UTC)

Michael Persinger? Dragons flight (talk) 19:03, 27 November 2007 (UTC)

Thanks a million! I've seen his name spelled differently on other websites (namely the CBC's) that's what was throwing me off... best 216.123.137.85 (talk) 20:00, 27 November 2007 (UTC)M.P.

What was the other spelling? Perhaps we need a redirect. Graeme Bartlett (talk) 02:38, 28 November 2007 (UTC)

We did need one, and we got one, which is why the two links are now both blue. -- 02:41, 28 November 2007 (UTC)

Accessory cell (immunology)

What is an accessory cell (in immunology)? --Seans Potato Business 19:18, 27 November 2007 (UTC)

My medical dictionary says: SYN antigen-presenting cell. (EhJJ) 20:16, 27 November 2007 (UTC)

That's what I had gleaned from other sources too. If anyone knows otherwise, they should go to the antigen presenting cell page and remove the addition I made (and also delete or rewrite the redirect). --Seans Potato Business 20:54, 27 November 2007 (UTC)

Liquidfy Diamonds? Solidify oxygen?

Is it ever possible, in our universe somehwere, to liquidy diamonds? Or to solidfy oxygen? --WonderFran (talk) 21:05, 27 November 2007 (UTC)

Diamond is an allotrope of carbon. Presumably, carbon can be liquid, but if it's liquid, it's not diamond anymore. Oxygen presumably has a freezing point, but I don't see it given in the article. - whoops, it's there, under "melting point". Friday (talk) 21:16, 27 November 2007 (UTC)

To rephrase on the point above (in simpler terminology), the name Diamond specifies a how the carbons are bonded together. So by definition, diamond must be solid. Someguy1221 (talk) 02:59, 28 November 2007 (UTC)

According to our article, carbon has a melting point that's higher than it's boiling point - so the only way to get it to liquify would be under huge pressures (it says 10 megapascals in the infobox). Normally, it'll presumably sublimate - which is to say go straight from a solid to a gas (imagine how 'dry ice' (solid CO2) turns into CO2 gas without ever becoming a liquid...that kind of thing). I don't think it matters whether it's diamond, graphite, amorphous or buckyball carbon. "Somewhere in the universe" could mean deep in the heart of a planet - with ridiculous temperatures and pressures - so probably there is liquid carbon somewhere. SteveBaker (talk) 21:50, 27 November 2007 (UTC)

Certainly going from the sublime to the ridiculous there Steve! —Preceding unsigned comment added by TreeSmiler (talk • contribs) 02:40, 28 November 2007 (UTC)

I remember answering a somewhat similar question on Usenet once... ah, here it is: "Boiling diamonds?" (The first link in the message is broken; the article it's supposed to go to, IIRC, is this one, but unfortunately the full text there is subscription-only. You could just Google for "phase diagram of carbon" instead.) —Ilmari Karonen (talk) 18:45, 28 November 2007 (UTC)

Or just see this article (Ghiringhelli et al., "Modeling the Phase Diagram of Carbon", Physical Review Letters 94, 2005). —Ilmari Karonen (talk) 18:52, 28 November 2007 (UTC)

Oyxgen evidentally has quite a number of different solid forms. See [3] and [4] Nil Einne 11:43, 3 December 2007 (UTC)

Why doesn't lightning damage antennas when it hits them?

When lightning hits a tree, it can make it explode sometimes. But when it hits an antenna at the top of a sky scraper, no damage occurs. Why is this? 64.236.121.129 (talk) 21:33, 27 November 2007 (UTC)

Lightning is just electricity. When electricity flows through metals, it passes quite easily due to their low resistance. When electricity flows through a tree - the resistance is considerable - so a lot of electrical energy is lost - and converted to heat. Hence the tree gets very hot. If the tree has lots of sap, it may even boil - and when that happens, a lot of steam has to go somewhere in a hurry and KABLAMMO! (That's a scientific term :-) SteveBaker (talk) 21:43, 27 November 2007 (UTC)

So if lightning hits a person covered in salt water, it'll prolly kill him, but won't make him explode. But if he's wearing some thick coat, he might explode? 64.236.121.129 (talk) 21:46, 27 November 2007 (UTC)

Probably not. Humans are rather good conductors (mostly salt water all through), and they also do not resist expansion well enough for a good explosion anyways. Also, as far as I know (but I may be wrong), much of the current will travel along ionized air on the outside of a human. --Stephan Schulz (talk) 22:04, 27 November 2007 (UTC)

