Wikipedia:Reference desk/Archives/Science/2006 August 28

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paranchute for jumping off building?

If somebody needed to jump from the 24th floor of a building (this building has no 13th floor) in an emergency, what type of parachute or other available technology should they use to ensure the safest landing on the pavement below?--Sonjaaa 01:31, 28 August 2006 (UTC)

How about a parafoil? I think 22 floors is enough to inflate the parachute. And you need to have lots of control over the chute, in order to not crash into the building or land on the road. --Bowlhover 02:48, 28 August 2006 (UTC)

You might want to do more research before trying it though. HighInBC 03:43, 28 August 2006 (UTC)

You need one that opens especially quickly. There's something about this at BASE jumping.--Shantavira 07:21, 28 August 2006 (UTC)

I believe there's a collapsible tube that can be placed in a window, then the people drop inside the tube. It's elastic, so friction between the tube and person slows their descent. You need a clear path below the window to use it, and only one person can be in the rescue tube at a time. Still, hundreds could potentially be rescued using each tube. StuRat 08:46, 28 August 2006 (UTC)

Yeah, but wouldnt your trousers get hot and ignite before you had dropped more than a few floors?--Light current 22:22, 28 August 2006 (UTC)

A parachute would be a bad idea because it needs to open. Instead use something that is already open, like a hang glider. Also a bit handier to carry around than a 70 m long tube. :) Of course, if the 13th floor is missing, the building would instantly collapse, so having something like that handy would be very handy. Of course this leaves the question how you got there in the first place. Or did something like a plane remove the floor? :) DirkvdM 09:07, 28 August 2006 (UTC)

A hang glider large enough to carry an adult may be difficult to manoeuvre through the window, especially under the pressure of an emergency. Also, it is not literally true that the building has no 13th floor. It just gets ignored. --Lambiam^Talk 09:55, 28 August 2006 (UTC)

Yes, the building has to have a 13th floor. I don't care if you call it the 14th floor, anybody who knows how to count will agree that it's actually the 13th. --Bowlhover 15:12, 28 August 2006 (UTC)

• I read about an "executive parachute" selling for $600 US or so designed for escape from a tall building. Seems like there would be a substantial risk of hitting the building and collapsing the chute, or hitting the ground long before the chute opened. With a hang glider, you would need considerable skill to soar down the street as opposed to crashing into the building across the street. Personally, I would look into rapelling or Abseiling whereby you make a controlled descent down a rope. Buy a rapelling rig and 250 feet of rope, and learn how to use it. Then you are all set. Presumably others could follow you down the rope with their own rapelling rigs. Edison 15:34, 28 August 2006 (UTC)

Executive Chute, that's hilarious! Sad thing is it's apparently real, the web site is here: [1]. Rappelling is sure to be the safer option even in the event of imminent collapse of the building you're in. Much less of a chance you will sail uncontrollably into high-voltage lines or even more likely, land atop someone who had the gall to use the stairs. --Jmeden2000 20:43, 28 August 2006 (UTC)

I've solved the 13th floor problem. The bottom half is British and the top half USian. The Brits count to 12, which the yanks call 13, so they continue with 14. :) DirkvdM 08:50, 29 August 2006 (UTC)

Speaking of Brits, wouldn't an umbrella work? Provided it is strong enough, it would at least greatly reduce the speed of descent. It seems that Brits have a tendency to fall of cliffs and such (eg Uluru) and this might be the reason. Half way down they realise that they forgot to bring their umbrella. DirkvdM 08:55, 29 August 2006 (UTC)

Not that I really think it's worth lengthy discussion, but we can thank Mythbusters (again) for showing that an umbrella will slow you for a few moments before your body weight collapses the flimsy frame and plummets you to the Earth. So... not exactly a life-saver. They're designed for small bits of falling water (sometimes not even that!) - not for Mary Poppins. CptJoker 11:03, 30 August 2006 (UTC)

Can solar panels be called "Free Energy Device"?

Can Solar Panels be called "Free Energy Device"? I asked this question because once the owner of the Solar Panel has paid for the device, they can obtain free energy forever without doing any work. Pity the amount of power (per square metre) of this device is limited. Ohanian 03:15, 28 August 2006 (UTC)

Er, no? Free energy is simply not possible. Splintercellguy 03:22, 28 August 2006 (UTC)

Solar panels cannot work without sunlight, which is a form of energy. So they can't be called free energy devices, because they need energy to work. --Bowlhover 03:26, 28 August 2006 (UTC)

I think in that context it just means that you obtain energy through something that is free: sunlight. AEuSoes1 05:41, 28 August 2006 (UTC)

In that context, yes. It is free (as in costs no money) after the initial installation. Of course, this is not completely true as maintanance plays a role. Solar power is being researched quite a bit, and some interesting and efficient technologies are being created. This is a transcript of an episode of Catalyst I saw recently. It is based on Australia's problems mostly, but it is very good. --liquidGhoul 06:59, 28 August 2006 (UTC)

