Wikipedia:Reference desk/Archives/Science/2008 May 27

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May 27

Mars rovers

If I understand correctly, the purpose of the latest rover is to ascertain whether life was once possible (or present) on Mars. My question is, what is the purpose of knowing whether it was or wasn't? If it was, does that make Mars any more of a candidate for terraforming? Or is it really just an expensive curiousity for scientists? Thanks. Vranak (talk) 00:02, 27 May 2008 (UTC)

If there was life in the past on Mars, it will tell us a lot about the chances of there being life elsewhere in the Universe. The question of "are we alone?" is actually pretty important for many people. Also, finding traces of past life would help us to better understand how life evolved on our own planet. Finding actual existing living things (maybe deep down in the rocks), of course, would be one of the greatest discoveries ever made by mankind. However, it's very unlikely Mars will ever be "terraformed", since it's lost its atmosphere and is really, really cold. Franamax (talk) 01:32, 27 May 2008 (UTC)

(edit conflict)The recent lander is not a "rover" although it is a digger and analyzer. It is indeed an "expensive curiousity" for those who are interested in learning about what is "out there" beyond their familiar environment, besides the scientists who build the space probes and operate them. That is one reason they are covered extensively in newspapers and tv news channels, for whom scientists are a vanishingly small fraction of the viewership. This one's chemistry set will not test for life, but it will do some chemical analysis to see if there are suitable conditions for life, or if there were in the past. Determining this will provide insight into whether our planet is the only place suitable for life to evolve. Edison (talk) 01:36, 27 May 2008 (UTC)

Thank you. Vranak (talk) 02:09, 27 May 2008 (UTC)

Someone once said something like: "To a scientist, there are only three interesting numbers: zero, one, and many, and 'one' is usually an aberration." That is, scientists are often involved with trying to decide whether a thing is impossible (so zero instances of it exist) or possible (so many instances of it exist). This includes the question "How many planets in the Universe have life?". To prove a second planet has/had life would shift the answer from "one" to "many, and this would require a very significant change in all of humanity's worldwview "universeview".

Atlant (talk) 14:24, 27 May 2008 (UTC)

I had the opportunity to attend a lecture from the former director of Jet Propulsion Laboratory. (Can't remember his name, unfortunately). According to him, the motivation for finding life was one of funding! (This should come as no surprise to anyone who works in any scientific field). Surprising (to me at least), the federal government is much more willing to fund Mars missions if the notion of "finding life" or "finding possibility of life" or some such stuff is mentioned in the mission proposal. This has become such a high priority that it defies scientific data... most of the Mars scientists I've ever met do not believe in life on Mars now or ever. (There's a few outliers, of course, and as the adage goes, the absence of evidence is not the evidence of absence, and so forth). All the NASA releases are careful to word their releases to discuss the possibility of sustaining life, because this is ambiguous enough to allow for many types of missions (after all, what does it really mean to be "possible" to sustain life?) Nimur (talk) 15:27, 27 May 2008 (UTC)

Huh? I thought the recent lander was a Canadian weather station set up at 70 degrees latitude to see if water is possible? Or am I confusing it for another lander? Or is it the same lander but different details? Thanks. ~AH1^(TCU) 01:28, 28 May 2008 (UTC)

Phoenix (spacecraft) is "a partnership of universities in the United States, Canada, Switzerland, the Philippines, Denmark, Germany and the United Kingdom, NASA, the Canadian Space Agency, the Finnish Meteorological Institute, Lockheed Martin Space Systems, and other aerospace companies." Nimur (talk) 05:01, 28 May 2008 (UTC)

From a letter (reproduced in his book) from Lazlo Toth to NASA on the occasion of the Viking_program: "But this [finding organic chemicals in the analysis of the sample] wouldn't mean that there is life on Mars; it would mean that there was life on Mars, but you killed it!" Gzuckier (talk) 15:18, 29 May 2008 (UTC)