( edit conflict) Lightning is unpredictable. Sometimes it mainly flows over the surface, sometimes it does you like a Presto Hotdogger. Antennas often have a spark gap at the base of the mast consisting of two points (> <), one connected right to the transmission line, and the other to ground. The points are just far enough apart not to arc when transmitting, but close enough to arc when lightning strikes. See lightning, lightning rod, spark gap, and lightning safety.--Milkbreath (talk) 22:12, 27 November 2007 (UTC)

Since Lead is a poor conductor of electricity, what would happen if lightning hit a chunk of lead? 64.236.121.129 (talk) 16:47, 28 November 2007 (UTC)

All metals are "good" conductors. Silver, copper, gold, and aluminum are great conductors. Lead has no problem conducting in your car battery. Too, there's lightning, and then there's lightning. It can range in intensity from a piddling couple of million volts up to a billion volts or more. The snappiest strikes can melt a copper antenna no problem, but they are rare, and they tend to hit the mast instead of the antenna, anyhow, because the mast is grounded. I would expect a piece of lead of reasonable size to disappear in a puff of incandescent lead vapor with any decent strike. Lightning is scary stuff. --Milkbreath (talk) 17:05, 28 November 2007 (UTC)

The article on lead said that lead is a poor conductor of electricity. Did it just mean, compared to other metals? Also since it has low resistance, shouldn't it be unharmed by the lightning? I thought lightning only damages objects that have high resistance. 64.236.121.129 (talk) 17:37, 28 November 2007 (UTC)

Poor compared to other metals. Lead has an electrical resistance of 208 nano-ohms per meter. Iron is at 96 and Silver is 16. So, yeah - lead is a poor conductor compared to iron or silver. But take a typical non-metal like (say) Sulphur and it has a resistance of 2x10¹⁵ ohms per meter (that's 10²⁶ times worse than lead!!) Compared to sulphur, lead is a spectacularly good conductor! SteveBaker (talk) 20:23, 28 November 2007 (UTC)

I just did some math, and if a lightning bolt carrying 300,000 amps of current passes through a lead stick one centimeter in cross-sectional area and one meter long, you get 189 million watts dissipated in it. That should be enough to turn it into plasma, don't you think? --Milkbreath (talk) 20:44, 28 November 2007 (UTC)

Don't you also have to factor in voltage? 64.236.121.129 (talk) 21:08, 28 November 2007 (UTC)

The voltage across the lead stick is determined by the current from the bolt; the current from the bolt is determined by the total voltage of the bolt (which doesn't depend at all on what you fire it through) and the total resistance in the bolt's path; the resistance in the bolt's path is almost entirely within the air, not the stick, so the stick has a somewhat negligable effect on the total current of the bolt. It might affect how much of that current goes in, across, or around the stick, but it won't really have an affect on the current (and thus, on the voltage across the stick). Someguy1221 (talk) 21:19, 28 November 2007 (UTC)

Right. All the current would probably go through the stick because its resistance is very much less than that of the air around it. As for the "voltage", power is calculated by P=IE (current times voltage). Algebra and Ohm's law let us do away with voltage if we know the current and the resistance, giving P=I²R. --Milkbreath (talk) 21:29, 28 November 2007 (UTC)

If lightning hit glass, it should shatter it right? But would it penetrate it, and hit whatever was behind it too, or would the glass stop the lightning from advancing further? 64.236.121.129 (talk) 17:43, 28 November 2007 (UTC)

The lighting will keep going until the current reaches the ground. As far as the lighting is concerned, the glass is just another, bothersomely-high-resistance medium to get through on its way to the ground, just like air and trees. --Chris, 20:48, 28 November 2007 (UTC) —Preceding unsigned comment added by 63.138.152.238 (talk)

Lightning is unpredictable. If it wants to go through glass, it will, blowing it to smithereens in the process, I suppose. Thing is, lightning follows a leader, and the leader wouldn't form through glass in the first place. --Milkbreath (talk) 20:57, 28 November 2007 (UTC)

I think the lightning strikes before the leader makes it all the way to the ground, and just arcs through the air. In any case, the lightning isn't going to just stop and have the ions sit next to the glass. — Daniel 02:23, 29 November 2007 (UTC)