It is only free as long as there is no tax on it. Once a government finds a viable way of taxing it, it won't be free much longer. There was a period in British history when each house was taxed for each window which let in sunlight, so the poorest residents bricked most of them up. It may be that sunlight will invite a tax again eventually. :) CptJoker 11:09, 30 August 2006 (UTC)

While the "per unit cost" may be zero for each kW hour, this isn't the best way to look at it. Instead, the purchase and installation price, plus any maintenance costs over the expected life of the solar panels, should be added up, then divided by the total kW hours expected, to find the cost of each kW hour. When this is done, solar energy is actually more expensive than other forms of energy, like fossil fuels. An exception exists in locations where fossil fuels can't easily be delivered, making them more expensive. StuRat 08:29, 28 August 2006 (UTC)

Indeed, one should look at the total cost of ownership. This is often not done for nuclear power either. And for fossil fuels the cost of (most of) the infrastucture is never included because those expenses have already been made. And if you want to include all the costs, you also have to include climate change. Gettting that right is tricky, because little is known about what precisely is happenning and where. But there is a rahter strong consensus that weather around the world will become less predictable and that will undoubtedly lead to bad harvests. Not just temporarily in some places, as we have experienced in the past, but constantly all over the world. The world's population has adapted to our present food production capabilities, so there is no 'room for error'. Any climate change will lead to mass starvation. What is the price of a human life? DirkvdM 09:22, 28 August 2006 (UTC)

In any case, if you mean "free" in terms of gratis, then it doesn't really work; if you mean free in terms of "no work is needed to be done," then it certainly doesn't work (the "work" that goes into sunlight comes from stellar fusion, which perfectly conserves energy and mass). --Fastfission 13:46, 28 August 2006 (UTC)

Don't all reactions perfectly conserve energy and mass (taken collectively) ? StuRat 21:58, 28 August 2006 (UTC)

About a kilowatt of solar energy hits each square meter in bright sunlight. But you may go days without bright sunlight, depending on your location, and most of us like electricity to be available 24/7. Thus you need energy storage, probably in the form of expensive batteries which must be replaced every few years in addition to the very expensive solar panels, which you cannot expect to last forever. An alternative to batteries is to convert the DC to AC and generate in parallel with the electric utiility, so they furnish power when your panel doesn't. In some places, if you generate more than you use the utility must buy your excess. But it can cost $30,000 to put solar panels on a house to generate electricity equal to their needs. I pay $77 per month for electricity, so that represents 32 year payback, probably longer than the panels and associated inverter would last. If IO put that $30,000 in an investment paying 5%, I would receive $125 per month. The economics do not appear to be there, so I would not call it free energy. Edison 15:43, 28 August 2006 (UTC)

Read my link above. The current commercial solar power is hopeless, and doesn't cover costs. That is why we needed better technology, and basically the new innovations are a lot cheaper once they are running, more efficient, more powerful and have less need for maintenance. It also covers the problem of storing energy for night (I live very close to the energy storage research centre). Solar isn't something which can be used by everyone. In Australia, we have the best opportunity to use it, as there are areas of Australia which have extremely high temeperatures, and never get overcast. It could probably be used well in America and Africa, but the Europeans need to come up with something more reliable for them. --liquidGhoul 05:31, 29 August 2006 (UTC)

Once solar panel reach the stage of mass production prices will drop considerably (but it won't get popular until it is cheap enough - catch 22). In that case it could still be one of the energy sources for Europe. Let's not make the same mistake again of focusing on one energy source, because that would likely cause other problems we can't foresee yet.

The problem of intermittent sunshine can be partly solved by using the electricity during excess hours to generate hydrogen (eg to run cars on). Also, when there is less sunshine there will often be more wind and vice versa, so it makes sense to use both sources of energy. DirkvdM 09:04, 29 August 2006 (UTC)

It's not just the cost that needs to come down, but the efficiency needs to go up. Currently, only a small portion of light hitting a solar panel is converted into electricity, which makes huge solar panels necessary to power a house, and make powering a car (with solar panels on the car) pretty much out of the question. StuRat 11:18, 30 August 2006 (UTC)

What is "Donnan effect"?

Hello all,

I'm a lost student. I found this word "Donnan Effect" in my notes but I failed to find any explaination. Can any kind souls pls enlighten me? Thanks.

