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May 24

Concrete dampening and evaporation

Recently I witnessed some light rain which evaporated fairly quickly after landing on the concrete. However, I noticed it on two sections of the sidewalk which were of about the same color and exposed equally to the rain, and one looked much wetter, as if the rain wasn't evaporating as fast. Why might this happen? What hidden variables might be in effect? 69.111.191.122 (talk) 00:08, 24 May 2008 (UTC)

I wonder if the roughness of the surface could affect the evaporation rate, or your perception of its wetness. -- Coneslayer (talk) 01:33, 24 May 2008 (UTC)

I think the damper part of the pavement was a little rougher, so that might have been it. Otherwise, they were about the same in terms of exposure to both sunlight and rain. 69.111.191.122 (talk) 02:05, 25 May 2008 (UTC)

not to mention the possible absorbancy of the micro-surface of the concrete. Richard Avery (talk) 07:12, 24 May 2008 (UTC)

Before the rain, was the sun out and was the wet pavement in the shade then? DirkvdM (talk) 18:48, 24 May 2008 (UTC)

Also one part of the pavement might be above someone's basement or a sewer tunnel and the other have earth directly underneath. --Lisa4edit (talk) 01:48, 25 May 2008 (UTC)

Could be due to the porosity or the concrete —Preceding unsigned comment added by 79.76.141.94 (talk) 04:03, 25 May 2008 (UTC)

Studies

Are there any studies being conducted (besides this one: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371%2Fjournal.pbio.0050193&ct=1#journal-pbio-0050193-box01) that are looking for the effect of bisphenol a in humans through out the lifespan? They must be looking at only bisphenol a's effect, I don't want any other chemicals in the study being studied for their effects.68.148.164.166 (talk) 01:16, 24 May 2008 (UTC)

There are more studies on this subject than you can possibly read. Searching Google Scholar for recent articles on bisphenol toxicity in humans returns 2890 hits as of today. Hope this helps ;) --Dr Dima (talk) 03:46, 24 May 2008 (UTC)

How to deal with very recent developments? Pulser pump, mechanical mathematician, accumulating solar barbecue, dripper trackers.

I tried a couple of years ago to add the pulser pump to wikipedia. It is a simple river driven pump for 3rd world use that has no moving parts. I made one in Ireland and it is now 20 years old and still working. I have posted details on the web including video but for whatever reason, nobody in the scientific community has ever bothered to independently verify it. Its component parts are well know. (Trompes and airlift pumps). So it is a very short mental hop to realize that they actually work. But nobody has bothered verifying it. I invented the mechanical mathematician in late summer 2007 and it is now on solarcooking.org It is a tool for making parabolic dishes and moulds from clay. I invented the dripper trackers early this year and solarcooking.org put them in their recent news section. Dripper trackers are appropriate tech timer/counterweight devices for tracking solar reflectors. There are no patents involved. Is there any way to fasttrack them onto wikipedia so more people can make and use them? Brian White BC Canada Gaiatechnician (talk) 02:07, 24 May 2008 (UTC) —Preceding unsigned comment added by Gaiatechnician (talk • contribs) 02:02, 24 May 2008 (UTC)

Short answer: no.

Long answer: Wikipedia is an encyclopedia. We have articles on things other people have reported on through reliable sources. We don't publish original ideas. What you need to do is either A) get your idea published in a respected engineering journal or B) get major news sources to publish articles about your idea, probably by proposing it to governments or corporations. Wikipedia isn't the place to come to promote your concept, I'm afraid. — The Hand That Feeds You:^Bite 02:36, 24 May 2008 (UTC)

Definitely, no! Wikipedia has strong policies that require that articles are about 'notable' subjects, that can be 'traced back to reputable sources' and are not 'original research'...your proposed articles fail all three tests - and if you wrote them, you'd probably fall foul of the 'no self-promotion' and 'anti-spam' guidelines too! That's mostly because we aren't going to take your word for it that these things work - we need to have 'references' to books and magazines that have independently reported on these things.

A better place to promote and discuss your ideas would be somewhere like World Changing - a Wiki designed for accumulating information on 'appropriate technology' - or Green Technologies - another Wiki which has similar goals. I'm sure there are others. Google 'Wiki Green Technology' for example. 70.116.10.189 (talk) 13:26, 24 May 2008 (UTC)

Ok then, the pump has been on the internet glossary of pumps for about 5 years. Does that count for anything? Also, since people who might use the pump often use wikipedia for reference, is there any chance that you can add a proper definition of trompe to wikipedia? They were widely used in Canada, spain, france, and the USA before hydroelctricity. In mines especially and even to operate pneumatic equipment for building alpine tunnels! Gaiatechnician (talk) 22:19, 24 May 2008 (UTC)

And with regard to your "pulser pump", have you seen our article about the well-known hydraulic ram? Two moving parts, but it sounds quite similar.

Atlant (talk) 15:44, 27 May 2008 (UTC)

Look, it isn't a ram. (The ram is also in the internet glossary of pumps).

I dont care what you call it, You can call it a combined airlift pump and trompe if you like but why not have at very minimum a definition for trompe on wikipedia? Trompes are real things that were used for over a hundred years and which are documented in engineering reference books. Pulser pump (I do not care what you want to call it) is a combined airlift pump and trompe and has no moving parts.

The difference between 2 moving parts and no moving parts should be enough to make people understand that they are different things but apparently not. It has nothing whatever to do with hydraulic rams and the tiniest bit of basic research would make that clear.

(http://members.tripod.com/~nxtwave/gaiatech/airliftreferences/trompinfo.html) is trompe info supplied to me as a result of a web request. but of course wikipedia cannot use it because it comes from my webpage and not from a book that I have. It is clear that nobody is bothered to get the info themselves. I am sorry to be annoyed but rams are absolutely nothing to do with trompes. I am done being bated by people who will not do their research. Gaiatechnician (talk) 07:20, 29 May 2008 (UTC)

Do you find that your attitude commnly leads to success? It seems not, based on what you've said here. Just "a word to the wise"...

Atlant (talk) 13:05, 29 May 2008 (UTC)

Knowelege of trompes can help riverside people in poor countrys have better lives. You can either provide them with that information or hide it from them. Feel free to concede that it is not a ram and lets make progress here. Why hide useful information away from poor people? Trompe still does not have a proper definiton in wikipedia. Why? It has been 5 days. Ample time indeed Gaiatechnician (talk) 00:01, 30 May 2008 (UTC)

WHAT IS THE HYPOTHALAMUS

Have you tried.... hypothalamus? :-) --98.217.8.46 (talk) 03:01, 24 May 2008 (UTC)

More simply, it is the part of the brain that sends the signals from your nerves to your hormones. Rockpocket 07:40, 24 May 2008 (UTC)

Earwax

What is the best way to prevent a buildup of earwax? —Preceding unsigned comment added by 79.76.238.57 (talk) 02:56, 24 May 2008 (UTC)

Clean your ear canals regularly with cotton swabs. —Keenan Pepper 03:12, 24 May 2008 (UTC)

...But do read the instructions, and don't be an idiot and puncture your ear drum like this man. —Keenan Pepper 03:16, 24 May 2008 (UTC)

I was told never to put anything in my ear that was smaller than my elbow! —Preceding unsigned comment added by 79.76.238.57 (talk) 03:20, 24 May 2008 (UTC)

Yea, that's pretty borderline medical advice there. I don't clean my ear canals with cotton swaps any more after I crammed so much ear wax that I couldn't hear out of one ear till a $300 doctor's visit (paid for by insurance, I think). I don't clean them at all any more and I haven't had any problems in 3-4 years (since the doctor visit). --Wirbelwindヴィルヴェルヴィント (talk) 03:27, 24 May 2008 (UTC)

Everything I've ever read or heard about this states pretty clearly that cotton swabs are a bad idea. They remove some of it, sure, but they also push the wax farther in and pack it in more tightly. In fact, even our own article on ear wax says, "Cotton swabs, on the other hand, push most of the earwax further into the ear canal and remove only a small portion of the top layer of wax that happens to adhere to the fibers of the swab." -- Captain Disdain (talk) 11:33, 24 May 2008 (UTC)

those cotton swabs r no good for that purpose, i have been told by an ear doctor (Otolaryngologist? ear MD?)... i personally use my shower head (where the water comes out) with low pressure and direct it in various angles at my ears... yesterday my ear doctor found nothing in my left ear (after more than a year) and in my other ear he found something that he removed with a special "shower head"... furthermore i think that apes wont do anything about their ear wax... --Homer Landskirty (talk) 04:08, 24 May 2008 (UTC)

There are a number of relatively safe dissolving preparations available over the counter from chemists. A few drops of solvent is dripped into the ear canal and the canal is then lightly plugged with cotton wool. The dissolved wax runs into the cotton wool. Do it at night and one ear at a time and you should be wax free in no time. Richard Avery (talk) 07:10, 24 May 2008 (UTC)

Any oil akin to say, soy oil, will produce similar results. Use a proper tool for the job, and inject a wee few drops before going to sleep. Use cotton to keep it in, and repeat next evening. At the end of the treatment (my doctor told me to do it three evenings in a row) some comfortably warm water should be used to rinse the ear canal. Showerhead excels here. Not too much pressure, as Homer pointed out, but enough and from many enough angles that you cover it all. You can use a cotton pin to check how much is left, a day and two after. Removal of earwax is nearly as easy as removal of snot, so I wouldn't mind the medical advice disclaimer. Scaller (talk) 08:48, 24 May 2008 (UTC)

I use 70% isopropyl or ethyl alcohol to wash off my earwax, free disinfectant too.--Lenticel ^(talk) 12:08, 25 May 2008 (UTC)

New portal

Hello every one! I've created a new template on molecular and cell biology. Since, I do not have much experience and confidence in editing such sophisticated material, and also don't possess the requisite expertise in the field, I request others to go through the template and edit it in accordance. Moreover, I felt this was a very fundamental topic, which didn't have any template, so created that.

I don't know if there is a provision to notify users accessing articles related to the template that such a template has been created, and that it could be included on the pertinent pages.

Regards.

KetanPanchal^talk-TO-me 07:12, 24 May 2008 (UTC)

Try Wikipedia:WikiProject Molecular and Cellular Biology - the talk page there would be the best place to contact people involved in the articles your template would be useful on. --Tango (talk) 15:06, 24 May 2008 (UTC)

Peer Reviewed?

[1]

I'm confused by the article. Are they saying that bisphenol A actually occurs naturally in the environment? Chemical reactions actually happen in the environment to creat bisphenol A with or without catalysts? And if so, is this peer reviewed?

Another entirely different question:

Does industry funding have any importance once a piece is peer reviewed?

I mean, if a piece is industry funded, and the funder decides that results are not in its intrests, they can pull out funding, or if in the middle of the research, they can decide not to pay for the rat, and then even if the piece get's peer reviewed, the peers would obvious see something wrong, and the piece would have to be revised.

If the piece is industry funded, and then it gets peer reviewed, if say the rat cage was not cleaned (and this was on purposely not cleaned, so that the results would indictate not bisphenol A release (let's just say)), the peers would find it and the piece would have to be revised anyways.

So is there any way that from where a piece is funded is important to know on top of peer reviewed statusstratification?68.148.164.166 (talk) 06:54, 24 May 2008 (UTC)68.148.164.166 (talk) 09:48, 24 May 2008 (UTC)

I don't think the implication (from reading the abstract) is that it occurs naturally. I think they are suggesting Bisphenol A is made synthetically, but then leaked into the environment where humans and other animals are exposed to it. It would appear that the greatest exposure comes from our diet.

On reading the information for authors, its not entirely clear whether review articles are peer reviewed in this journal. Some journals do peer review reviews, others do not. You could always email the editor and ask him or her.