Pathogens in body

How would you be able to tell if you body detected a pathogen? I was wondering what would be the tell tale signs or even symptoms —Preceding unsigned comment added by 220.235.59.49 (talk) 00:03, 27 May 2008 (UTC)

Fever--Lenticel ^(talk) 00:18, 27 May 2008 (UTC)

Immune system and infection may hold some answers. Apart from fever there's increased white blood cell count. If you have a wound, pus will show. And there's the signal system reporting pain to rally the troops to the site where an infection has caused tissue damage. (Don't we really enjoy that part.:-) In case of your body detecting cold viruses you'll notice the increased histamine levels by your stuffy head. If your body detects harmful pathogens in the digestive system it will effect a purge. (either up or down). Your body is also likely to produce sleep inducing chemicals. These help the immune response and free up resources for healing. --71.236.23.111 (talk) 03:01, 27 May 2008 (UTC)

Revise your understanding. Your body encounters and deals with pathogens all the time. A pathogen is simply an organism that can sometimes cause noticeable harm to some people in some circumstances. Some pathogens are so virulent that the likelihood of noticeable harm is high, others are usually so benign that only people with severely compromised defenses are harmed. 159.14.240.230 (talk) 12:00, 27 May 2008 (UTC)

Drunk animals and Marula trees

There is a video on youtube of African animals supposedly getting drunk off the fruit of the Marula tree (www.youtube.com/watch?v=vCu5s80uAMQ) --and apparently the video is a hoax: http://news.nationalgeographic.com/news/2005/12/1219_051219_drunk_elephant.html But that article doesn't say anything about what's actually going on in the video--does anyone know how it was made? Were the animals just given alcohol and filmed stumbling around or was something else going on? Thanks! —Preceding unsigned comment added by 204.73.103.253 (talk) 00:52, 27 May 2008 (UTC)

Marula (see the article under its scientific name Sclerocarya birrea) is the source of berries that makes the delicious Amarula liquor. There was a film that showed animals getting drunk from the fermented fruit but was likely to be staged scenes. Also, elephants would need to eat a large amount to get drunk. -- Alan Liefting (talk) - 06:56, 27 May 2008 (UTC)

Sure, that was all in the national geographic article--I'm wondering if anyone knows what was REALLY going on. Who made it, how and why? —Preceding unsigned comment added by 204.73.103.253 (talk) 16:07, 27 May 2008 (UTC)

The same phenomenon features in the 70's South African documentary by Jamie Uys (which I recall seeing as a kid) called Animals Are Beautiful People. I can't quite imagine how they would have staged it. --Anonymaus (talk) 08:17, 1 June 2008 (UTC)

Tasting a meadow in butter

I normally eat margarine, but I bought some organic butter recently. I thought I could taste the grass and flowers of the meadow where the cows ate. Was this just my imagination or not? 80.0.110.30 (talk) 01:22, 27 May 2008 (UTC)

Flavor shows that what we call "taste" is a 2 part process involving olfaction and taste. Since the smell component are substances that can be "carried" in fat, it's not that far out. However it might just be a clever ploy by a flavorist selecting natural ingredients that have that effect. organic doesn't mean they are not permitted to use additives, as long as those are organic, too. There was an odd experiment they used to do in biology classes when I was a kid. I can't recall what went into the recipe, apart from peas. The end result tasted like strawberries, although there were none in there. You just had to blindfold people or the color would give it away. Although some flowers are edible, most meadow flowers and the grass would probably add up to a taste that would be rather not like the "idea" of meadow taste. --71.236.23.111 (talk) 03:28, 27 May 2008 (UTC)

If a cow manages to eat some wild garlic, the flavor shows up in, and spoils the milk. If a lactating female human eats strongly flavored food, the milk produced may be upsetting to a nursing infant. From these observations, it seems plausible that a "meadow" flavor might present in cow's milk and hence in the butter. Or it could be the power of suggestion. Edison (talk) 05:55, 27 May 2008 (UTC)

Milk flavour varies a lot according to season etc., a friend rang the milk company to ask about the different flavour. Polypipe Wrangler (talk) 11:08, 27 May 2008 (UTC)