It's also called the Gibbs-Donnan effect, but we don't have an article on it. See [2].-gadfium 05:40, 28 August 2006 (UTC)

It is an effect in Membrane chemistry where charged ions on one side of a semipermeable membrane will create an osmotic pressure across the membrane because they are not able to come to an ionic equilibrium. Ansell 07:04, 28 August 2006 (UTC)

There's a stubby article now. -- Plutor 15:17, 28 August 2006 (UTC)

Another grass question

Why does grass go yellow when it has been shielded from sunlight for a while? BenC7 09:02, 28 August 2006 (UTC)

Grass derives its green colour from the chlorophyll in the leaves. Chlorophyll is a green pigment, used in photosynthesis. Over time, chlorophyll breaks down, but new chlorophyll gets produced, replenishing the supply and thus achieving a balance. But when the plant receives no light, photosynthesis is not possible and chlorophyll production comes to a halt. Eventually the chlorophyll supply dwindles, and the green disappears. --Lambiam^Talk 09:48, 28 August 2006 (UTC)

so that is why a freshly unwrapped bagel is also not green? Xcomradex 10:43, 28 August 2006 (UTC)

Not if it's St. Patrick's Day. --Russoc4 11:43, 28 August 2006 (UTC)

The yellow is always present in the grass, but the green from the chlorophyll "outshines" it. I believe the yellow is caused by carotene. --liquidGhoul 11:48, 28 August 2006 (UTC)

Happens to all plants, plants so affected are described as etiolated. Rentwa 15:36, 28 August 2006 (UTC)

Maltodextrin - "the ultimate complex carb"

In the jungle of bodybuilding supplements some products contain allegedly "complex carbohydrates", only to find out that this carb is maltodextrin, glucose polymers - "the ultimate complex carbohydrate". I've always learned that maltodextrin is essentially the same as sugar in terms of absorption and causing insulin spikes, but I may be wrong. Is it possible for "glucose polymers" to ever be large enough to resemble the carbs found in say potatoes? I'd appreciate an answer very much (and I do think this subject goes under science, otherwise correct me ;) ) Jack Daw 13:02, 28 August 2006 (UTC)

I wouldn't believe anything written on a jar of bodybuilding supplement, they will lie as much as they have to in order to get a sucker to buy it. Pretty much all those formulas have in them is calories, and it's easy enough to get all the calories you need from food. You can adjust the balance of complex carbs, sugars, protein, fat, and alcohol by being selective about what you eat and drink. StuRat 21:18, 28 August 2006 (UTC)

This is a completely different discussion of course, but don't you think it's different from person to person how easy or difficult it is to eat a lot of food? Some can eat tons, others, like myself, can't eat that much without getting very sick and thus it's easier to chuck down a drink instead. Regardless, irrelevant to the original question. Jack Daw 15:59, 29 August 2006 (UTC)

Unless you are sick (stomach cancer, for example), you should have absolutely no problem consuming all the calories you need. StuRat 05:41, 30 August 2006 (UTC)

I guess I'd better call my doctor then... Jack Daw 13:04, 30 August 2006 (UTC)

Why does blueberry juice thicken cream?

The title says it all really. I've just eaten some blueberries and cream for dessert and noticed that the cream in contact with the juice was a fair bit thicker. What's going on? Perhaps people can experiment with other friut juices to see if they have the same effect - in the name of science! Theresa Knott | Taste the Korn 13:14, 28 August 2006 (UTC)

Blueberry juice is moderately acidic, and will cause the cream to curdle. Tarter, more acidic fruit juices (lemon, for example) will curdle milk or cream more rapidly. TenOfAllTrades(talk) 15:35, 28 August 2006 (UTC)

There's a knot tightening blueberry molecules that tightens cream too. -- DLL ^{.. T} 18:18, 28 August 2006 (UTC)

Nice plat on my name but bit of a tease of an answer. Does anyone know the name of these molecules so that i can do a google search? Theresa Knott | Taste the Korn 09:14, 29 August 2006 (UTC)

Referencing Wikipedia

I would like to include information pertaining to x-rays (page heading = radiography)in my MSc dissertation. Could you please tell me the authour of this page and what is the place of publication and who is the publisher - is it just Wikipedia?

Many thanks

KElly Rees

Wikipedia:Citing Wikipedia tells you what you need to know. Theresa Knott | Taste the Korn 13:35, 28 August 2006 (UTC)

I would recommend not citing it at all. For high school and above, usually Wikipedia is not taken seriously as a source and it can be negative. — [Mac Davis] (talk) (Desk|Help me improve)

Unless, of course, you want to write yet another article on, "I went to Wikipedia and XXXXXX was not correct. I didn't edit the page and fix it, so it is still incorrect. I went back later and it was fixed, but now I found XXXXX which is not correct. I still didn't edit it to fix it. Oh - it is fixed now. Let me look for something else..." --Kainaw ^(talk) 13:52, 28 August 2006 (UTC)