Authors typically have to declare any conflict of interest at the end of a manuscript, where industrial funding would be declared. However, since this is a review article (rather than original research) the scope for COI is limited. The authors are simply summarising the literature, rather than reporting new findings. However, to address your concerns. If you wanted to purposely hide or lie about some information then it is unlikely reviewers would be aware of that on a one off occasion. In time your work would be discredited though, as other people in the field would not be able to repeat your experiments. It is reproduction and repetition that determines the authenticity or scientific reports in the longer term (which is why you should take conclusions of any single paper at your own risk). Cheats may prosper in science for a while, but eventually their work will be marginalized. That all said, most scientists do factor in COI when reading articles. For example, I also treat research on lung cancer that is funded by the tobacco industry with a healthy dose of skepticism. There are also conditions factored into corporate funding sometimes. The money men may have the final say on whether you can publish some data, so if your findings are not strategically favorable to them, they could stop you from publishing it. So its very much in your interest to ensure that the funders like the outcome. For this reason, a lot of scientists refuse to accept corporate funding: because it can leave you in a, shall we say, morally ambiguous situation. Rockpocket 07:37, 24 May 2008 (UTC)

The article states that the source for exposure is enviroment or food, but the bisphenol A in the enviroment and food does 'NOT occurs naturally in this sources, but is added by pollution through human products and waste.--Stone (talk) 08:38, 24 May 2008 (UTC)

Note that peer review does not guarantee anything is correct. It also does not really attempt to spot deliberate falsification. All it does is try to make sure that the article can pass a very elementary analysis by people who are versed in the same knowledge. They are just checking to make sure it isn't totally worthless, totally embarrassing to the journal it is in, or taking up space that would be better served by just about anything else. I'm not knocking peer review, though it is hardly the wonderful system that many of those who are not involved in it think it is. It's one way of handling the question of what should be published; it is also somewhat of a deliberate screen to keep out "cranks" and non-professionals. It does not, and never has, guaranteed validity, freedom from bias, or even something simple like coherency. Don't over-trust in it. --98.217.8.46 (talk) 19:52, 24 May 2008 (UTC)

automobile wheel size

I am buying a car soon and I have a choice between the base model and a higher model.

They are practically identical except that the base model has 15 inch wheels while the higher model has 16 inch wheels.

Does this mean that the base model will run at a higher rpm (engine speed) for the same on road velocity?

Does it mean that the base model (15 inch wheels) can accelerate faster because it can put a higher torque on the road due to its smaller wheel size? 122.107.199.2 (talk) 10:47, 24 May 2008 (UTC)

The "15 inch" and "16 inch" numbers are the diameters of the wheels (tire rims). The size of the wheel does not by itself determine the diameter of the tire, because the height of the tire walls are not taken into account. See the Wiki article on tire specification for more details. --71.162.249.240 (talk) 12:45, 24 May 2008 (UTC)

The larger rims have skinnier tires - which gives the car a more agressive look that's very trendy today.

Sadly, the people who go for bigger rims and skinnier tires are not physicists. Rubber (even with steel 'belts') weighs less than aluminum so the 15" wheels (having more rubber and less aluminum than the 16" kind) are typically lighter. Whilst the difference isn't all that great compared to the weight of the entire car, driving experts like to distinguish 'unsprung weight' from 'sprung weight'...the weight of things like wheels, brakes and axles that are not being isolated from the road surface by springs and shocks is much more important to performance than 'sprung weight' - the engine, transmission, body, etc. Saving even a few pounds of unsprung weight can have a big performance impact. Also, the heaviest part of the entire rim/tire assembly is further out from the hub in the case of 16" wheels - which gives them a higher moment of inertia - which makes them harder to start and stop spinning - so you actually get more accelleration and better braking from 15" wheels than 16". The only benefit (performance-wise) of 16" wheels is that the side-walls of the tires are shorter so they flex less while cornering and braking - which somewhat improves handling but produces a slightly harsher 'ride' than the 15" wheels.

One cool trick is to buy the 15" wheels - but then swap out the tires for skinnier ones and sell the old (but unused) tires on Craigslist or whatever. Now you have the 'look' of the 16" wheels but a smaller diameter. You truly get the best of both worlds AND the reduced overall diameter gives you better accelleration (although a lower top speed) - and has the effect of lowering the car a half inch - without the cost of 'lowering springs' which looks cool (if you like that kind of thing) and typically produces better handling. The only real downside is that you have less ground-clearance and (strictly speaking) your speedometer and odometer need to be recalibrated. 70.116.10.189 (talk) 13:09, 24 May 2008 (UTC)

Studies

I know there are no completed studies that are looking for the effect of bisphenol a in humans through out the lifespan, but are there and studies in the progress or are planned (besides this one: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371%2Fjournal.pbio.0050193&ct=1#journal-pbio-0050193-box01)? They must be looking at only bisphenol a's effect, I don't want any other chemical(s) in the study being studied for their effects. Thanks!68.148.164.166 (talk) 11:30, 24 May 2008 (UTC)

You just asked that, and got an answer, 7 sections up. --Tango (talk) 12:47, 24 May 2008 (UTC)

Water Clouds

Recently returning on a flight i just happened to notice that flying at 37,00oft there was on the wings what seemed to be water but it was moving more like a gel ???? At this altitude the temperature is as far as i am aware about between -80 to -100 . Surly the rain droplets would have frozen then fallen to earth??? Which technically would mean that the clouds would become too heavy and (fall from the skies)??? How is this???? —Preceding unsigned comment added by Mmm311068 (talk • contribs) 11:57, 24 May 2008 (UTC)

Water droplets won't get any heavier when they freeze - as long as it's a very small frozen droplet it will still be suspended in the air. When the droplets get too large, they will fall from the sky as rain. I don't know why the water droplets on the wings would act strangely - my guess would be an aerodynamic effect. --Tango (talk) 12:50, 24 May 2008 (UTC)

What you saw on the wings might not have been water (particularly not that high up) but rather Deicing fluid. That will get gel-like when you freeze it. --Lisa4edit (talk) 09:33, 25 May 2008 (UTC)

Dosage of a Drug

When dosages of a particular drug are calculated such as "1mg per kg" does it matter that someone may be 60% fat and another 20% fat but weigh the same?

What is really being estimated by using the weight, is it total blood volume, metabolism etc? 78.148.84.63 (talk) 12:44, 24 May 2008 (UTC)

Pharmacokinetics#Compartmental_analysis should give some hints... surely adipose people with liver damage need different dosage and sometimes even different medication... dosage is often symptom based, too... i think those "per kg body weight" numbers r just a rule of thumb and that doctors often cant even measure the weight of the patient when they "compute" the dosage (e.g. in case of an emergency on the street...)... --Homer Landskirty (talk) 13:39, 24 May 2008 (UTC)

Usually the dosage is given as "mg per kg of ideal body weight". Often this is just ignored, as there are only certain drugs for which the adjustment for obesity is crucially important. The volume of distribution for lipophilic drugs may be greatly increased in the obese. - Nunh-huh 15:59, 24 May 2008 (UTC)

Scientists

Are doctors or engineers considered as scientists? If not, what are they considered as. Clover345 (talk) 13:03, 24 May 2008 (UTC)

An engineer isn't a scientist, they're an engineer. It's a separate category. I'd say a doctor probably does count as a scientist though - they certainly are if they're involved in research. --Tango (talk) 13:11, 24 May 2008 (UTC)

The short answer to your question is that most doctors and engineers are considered to be doctors and engineers. A more detailed answer would depend greatly on the nature of the work that a particular engineer or physician did, as well as how broadly one chose to define the term 'scientist'.

If we say that a scientist – roughly speaking – is someone who is paid to employ the scientific method to answer questions about the way the world around us works, then some physicians and engineers would fit the category while others would not. While engineers often are involved in using known principles to solve specific problems, there absolutely are engineers who conduct basic research into metallurgy, corrosion processes, aerodynamics, semiconductors, etc. Many doctors use established techniques and protocols to treat patients, but at least some participate in clinical research projects. (Any large medical research institute will have at least a few 'double docs' floating around: individuals who have both MD and PhD degrees.)

It might help if you could give us some idea of why you want to put each of these professions into a 'scientist' or 'not-scientist' box. TenOfAllTrades(talk) 14:34, 24 May 2008 (UTC)

More generally, people who are researchers are often considered scientists. Doctors and engineers, as trades, are not researchers. There are people with MD degrees and all sorts of engineering degrees who are researchers, though. And sometimes they put on different hats and become doctors and engineers, practicers of a trade, as well. --98.217.8.46 (talk) 17:18, 24 May 2008 (UTC)

Engineers read; scientists write. --Sean 00:16, 27 May 2008 (UTC)

And vice-versa. Both engineers and scientists contribute to original research frequently, but the distribution of publication frequency and the (direct) applicability of their publications differ. Depending on the field, this line is often quite blurred. Sjschen (talk) 00:24, 27 May 2008 (UTC)

Metallurgy

I have to do a presentation about metallurgy, and I need a good demo to accompany the presentation. Any suggestions? --Sturgeonman (talk) 17:59, 24 May 2008 (UTC)

Perhaps a shape memory alloy demo. --hydnjo talk 22:52, 24 May 2008 (UTC)

Spin

If I was to throw an object at a certain speed and spin, what angular velocity would I need to spin it at such that it comes to a rest? I worked it out to 5v/2r, but I'm not sure whether my answer is right. During the calculation, I saud that F=ma, and so F(k)=Ma, μMg=Ma, a=μg. Is this right? —Preceding unsigned comment added by 76.69.241.74 (talk) 18:04, 24 May 2008 (UTC)

I don't understand your question. Whatever speed and spin you throw it with, it will come to rest quite shortly afterwards, but I guess the quickest way to achieve this is to throw it with zero speed and zero spin.--Shantavira|^{feed me} 18:32, 24 May 2008 (UTC)

Yeah, sorry the question's badly worded. If I wanted to throw a ball at velocity v (say 5 m/s), what angular velocity would it need to have so that it comes to rest and doesn't roll afterwards (for example, if I spun it faster it would roll back towards me, and if I spun it slower it would continue in the same direction, just slower). —Preceding unsigned comment added by 76.69.241.74 (talk) 19:22, 24 May 2008 (UTC)

Sounds like a case where friction is causing a force to be applied to the lower edge of the ball in the direction opposite both the ball's travel and the spin. You want that force to zero out both the momentum and angular momentum at the same time. One critical factor is the mass distribution of the ball. Is it uniformly dense, or is it a hollow shell? The relationship between mass, spin, and angular momentum are different for each. (That said, someone else will have to work out the mathematics - I'm too rusty for that.) -- Tcncv (talk) 21:55, 24 May 2008 (UTC)

You should probably also take into consideration the coefficient of friction of the ball and of the surface as well as the air resistance on your ball. Bastard Soap (talk) 23:53, 24 May 2008 (UTC)

Well, I'm assuming air resistance to be zero. As per friction, I did take it into account, for friction is a necessary component for this to work. That's what F(k) is (force of kinetic friction). —Preceding unsigned comment added by 76.69.241.74 (talk) 01:20, 25 May 2008 (UTC)

Yeah, the air resistance would be negligible assuming a smooth ball (such as one of plastic) that is not light. However, air resistance would probably need to be calculated on something such as a tennis ball or other "fluffy" ball. It definitely would need to be taken into account for a light-weight, "fluffy" ball. For simplification of the situation, though, I would have assumed the OP to be negating that (which s\he is). Ζρς ι'β' ^¡hábleme! 01:45, 25 May 2008 (UTC)

What if we leave the force of friction unknown for the moment, but simply assume it creates enough of an impulse while the ball is in contact with the surface to negate the ball's forward momentum? Ignoring deformation due to the impact, what will the ball's angular momentum then be as a function of its initial velocity and angular momentum? That might be an easier way to approach the problem I'd think. I'll think about that some more though. Hmm. --Prestidigitator (talk) 03:35, 25 May 2008 (UTC)

Suggestion: Think about the problem in reverse. The ball has just stopped. Immediately prior to stopping, the a force due to friction was being applied to the bottom surface of the ball in the opposite direction of its motion (and backspin). Any such force would (I believe) affect both momentum and angular momentum in some proportion. That proportion would be independent of the amount of force involved. Calculate the relationship between that force and changes to both momentum and angular momentum, and then combine to eliminate force, and you should have the answer. -- Tcncv (talk) 04:31, 25 May 2008 (UTC)

Well, as I said earlier, I already got an answer (5v/2r). I just wanted to know if it was right. —Preceding unsigned comment added by 76.69.241.74 (talk) 17:29, 25 May 2008 (UTC)

I'm surprised that the answer doesn't depend on the coefficient of friction. A completely smooth ball won't stop regardless of the amount of spin you give it and I would expect the required spin to vary continuously with friction (this expectation could well be wrong), which would require it to either be always impossible (doesn't seem right to me) or be non-constant. --Tango (talk) 19:28, 25 May 2008 (UTC)

My calulations involved cancelling the coefficient of friction, such I guess it's assumed to be non-zero (0/0 is indeterminant). If I'm right, friction only affects the time it takes (t=v/μg).