Well, have you ever tasted grass and flowers from a meadow? If no, then how can you be sure that this is what the butter tasted like? If yes... why? Nimur (talk) 15:29, 27 May 2008 (UTC)

That's where olfaction comes into it. We are all familiar with the smell of grass and flowers. Scientists should read "I could detect the flavour..."--Shantavira|^{feed me} 06:09, 28 May 2008 (UTC)

The organic butter that I buy is cultured, whereas most butter sold in the U.S. is not cultured. The cultured butter has more of a sour "tang" like yogurt, and a more complex flavor in general. If your butter is cultured, that would be a major factor in its taste. -- Coneslayer (talk) 11:32, 28 May 2008 (UTC)

See also terroir. arkuat (talk) 06:32, 2 June 2008 (UTC)

Blowing one's nose

Does blowing ones nose have any real known and scientifically measured effect on reducing the chances of getting a cold (or other infection), compared with people who only sniff the phlegm (?) up and do not blow? 80.0.110.30 (talk) 01:27, 27 May 2008 (UTC)

Well, I don't know about measured, but it makes sense. The mucous collects all sorts of things from the air, and it's probably better off to expel them rather than to take them into the system. --98.217.8.46 (talk) 02:04, 27 May 2008 (UTC)

I believe it's been shown that rinsing the sinuses with salt water does reduce the chances of catching a cold. It would make sense that blowing the nose would have a similar effect - removing microorganisms from the body, rather than moving them to the throat or elsewhere. -- Beland (talk) 16:14, 27 May 2008 (UTC)

Clearing your nose is something your going to do pretty automatically. It's like scratching an itch. There wouldn't really be any way of testing this. The type of experiment you're asking about would require that people not blow their noses, but if your nose is full of snot it's going to come out somehow: either you blow it, snort it into your nasopharynx (spit or swallow is your choice), or it's just going to dribble out. I think more than anything, once the mucus is there, it's just uncomfortable not to blow your nose. --Shaggorama (talk) 18:56, 27 May 2008 (UTC)

The problem with blowing one's nose is that sometimes it blows things into the sinuses. That's one reason I remember being stated for the results coming out ambiguously. (The article I remember predates the internet archives.:-( Salt water has been proven and we have a page Nasal irrigation. --Lisa4edit (talk) 19:11, 27 May 2008 (UTC)

You probably get this question all the time...

... but what would be the Latin name of a species of Woolly Mammoth found only in cathedrals?

Ta

Adambrowne666 (talk) 01:49, 27 May 2008 (UTC)

I assume you mean this cathedral not this one Cathedral. Sounds like an odd thing to happen with a Woolly mammoth find in any case. "Mammuthus primigenius" would be all of them.--71.236.23.111 (talk) 02:31, 27 May 2008 (UTC)

No, I mean the latter - and not just cathedrals, also large chapels and basilicas - I don't deny it's an odd thing to happen. Adambrowne666 (talk) 02:45, 27 May 2008 (UTC)

Given that the last Woolly mammoth died around 1700 BC, and cathedrals are decidedly AD, that's more than odd. Can you give a bit of context as to how the two would meet? And, for that matter, why the ones found in cathedrals would be a different species to those found elsewhere? Confusing Manifestation(Say hi!) 03:41, 27 May 2008 (UTC)

It's for a science fiction novel I'm working on in which some time periods have been mixed up - as for how ones found in cathedrals would be a different species to those found elsewhere, that's a good question, but would take too long to answer here - suffice it that it's a very weird science fiction novel. Adambrowne666 (talk) 03:55, 27 May 2008 (UTC)

It makes perfect sense to me. If, suddenly, woolly mammoths started turning up in cathedrals, we'd need to call them something. Due to my basic Latin knowledge, I can only suggest Mammuthus basilica or Mammuthus ecclesia. To be specifically a woolly mammoth, then perhaps Mammuthus primigenius ecclesia would be appropriate. The language desk might come up with something clever. Gwinva (talk) 04:10, 27 May 2008 (UTC)

I like it - Mammuthus primigenius ecclesia or basilica or basilicensis or something like that - thanks, Gwinva.