Of course our articles are usually well sourced, and decently well researched, you could read the citations themselves, and use those as source material. Just don't take the content directly from wikipedia. For instance, our article on X-rays, cites imagers.gsfc.nasa.gov, so if you wanted to, you could go to imagers.gsfc.nasa.gov, then cite imagers.gsfc.nasa.gov as a source. It also cites Reagan, Star Wars and the End of the Cold War, so if you wanted, you could go to a library, and take out the book Reagan, Star Wars and the End of the Cold War, given at the end of the article, complete with an ISBN. I of course have no idea what X-rays have to with Reagan, but then, I didn't write the article. The external links section is also a good place to look for a primary source, in the case of X-rays, the only one that might make a good academic source, would be probably, the BBC link all the way at the bottom, h2g2 X-Rays Edited Guide Entry. Just make sure you're NOT USING WIKIPEDIA AS A PRIMARY SOURCE, your teacher/professor isn't an idiot. If they see a lot of web based sources, the first thing they'll do, is come here, and see if you ripped off wikipedia--71.247.243.173 14:01, 28 August 2006 (UTC)

The cliff notes version: A wikipedia external links/citation section is a good reading list on a given topic--71.247.243.173 14:04, 28 August 2006 (UTC)

I've seen it done before in serious papers, but I wouldn't recommend it either like Mac Davis. It would be like referencing other tertiary sources like paper encyclopedias, except Wikipedia is "delegitimized" because anybody can edit it. Besides, all of the secondary sources are available if you want to reference those. ColourBurst 21:24, 28 August 2006 (UTC)

Yes, consult the referenced sources, but if you are looking for a specific piece of information from the document, you may be able to contact the person who wrote it by using the "discussion" page link (in a tab at the top) above the X-Rays article. I'd reccomend that you go to that discussion page and leave a message asking for the source for the information you wish to site. - Rainwarrior 17:16, 28 August 2006 (UTC)

About the 'athor' of a Wikipedia article - click on the 'history' tab above it and you will see a whole list of authors. As for 'publisher', I don't know if that term applies to Internet sites. DirkvdM 09:10, 29 August 2006 (UTC)

Quartz watches powered by the pulse of our hand

Hello,

I had heard sometime back that there used to be some quartz wrist watches earlier whose quartz crystal used to get the energy for vibration from the human pulse (as the watches are worn on the wrist). I was also told that when the watches are not worn for a long period of time, they tend to "fall behind". Is this true or somebody was taking me for a ride.

Appreciate your time and help.

Thanks and Regards,

Namit Tamhane

I believe it's more from moving around than from your pulse, but the general idea is true. See for instance the article about Automatic quartz - Dammit 13:54, 28 August 2006 (UTC)

See automatic quartz. --Kainaw ^(talk) 13:58, 28 August 2006 (UTC)

Or if that fails, you could always visit our article on Automatic Quartz--71.247.243.173 14:13, 28 August 2006 (UTC)

Or, possibly, you could check AuToMaTiC QuArTz. I forgot. Why are referring people to the same article multiple times? --Kainaw ^(talk) 14:25, 28 August 2006 (UTC)

No idea. Perhaps it's for the same reason that are writing clauses lacking an object? EdC 15:45, 28 August 2006 (UTC)

Subject actually. :P Rentwa 20:26, 28 August 2006 (UTC)

4u70m471c qu4r75 — [Mac Davis] (talk) (Desk|Help me improve)

If your watch runs on your pulse, and then falls behind, you need to view some porn to get your pulse rate back up. :-) StuRat 21:03, 28 August 2006 (UTC)

Oh, StuRat. I know exactly where your brain would have wandered if you were in my morning meeting in which the speaker began, "The Internet is not a human body..." --Kainaw ^(talk) 22:16, 28 August 2006 (UTC)

My father's pocket watch hadn't worked for years. So he gave it to me and one year I used it at Carnaval and it started running again, keeping perfect time. After Carnaval it 'died' again. Next year new Carnaval, watch ran again. It must have been the movement. Uri Geller also used this trick on tv, telling people to get an old watch that doensn't work anymore and he would concentrate and fix it. Sure, some watches started working. People tended to ignore the majority of cases where it didn't work and thought it a miracle. DirkvdM 09:18, 29 August 2006 (UTC)

Changing of Centre of Gravity

This is not homework.

While reading through an article in a magazine, I came across these Adidas Football Studs(Boots), which changed its centre of gravity to the spot where the player makes contact with the ball. Is this practically possible , and if so how ? Please explain. ---User : Veda, Sanchit

There is a shifting weight inside the Adidas Predator. That moves the center of gravity of the shoe - which isn't hard because the shoe weighs something around 300g. So, add a 200g weight and wherever the weight sits is the center of gravity. I read about them for a different reason. Some people buy them to remove the weight and have extremely light shoes. --Kainaw ^(talk) 16:01, 28 August 2006 (UTC)

Even if the shifting weight is a point mass, it could not move the centre of gravity by more than 200/(300+200) = 40% in its direction. Another issue is that as the player's leg accelerates to kick the ball, a shifting weight will lag behind, and is thus more likely to be at the opposite side of the shoe's point of contact. --Lambiam^Talk 19:12, 28 August 2006 (UTC)

Yea, that seems like a silly marketing gimmick to me, not of any real value. StuRat 20:58, 28 August 2006 (UTC)