Well, here goes. Analyzing the angular momentum about the center (of mass of) the ball:

$\Delta p=-p_{0}=-mv_{0}$

$\Delta L=-L_{0}=-Iw_{0}=r\Delta p=-mrv_{0}$

$w_{0}={\frac {mrv_{0}}{I}}$

Using a list of moments of inertia, for a solid ball:

$I={\frac {2mr^{2}}{5}}$

$w_{0}={\frac {mrv_{0}}{2mr^{2}/5}}={\frac {5v_{0}}{2r}}$

And for a hollow ball:

$I={\frac {2mr^{2}}{3}}$

$w_{0}={\frac {mrv_{0}}{2mr^{2}/3}}={\frac {3v_{0}}{2r}}$

which seems to agree with yours, if you were talking about a solid ball. --Prestidigitator (talk) 05:55, 26 May 2008 (UTC)

I think it's only a coincidence that we got the same answer this way. When using the equation ΔL=rmΔv, the v refers to the tangential velocity of the ball, which is only equal to its actual velocity when the ball isn't slipping.

I got an answer using the following method:

Στ=Iα, F(k)R=Iα, α=F(k)R/I.

ΣF=ma, F(k)=ma, a=F(k)/m.

Then, using the equations of motion, I solved ω=mRv/I. —Preceding unsigned comment added by 76.69.241.74 (talk) 01:15, 27 May 2008 (UTC)

It had nothing to do with slipping or not slipping. I used $\Delta L=r\Delta p=-rmv_{0}$ because you stated the ball was to stop both its linear and rotational motion. You did exactly the same when you stated $F_{k}R=I\alpha$. --Prestidigitator (talk) 00:21, 29 May 2008 (UTC)

May 25

Genetics: Linked genes

I would like to know if there are any linked characteristics with a particular gene, is ther a good resource for this? In particular I would like to know if there are any traits associated with curly hair and pointed canines in humans. Bastard Soap (talk) 00:11, 25 May 2008 (UTC)

Well first you have to find out whether there are known genes that have a phenotype resulting in curly hair or pointed canines. Then you can you find the other traits associated with those genes. A good way to do this is is via OMIM. A search for "curly hair" reveals a number of genes that have alleles associated with curly hair, these include the plakoglobin gene which is responsible for Naxos disease. In these people, curly hair is associated with palmoplantar keratoderma and cardiac abnormalities. However, these alleles tend to be rare, extreme examples. Genetic association with "regular" curly hair is unknown, See: Online Mendelian Inheritance in Man (OMIM): 139450 Rockpocket 07:37, 25 May 2008 (UTC)

Transformers

Do the actual number of turns have any effect on the general system, or is it only the ratio that counts? 2000:1000 is equivalent to 2:1 in all respects? Bastard Soap (talk) 00:44, 25 May 2008 (UTC)

The greater the number of turns in the winding (other things being equal) the greater the inductance (and resistance). If you took a transformer designed to be connected to a 120 volt source in the primary winding which had 2000 turns and connected a 1 or 2 turn winding across the same 120 volt source, with no load on any other winding, I would expect extremely high current to flow due to the low inductance, causing a fuse to blow or the winding to burn out. The higher number of turns in the original transformer would have limited the no-load current to a safe value due to the higher no-load inductance. Tinkerers have sometimes taken a transformer and left the 120 volt (240 volt in other countries than the US) primary winding alone, since it has enough turns to work properly, then changed the number of turns in a the secondary wound over it to produce a high current-low voltage secondary, or a high voltage low current secondary, as desired. In summmary, a transformer with too few primary turns would draw excessive current even when there was no load on the secondary, but the no-load voltages would still vary pretty much as the turns ratio. Edison (talk) 03:49, 25 May 2008 (UTC)

The actual number of turns does have an effect. The number of primary turns must be sufficient to avoid saturation of the core or keep down the magnetising current. This is one reason that, generally, one cannot use a step down transformer backwards as a step up transformer.

Also, increased turns will, of course, put up the winding resistances. This is important when you consider losses and heat generation etc. —Preceding unsigned comment added by 79.76.141.94 (talk) 03:39, 25 May 2008 (UTC)

I've seen lots of utility power transformers and instrument transformers which worked fine to step up or to step down voltage. Step-up, step down, or unity isolation transformers. Edison (talk) 03:51, 25 May 2008 (UTC)

Isn't that the point though? You can design a transformer so it's suitable for stepping upping a voltage say 22kV to 44kV. This will work fine for other things like 44kV to 22kV, 22kV to 11kV, 440V to 220V etc. But you wouldn't want to use it for 44kV to 88kV or 88kV for 44kV Nil Einne (talk) 15:41, 25 May 2008 (UTC)

For one thing the strength of the magnetic field in the core will be different between those cases, and I think it might be possible to saturate the material in the transformer's core if the magnetic field strength is too high. But I'm not sure. I don't see any allusion to it in the articles I've looked through so far. I might have to go digging through electrodynamics textbooks at some point. --Prestidigitator (talk) 04:09, 25 May 2008 (UTC)

Therefore assuming that there are enough turns to limit the current and prevent saturation of the core, there would be no advantage what so ever in addind more turns? 88.203.106.28 (talk) 07:00, 25 May 2008 (UTC)

First, in response to Nil Einne, I agree that the 44kV to 22kV transformer can step down 44kV or step up 22 kV equally well. The problem with applying, say, 44 kV to the 22 kV winding is that the voltage stress would exceed the insulation level and could cause a short between turns or to the core or a flashover of the insulators or bushings. I would also expect the exciting current (with one winding energized and no load on the other windings) would increase with a higher than rated voltage applied. With a utility transformer, there is quite a bump when the voltage is applied, with the mechanical shock to thr transformer causing dust to fly off, and sometimes causing protective relays to trip because the harmonics or inrush current seem like there is a fault, with normal voltage applied. If it did not fail instantly from higher than rated voltage, it would at least have a greatly decreased service life. In response to 88.203.106.28, remember that each turn takes up space. If the conductor has to be of a certain diameter to carry the rated current, and the insulation has to be of a certain thickness to withstand the turn to turn and winding to winding potential differences, then having more turns per winding (while keeping the turns ratio constant) would mean a physically larger, heavier and more expensive transformer. Edison (talk) 18:56, 25 May 2008 (UTC)

Ooops you're right, I got somewhat confused while writing that, too tired or something perhaps. I'd intended to say you could design a transformer to step down 44kV to 22kV and you could use it for 22kV to 11kV, 11kV to 22kV etc, but you wouldn't want to use it for 22kV to 44kV (unless it was designed for that as well). Similarly you could design a transformer to 22kV to 44kV and use it for 22kV to 11kV or 11kV to 22kV etc etc but not 44kV to 22kV. Nil Einne (talk) 20:50, 26 May 2008 (UTC)

So turns are always kept at a minimum which doesn't saturate and limits the current? Bastard Soap (talk) 09:06, 27 May 2008 (UTC)

That's pretty much true. But it's also worth noting, especially for high-frequency transformers (that aren't so limited by the need for a large inductance) that transformers are basically "whole number" devices where each winding is counted in full turns around the core. This may keep you from using a transformer with a two-turn primary if the voltage ratio you need is a step-down of 50 volts to 40 volts. Fractional turns can be hard to realize in practice, especially when you consider that the external wiring may also act as part of a "turn" of the coil. So you tend not to see too many transformers with really low numbers of turns, even though they are theoretically possible. (Interestingly enough, really high frequency DC to DC converters now use transformers where the windings are a very few "turns" formed by circuit traces on the printed circuit board.)

Atlant (talk) 15:34, 27 May 2008 (UTC)

Signal fade

How far away from the Earth would you have to go before TV signals etc become indistinguishable from natural background noise? (Assuming that we are waiting long enough for the signals to actually arrive.) --Fangz (talk) 01:02, 25 May 2008 (UTC)

I wouldn't imagine it to be very far. Giving the signal such a boost for space travel would be wasted energy after all, a useless added cost for the company (assuming E.T. doesn't pay for satellite). Bastard Soap (talk) 01:28, 25 May 2008 (UTC)

I'm no electrical engineer, but I believe that the ability of an antenna to pick out a point signal source from evenly distributed background radiation is in some proportion to the antenna's size or dish diameter. Theoretically, given a sufficiently large (and perfectly constructed) parabolic dish antenna, the TV signals could be resolved at any distance. Other factors might come into play though, such as the effects of interstellar gas and dust or gravitational distortion. -- Tcncv (talk) 02:16, 25 May 2008 (UTC)

TV signals are Electromagnetic radiation, i.e. light but at radio frequency (see: Radio propagation). As light propagates through free space, its intensity spreads out, according to the Inverse square law which states that the power density of an electromagnetic wave is proportional to the inverse of the square of the distance from the source. So, "doubling the distance from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value." Consider the radiation from the sun. The intensity of the radiation from the sun is 9 times greater than that at Earth. At Pluto, which is approximately 39 times further away from the sun than the earth, the intensity is reduced to next to nothing, the sun just appears like a star. However, there is still some solar intensity getting to Pluto. Since radio waves are the same as light waves, the same applies. So on Pluto, you would get a very weak TV signal from the Earth (which would also be delayed since light travels at a finite speed, however if Plutonians have a decent receiver and amplifier, they will be able to watch their favourite programs. In the same way that we can see distant stars and galaxies using powerful telescopes, E.T. will be able to pick up radio transmissions from the earth using a radio telescope. The cosmic background radiation is incoherent noise, whereas the TV radio waves will contain a coherent signal, which theoretically, could always be extractable from the background noise, using a specialised Low-noise amplifier for example. Astronomers are able to detect and extract radio signals from stars, galaxies or other cosmic bodies, that are billions of light years away. I hope this helps, Jdrewitt (talk) 08:53, 25 May 2008 (UTC)

But the sun emits a much stronger signal (by many orders of magnitude) than a man-made source, so your analogy fails. We cannot detect individual stars as far away as the furthest detectable galaxy. Another example: when the sun enters the field of view of a VSAT antenna, the VSAT cannot detect the signals from the geosynchronous satellite because the sun is so much more powerful than the (much closer) satellite. This occurs for brief periods once a day near the equinoxes. -Arch dude (talk) 22:33, 26 May 2008 (UTC)

My point was that the inverse square law means that the intensity of the light reduces very quickly, yet we are still able to detect individual stars from very, very large distances. The signal emitted from radio transmissions might be small but it is still there, it doesn't disappear, it continues to propagate through space and theoretically is still detectable! The radio signal from the voyager spacecraft is extremely small indeed but it is still detectable on Earth from what is now pretty far beyond the extent of the solar system. Detection of weak signals relies on having an extremely powerful and sensitive detector to receive them but theoretically, the signal can be extracted from the background noise. The point about not being able to detect individual stars from the most distant galaxies is simply a resolution problem. When Gallileo built his telescope and looked at Jupiter, he was able to resolve four of the planets moons from what was previously just visible as a signal blob of light. As technology advances, more sensitive telescopes, photodetectors, spectrometers etc. are developed and ever more distant radio, x-ray and other manifestations of light signals are being detected on Earth. If ET is sufficiently advanced and has sufficiently sensitive instruments and data analysis techniques, they they too will be able to detect signals from very large distances. Jdrewitt (talk) 21:27, 28 May 2008 (UTC)

Don't the companies transmit the signal at the minimum power possible which allows clear reception over their area of operation? 88.203.106.28 (talk) 09:48, 25 May 2008 (UTC)

They probably do, but the signal will propagate in all directions, including into space. Electromagnetic radiation will continue to propagate indefinitely through free space, and with powerful enough receivers will be detected from any distance. Jdrewitt (talk) 11:54, 25 May 2008 (UTC)

"Free space" is only a theoretical idea, though. This paper from NASA about SETI estimates that beyond about 1000 light years, signals outside the range 10^-3 Hz to 10⁶ Hz would be lost to space dust, free electrons, and stray fields. Beyond a certain distance, the signals will lose their coherence and no amount of signal processing will be able to recover them. --Heron (talk) 14:58, 25 May 2008 (UTC)

Our Fermi paradox claims :

SETI estimates, for instance, that with a radio telescope as sensitive as the Arecibo Observatory, Earth's television and radio broadcasts would only be detectable at distances up to 0.3 light years.[44] Clearly detecting an Earth type civilization at great distances is difficult.