If it's a species the name should only have two parts, genus and species. When a third word is added, this indicates a subspecies. The basic rule is that if it interbreeds with other mammoths and produces fertile offspring then it's the same species as them, and if not, it isn't; but this is a simplification. --Anonymous, 23:58 UTC, May 27, 2008.

Yes, I assumed a sub-species of woolly mammoth when I offered the three name version (Adam said they were only found in cathedrals and churches, so they cannot be the same as a normal woolly mammoth. In any case, they can't mate and produce fertile offspring; they are separated by several millenia, after all. Gwinva (talk) 09:05, 28 May 2008 (UTC)

Primates are more often found in cathedrals than are mammoths. Edison (talk) 05:51, 27 May 2008 (UTC)

Had to think about it, then chortled, thanks, Edison. Adambrowne666 (talk) 12:09, 27 May 2008 (UTC)

Sounds like a cool book, can you tell me when it's done? Ziggy Sawdust 15:36, 27 May 2008 (UTC)

Thanks for saying so, Ziggy - I like your name btw - I'll let you know - will be a coupla years, though - I'll make a big announcement in the Ref Desk Talk Page. Adambrowne666 (talk) 10:53, 28 May 2008 (UTC)

Question

Can something that travels faster than light escape a black hole? Interactive Fiction Expert/Talk to me 05:59, 27 May 2008 (UTC)

If you can answer the question, "can something travel faster than light?", you may have the start of an answer. 63.224.79.202 (talk) 06:25, 27 May 2008 (UTC)

Particles cán escape from a black hole however: as the article on Hawking Radiation quotes: "Because Hawking radiation allows black holes to lose mass, black holes which lose more matter than they gain through other means are expected to evaporate, shrink, and ultimately vanish." —Preceding unsigned comment added by 87.67.39.188 (talk) 11:07, 27 May 2008 (UTC)

The particles in Hawking radiation are created just outside the event horizon - they're never actually in the black hole, so don't escape it. --Tango (talk) 19:52, 27 May 2008 (UTC)

I have no idea how tachyons would interact with black holes. It's an interesting question, though. I suspect they wouldn't be able to leave, either, but I'm not sure why not. --Tango (talk) 19:52, 27 May 2008 (UTC)

Since tachyons seem to experience time backwards, I'd say (based on the point of view) that it would moonwalk out of the black hole. 63.224.79.202 (talk) 04:29, 29 May 2008 (UTC)

Tachyons (by definition) travel on spacelike paths. Inside a (for the sake of simplicity Schwarzschild) black hole the time coordinate becomes spacelike and the radial coordinate becomes timelike, so inside the black hole tachyons would travel somehow like normal particles outside the black hole. Icek (talk) 14:55, 30 May 2008 (UTC)

Battery sizes

After reading the articles, I am a bit confused about what might happen if I were to use a C battery to power (for example) my mp3 player which normally uses a AAA battery. Since the C is rated for higher current, would that damage the mp3 player? Or would the set 1.5 voltage mean it would give me a longer play time? In other words, does the electric current depend on my device, or the size of the 1.5-volt battery I'm using? 63.224.79.202 (talk) 06:11, 27 May 2008 (UTC)

You can use any battery on your MP3 player as long as it is the correct voltage. The larger batteries can supply a higher current and for a longer time but the MP3 player will only draw the current that it needs. -- Alan Liefting (talk) - 06:59, 27 May 2008 (UTC)

To avoid any confusion: the "can supply a higher current" part is correct but irrelevant. The larger battery would be safe and would last longer. Of course, it would also be less convenient. --Anon, 00:00 UTC, May 28, 2008.