Mr. Lambian, could you please explain how does the shifting weight lag behind. We tried it with a fully filled water bottle , but found out that the air vacuole moved in the direction of motion of the bottle and only went back after the point of impact. User : Veda, Sanchit

high pressure air plasmas

Are high pressure air plasmas always visible like ordinary plasma? and what kind of things besides air plasma can create the mechanical pressure effect caused by the heated air shockwave. These are used in pulsed impulse weapons. Curious

Actually, the main factor affecting in light emission from plasmas is the temperature. Basically, in a plasma with temperature T, the ions crashing into each other will emit photons of (average) energy $kT$ where k is boltzmann's constant. So, let's say you're looking for a plasma that emits visible light, which has a wavelength $\lambda =500nm$, and an energy $E_{photon}=h\nu ={\frac {hc}{\lambda }}=3.9710^{-19}J$ (where $\nu$ is the photon's frequency, and h is planck's constant). So you need a plasma with a temperature such that $kT=E_{photon}$. Therefore, the temperature must be $T={\frac {E_{photon}}{k}}={\frac {hc}{\lambda k}}=28,800$ kelvin. Hope that helps with the first part. --bmk

Hmmmm well the main question was "are all plasmas that can apply mechanical pressure [ such as laser propulsion and such] always visible by produced light or are there certain kinds that can greate pressure but not be seen? Thanks Robin

planets

Do planets rotate around the sun in the same plane? 209.163.204.144 18:11, 28 August 2006 (UTC)

See ecliptic - R_Lee_E (talk, contribs) 18:13, 28 August 2006 (UTC)

So, the answer is that all the planets do pretty much occupy the same orbital plane. The one exception was Pluto, which is one reason why it was excommunicated ("for deviating from the true path"). :-) StuRat 20:39, 28 August 2006 (UTC)

Thats actually not the only reason, another was it failed to clear it orbit of other objects. 69.179.249.197 20:53, 28 August 2006 (UTC)

Note that 'pretty much' means 'not entirely'. DirkvdM 09:21, 29 August 2006 (UTC)

Also note that the Moon is inclined by 5°, which is the reason we don't have a solar and lunar eclipse every month. DirkvdM 09:28, 29 August 2006 (UTC)

What kind of fish "gives birth" to baby fish instead of laying eggs?

A friend observed a phenomenon: Two tropical fish in a regular glass tank (36 x 18 x 18 inches) have produced a baby fish - without eggs. What kind of fish can this be? Where to find more info about the kinds of fish that "gives birth" as apposed to lay eggs?

Any information will be appreciated!

See live-bearing aquarium fish. --Kainaw ^(talk) 19:57, 28 August 2006 (UTC)

Some sharks also give live birth, although I doubt that's what your friend has in the aquarium! --Ginkgo100 ^{talk · e@} 21:17, 28 August 2006 (UTC)

Well, there are some small shark species that are used in aquariums, IIRC. Confusing Manifestation 00:25, 29 August 2006 (UTC)

Not beginners' aquariums. Sharks are saltwater-only and difficult to keep in an aquarium. You may be thinking of some of the various minnows with trade names including the word "shark", though. These are all egg-layers. --Ginkgo100 ^{talk · e@} 03:42, 29 August 2006 (UTC)

In any case, guppies have got to be one of the most common of aquarium fish, probably second only to goldfish, as both don't even require heated water to survive. Guppies also happen to be live-bearers. A description of the two your friend observed would be helpful. Guppies are rather small (maybe 2cm in length) and slim, with a rather oversized tail. The male guppy always has a much larger brighter, colorful and generally more impressive tail, whereas the female's tail tends to be smaller and rather bland in comparison with perhaps only a touch of colour. Does this sound like a description of the fish your fish saw? (And by the way, is it just me or isn't it odd that humans seem to be the only species of animal where the female is much prettier than the male? I know, I know, I'm just being biased :) Loomis 23:24, 31 August 2006 (UTC)

Specific Heat

What is the specific heat of PEEK & PPS powders?67.78.79.182 21:29, 28 August 2006 (UTC)Deepak

What are PEEK & PPS powders?--Light current 22:14, 28 August 2006 (UTC)

Two-hybrid System

Is the two hybrid system exclusively for detection of protein-protein interaction? I'm reading a journal article that speaks of a bacterial two hybrid system for detecting protein-DNA interaction (reference: Hurt, J. A., S. A. Thibodeau, et al. (2003). "Highly specific zinc finger proteins obtained by directed domain shuffling and cell-based selection." Proc Natl Acad Sci U S A 100(21): 12271-6) --Username132 (talk) 21:40, 28 August 2006 (UTC)