No idea how accurate that is. 200.127.59.151 (talk) 19:00, 26 May 2008 (UTC)

There's yet another fly in the ointment, of course. Let's consider American TV channel 7. There isn't just one transmitter (on the entire half of the planet facing ET) that is transmitting on Channel 7; there are probably a dozen or more. And at great distances, your antenna needs to not only be able to catch enough signal to distinguish the signal from the universe's noise, it also needs to have enough angular resolution to be able to separate Boston's Channel 7 (WHDH-TV) from New York City's Channel 7 (WABC-TV). Otherwise, about all you'll be able to decipher from the signal is that there are a bunch of different signals sharing the same frequency allocation and modulation methods, but you'll have a very hard time demodulating them.

Atlant (talk) 15:14, 27 May 2008 (UTC)

Chemistry.

If one takes a thin layer of water (say 3-5 mm thick) and pours a bit of isopropyl alcohol in it, the line of the water recedes as the alcohol spreads out and at the boundary there is vibration in some spots. What causes this? Also, what allows some things to evoporate (water, alcohol, gasoline, etc.), while others can't (oil)? Thanks in anticipation, Ζρς ι'β' ^¡hábleme! 01:18, 25 May 2008 (UTC)

Surface tension, Evaporation--Lisa4edit (talk) 10:30, 25 May 2008 (UTC)

Ok, would anyone like to explain? From the surface tension article: "Its cause is a complex interaction between the differing surface tensions of water and ethanol." Please explain this complex interaction. I knew it had something to do with the surface tension; I just don't know what. I couldn't find anything pertaining to my question in evaporation. Well, except it does say that if the interactions of the molecules are strong enough, the substance will not evaporate. Is this the case with oil. Please explain, Ζρς ι'β' ^¡hábleme! 00:15, 26 May 2008 (UTC)

Your quote from the article relates to "tears" in alcoholic drinks. I think that description is missing a bit about capillary action, which draws the water-alcohol azeotrope up the walls of the glass. The higher vapour pressure of the alcohol causes it to deplete more rapidly, and then the surface tension of the remaining water causes it to form droplets or "tears".

To your first question, adding alcohol to the water changes the surface tension, and as the shape of the meniscus changes, the area occupied by the given volume will change.

To your second question, pretty much everything evaporates, some things much faster than others, vapour pressure is what makes it happen, you can also look at partial pressure. Franamax (talk) 11:14, 26 May 2008 (UTC)

Leaky o-ring

Why is is that steatorrhea is so often associated with fecal incontinence, while diarrhea is not (or is less-so)? Tuckerekcut (talk) 02:12, 25 May 2008 (UTC)

It's because of the oily nature of steatorrhea as it contains undigested fats and oils by definition. It acts as its own lubricant.Fribbler (talk) 14:03, 25 May 2008 (UTC)

How can I change reality?

I'll be honest with you. My life is miserable and sometimes I get tired of scientific laws.- i.e. "the way things are". Facts, nature, atomic structure, etc. Science says that one day we'll be able to create a universe in the labratory, so is there hope for dreamers like me? —Preceding unsigned comment added by Dr. Carefree (talk • contribs) 03:34, 25 May 2008 (UTC)

You cant change reality, but you can change your mind! —Preceding unsigned comment added by 79.76.141.94 (talk) 03:41, 25 May 2008 (UTC)

Yeah. There's always mind altering drugs. --Fangz (talk) 11:27, 25 May 2008 (UTC)

You can change a lot about how you as a human interact with reality. You can't change reality at the physical level. Sorry. It would not be a good idea if you could—lots of problems would result. (Imagine if you weakened the strong nuclear force and all the atoms fell apart. Total bummer. No dreams, no nuthin'.)

Here's a wild idea, though: have you read any somewhat radical philosophy of science? Give Paul Feyerabend a whirl—especially Against Method. You might feel comforted to know that there are some compelling arguments out there (not compelling to scientists, of course, but who asked them?) that reality ain't all that it's cracked up to be, that facts are less concrete than they appear in textbooks, that the way of making something into a "fact" is a bit more complicated and fraught than the scientists let on. --98.217.8.46 (talk) 04:04, 25 May 2008 (UTC)

You mentioned that you were a dreamer. Well, you could try Lucid Dreaming. That way, instead of having to obey scientific laws, scientific laws have to obey you. Digger3000 (talk) 15:47, 25 May 2008 (UTC)

Reality is that which, when you stop believing in it, doesn't go away.

- Philip K. Dick

It was always my hope, in writing novels and stories which asked the question "What is reality?", to someday get an answer. This was the hope of most of my readers, too. Years passed. I wrote over thirty novels and over a hundred stories, and still I could not figure out what was real. One day a girl college student in Canada asked me to define reality for her, for a paper she was writing for her philosophy class. She wanted a one-sentence answer. I thought about it and finally said, "Reality is that which, when you stop believing in it, doesn't go away." That's all I could come up with. That was back in 1972. Since then I haven't been able to define reality any more lucidly. - Philip K. Dick 1978

202.168.50.40 (talk) 23:42, 25 May 2008 (UTC)

I just posted to your question in the 'Miscellaneous' section about 'Change'. Then I saw this one. Anyway, read Peter Berger/Luckmann's 'The Social Construction of Reality' just to get your pump primed. --Ckdavis (talk) 15:09, 30 May 2008 (UTC)

Stephens aldehyde synthesis

In the Stephens aldehyde synthesis, we have a nitrile. Nitrogen is more electronegative tha Carbon. So it will develop a partial negative charge and the Carbon will have a partial positive charge. So when H⁺Cl^-reacts with it, Cl^-must attach to the carbon. But the hydrogen(H⁺)only attaches? How does this happen?

Can you kindly explain the mechanism? —Preceding unsigned comment added by 59.92.106.218 (talk) 03:34, 25 May 2008 (UTC)

Have you looked at the Stephen aldehyde synthesis page and Tin(II) chloride? It seems that the Cl^- does bond to the carbon atom, and then the tin(II) chloride reduces it (I don't know how exactly the reduction occurs though). --Mark PEA (talk) 15:05, 25 May 2008 (UTC)

Pronunciation of Name

How is L'Hospital (the mathemetician)'s name pronounced? Does it go like "L-apital"?? 117.194.226.87 (talk) 05:38, 25 May 2008 (UTC)

I've always heard it pronounced Low-pi-taal. Clarityfiend (talk) 06:50, 25 May 2008 (UTC)

I don't know how it was pronounced in his day, but I've always heard (an English mangling of) the usual pronunciation of the word. Algebraist 09:11, 25 May 2008 (UTC)

The modern French pronunciation of the name is "Loh-pee-tahl" — almost exactly as given by Clarityfiend, but note that the first syllable has no diphthong (as "low" might suggest). --Tardis (talk) 21:52, 28 May 2008 (UTC)

I generally hear people say either "Le-hop-it-al" or "Lop-it-al" - which, as Algebraist says, are probably English manglings of the correct pronunciation. --Tango (talk) 13:02, 25 May 2008 (UTC)

First off: Its much easier to pronounce when spelled non-anglicanized. L'Hopital is pronounced, to my knowledge, Lahoh-pee-tal (thats 3 syllables, not 4). Its tricky because its French 63.172.27.2 (talk) 14:44, 30 May 2008 (UTC)

Education & Career

What are the prospects of the animation industry in the next ten years? 117.194.226.87 (talk) 05:40, 25 May 2008 (UTC)

You might have more luck with this question at the Entertainment desk unless you'd be looking for Forensic animation maybe. --Lisa4edit (talk) 08:57, 25 May 2008 (UTC)

I copied your question over there. You can click this link Wikipedia:Reference desk/Entertainment to look for answers. —Preceding unsigned comment added by Lisa4edit (talk • contribs) 11:44, 25 May 2008 (UTC)

Wonder bar

How is it that bacteria(?) can develop immunities to various medicines like penicillin, but not against the lowly bar of soap? Clarityfiend (talk) 06:59, 25 May 2008 (UTC)

Penicilin and other medicines work on bacteria that have already infected your body. Soap reduces the number of bacteria on your skin [2]. That reduces the number of invaders your immune system has to deal with. --Lisa4edit (talk) 07:21, 25 May 2008 (UTC)

Up to my knowledge it is because the soap doesn't fragmentate, it remains of a certain concentration. While medicines, anti-bacterial soap and other stuff fall to concentrations low enough that don't finish off all bacteria. The bacteria which remain have a higher resistance to the agent (otherwise they wouldn't have survived it). These bacteria then reproduce and you have a population which is more resistant than before. Soap on the other hand just kills all the mos before they can do anything. 88.203.106.28 (talk) 07:31, 25 May 2008 (UTC)

As Lisa4edit says, it is because of a different mechanism of action. Regular soap is a physical weapon of hygiene - it is a surfactant that helps wash bacteria away. Its very difficult for anything to evolve immunity to that (beyond getting better at attachment, I suppose). In contrast, antibiotics are like chemical weapons. Because bacteria can evolve quickly as a population, they are pretty good at adapting their biology so that our chemical weapons are no longer effective. Rockpocket 07:48, 25 May 2008 (UTC)

Doesn't soap lyse open their cell wall as well? In that sense isn't it a weapon as well? Frankly I don't see any difference with regards to evolution in inside the body and outside. 88.203.106.28 (talk) 08:55, 25 May 2008 (UTC)

With antibiotics you create Evolutionary pressure. Only resistant bacteria survive and multiply. And they are already in the body. With soap everything gets flushed down the same drain, no matter what variation evolved. Even if bacteria somehow developed a superior attachment and thicker cell wall, they'd still have to get into the body and battle the body's defenses. The intent of soap is to prevent infection, antibiotics are used to fight it. Lisa4edit (talk) 10:10, 25 May 2008 (UTC)

There's another reason for this, that you seem to be overlooking. Inside the body, there are lots of delicate things, so any antibacterial weapons we feed into our systems have to be very selective, or they'll kill us as well. Our cells are based on similar principles to those of the bad guys. It's easy enough to get resistant to something that targets, say, DNA transcriptase, or some other wacky enzyme that might be found, in a particular form, in just a handful of species. It's a whole different ball game trying to build up a resistance to acid, heat, cold, or just plain washing stuff down the sink. 203.221.126.247 (talk) 11:08, 25 May 2008 (UTC)

In other words (and I don't think this goes quite so far as to be medical advice, as it falls pretty well under the category of common sense), don't eat soap. ;-) --Prestidigitator (talk) 18:53, 25 May 2008 (UTC)

Striking out medical advice. ;-) --Tango (talk) 19:24, 25 May 2008 (UTC)

'Lest you go blind from Lifebuoy Poisoning!