You can damage the mp3 player with two batteries placed in series (lined up one end to another). If you can somehow get your hands on a lower-voltage battery, the damage will be slower and less predictable. Imagine Reason (talk) 00:33, 28 May 2008 (UTC)

Minor nitpicking here but two batteries line in a series where the total voltage in the series is higher then the voltage expected by the device. If you get your hand on a significantly lower-voltage battery i.e. 0.75V or lower and place two of these in series, you're not going to damage your MP3 player since the voltage supplied will still be 1.5V or lower Nil Einne (talk) 15:28, 28 May 2008 (UTC)

If that mp3 player uses one AAA battery and you are going to use one C battery instead, the only problem i could imagine is that C battery will not physically fit in a place designed for AAA battery. If you connect it with wires (and duct tape on outside of device) it should work as good as AAA battery (+ last longer than AAA battery). -Yyy (talk) 07:28, 29 May 2008 (UTC)

Questions about acceleration due to gravity

I have two question about physics

(1)where will be the value of "g" high,at equator/poles/surface of earth.

(2)what are the number of molecules in kilometer of a gas.

thanks —Preceding unsigned comment added by 202.125.143.74 (talk) 07:00, 27 May 2008 (UTC)

(1) g will be the same anywhere on the surface of the earth (9.81ms^-2. It will differ slightly because of difference in elevation and the fact the earth isn't a perfect sphere, but negligibly.

(2) A cubic kilometer? I can tell you that the number of molecules of 1 mole of a gas is 6.02E23, and 1 mole of a gas occupies 22.4 litres. Try working it out from there. 61.69.132.119 (talk) 07:51, 27 May 2008 (UTC)

(1) According to our earth's gravity article, variations can indeed be significant depending on the precision required. I'd think that differences on the order of 0.4% would be quite significant for say, missile launching. --hydnjo talk 08:07, 27 May 2008 (UTC)

I beg to differ. If you could get a missile engine large enough to fly in an orbital or sub-orbital path with thrust that could be reliably measured to with 0.4%, you'd be way better than any current system. I think there are many other variations (wind, engine efficiency, target location / trajectory), which introduce errors significantly larger than graviational perturbation. Of course the issue is moot because a modern launcher will use feedback control and some type of tracking (RADAR or GPS) to update its current position and correct for any error from desired trajectory, regardless of the cause... Nimur (talk) 15:36, 27 May 2008 (UTC)

(1) Largest effect on the apparent value of g seems to be the effect due to latitude, with a difference of about 0.5% between poles and equator. Altitude has a smaller effect (about 0.3% difference between sea-level and the summit of Mt. Everest); local topography, atmospheric density and gravitational influence of Sun and Moon have still smaller effects.

(2) Depends on the temperature of the gas, the pressure of the gas and its equation of state. If you can assume that the gas obeys the ideal gas law then this will simplify your calculation considerably. Gandalf61 (talk) 09:23, 27 May 2008 (UTC)

Car economy accuracy

How accurate are the fuel economy figures that cars report? My car has a little digital display that says I do around 50 miles to the gallon, and I can see this figure go down if I drive faster and up if I keep my speed around 65 miles per hour, but is it reliable? Of course the reliability could vary from one manufacturer to another, but I'd expect the major manufacturers will have been independently checked. — PhilHibbs | talk 10:33, 27 May 2008 (UTC)

I have not looked into this in depth but given the improving technology and accuracy of fluid quantity and distance measurement devices I would say there is a good accuracy. (if tyres are correctly inflated of course). -- Alan Liefting (talk) - 10:41, 27 May 2008 (UTC)

The average MPG display in both my Audi A8 and Dodge Caravan seem to correlate pretty well with the values I compute at the gas station (miles driven on this tank of gas versus gallons refilled). The instantaneous MPG figures are wildly varying, of course and only help to train you to be a more-efficient driver.