Doesn't have to be. The concept behind the two hybrid is that most transcriptional regulators can be separated into a DNA binding domain and an activation domain. As long as they are brought physically close, they function -- they don't need to be covalently linked. The two hybrid brings the two modules together through a non-covalent interaction between two other proteins, one linked to the DNA binding domain, and one to the activation domain. This interaction doesn't need to be protein-protein. Any sort of non-covalent interaction will suffice. This has been used in both "three hybrid" and "2.5 hybrid" techniques, where RNA and small molecules modulate the noncovalent interaction. I, personally, wouldn't consider your reference (http://www.pnas.org/cgi/content/abstract/100/21/12271) to be a "two hybrid" system. In it a library of zinc fingers covalently fused to the yeast Gal11 protein are created. Although the Gal11 binds to Gal4, the Gal4 in this case is endogenous, not externally applied as in the case of most of the "hybrid" experiments. Also, the interaction they are testing for is not bringing together the DNA binding domain and the activation domain, but is the DNA binding domain - DNA interaction itself. That said, Carl Pabo is a member of the National Academy and I'm not, so my opinion doesn't count much in comparison. -- 17:04, 29 August 2006 (UTC)

Friction

How does the direction of a friction force compare with the velocity of a sliding object?

Why, friction will act in the opposite direction to the sliding objects velocity, of course. --Username132 (talk) 21:51, 28 August 2006 (UTC)

I am not a ware of a link between the velocity af a sliding object and the direction of the friction. In other words, it's what 132 said, irrespective of speed. DirkvdM 09:38, 29 August 2006 (UTC)

Keep in mind that in physics a distinction is usually drawn between velocity as a vector and speed as a scalar. Thus, the friction force vector will point in the opposite direction of the velocity vector, but may have minimal to no relationship to the magnitude of the velocity vector. -- 17:10, 29 August 2006 (UTC)

Mass

I am trying to help my son with his homework and we are stumped, please help? Which has more mass, a 2-kg fluffy pillow or a 3-kg small piece of iron? More volume? Why are these answers diferent. Also if you push horizontally on a create and it slides across the floor, slightly gaining speed, how does the friction acting on the create compare with your push? THANKS!!

Well, since 3kg is greater than 2 kg, the larger mass must be the iron. But the fluffy pillow has more volume (is takes up more space) beacause its density is much lower than that of iron. Mass = Volume X density.

If you push something along the floor, friction will act in the opposite direction to your push. Now there is something called the coefficient of friction that tells you how much frictional force you get per unit weight (related to the mass of course) of the object.--Light current 22:07, 28 August 2006 (UTC)

For the crate, if the friction force were exactly equal to the pushing force, the crate would move at a steady speed. Since this is homework, I'll leave it to you're son to figure out the rest. --Gerry Ashton 22:57, 28 August 2006 (UTC)

Cutting veines

What does it call when someone cuts his arms' veines mostly because of depression? CG 21:57, 28 August 2006 (UTC)

Attempted suicide? Cry for help? Self harming? Attention seeking behaviour? 'Didn't mean it' cuts? I suppose it depends on the person and the circumstances... --Kurt Shaped Box 22:01, 28 August 2006 (UTC)

No I think the user wants the common term which is : Slitting your wrists--Light current 22:09, 28 August 2006 (UTC)

I thought it was called cutting. The disambiguation page points to self-harm. --Joelmills 01:03, 29 August 2006 (UTC)

Sorry Im wrong. Its slashing!!

That's Micheal Myers. Everybody calls it cutting, but formally and less generically "self-mutilation." See emo kid. — [Mac Davis] (talk) (Desk|Help me improve)

No, over here, its called slashing! (as in slashing tyres)

"Slash", a term used to describe cutting with forceful sweeping strokes --Light current 02:44, 29 August 2006 (UTC)

Yeah I was thinking of cutting someones throat! (No one in particular) Thats slitting--Light current 04:11, 29 August 2006 (UTC)

Thank you for the gory explanation :-P. CG 07:04, 29 August 2006 (UTC)

Keep in mind that the questioner asked about cutting veins, not cutting the skin. Cutting/slashing - whatever you want to call it - is only skin deep. It does not cut the veins, unless you make a terrible mistake. --Kainaw ^(talk) 16:05, 29 August 2006 (UTC)

Dissagree. Veins are very near the surface on the inside of the wrists, and thats why you so it there! THe purpose is suicide after all! 8-(--Light current 16:15, 29 August 2006 (UTC)

The phychiatric building here is full of people who cut themselves - not for suicide. They cut themselves on the arm, stomach, and legs. They do not cut veins. That is suicide - that is not self-mutilation due to depression. There is a huge difference between just wanting to cut yourself and wanting to kill yourself. --Kainaw ^(talk) 19:26, 29 August 2006 (UTC)

Ear pain - what does this sound like to you?

I'm going to the doctors tomorrow with this, before anyone quotes the "please consult a doctor for medical advice" rule at me. It's been a bank holiday weekend in the UK and I've been suffering with this for two days (I always seem to get ill at times like these and there's no way I'm going to walking into my local hospital's A+E with this and wasting the doc's time when people could be dying).