Atlant (talk) 14:58, 27 May 2008 (UTC)

Some very good points and I'd also like to say who said bacteria aren't 'resistant' to soap (in as much as this has any meaning which is not much). If I get a resonably deep wound from a dirty sharp object, I'd take the antibiotics over the soap/soapy water any day you force me to choose Nil Einne (talk) 15:26, 25 May 2008 (UTC)

NE, I think you'd be fighting against every tenet of medical practice - first, you cleanse the wound from the outside. Antibiotics are the last line, not the first line of defence, for reasons of evolution of antibiotic resistance given above. In your deep-wound case, you might do both, but surely you'd wash yourself off first? Franamax (talk) 10:58, 26 May 2008 (UTC)

Well as I said, if you FORCE mt to choose I would choose the antibiotics. You're right that antibiotics are supposed to be the last line of defence, but if you're force me to choose only one option, most people who know abit about bacteria, antibiotics and soap (I think even most doctors) would choose the antibiotics (particularly if it's one with a low level of resistance in the environment) at least for a deep wound from a dirty object. My point was that antibiotics are far better at killing bacteria then soap (since of course soap primarily washes away the bacteria, as has already been discussed) so it's even more meaningless to say bacteria has no 'resistance' soap then it seems from the discussion. (Of course bacteria are not likely to develop greater 'resistance' to soap, for the reasons already highlighted.) This doesn't mean you should go around using antibiotics willy nilly, as you said, it's a bad idea because your going to help the development of resistance. (In fact I personally very rarely apply topical antibiotics and I seem to cut myself a lot. I don't even disinfect a lot of the time which probably isn't good practice but anyway...) N.B. Obviously it's still far better to wash first whatever the case since beyond the resistance, even if you do feel the need for antibiotics, it's far better to wash away (and perhaps then kill with a disinfectant) 95%-99% of bacteria first rather then hope to kill them all/stop an infection with the antibiotics. Nil Einne (talk) 20:40, 26 May 2008 (UTC)

Very interesting. And there I was, thinking soap killed bacteria. Thanks. Clarityfiend (talk) 23:07, 25 May 2008 (UTC)

You might find this article interesting [3]--Lisa4edit (talk) 08:01, 26 May 2008 (UTC)

Evolutionary Anthropology and Psychology

Are evolutionary anthropology and evolutionary psychology legitimate sciences? If not what is the scientific rationale for ethology and evolutionary biology applying to animals but not to humans? 71.231.121.77 (talk) 13:22, 25 May 2008 (UTC)

evolutionary anthropology Evolutionary psychology Evolutionary psychology controversy may help.--Lisa4edit (talk) 13:46, 25 May 2008 (UTC)

Of course they are legitimate sciences - they both have peer-reviewed journals, which is one of the defining traits of "good science" (i.e. a lot of people who are educated about the field have come to a consensus about most of the basic facts, and these provide the foundation for published work on the topic). This does not mean that every theory, hypothesis, or publication about evolutionary anthropology or psychology is guaranteed to be accurate or correct; but it has probably passed a review process. Nimur (talk) 15:04, 27 May 2008 (UTC)

There is actually debate in contemporary philosophy of science as to whether or not social sciences such as anthropology, sociology, and psychology in general should be labeled "sciences" at all. Just putting that out there, not stating an opinion. --Shaggorama (talk) 19:16, 27 May 2008 (UTC)

"For shaver only"

I have here a NiMH AA batter charger with an ungrounded unpolarized US plug. It says "Input: 100-240 VAC, 50/60 Hz, 0.16 A". I also have a US-to-UK plug adapter which says "250V, 1A fuse, for shaver only". Is there any reason I can't use this adapter to plug this non-shaving device into a UK outlet? And what are the specs of those "shavers only" outlets in airplane lavatories and hotel bathrooms and the like? Thanks. 81.98.253.215 (talk) 17:37, 25 May 2008 (UTC)

I would guess that the "shaver only" thing is there because it's only rated at 1 amp, which is quite a lot lower than other devices expect (13 amps is the standard for a UK plug, I think). If the charger only draws 0.16A, though, it should be fine. The other problem is that 250V is more than 240V, although it's not far off, so you might get away with it, but if it blows up and burns your house down, don't blame me! When in doubt, follow the instructions! --Tango (talk) 18:11, 25 May 2008 (UTC)

You should be OK. The "shavers only" plugs are indeed current-limited (on planes due to limited power supply, in bathrooms due to risk of electrocution due to proximity to water), since your charger only draws 0.16A you ought to be fine. Your UK-to-US adapter is probably limited to 1A due to the internal transformer which can't handle higher currents (it would melt if it didn't have a fuse). Bottom line - you should be able to plug your charger into a "shavers only" outlet. — QuantumEleven 21:27, 25 May 2008 (UTC)

And a typical 240 V "shavers only" wall outlet is limited to 200 mA [4], so you will just about get away with plugging your battery charger into it. --Heron (talk) 11:04, 26 May 2008 (UTC)

I would have no qualms about plugging a "universal voltage" (100-240 VAC, 50/60 Hz) batery charger into a "shaver only" outlet, but I must relate a cautionary tale to you: While travelling in the UK, I plugged my transformer-equipped 120 VAC-only NiMH battery charger into an outlet that was labeled "115 VAC shaver only" and the transformer in the charger overheated overnight, opening its internal thermal fuse and killing this charger. This was early in the NiMH days so we ended up scrambling through a lot of UK electrics shops before we found another charger. Oddly enough, it was the same model family as our American charger, but equipped with a BS 1363 plug instead. I concluded after the fact that the "115 VAC" shaver outlet probably just had a rectifier diode in series with the line; this would have worked with the motor of an electric razor but was death to the transformer in my charger. Nowadays, in Europe, I carry a universal-voltage charger and plug adapters but for the UK, I'd bring my souvenir BS 1363 charger ;-).

Atlant (talk) 14:53, 27 May 2008 (UTC)

Glass & Acid

Why is glass resistant to acid? I assume it's due to some element or compound not present in other materials. And is this property unique to glass or are there other substances that are not affected by acid? 92.2.194.36 (talk) 19:46, 25 May 2008 (UTC)

If I remember my chemistry correctly glass does not react with acid because the electrons of the silicone dioxide that glass is composed of are too strongly attracted to its own molecule. That is they are not available to react with the relatively free protons of an acid. This property is not unique to glass but is the same for any highly non-polar molecule. For instance wax or plastic. 71.231.121.77 (talk) 20:00, 25 May 2008 (UTC)

Hydrofluoric acid can dissolve glass however, due to the presence of fluoride than can react with silicone dioxide. Graeme Bartlett (talk) 22:12, 25 May 2008 (UTC)

So why does dishwasher detergent etch glass? Does it contain hydrofluoric acid? Or is some other process? —Preceding unsigned comment added by 71.236.23.111 (talk) 23:31, 25 May 2008 (UTC) oops darn bot Lisa4edit

Abrasives in the detergent. My mom got paid for ruined glassware because they had a shipment of scratchy detergent. But HF does dissolve glass - I worked for an engineering company where we quoted equipment for a confidential process, which turned out to be HF: boom goes all the fiberglass insulation, now let's look at the expensive stuff. Franamax (talk) 23:57, 25 May 2008 (UTC)

The expensive stuff was Grafoil, in case anyone asks :) Franamax (talk) 00:04, 26 May 2008 (UTC)

Should we have a page on "flexible graphite"? It seems to have unique properties that I can't find covered in any of our articles I looked at. --Lisa4edit (talk) 05:56, 26 May 2008 (UTC)

I've been out of the refining biz for 10 years, but at least at the time, Grafoil was the go-to gasket, and wildly expensive. Seems notable to me... Franamax (talk) 10:42, 26 May 2008 (UTC)

If dishwasher tablets contained Hydroflouric acid (HF) then they would be extremely dangerous, not only does it dissolve glass but also very small quantities of HF will attack human tissue and bone leading to extreme pain and even death. HF won't dissolve all forms of glass though, only glass that contains SiO2, which is one of the most common forms of glass but there are many other compositions, e.g. chalcogenide glass. Many other materials are resistant to acid, for example most plastics, many chemicals are stored in plastic containers.

I'm not certain of this, but it has always been my impression that ordinary cheap soda-lime glass degrades in a dishwasher because it isn't pure fused silicon dioxide (silica). As a result, some of the other constituents of the glass can eventually be dissolved out of the glass by repeated washings in the harsh chemicals found in automatic dishwashing detergents. I'm disappointed by our article on soda-lime glass to find that even Pyrex is now made of this stuff rather than the tougher borosilicate glass it used to be made of.

Atlant (talk) 14:43, 27 May 2008 (UTC)

Thanks for that tip on Pyrex! I share your disappointment, I'm from the "only use Pyrex" school, or I was until today. Another totem toppled :( Franamax (talk) 17:15, 27 May 2008 (UTC)

I believe detergents and soaps are also often basic rather than acidic. If I recall correctly, bases are always kept in plastic containers rather than glass in the lab. Is that right? Why? --Prestidigitator (talk) 00:49, 29 May 2008 (UTC)

Thats not quite true. Bases are sometimes kept in plastic over glass. Its mostly an issue of the concentration of the base. The reason is because is that if, for example, you have ground glass the base can fuse ground glass joints together in as little as 30 seconds because of the extremely high surface area they have. Basically, the hydroxide ions are dropping their hydrogen atoms and becoming part of the glass network. In standard glass, the effect is much slower, but if you're using the glass bottle for storage, I could see it happening eventually. 63.172.27.2 (talk) 14:53, 30 May 2008 (UTC)

Same protein with two names?

This question is a little involved: Here is a paper. It talks about PIG2 and says that due to similarity between it and GREM1, that what they found for PIG2 must apply to GREM1. I think that's awful reasoning, but when I follow the given accession numbers I get this and this. Are they actually the same protein? If so, why were they thought to be two "similar" proteins and not one ["exactly the same"] protein? ----Seans Potato Business 21:41, 25 May 2008 (UTC)

Are you linking the right paper? I couldn't find either of PIG or GREM. In any case, the accessions you give show different genetic loci, different lengths and different sequences. A case of convergent genes/convergent structures? They have different sequences, what is the resulting amino sequence? Franamax (talk) 22:46, 25 May 2008 (UTC)

Sorry, I'd linked to the wrong paper (fixed now). There is a string of characters, the translation, which is the same for both proteins, but it's exactly the same (not similar). Could they have been thought to be different but now they're known to be exactly the same? Are you sure that they are different genetic loci? I cannot interpret 'AY232290' as a locus. These databases are very user-unfriendly. Wont someone think of the children? ----Seans Potato Business 23:10, 25 May 2008 (UTC)

That's more clear now (or less clear lol). It looks to me like two separate loci with different DNA/mRNA sequences producing apparently identical amino-acid sequences. That would be an example of gene duplication with accumulated null mutations? The essence here is that the CATG sequences are different, but the amino-sequences are identical. Interesting. You're right that we should think of the children, children are our future - "unless we stop them now-w-w" :) Franamax (talk) 23:50, 25 May 2008 (UTC)

Electroelution

In Electroelution, wont the DNA be daamged when it gets free from the gel and encounters the anode? ----Seans Potato Business 23:19, 25 May 2008 (UTC)

I'm not sure, and this is based on a quick scan of the document, but this may provide a bit of info on the effects of electricity on DNA. Fribbler (talk) 23:53, 25 May 2008 (UTC)