Atlant (talk) 14:09, 27 May 2008 (UTC)

Yeah- most cars will have some way of viewing "average" mileage instead of "instantaneous" or "average over the last 5 seconds" mileage. I'd generally expect this to be quite accurate on newer vehicles. On a related question.. I know the EPA has been trying to make their figures more accurate. Does anyone know a source for real-world results compared to EPA ratings? I bought a car a year ago that consistently outperforms EPA rating on the highway (even with a few passengers and AC on). The identical car has a lower highway rating for 08 than it did in 07. It sounds to me like (on this particular car, anyway) the EPA ratings are now unrealistically low instead of unrealistically high. Is this how it goes now, or does it vary from car to car? Friday (talk) 15:33, 27 May 2008 (UTC)

The EPA has just reformulated the way they require the manufacturers to test for and report the MPG ratings. I always found I could meet or exceed the old EPA ratings, at least for the particular American and European cars that I've bought so I am confident that the new rating system is "too pessimistic" for my driving habits. I was down at the Audi dealer looking at the stickers and even the little two-ish litre four-bangers are now stickered as getting lower highway mileage than I routinely achieve in my Audi A8.

Atlant (talk) 16:01, 27 May 2008 (UTC)

Most modern cars use electronic fuel injection, and as such have pretty acurate measurement as to the volume of fuel being used at any given second. (The car's computer needs this information as it adjusts the amount of fuel injected to match operating conditions.) The car also has rather accurate distance measurements through the (electronic) odometer. So as long as your EFI is operating correctly (and if it isn't, you should see a mechanic), and your odometer is correctly calibrated (e.g. you haven't changed your tire size), the miles per gallon should be relatively accurate. -- 128.104.112.147 (talk) 01:37, 28 May 2008 (UTC)

Chemistry project Help

I am a 10th grader. My Science teacher asked us students to make a working model on any topic of Physics and Chemistry but I'm confused on which topic to take. Can you please suggest some topics for me to make the projects. —Preceding unsigned comment added by 220.224.98.54 (talk) 14:30, 27 May 2008 (UTC)

In before "we don't do your homework". I can't help you on the project itself, however I can give you some ideas. You could try a Foucault pendulum or some such thing if you had enough time, or even just demonstrating that a pendulum's period remains constant. Another idea would be to mix baking soda and vinegar, demonstrating the reaction therein, or Mentos + Diet Coke, or any similar reaction. Ziggy Sawdust 15:15, 27 May 2008 (UTC)

(edit conflict) The problem with the Foucault pendulum experiment, is it takes quite some time to show a visible effect and most pendulums that are practical for a high school student to set up in school, will have decayed long before the effect can be seen. However, if you are still interested in the experiment, there are plenty of them set up in various places around the world. There are other experiments you can do with pendulums, such as showing the period is dependant on length and not amplitude, or the effect of drag on the decay of the pendulum's motion. Astronaut (talk) 15:51, 27 May 2008 (UTC)

How about a steam generator rigged up for electric generation? You can buy a small motor at your local electronics or hobby store, hook it up to a fan, and boil water underneath the fan to spin it. Nimur (talk) 15:39, 27 May 2008 (UTC)

I've seen students make models of trebuchets. Not a very peaceful idea, but probably fun if you're careful. --Allen (talk) 15:54, 27 May 2008 (UTC)

Cutting sheet glass under water with a pair of ordinary household scissors usually gets a couple of oohs and aahs. Make very sure to wear proper protective gear (gloves) and don't make uncontrolled movements. Those edges are sharp!!! Somewhat safer and easier to set up: Continuing from Nimur's steam idea, you could also put a couple of mirrors and plates above a steaming pot. Use different materials, temperatures and chemicals like e.g. oil, saltwater etc. on the surfaces and see what happens to condensation. (For a trick show and some laughs you can color the water and show that "the red water will condensate, while the blue doesn't. Just make sure to reveal the solution at the end, to catch the right grade from your teacher.)Lisa4edit (talk) 16:43, 27 May 2008 (UTC)

Cutting glass with a pair of scissors - are you serious? Do you have a link to a description or a video? I gotta check it out, sounds amazing. Franamax (talk) 18:10, 27 May 2008 (UTC)