Anyhoo. My right ear hurts like hell inside. Ever been swimming and got water trapped inside and you can feel it sloshing around? Well, it's like that but *really* sore/throbbing too - also feels like my ear has 'popped', like when flying in a plane. My hearing is also distorted, the lobe is tender on the outside and the glands on my neck are up on that side. Tried cleaning my ear out with a cotton bud but there's nothing in the canal. Anyone have any idea what I might've got? Abscess? --Kurt Shaped Box 21:58, 28 August 2006 (UTC)

Sounds like an infection or other serious condidtion. Do not wait, Go to Accident and Emergency immediately!--Light current 22:13, 28 August 2006 (UTC)

I don't think I'm about to keel over. It's an earache, basically - aside from being irritated by it, the rest of me is just fine. Just curious about it'sall... --Kurt Shaped Box 22:17, 28 August 2006 (UTC)

Hey Kurt, try giving NHS direct a call. Hopefully they will be able to tell you what it is without you visiting a hospital!

The problem is that you could suffer permanent hearing damage if the infection gets bad enough. Burst or perforated eardrums only take a second. Anchoress 22:22, 28 August 2006 (UTC)

Yes thats why I suggested going to A&E NOW! Its not just earache as you said your glands were swollen.--Light current 01:13, 29 August 2006 (UTC)

I think my sister used the same excuses. Quite a few surgeries were needed. --Zeizmic 23:03, 28 August 2006 (UTC)

Just finished speaking to the on-call emergency doctor. She said to just take ibuprofen and paracetamol at the same time, try to get a good night's sleep, then see my usual doctor tomrorrow. If the pain gets any worse I could to go see them tonight to get some opiates but otherwise it is just an annoying earache that needs a course of antibiotics by the sound of things... --Kurt Shaped Box 23:09, 28 August 2006 (UTC)

Since you are in Britain, you could pay a quid for an answer [3] I just read this and I'm quite insulted that our good advice is worth what people pay for it. Up with the Intellectual Sweatshops! --Zeizmic 23:45, 28 August 2006 (UTC)

Well of course, people who think they've got some good answers here could actually donate £1 (each) to WP--Light current 01:17, 29 August 2006 (UTC)

Kurt, if you are saying that your lymph nodes are swollen, that could be a sign on a serious infection. If so, permanent hearing damage could be the least of your worries. I agree with the others that you shouldn't hestitate to take a taxi to the nearest ER and get an examination from a medical doctor, blah, blah. ---CH 03:22, 29 August 2006 (UTC)

I agree that this is very serious. A normal ear ache would not cause in inflammation in the ear lobe. This shows the infection has spread beyond the ear canal. I agree with the majority of advice above, and think you should go to an Emergency Room. You need some meds, quick ! PS: Have you been letting seagulls peck at your ears ? StuRat 03:29, 29 August 2006 (UTC)

BTW thats the other disadvantage of pushing cotton swabs in-- it pushes infected material IN.--Light current 04:04, 29 August 2006 (UTC)

You seem to assume this "infected material" is a solid. I would expect it to be a liquid or gel, and to easily stick to a Q-tip and then be pulled out. Of course, once the infection has gone this far, pain would likely prevent putting anything in the ear. I would suggest putting nothing but ear medication in the ear until the infection clears up, then use Q-tips to clean it out. StuRat 05:47, 29 August 2006 (UTC)

Just FYI, guys - I'm still alive after a reasonable night's sleep (my ear drum has not exploded yet, at least). Still feel pretty rough though (but no worse), and I'll be seeing my doctor today, as soon as I can get an appointment. Part of me hopes that it's somewhere easy to get to and he lances the damn thing. --Kurt Shaped Box 06:39, 29 August 2006 (UTC)

Sounds like a simple otitis externa. Hopefully you get some antibiotic drops and are better in a few days. InvictaHOG 08:33, 29 August 2006 (UTC)

From that article: Ordinarily, inflammation of the ear canal skin starts off with the loss of protective oils and ear wax (cerumen) along with minor injury to the skin. That injury often stem from attempts at self-cleaning or scratching using cotton swabs, hair pins or other implements small enough to fit in the ear canal. Prolonged water exposure (either swimming or exposure to extremely high humidity) is enough alone to both decrease the protective barrier of ear wax and to cause tiny breaks in the waterlogged skin, hence the name, "swimmer's ear". Since the swollen ear canal skin often is both itchy and painful, and sometimes associated with a feeling that something is stuck in the ear, a vicious cycle of self-cleaning or scratching can perpetuate the condition.