After reading it fully, I think the only useful sentance is And biologists have agonised about how conductivity might affect its function. Fribbler (talk) 00:01, 26 May 2008 (UTC)

In practice, electroelutors "catch" the DNA with dialysis tubing or DEAE paper or a salt bridge before it contacts the anode. Woodlore (talk) 03:29, 26 May 2008 (UTC)

May 26

Alka-Seltzer Neutralization

Hello. The chemical equation of Alka-Seltzer's effervescence is C₆H₈O₇ (citric acid) + 3NaHCO₃ → 3H₂O + 3CO₂ + Na₃C₆H₅O₇ (trisodium citrate). If I add hydrochloric acid to a solution of water and Alka-Seltzer, then is the neutralization chemical equation Na₃C₆H₅O₇ + 3HCl_(aq) → C₆H₈O₇ + 3NaCl? If so, then how does Alka-Seltzer neutralize the hydrochloric acid? Isn't C₆H₈O₇ an acid? Thanks in advance. --Mayfare (talk) 01:24, 26 May 2008 (UTC)

If dissolved Alka-Seltzer is trisodium citrate as you have written (I had no idea), then it can't neutralize HCl. I expect Alka Seltzer works because it contains less citric acid per sodium bicarbonate than you describe in your equation; perhaps it's more like 6 moles of bicarb per mole of citric? Woodlore (talk) 03:41, 26 May 2008 (UTC)

About 4 to one. The result is excess bicarbonate, and that buffers both excess acid or excess base:

HCO₃^-_(aq) + H⁺_(aq) → CO_2(g) + H₂O_(l)

HCO₃^-_(aq) + OH^-_(aq) → CO₃^2-_(aq) + H₂O_(l)

Sound right? So the effervescence is just a nice and flashy delivery system for bicarb. --jpgordon^∇∆∇∆ 04:12, 26 May 2008 (UTC)

Yup, as well the carbonic and citric acids makes taking a sodium bicarbonate solution far more palatable. Sjschen (talk) 23:52, 26 May 2008 (UTC)

Partial UV protection in sunglasses

When a sunglass or any other lens such as contacts offers partial, say 90%, UV protection, is it referring to 90% of the UV spectrum of the less energetic portion of the spectrum? In other words, if I wear a contact lens with 90% protection behind sunglass with 50% protection, am I exposed to .1x.5=5% of UV or closer to 10%? Thanks. —Preceding unsigned comment added by Imagine Reason (talk • contribs) 03:59, 26 May 2008 (UTC)

Most UV absorbing substances have strong absorption responses with relatively sharp cutoffs as a function of frequency, i.e. everything above wavelength X passes and nearing nothing below it does. As a result, my expectation is that the effects are not additive and that the cumulative effect will be closer to 10%. However, I have no specific experience looking at the frequency response of either sunglasses or contacts, so I could be mistaken. Dragons flight (talk) 04:14, 26 May 2008 (UTC)

Most sunglasses polarise light as well, reducing the overall intensity of the light, see polaroid--Shniken1 (talk) 12:31, 26 May 2008 (UTC)

Indeed - you take two sets of polarising sunglasses and put them one in front of the other and rotate one of them you'll find at one angle they block virtually all the light, since one only lets through light with one polarisation and the other the opposite polarisation, so no light can get through both. --Tango (talk) 14:13, 26 May 2008 (UTC)

The notion that each polarizer independently removes part of the light is flawed: by Malus' Law, some light does pass through two crossed polarizers so long as their transmission axes are not orthogonal. This leads to the counterintuitive result that, given two crossed polarizers passing little or no light, a third may be inserted between them at an intermediate angle and increase the transmissivity. It reduces the intensity, but the light that passes it is not so poorly aligned with the last polarizer and so survives with a larger final intensity. --Tardis (talk) 21:43, 28 May 2008 (UTC)

When I put two of my sunglasses one in front of another, I can still see, no matter how I rotate them. What gives? Imagine Reason (talk) 13:13, 29 May 2008 (UTC)

If you see no changes in brightness with rotation at all, then at least one of your two pairs is unpolarized. If you are rotating only one of the pairs and see only weak changes, then the one you are rotating is polarized and the other is not (and the light passing through them is already mildly polarized, as it often is). If you see strong changes, but never complete darkness, you have discovered that polarizers are not perfect: they always block some light in the "correct" direction and pass some light in the "wrong" direction. --Tardis (talk) 15:27, 29 May 2008 (UTC)

Oilfield Volcano

If say a volcano erupts under a oilfield, wouldn't it be possible that phenols be created and keytones be created, and then bisphenol a be created?

If say a volcano erupts under a oilfield, wouldn't it be possible that, phthalate be created?68.148.164.166 (talk) 02:26, 26 May 2008 (UTC)

The temperature our article gives for magma is 700°C to 1300°C the autoignition point given for bisphenol A is 600°C. You'd need just the right coincidental conditions to create it and then there's a question of whether it would be around long enough for anyone to detect it. (And they'd preferably have to stay alive long enough to tell anyone, with a volcano erupting under their pants and all.) That sounds like an awful lot of "what ifs" happening simultaneously. Lisa4edit (talk) 05:10, 26 May 2008 (UTC)

Thanks. What about phthalate?68.148.164.166 (talk) 06:51, 26 May 2008 (UTC)

Given enough heat and pressure, you'll get one of everything. As Lisa notes though, it will be largely decomposed by the time it gets to the surface - you'll only have to worry about the deadly carbon monoxide gas. And the sulfur dioxide. And the pyroclastic flows. There will likely be a few phthalates in there, but nothing to worry about. Franamax (talk) 11:31, 26 May 2008 (UTC)

as you may have gathered from the above responses, the short version is: if a volcano erupts anywhere, you have much bigger health concerns than BPA and phthalate, such as lava, fire, earthquakes, flying rocks and toxic fumes. --Shaggorama (talk) 19:12, 27 May 2008 (UTC)

Solar panels on the Moon

Every plan I've seen for long-term human activity on the Moon calls for using solar panels for power. But those solar panels would be exposed to solar flares, cosmic radiation, and other phenomena not present on Earth or in near-Earth orbit. What effect would those have on the solar panels? --Serie (talk) 07:35, 26 May 2008 (UTC)

If I'm reading the articles right, the geostationary orbit is above the Van Allen belts, so we already have many solar panels exposed to full intensity solar and cosmic radiation. Also the SOHO spacecraft is way out there, looking right at the sun, and it has solar panels [5], so they must work. Presumably though, the high-energy particle flux will progressively degrade the panels and eventually, like most other things, they would stop working and need replacement. Franamax (talk) 10:35, 26 May 2008 (UTC)

It's a feasible idea, theoretically. However, the main issue is down to the economics of it all. Solar panels in space aren't as efficient as those used on the ground and theres a huge cost involved in getting them into space and installed. Regards, CycloneNimrod^Talk? 13:53, 26 May 2008 (UTC)

Huh? Space-grade solar cells are more efficient than typical earth use ones (and much more expensive). Where would the lower efficiency come from? You would have a higher solar influx on a more efficient cell, does temperature variance make them that much more inefficient? Rmhermen (talk) 20:12, 26 May 2008 (UTC)

Remember efficiency is the amout of energy input that you convert to electricity (your output). It is easily possible I would suspect that current solar panels are significantly less efficient in space because they are generally designed for earth-like conditions (yes you would modify them somewhat for space but given the fact the field is of minute interest it's likely it still lags far behind earth-based solar panel design) including temperatures and light levels (amount and spectrum of light). However it does seem extremely likely that given the far greater amount of light reaching solar panels in space, they will generate a significantly higher amount of electricity per cell even though they are a lot less efficient at converting the solar energy that reaches them to electricity so I'm indeed not 100% sure if CycloneNimrod is correct. Nil Einne (talk) 20:22, 26 May 2008 (UTC)

In fact I think it is almost the opposite - that solar cells for space use led the design which trickles down to earth use. At least that is always the impression I was given.[6] Our article on Solar cells seems to support my memory as well. Rmhermen (talk) 20:47, 26 May 2008 (UTC)

This quote is the closest I have come to understanding the efficiencies: "The space solar spectrum or air mass zero (AMO) spectrum is richer in ultraviolet light than the typical terrestrial solar spectrum (air mass 1.5 or AM 1.5). The ultraviolet light is typically converted into electrical power less efficiently than other parts of the spectrum, resulting in lower AMO efficiencies. For example, production muInjunction solar cells are currently -28% AMO, but these cells are over 32% efficient in the AM 1.5 spectrum. Since cells are typically measured under the spectrum for their intended use and efficiencies are not easily converted..."[7] So I still don't know if a panel actually produces less power in space than on Earth. Rmhermen (talk) 21:09, 26 May 2008 (UTC)

The overall efficiency is a little less because there is more UV in the spectrum, but this is outbalanced by the far greater light flux (what with there being no clouds and all). This GaAs 3-layer solar cell for use in space rates 135 mW/sq.cm. at 28% efficiency, whereas this writeup for a terrestrial silicon cell works out to ~9 mW/sq.cm. Check my math on this, but there is a lot more sunlight in space. Franamax (talk) 22:26, 26 May 2008 (UTC)

Solar power is considered more likely at least because launching Radioisotope thermoelectric generators large enough to power a moon base is probably politically infeasible and perhaps environmentally questionable. Rmhermen (talk) 20:16, 26 May 2008 (UTC)

The 28 days of night on the moon make solar cells good for production of electricity, but the storage of the power is more important. The moon station at the north pole with sun at some peaks with no night are the place to go!--Stone (talk) 07:26, 27 May 2008 (UTC)

Just a nit, but would you believe ~14 days of daylight and ~14 days of night?

Atlant (talk) 14:33, 27 May 2008 (UTC)

I can't see why a solar flare would damage the panel. Solar flares can temporarily or permanently scramble digital systems; they can permanently affect analog system performance by introducing a total radiation dosage significant to affect the dopant concentrations; but solar panels are basically the simplest kind of semiconductor - just two layers of material which create current when light hits them. I can't think how a large blast of solar wind (even way beyond the normal levels) would permanently damage the panel. Nimur (talk) 15:09, 27 May 2008 (UTC)

In any event, solar panels on the moon are bound to work far better than would lunar panels on the sun. Edison (talk) 15:43, 27 May 2008 (UTC)

The data sheet I link above for the space-use solar cell has a specific section called "Radiation Degradation". High-energy particles will eventually disrupt the crystal structure of the material. How long it would take for 10E15 1MeV electrons to hit 1 sq.cm. of the panel and reduce its performance by 14%, I have no idea. Franamax (talk) 17:04, 27 May 2008 (UTC)

To what other uses can a water pump/ motor be put to?

I am a resident of New Delhi, India. Due to frequent low pressure of water supply in our pipeline, I bought a brand new self priming mono block pump/ motor a few days back. After I bought it, to my astonishment, water started coming at good pressure. Now it is lying idle.