It works. I could never get those glass cutters to work. You don't get quite as predictable a cut with scissors. I came across a demonstration once (must have been at some science fair, can't remember) and then tried it at home. You can also use a hand drill or a hand saw under water. But watch those edges. (3 guesses why I'm stressing that!) You tube has this [1] and this [2]. Lisa4edit (talk) 18:37, 27 May 2008 (UTC)

zOMG! Thanks :) My first guess about the edges would be that when the water is red, it's hard to see the demonstration, right? Kevlar gloves are in order. I found another one, how to cut a bottle with a string [3], also quite cool. If only they'd had youtube when I was a kid, I'd be long since dead :) Franamax (talk) 18:50, 27 May 2008 (UTC)

Even worse for the OP any sight of blood might make the teacher forget to assign a good grade. Back to ideas: I've only seen this done once, but if you're willing to give it a try it can be amazing. It is very difficult to pull off though. You'll need an aquarium, an old pair of headphones (Make sure you get sound out of one side. I don't think earbuds would work)and a balloon. Put the working "speaker" in a balloon (easier said than done!). Inflate the balloon and tie off the end and tie the string around a rock at bottom of the aquarium. Fill with water, add a layer of colored lampoil on top. Play music through the headphone and watch the movement in the water. @Franamax surviving childhood is entirely coincidental when even shoe-polish can become a hazardous material (Without you-tube, and no, I'll not elaborate the details, my backside still remembers 4 decades later, though.) As a relative once commented we should give up sending soldiers anywhere and just send our kids to go wreak havoc :-). Lisa4edit (talk) 19:55, 27 May 2008 (UTC)

tire/wheel diameter

Why wheel diameter of car, truck and tractor are different?

Why truck can't have small diameter wheels?

Is there any answer in context of radius of gyration? Neel shah556 (talk) 17:06, 27 May 2008 (UTC)

Bigger wheels are heavier and "waste" more energy. So a given vehicle will tend to have wheels large enough to do the job but not (much) larger. Also, when it comes to things like tractors, the muchlarger outside diameter of the wheel improves traction and ability to get over bumps in the surface or other obstacles. Friday (talk) 17:09, 27 May 2008 (UTC)

Tractors attempt to distribute their weight (and tractive effort!) over a large contact patch so that they don't either tear up or compress the soil over which they are rolling.

Trucks, meanwhile, use large tires no only for their larger load-carrying capacity but because, all other things being equal, a tire with a larger circumference will go farther before it wears out. To a first approximation, the rubber of the tire only wears when it is in contact with the road so a larger circumference leads to fewer "touchdowns" per mile which leads to more miles per tire. And then there's recapping/retreading...

Atlant (talk) 17:51, 27 May 2008 (UTC)

Thank you Atlant for your reply, i appreciate that inceased contact patch distribute the tractive force, but still it's not very clear to me that...

How larger diameter wheels possess more load carrying capacity? Do greater radius of gyration play any role in that?

Rather I doubt that largter dia wheel would be more prone to lateral buckling and cambering.

I mean why truck wheel can't be with smaller diameter and wider tread for the sake of increasing load carryin capacity and contact patch? Neel shah556 (talk) 09:50, 28 May 2008 (UTC)

I think that the principal reason tires get larger as the load-carrying capacity goes up is that the "contact patch" for a practical tire can only exert a certain force per unit area of the contact patch. Let's take the weight of a truck as 90,000 pounds (that's slightly high, but makes the math easy.) That weight is divided among 18 wheels so each wheel is bearing (about) 5,000 pounds. That 5,000 pounds must now be spread over a large enough area of the road surface so that it doesn't damage the road surface. On a hot summer day, macadam paving is pretty soft, so you want the weight spread over a pretty large area.

Meanwhile, we have a question of inflation pressure. What actually determines the area of the contact patch? To a first approximation, it's the inflation pressure of the tire. To continue our example, let's assume 50 PSI inflation pressure. That means that we need 100 square inches of "50 PSI" contact patch to support the 5,000 pound load on each tire. Now we don't want the tire flexing much to create the flat contact patch because flexure creates heat through frictional losses and heat shortens the life of the tire. This means that the tire must have a pretty large diameter so that 100 square inch "flat patch" doesn't represent much bending of the tire. So heavily loaded tires tend to be large tires.