As I said before many times, ears are self cleaning and you shouldnt stick anything inside em (except proper earplugs--Light current 16:24, 29 August 2006 (UTC)

The doctor told me to pour warm olive oil in my ear three times a day and it should sort things. He's not my usual doctor and he's a guy I've had problems with before and who I'm pretty certain doesn't like me (I was in and out of his office in less than two minutes and he was very rough with my ear) - so I have my doubts as to whether this will work. Oh well, I can but try. --Kurt Shaped Box 00:34, 30 August 2006 (UTC)

EDIT: Can I use the word 'cunt' on the reference desk? Because this particular medical practitioner certainly is one. He's always really easy to get an appointment with because all the patients avoid him like the plague, due to him being a really bad-tempered, nasty, sharp-tongued little troll with very little in the way of compassion and/or empathy... --Kurt Shaped Box 00:39, 30 August 2006 (UTC)

Ok, I'll be the bunny. Given your description of him, why do you go to him? JackofOz 05:16, 30 August 2006 (UTC)

He certainly seems like an idiot to me. It sounds like you have a bacterial infection, so you need an antibiotic administered by drops into the ear canal, and possibly a general oral antibiotic, since the infection has now spread. Ignore that doctor and go find a competent doctor before you lose hearing in that ear or die (once the infection spreads to your brain). StuRat 05:33, 30 August 2006 (UTC)

He was the only one available at the time at the place I go to and I figured that even he couldn't screw this one up - even if he is a dislikable person (yeah, the guy's a jerk - but I thought he'd at least know his medicine). --Kurt Shaped Box 08:10, 30 August 2006 (UTC)

Any new updates ? Have you started to hallucinate from a brain infection yet ? StuRat 08:28, 31 August 2006 (UTC)

Had a very bad night, though I actually feel a bit better today (woke up and my pillow and the side of my head was covered in pus). Seeing a different doctor in a couple of hours time. --Kurt Shaped Box 12:53, 31 August 2006 (UTC)

You could request to be transferred to another doctor in another surgery so you'll never have to see the doctor you don't like again - I believe these requests are always complied with. I expect it involves filling in a form. I'm surprised you have such problems in the NHS - myself and relatives and friends have always recieved very kind and good service.

Yesterday I was going to write that they may be reluctant to use antibiotics willy-nilly as that encourages drugs resistance, but if you've got pus coming out of your ear that's another story.

I recently read somewhere about a man in the third-world somewhere who had got maggots in his ear. It was thought he had broken the tender skin by poking things in his ear like cotton buds. Once this problem is settled, I also suggest you stop putting things in your ears. I've heard of people whove badly damaged their ears by slipping in the shower while sticking cotton buds in them. 81.104.12.9 11:30, 1 September 2006 (UTC)

Feels a little better today. Whether that's due to the antibiotics kicking in, or simply because the abscess has partially drained, I'm not entirely sure. All the sounds in my right ear still sound distorted/full of reverb - my own footsteps on concrete sound particularly odd. Reggae basslines have to be heard to be believed in this condition - it's like the music has been taken to another level of greatness... ;) --Kurt Shaped Box 00:08, 2 September 2006 (UTC)

So do you have any antibiotics yet, or are they still denying that you have an infection ? I suppose they can settle the issue for sure at the autopsy. StuRat 05:49, 2 September 2006 (UTC)

Yup. Got pills. --Kurt Shaped Box 14:29, 2 September 2006 (UTC)

Plant metabolic rate.

Does anyone know of a source that describes how plant biologists measure the metabolic rate of something like a tree? --Seejyb 22:50, 28 August 2006 (UTC)

I dont know but I would put it in an enclosed environment and measure its CO2 demand.--Light current 15:20, 29 August 2006 (UTC)

Look up information on paper companies. I worked for Mead-Westvaco for a couple contracts. They put a lot of work into measuring soil and air chemicals. They measure tree heights, distance apart, root spread, animals in the area, bark density... it goes on and on. I found that the paper plant's forest had much healthier trees than the Federal forest right next to it - primarily because the Federal forest had no human intervention to improve tree health at the expense of other plants/animals. --Kainaw ^(talk) 16:10, 29 August 2006 (UTC)

biology

What is the only evolutionary mechanism that leads to adaptation 201.112.65.25 22:57, 28 August 2006 (UTC)

This sounds like a homework question, and a bad one at that. There are many mechanisms of evolution, and I don't believe any one of them stands alone in its ability to effect adaptation. --David Iberri (talk) 23:20, 28 August 2006 (UTC)

Natural Selection?

Do your own homework: if you need help with a specific part or concept of your homework, feel free to ask, but please do not post entire homework questions and expect us to give you the answers. Letting someone else do your homework makes you learn nothing in the process, nor does it allow us Wikipedians to fulfill our mission of ensuring that every person on Earth, such as you, has access to the total sum of human knowledge. Rockpocket 01:55, 29 August 2006 (UTC)

Depends on what state you live in. Down here, it is God. He made all animals as they are and anything you think is adaptation is actually just Satan playing tricks on you. --Kainaw ^(talk) 16:07, 29 August 2006 (UTC)

Luck. CptJoker 11:28, 30 August 2006 (UTC)

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Hello all, i have to do a project on parts of plants for science. can anyone tell me what websites to look at? i am really desprate coz im going away for the weekend and its due soon!!! HELP!!!!!