(i) Can anyone please tell me as to what other uses can the pump/ motor be put to? (ii) If I want to use it as a shower to take bath, what (modifications, if any) should be done? Bye. Signed; Kvees. —Preceding unsigned comment added by 164.100.5.4 (talk) 08:16, 26 May 2008 (UTC)

One other use would be to set up a storage tank and attach a fire hose so you are prepared for emergencies. If your local water pressure is not enough to get a decent shower, you would need to add a pressure tank to control the pump. I'm not sure that connecting a pump to the waterline will help much when the line pressure is low, you might just cause cavitation in the pipeline. In any case, it sounds like installing a storage tank would be a good idea, waterline -> storage tank -> pump -> pressure tank -> house. Franamax (talk) 10:05, 26 May 2008 (UTC)

You could drop it from the top of a building and measure the time taken for the fall to calculate the height of the building. You'd need a stopwatch 125.21.243.66 (talk) 14:35, 26 May 2008 (UTC)

In Turkey they heat their water in tanks on top of the roof. They're just barrels painted black. (See Franamax's storage tank for details). You might try that. A garden water feature would also be possible, but those are rather a bit wasteful water wise (and waste power, too, now that I think of it.) Your low pressure might have been caused by an air-bubble lodged somewhere. Once it became dislodged the pressure went back up. I haven't encountered that with municipal water, but know of it with well water. Dropping a perfectly working object from a roof just to see it shatter should be punishable under some law. You could always see if there's a charity that would like to have it, if you don't want to keep it.71.236.23.111 (talk) 03:54, 27 May 2008 (UTC)

You might rent it out to other users. Maybe that would give you some extra money.--Lenticel ^(talk) 00:39, 28 May 2008 (UTC)

Vesna Vulović's fall duration (pt. 2)

Brought across from the misc helpdesk - How long did it take Vesna Vulović to fall the 10,000 meters? So far, the best guess is about 3 minutes. TIA. Lugnuts (talk) 09:20, 26 May 2008 (UTC)

Using a terminal velocity of 193 Km/h I got 2.77 minutes.61.68.255.246 (talk) 10:12, 26 May 2008 (UTC)

Vesna didn't "fall 10,000 m ". She was in a plane that traveled at an altitude of 10,0000 m when it disintegrated. As Algebraist already stated back there, there is no way of telling how much residual forward motion the part of the plane she was in had, nor what it's aerodynamic properties were (see Drag (physics). All we can say is that it probably took quite a bit longer than 3 min. One might get a certain upper range by applying average airspeed for that type of aircraft and treating the plane fragment as if it were a parachute, but it'd be mostly guesswork. --Lisa4edit (talk) 10:12, 26 May 2008 (UTC)

(That's a typo - it should be ~10,000 meters, not 10,0000! Minor typo, major implications!) Nimur (talk) 15:11, 27 May 2008 (UTC)

Why is the airspeed/forward motion important? It would make no difference to the time it takes to fall down, would it? (Unless the airspeed is so large as to make the earth curve under before the aircraft hits the ground)? -- ReluctantPhilosopher (too lazy to login) —Preceding unsigned comment added by 125.21.243.66 (talk) 14:34, 26 May 2008 (UTC)

As lisa explained, forward motion can generate lift. Almost any shape has at least some aerodynamic lift. This will increase the time to impact because the debris is still partially "flying". SpinningSpark 21:40, 26 May 2008 (UTC)

Oh yeah, I never thought about the lift due to forward motion. Silly me. 125.21.243.66 (talk) 14:12, 27 May 2008 (UTC)

stomach

why do our stomach move like a heart beat when we hold our breathe? —Preceding unsigned comment added by Miley 7 (talk • contribs) 09:28, 26 May 2008 (UTC)

What happens when you hold your breath is that you expand your lungs and tighten your diaphragm. This stretches the area around your stomach and now you can feel your pulse more easily. I don't think anything actually changes with how your stomach works, you can just more easily feel the arteries in that area. Franamax (talk) 10:14, 26 May 2008 (UTC)

What is SUTWELL Nursing Device?

Search on google and other search engines present SUTWELL as a nursing device. The question is: What really is SUTWELL device? Does it have a generic name? If it does not have a generic name can it be given one? What is the purpose of this invention? Who invented it? How far is it in the development process? Can it pass as another artefact to our stock becoming a household appliance like spoon, cup, knife, chair etc? —Preceding unsigned comment added by Sutwell (talk • contribs) 10:04, 26 May 2008 (UTC)

There's lots of useful information on the Sutwell device at your user page, I'd start there ;) Franamax (talk) 10:07, 26 May 2008 (UTC)

Only Black and White pictures from Mars

Why are the pictures take from new spacecraft such as Phoenix still in black and white (like [[8]]? I have serious doubt that it's due to them not being able to afford a color camera, so is there any other reason why a color camera wouldn't be able to operate on Mars? Is the data transfer rate to slow to support this, or are the technology involved not space-proof (doubtful)? 90.230.54.138 (talk) 11:48, 26 May 2008 (UTC)

The Mars rovers can see in 11 colours from the cameras made for colour vision, but they do this by using filters over the camera. I think the basic reason for B&W is that you can transfer 3 (RGB) to 4 (CMYK) times the information in the same time = higher resolution. Franamax (talk) 12:06, 26 May 2008 (UTC)

How long does it take to send an image through? Zain Ebrahim (talk) 19:59, 26 May 2008 (UTC)

A lot longer than you would on a dialup connection, according to this, except when an orbiter is overhead. Franamax (talk) 21:46, 26 May 2008 (UTC)

The reason is to get a higher resolution and a greater spectrum range. There is no such thing as a full-color sensor -- your color camera has red, green, and blue sensors in a pattern known as a Bayer array. This lets you take a full-color picture with just a single shot (essential for moving objects), but the interpolation used to give the appearance of full-color sensors makes things slightly blurry and sometimes causes colored fringes to appear that don't really exist.

The Mars landers and rovers use a single wide-spectrum sensor (sensitive to all light from mid-infrared to near-ultraviolet) and a collection of color filters that can be put in front of the sensor. If you want a color picture, you combine a red-filter picture, a green-filter picture, and a blue-filter picture. Since there's not much movement on Mars, this works well, and because there's no interpolation being used, there's no blurring or fringes.

Further, since the camera has a wide-spectrum sensor, it can take pictures using frequencies outside of the relatively narrow visible spectrum. Those "black and white" pictures you're talking about are probably actually near-infrared photos, because near-IR shows better detail in shadowed areas. By using combinations of infrared and ultraviolet filters, scientists can identify ice (ice has a distinctive reflection in certain IR bands), make estimates of mineral content of rocks, measure atmospheric dust, and do other things you can't do with a mere color camera. --Carnildo (talk) 23:42, 26 May 2008 (UTC)

Another note is that these images just arrived. Surely the first batch was a test to make sure the camera was operational after the descent and landing... the faster it could be transmitted to eager controllers, the sooner they could relax and get to serious work. Sending back a black/white image requires lower bandwidth ("smaller file") and thus can be transmitted in less time. Over the next few days, the ground team will have time for post-processing of the data that comes back, and we will certainly see re-colored images (combining the multi-band spectral photos into standard color or false color images). Nimur (talk) 15:15, 27 May 2008 (UTC)

polymers

what is the identification of hdpe/lldpe —Preceding unsigned comment added by ASIMDASH (talk • contribs) 12:03, 26 May 2008 (UTC)

If you type LDPE and HDPE into the Wikipedia search box, you should get lots of information, including the recycling symbols. Franamax (talk) 12:09, 26 May 2008 (UTC)

Article with explanation

I was looking for an article to explain what the difference is beween specific gravity, density and specific weight to somebody who knows even less than I do. I read the definitions in these three articles, but what, in layman's language they mean and how they differ, I am at a loss. (I am not really totally ignorant, but I am not very good in explaining.) Can anyone help? It is almost worth an article, I think. --VanBurenen (talk) 12:07, 26 May 2008 (UTC)

Density is mass per unit volume – the quantity of something in a certain space.

Specific gravity is this density relative to that of water – how much more (or less, of course) of something you get in a certain space than you would get if you filled that space with water.

Weight is the force that a mass experiences in a gravitational field – specific weight is how strongly something is being pulled by a gravitational field, given a certain volume of the substance.

HTH? Angus Lepper^{(T, C, D)} 12:22, 26 May 2008 (UTC)

(since I hate edit conflicts so much, I'll put my answer in too, but I think Angus did it better :) Density is the fundamental measurement, the mass in a given volume - in other words, if I pick up a 1-foot cube of this stuff, how hard it that to do? Specific gravity is a comparison to water - will it float or sink? (If it has less density than water, it floats, the less dense it is, the higher it floats) Specific weight is how heavy the 1-foot cube is on the Earth's surface, I lied a bit about density, which is true everywhere in the universe. Mass is about how hard it is to accelerate the object any place in the universe, weight is about how hard it is to do it here on Earth. Maybe an article, or a mathematical disambiguation page, 'cause they're all the same thing. Does that help? Franamax (talk) 12:25, 26 May 2008 (UTC)

And how does relative density fit the picture? 125.21.243.66 (talk) 12:47, 26 May 2008 (UTC)

It fits relatively. Relative density == specific gravity. Franamax (talk) 12:56, 26 May 2008 (UTC)

Are you sure? Because my high school physics teacher scared the bejesus out of every student by asking the difference between relative density and specific gravity. 125.21.243.66 (talk) 14:27, 26 May 2008 (UTC)

Specific gravity is a particular instance of relative density (which is, generally, the ratio, $\rho _{A}/\rho _{B}$, of the densities of two substances A and B) where 'substance B' is water. i.e. specific gravity is a special case of relative density, or relative density a generalization of specific gravity, depending on which way you want to look at it. Angus Lepper^{(T, C, D)} 18:41, 26 May 2008 (UTC)

Colour photos of Mars

Inspired by the question above, I'd love to see some true-colour photos of Mars; I know that there are colourized versions of the greyscale photos, but does anyone know if there are any 'real' colour photos produced by taking photos with red, green and blue filters separately? Angus Lepper^{(T, C, D)} 14:00, 26 May 2008 (UTC)

As I understand it, most of the colour images are done like that. It's a little difficult to work out what "true colour" really is, though - they have to determine how to balance the different images (one in each colour) to try and get it as close as possible to what a human eye would see, and since there have never been any human eyes on Mars, that's a little tricky. I think the modern images are pretty good approximations, though. --Tango (talk) 14:08, 26 May 2008 (UTC)

Ah, I thought the colour images were colourized! Thanks, Angus Lepper^{(T, C, D)} 14:09, 26 May 2008 (UTC)

I think some are. Some are certainly as close to true colour as you can get. --Tango (talk) 15:32, 26 May 2008 (UTC)

See [9] for one example of an "(Approximate True Color)" image and a short description of how it was produced. Additionally the calibration target on the rovers includes color samples to provide known comparison values.[10] Rmhermen (talk) 19:57, 26 May 2008 (UTC)

For accurate color you need filters that match the response of the three cone types, which is not red, green and blue but more like yellow, green and blue. Red is used for reproduction because it stimulates the L cones while minimizing crosstalk with M and S; it's not what the L cones are primarily sensitive to. The first page linked by Rmhermen says they used filters centered at 753 nm, 535 nm and 432 nm, which doesn't make sense since 753 nm is way outside the visual range. I assume 753 is a typo for 573. -- BenRG (talk) 23:07, 26 May 2008 (UTC)

753 nm isn't a typo. Most of the "true-color" photos use near-infrared rather than red, because it shows more detail in shadowed areas. --Carnildo (talk) 23:51, 26 May 2008 (UTC)

Disagreeing a bit with the claim that accurate color reproduction requires matching yellow, green and blue cone response curves. Edison (talk) 01:43, 27 May 2008 (UTC)

There's been a continuous storm of comments from people who are rather unhappy with NASA's ideas and rendering of color. Look at these e.g. [The Colors of Mars: Reality and Illusion Sky and Telescope, volume 97, number 4, page 116], [11], [12], [13] 71.236.23.111 (talk) 08:22, 27 May 2008 (UTC)

Carnildo, having now read a lot more about the rovers I see that you're right. But then the whole thing makes no sense. You say they use near infrared for the R channel to show more detail, but if the goal is to make a better looking or more useful image then they might as well go all the way. And they do—the Pancam images also come in false-color versions which are prettier and more interesting than the "true color" versions. I can't believe that the boring brown "true color" images exist for any reason but to satisfy a public demand for pictures showing the colors that an astronaut on Mars would see. And they don't show that. It seems like NASA's best course of action, faced with a demand for true color, would be to educate the public about color vision and why true color images aren't "truer" in any meaningful scientific sense. Then they could pick all their filters based on scientific merit and use the prettiest possible false colors for their pictures of the day. The next best course of action would be to ship the correct color filters and give the public what it wants. The worst course of action would be to try to pass off false color images as true color, which is what they seem to be doing.