You could use a much smaller tire with a much higher inflation pressure (much like some cars have miniature spare tires), but it gets harder and harder to build a higher and higher-pressure tire. And eventually, the PSI load on the surface of the road gets to be too high anyway and the tire sinks into the hot pavement.

Atlant (talk) 12:45, 28 May 2008 (UTC)

Unidentified concept car

Hello,

Does anyone have an idea of what this car might be?

• 
• 

Thank you very much in advance ! Rama (talk) 18:03, 27 May 2008 (UTC)

Based on the nearly inscrutable logo behind the car in the pic on the left, it seems to be a Fioravanti Hidra. (see also Fioravanti) --LarryMac | Talk 20:03, 27 May 2008 (UTC)

Brilliant, thank you so much! Rama (talk) 15:37, 28 May 2008 (UTC)

Plasma TV surface hot after use?

Is it normal for a Plasma TV to have be extremely warm after watching for a few hours? I'm talking about the actual screen; I can feel it radiate heat. When I hold my hand over the air vents on the top and back of the TV, it's relatively cooler than the screen is. --70.167.58.6 (talk) 21:49, 27 May 2008 (UTC)

Plasma screens are noted for their generation of heat, take a peek here. Fribbler (talk) 22:53, 27 May 2008 (UTC)

IIRC, they used to get *really* hot. I remember seeing some TV footage from the early 90s where a presenter decided to (for some reason) put his lips against a plasma screen live on air and ended up with his skin stuck to it... --Kurt Shaped Box (talk) 23:21, 27 May 2008 (UTC)

See plasma physics. Nimur (talk) 00:26, 28 May 2008 (UTC)

Early plasma panels back in the 1970's did not generate appreciable heat. Edison (talk) 06:58, 28 May 2008 (UTC)

Follow-up on Geographic feature

Thank you for your feedback on the meaning and scope of "geographic feature".

The article has been expanded to include your suggestions.

Please take a look to see if it is accurate and complete.

Have all types of geographical feature been included? Is anything missing?!

Are there any errors???

I look forward to your observations and suggestions.

The Transhumanist 00:05, 28 May 2008 (UTC)

Strange parrot behaviour - what's really going on?

Just found this YouTube video of someone's pet Green-cheeked Conure skulking around under a sofa and behaving rather strangely. A few people have commented on the video with suggestions as to what the parrot is doing - but does anyone here know for sure (there's someone here that owns Conures, right)? I've certainly never observed any of the psittacines I've personally owned over the years doing anything that even remotely resembles that. A pattern of behaviour limited to this particular species, perhaps? --Kurt Shaped Box (talk) 23:58, 27 May 2008 (UTC)

This is undoubtedly sexual behavior: the bird is masturbating. Why under the couch? Almost all parrots nest in cavities, and seek out similar locations when in breeding condition--quite often under the couch. Check out these sites: [4], [5], [6], [7]. Good thing that Wikipedia is not censored!--Eriastrum (talk) 18:24, 28 May 2008 (UTC)

Interesting. I'm far from being a bird novice - but it literally never occurred to me that this Conure might just be humping the floor and getting herself worked up... :) --Kurt Shaped Box (talk) 21:06, 28 May 2008 (UTC)

Eriastrum: you sure? the folks who posted the video seem pretty certain their bird is female. Would a female exhibit humping behavior like that? --Shaggorama (talk) 03:44, 29 May 2008 (UTC)

Yes, females do masturbate. Did you look at some of the links I provided? Especially take a look at [8].--Eriastrum (talk) 16:34, 29 May 2008 (UTC)

From my own experience with keeping birds, the females can be every bit as filthy, wanton and sinful as the males. :) --Kurt Shaped Box (talk) 22:57, 29 May 2008 (UTC)

Which just goes to show that we are even more like parrots than we thought!--Eriastrum (talk) 23:47, 29 May 2008 (UTC)