I wouldn't say that lightning is unpredictable - it's HARD to predict - but it's not some magical thing, the laws of physics that it follows are well understood. I imagine that the kind of thing that'll happen with a window in (say) an aluminium frame - is that the lightning will be trying to find the lowest resistance path to the ground. That's not the glass - it's the frame - so the frame gets hit - a bazillion amps of current flows - and the frame duly melts, then boils in a very little amount of time. This heat will shatter the glass because it can't expand evenly enough - just as if you pour boiling water into a cold jamjar. As soon as the glass opens up a small crack - the lightning can head through (presuming there is a lower resistance route to ground inside than outside). Your bathroom window is probably next to some nice copper pipes that lead in exactly the right direction - so if your house got struck by lightning, this is a very possible outcome. SteveBaker (talk) 03:05, 29 November 2007 (UTC)

Lightning hasn't read those physics books you put so much faith in. It can hit a chicken standing on a rubber mat two feet away from a 300-foot-high grounded tower if it wants to. The underlying physics may be known, but real-world chaos makes the event unpredictable. --Milkbreath (talk) 03:38, 29 November 2007 (UTC)

That's nonsense - and you know it. "if it wants to"?!? It doesn't "want" anything - it's an application of field theory - and it most certainly follows the same laws of physics as the rest of the universe. If you set up an FEM model of the tower, the air and the chicken with the appropriate laws of physics built into your mesh and cycled it at a small enough time step, you'd be able to predict pretty accurately where any given lightning bolt would disperse to. It's not a chaotic system at all. Not all systems that are complicated are also chaotic (and not all chaotic systems are complicated) - that's a horrible misconception. People can and do model the behavior of lightning. My first job out of college was doing research into telephony systems - and there were people where I worked who calculated how a lightning strike on the telephone exchange would propagate out into the phone lines - and vice-versa. SteveBaker (talk) 04:21, 29 November 2007 (UTC)

Lightning is unpredictable not because it has volition. I'm not a voodoo witch doctor, in case you thought that. Not chaotic? Are you saying that there is a model for the progress of a leader through the atmosphere that can predict its path? That is absurd, and you know it. "According to my calculations, it will strike right over there", he declared confidently, only a moment before a rogue bolt leapt from a thunderhead 10 miles away and vaporized his pointing finger. --Milkbreath (talk) 11:51, 29 November 2007 (UTC)

I didn't say it would be easy to predict - you'd need some insane amount of data about the air on the way down - but it's not SENSITIVELY DEPENDENT on that data in a way that would make it chaotic. Maybe you need to read some more about chaos theory. Not all complicated, hard-to-predict things are chaotic. SteveBaker (talk) 14:10, 29 November 2007 (UTC)

Who said no damage would occur to an antenna from a direct strike? Induced currents can however be mitigated by connecting the mast to earth. I beleive this is normal practice in the professional and ham radio world. —Preceding unsigned comment added by TreeSmiler (talk • contribs) 03:46, 29 November 2007 (UTC)

Heres a link [5]--TreeSmiler (talk) 04:03, 29 November 2007 (UTC)

Theropod dinosaurs and birds

Only Theropod dinosaurs are considered to have evolved into birds right? Other dinosaurs like Sauropods and Cerapods aren't. Correct? Hmm, if this is true, can we consider Sauropods and Cerapods to be 100% reptiles, while Theropods to be part reptile, part bird?64.236.121.129 (talk) 21:37, 27 November 2007 (UTC)

We have an article on bird evolution about this. (And yeah it looks like theropods are considered their ancestors.) I don't know that the second half of the question is very meaningful- we lump things together as reptiles or birds because it's a useful classification. These classifications may be fuzzy around the edges. Friday (talk) 21:47, 27 November 2007 (UTC)

Of course it's meaningful, otherwise we wouldn't classify animals at all. 64.236.121.129 (talk) 21:54, 27 November 2007 (UTC)

We classify, and often reclassify as our understanding improves. Theropod classification is described in the article. They are considered dinosaurs, which are considered reptiles. Friday (talk) 22:03, 27 November 2007 (UTC)

Perhaps what Friday meant by "meaningful" was monophyletic, while your suggestion of some species being "part reptile, part bird" would be paraphyletic along the lines of saying something is "part fruit, part apple". --Sean 00:15, 28 November 2007 (UTC)

The sauropods almost completely died out before the Cretaceous, and the final species died out in the Cretaceous–Tertiary extinction event. Other interesting suborders are the ornithopods (bird-feet, with bird hips and duck bills) which also died out, and don't seem to have connection to modern birds besides analogous evolution. SamuelRiv (talk) 23:17, 27 November 2007 (UTC)

Sauropods didn't die out before the Cretaceous. Argentinasaurus lived in the middle of the Cretaceous for example. 64.236.121.129 (talk) 16:32, 28 November 2007 (UTC)

Why does Carbon nanotube have stronger properties than buckyballs?

They are made out of the same matter right? So why the differences? Would a buckyball have better compression strength due to its shape? 64.236.121.129 (talk) 22:00, 27 November 2007 (UTC)

Buckeyballs contain both hexagonal rings and pentagonal rings, whereas carbon nanotubes ideally contain only hexagonal rings. Hexagonal rings are significantly more stable, and thus require greater strain to break. Indeed, pentagonal rings of carbon are naturally under stress (see ring strain) already due to their non-ideal bonding configuration. Adding further to that, forcing carbon rings to form spheres or cylinders instead of sheets also strains the bonds, and I suspect this to be greater in a buckeyball than a nanotube. And finally, buckyballs aren't resonance stabilized, whereas nanotubes are. Someguy1221 (talk) 10:51, 28 November 2007 (UTC)

Is there any shape that is potentially stronger than a hollow cylinder, since a hollow cylinder is weak in compressive forces? 64.236.121.129 (talk) 17:39, 28 November 2007 (UTC)

I don't know much about that specific question, but it pays to be cautious when considering questions like this. It sounds like you're assuming that what's true on a large scale would also be true on a molecular scale, which is always a dangerous assumption. Friday (talk) 21:24, 28 November 2007 (UTC)

I'm well aware of that. 64.236.121.129 (talk) 20:38, 29 November 2007 (UTC)

When people talk about carbon nanotubes being strong, they're referring to tensile strength, not compressive strength. — Daniel 02:15, 29 November 2007 (UTC)

Yea, I know. They have terrible compressive strength because they are hollow cyclinders. It's naturally bad at compression. That's why I'm asking if there's a better shape to handle that kind of stress, while maintaining CNT's other strong properties. 64.236.121.129 (talk) 20:38, 29 November 2007 (UTC)

How come the buckyballs aren't resonance stabilized? Don't they also have delocalized electrons like the tube or graphite? – b_jonas 16:03, 29 November 2007 (UTC)

How much would someone weigh on mount everest

I weigh 130 pounds and for science class i need to know the formula to calculate how much i would weigh on the summit of mount everest? Any Help???? —Preceding unsigned comment added by 71.219.144.66 (talk) 22:23, 27 November 2007 (UTC)

See Newton's law of universal gravitation RJFJR (talk) 22:28, 27 November 2007 (UTC)

On Mount Everest, your weight will not change much. You will weigh the same as much you weigh here. Though, if you want to be more precise, the value of 'g' will slighly change, because distance between you and the centre of earth has increased, but this will be very insignifacnt because radius of earth is much more than the additional 8 KM that you would add if you reach Mount Everest, so there is not much difference in your weight here and on mount everest. However, your weight will drastically change, if you reach moon. The reason is because of the difference in radius and mass of the moon, that account for your weight on its gravitational field. For further clarification, read article posted by RJFJR and other related articles. DSachan (talk) 22:37, 27 November 2007 (UTC)

If you really want to be pedantic, you can try adding another quite small term for the gravity caused by Everest itself. Historically, trying to directly measure the gravity of mountains was one of the methods used when attempting to quantify Newton's constant, G. Dragons flight (talk) 23:02, 27 November 2007 (UTC)

A gravity map of earth's surface I found here, suggests that the large mass of earth beneath you largely outweighs the decrease in gravity caused by the altitude gain. So you would weigh more on everest then somewhere else. 71.214.181.11 (talk) 03:52, 28 November 2007 (UTC)

Actually, you are misinterpreting a poorly explained graphic. What that shows, I'm virtually certain, is the gravity anomaly from "normal" gravity that general models would predict for each particular latitude and elevation. Not variations is the acceleration of gravity in an absolute sense; not variations from some constant value. These anomalies are much smaller in magnitude than the variations with latitude and elevation. Gene Nygaard (talk) 15:49, 29 November 2007 (UTC)

See Earth's gravity#Altitude (Why doesn't this link work right?). --Milkbreath (talk) 22:43, 27 November 2007 (UTC)

Corrected your link for you. (EhJJ) 22:56, 27 November 2007 (UTC)

For the purposes of your science class: the fact you need to know is that gravity decreases in strength in proportion to the square of the distance you are from the center of gravity of the source. So - your weight at sea level is proportional to one over the radius of the earth squared. Your weight at some altitude is proportional to one over the radius of the earth at sea level PLUS your altitude - all squared. We can lose the annoying constants of proportionality by dividing one equation by the other. Hence your weight at altitude A as a percentage of your sea level weight is: 100 x R²/(R+A)² - so go to Earth and look up the radius of the earth, go to Everest and figure out it's height - get the percentage increase and add that to your present weight. Problem solved.

BUT: We have to whine and complain a bit - because this is the reference desk and we all want to show how complicated things really are! So:

• The earth isn't spherical. It's an oblate sphereoid. You might think this is negligable - but the difference between the polar radius and the equatorial radius is about 20km. Everest is less than 9km tall. So the weird shape of the planet has more to do with where you are in latitude than where you are in altitude!
• The mass of mount everest itself is not negligable. Normally one may assume that the center of gravity of a spherical body is at it's center. But not so when you are standing really close to a GIGANTIC chunk of rock. So while your altitude will reduce your weight a bit...the mass of Everest itself will increase it some. Is this negligable? I don't know and I can't be bothered to work it out.

SteveBaker (talk) 01:04, 28 November 2007 (UTC)

"Increase", I like that.

A really complete, nitpicky solution would also allow for the variation in one's weight with latitude, due to the Earth's rotation.

On the other hand, a counter-nitpick is that if the initial weight is given as "130 pounds", it's a number with only two significant digits and therefore the answer should be rounded o the same precision. In which case it's going to be 130 pounds.

--Anon, 02:54 UTC, November 28, 2007.

I think that the amount of mass underneath a mountain should be about the same as the amount of mass under non-mountain areas, because the crust floats on top of the mantle, so as with all things that float, the crust must displace its equal weight in the underlying mantle. So if the mountain were not there, it would be filled with the same weight of mantle. --Spoon! (talk) 11:59, 28 November 2007 (UTC)

This is true only on the large scale (e.g. ~100 km or so), on the moderate to small scale, the crust is rigid enough to support local anomalies (i.e. mountains) that deviate from bouyancy. That is what the gravity map that an anon linked above is getting at. Dragons flight (talk) 17:50, 28 November 2007 (UTC)

The gravity map was made by a pair of satellites. It doesn't depict the gravity at the elevation of the ground - it measures it at the altitude of the satellite. So it's not taking account of the altitude of the mountains at all. Hence we don't know (without knowing what the colours on that map mean numerically - and doing some more math) whether the effects of the mass of mountains outweighs (hehehe!) the effects of their altitude. SteveBaker (talk) 20:16, 28 November 2007 (UTC)

An even bigger but than Steve Baker's above: But for real-world purposes such as the medical sciences and sports, in contrast to his "for purposes of your science class", your weight on Mount Everest is the same as it is anywhere else: 130 lb, or in the units used for this weight throughout the world including many hospitals in the United States, 59 kilograms. Gene Nygaard (talk) 14:06, 29 November 2007 (UTC)

I also find it rather strange that so many teachers would choose to try to make a point about the strength of the gravitational field, involving that jargon meaning of the word "weight". It is Mount Chimborazo which is the highest mountain on Earth in both ways relevant to this question, something like 2,000 meters farther from the center of mass of the Earth, and hundreds of kilometers farther from the axis of rotation.

Reminds me of an example Aviation Week used to have on their aviationnow.com website (apparently lost in reorganization), concerning the "weight" in the physics jargon sense (even though they used kilograms for the units of this weight, and the kilogram-force is no longer an acceptable unit) of an elephant at the Denver Zoo and at the San Diego Zoo. Problem is, they got it all wrong. An elephant of the same mass will exert more force due to gravity at the Denver Zoo than at the San Diego Zoo, not less. The author of that piece, like the teachers who use Mount Everest as an example, failed to understand the simple fact that latitude is a more inportant factor in this regard than elevation above sea level is. Gene Nygaard (talk) 14:21, 29 November 2007 (UTC)

It should be noted that "pounds" can refer to "pound mass", which is the same regardless of gravity, or to "pound force", which is dependant on gravity. From the original question I think we can assume that by "pounds" they meant pound force, not pound mass. -- HiEv 04:06, 2 December 2007 (UTC)