Edison: Okay, but the farther you get from the cone response curves the more assumptions you have to make about the shape of the spectrum to get accurate colors. I'm beginning to wonder if I'm missing something fundamental about color photography, though. I can understand a layperson thinking that the best way to get the red/green/blue channels of a digital photograph would be to use red/green/blue sensitive detectors. That's not true, but it's a reasonable mistake to make. What I don't get is that real cameras designed by experts do seem to use RGB sensitive detectors. At least that's what I gather from articles like Bayer filter. Do they really use a red filter? If so, why? Is it just cheaper, or is there something else going on?

Atlant (below): I assume the calibration target is for adjusting the white balance; I don't see how it would help in computing the right tristimulus values if you started off with the wrong color filters. -- BenRG (talk) 23:33, 27 May 2008 (UTC)

Well, the camera isn't a tri-stimulus device. Instead, it has many different filters (spectral channels) that can be switched-in. If the color swatch chart contained either filters that are accurate to the human trim-stimulus response or are fairly narrow-band filters, you could calibrate the camera's many spectral channels to come up with a transform function that will produce the same color images a human eye would see from the many-channel images produced by the camera.

Atlant (talk) 17:37, 28 May 2008 (UTC)

The landers have all contained a "colo[u]r test chart" within view of their cameras. This allows the camera (and its "filters of many colors") to be calibrated so we can come up with a pretty-accurate representation of the colors in the scenes as a human would perceive them.

Atlant (talk) 14:29, 27 May 2008 (UTC)

Carrier concentration in doped semiconductors

For Intrinsic semiconductors $np=n_{i}^{2}$ and this makes sense as mentioned in semiconductors. However my textbook states that this is true for extrinsic semiconductors as well. I would say in this case $np>n_{i}^{2}$, but I can't see why that's wrong? Thanks in advance, Gnorkel (talk) 15:35, 26 May 2008 (UTC)

Regardless of whether it is pure (intrinsic) or doped (extrinsic) the number of electrons (n) and holes (p) must be the same. You cannot have an electron hole without an electron on average in the complete semiconductor. There will be more electrons than holes (and vice versa) in some parts of the semiconductor and this is what give it the properties employed in the semiconductor devices. The doping changes the number not the ratio of n and p. -- Alan Liefting (talk) - 07:23, 27 May 2008 (UTC)

That's not true. Changing the ratio of electrons in the conduction band (n) to empty/available states in the valence band (p) is exactly what doping does. Besides, the fomula is showing that the product of n and p is the same, not the ratio. I believe the relationship is understandable through quantum statistical mechanics (see Semiconductors#Carrier generation and recombination). --Prestidigitator (talk) 01:50, 29 May 2008 (UTC)

Gravity powered electricity generator

Why isn't there such a thing? Why can't we turn gravity into electricity? I can only think of turbines in adam as a type of generator that uses gravity. Are there others? Thank you. 200.127.59.151 (talk) 18:49, 26 May 2008 (UTC)

Tidal generators can be said to use gravity as a power source. --Milkbreath (talk) 18:55, 26 May 2008 (UTC)

Pumped-storage hydroelectricity is a way of storing energy, then using gravity to recovery most of it. Rmhermen (talk) 19:54, 26 May 2008 (UTC)

Going on the "gravity into electricity means 'dropping things'" idea, the problem is "where do you get the things to drop?" Either you need a steady supply (hydroelectricity, for instance) or you lift things -- which uses the energy you're about to gain, and then some. All practical energy sources have to be built on the former, so unless you've got a ready stream of something falling, gravity won't do you much good for a power plant. — Lomn 20:08, 26 May 2008 (UTC)

You need some prime mover to put energy into raising the thing that generates electricity when it drops. For hydroelectric, I suppose solar power fuels the evaporation of water which falls as rain or snow and runs down the river to create the head which allows the hydro turbine to operate. A tidal generator is more interesting: it seems to extract energy from the tidal sealevel changes which result from movement of the moon around the earth, which implies that if you harness the tidal power, it would have a tiny effect of bringing the moon into a lower orbit. Edison (talk) 01:40, 27 May 2008 (UTC)

Hmm, not sure here. My understanding is that tidal effects are moving the moon into a higher orbit by energy exchange as the Earth's orbit slows in reciprocal action. Physicists needed here: does obstructing tidal changes increase or decrease the energy transfer that extends the moon's orbital distance? Franamax (talk) 07:03, 27 May 2008 (UTC)

It boils down to more drag, which is more energy lost in the transfer, which accelerates the Moon's progress to a tidally-locked orbit. — Lomn 13:19, 27 May 2008 (UTC)

flu

HOW LONG AFTER YOU ARE IN CONTACT WITH THE FLU VIRUS WILL YOU BECOME SICK. Does it happen right away or in a week or so? Thanks, \ —Preceding unsigned comment added by 70.73.149.192 (talk) 21:26, 26 May 2008 (UTC)

Our flu article does not say, but accoding to this site it is one to two days. -Arch dude (talk) 21:47, 26 May 2008 (UTC)

Pathogens in body? —Preceding unsigned comment added by 220.235.59.49 (talk) 23:55, 26 May 2008 (UTC)

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)

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)

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)

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 [14] and this [15]. 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 [16], 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: [17], [18], [19], [20]. 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 [21].--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)

May 28

Can you make black holes move?

If you throw something at it... Like the sun, and throw it hard. Like 99.99% the speed of light, what will it do to the black hole? Will it affect the black hole's velocity? 65.41.92.123 (talk) 00:25, 28 May 2008 (UTC)

Yes, it would work the same way as any other object, assuming the other object would be able to absorb a star. In fact, absorbing any object would make it move, just more slowly. See conservation of momentum. *Max* (talk) 00:45, 28 May 2008 (UTC)

A gravitational tractor would likely be the most reliable way to move a black hole. (Although given the likely masses involved, it would take a long time and a lot of energy.) -- 128.104.112.147 (talk) 01:25, 28 May 2008 (UTC)

Magnetic Moment

In dipole, two equasions for the magnetic field are given; one describes it as a scalar, the other as a vector. They are

$B(\mathbf {r} ,\lambda )={\frac {\mu _{0}}{4\pi }}{\frac {\mathbf {m} }{r^{3}}}{\sqrt {1+3\sin ^{2}\lambda }}$

and

$\mathbf {B} (\mathbf {r} )={\frac {\mu _{0}}{4\pi r^{3}}}\left(3(\mathbf {m} \cdot {\hat {\mathbf {r} }}){\hat {\mathbf {r} }}-\mathbf {m} \right)+{\frac {2\mu _{0}}{3}}\mathbf {m} \delta ^{3}(\mathbf {r} )$

Setting them equal,

${\frac {\mu _{0}}{4\pi }}{\frac {\mathbf {m} }{r^{3}}}{\sqrt {1+3\sin ^{2}\lambda }}=|{\frac {\mu _{0}}{4\pi r^{3}}}\left(3(\mathbf {m} \cdot {\hat {\mathbf {r} }}){\hat {\mathbf {r} }}-\mathbf {m} \right)+{\frac {2\mu _{0}}{3}}\mathbf {m} \delta ^{3}(\mathbf {r} )|$

Dividing by common stuff and since the Dirac delta will gives zero,

${\mathbf {m} }{\sqrt {1+3\sin ^{2}\lambda }}=|\left(3(\mathbf {m} \cdot {\hat {\mathbf {r} }}){\hat {\mathbf {r} }}-\mathbf {m} \right)|$

Now, $\mathbf {m} =(1,0,0)$ and $\mathbf {r} =({\frac {\sqrt {3}}{3}},{\frac {\sqrt {3}}{3}},{\frac {\sqrt {3}}{3}})$, so $\lambda =\arctan {\sqrt {2}}$. But,

$1{\sqrt {1+{\frac {2}{3}}}}=|\left(3({\frac {\sqrt {3}}{3}}){\hat {({\frac {\sqrt {3}}{3}},{\frac {\sqrt {3}}{3}},{\frac {\sqrt {3}}{3}})}}-(1,0,0)\right)|$

${\sqrt {\frac {5}{3}}}=|\left((1,1,1)-(1,0,0)\right)$

${\sqrt {\frac {5}{3}}}=|(0,1,1)|$

${\sqrt {\frac {5}{3}}}={\sqrt {2}}$

These are not equal. Am I doing something wrong or is one formula wrong? Thanks *Max* (talk) 00:41, 28 May 2008 (UTC).

Isn't $\lambda$ a function of r. For your example r , $\lambda =\arctan(1)$ or 45°. Graeme Bartlett (talk) 02:47, 28 May 2008 (UTC)

Second equation is the one I remember since undergrad, it is correct. The first one, as you say quite correctly, gives B as a scalar, that is, gives an absolute value of B. Therefore, m should not be boldfaced in that equation. Now, as you know, absolute value of a vector is a square root of sum of squares of its orthogonal components. Let us take z-axis along m and x-axis in (m, r) plane. B has no y-component then. The second equation gives, for $cos\theta =\mathbf {m} \cdot \mathbf {r} /mr$ and r > 0, the following value of B components:

$B_{z}={\frac {\mu _{0}}{4\pi }}{\frac {m}{r^{3}}}\left(3\cos ^{2}\theta -1\right)$,

$B_{x}={\frac {\mu _{0}}{4\pi }}{\frac {m}{r^{3}}}\left(3\sin \theta \cos \theta \right)$.

Root of sum of squares of the two is

$B={\frac {\mu _{0}}{4\pi }}{\frac {m}{r^{3}}}{\sqrt {1-6\cos ^{2}\theta +9\cos ^{2}\theta (\sin ^{2}\theta +\cos ^{2}\theta )}}$

$={\frac {\mu _{0}}{4\pi }}{\frac {m}{r^{3}}}{\sqrt {1+3\cos ^{2}\theta }}={\frac {\mu _{0}}{4\pi }}{\frac {m}{r^{3}}}{\sqrt {1+3\sin ^{2}\lambda }}$.

Thus, the first equation is also correct, provided you replace the boldface m by m in it. Hope this helps. --Dr Dima (talk) 03:50, 28 May 2008 (UTC)

And this is why I shall not be studying physics at anything beyond 'A' Level :| Regards, CycloneNimrod^Talk? 09:11, 28 May 2008 (UTC)

I'll unboldface m in the article. I calculated λ based on r. The opposite side is ${\sqrt {3+3}}={\sqrt {6}}$ and the adjcent is ${\sqrt {3}}$, so shouldn't λ be $\arctan {\sqrt {2}}$? Does the value of B mean that a point dipole fixed here by other forces here will orient itself perpendicular to the first dipole? I was not expecting that. *Max* (talk) 17:24, 28 May 2008 (UTC)

In the example you give, m = (1,0,0) and r = (1,1,1) / 3^1/2. Therefore, one gets $\sin \lambda \equiv \cos \theta ={\sqrt {(}}1/3)$. As you know, $1+\tan ^{2}(\lambda )\equiv 1/(1-\sin ^{2}(\lambda ))$, thus, for $\sin ^{2}(\lambda )=1/3$ you get $\tan ^{2}(\lambda )=1/2$, which means $\lambda =\arctan \left(1/{\sqrt {2}}\right)$ . Please check. As for your second question, I did not quite understand what you mean. If you ask whether there are points in space where B vector is perpendicular to m vector, then the answer is certainly yes, for any r > 0. --Dr Dima (talk) 02:32, 30 May 2008 (UTC)

Zero point energy

Is there any way to magnify the scalar forces? So that it works on large objects? Like make a car levitate or anything? 65.41.92.123 (talk) 02:13, 28 May 2008 (UTC)

I don't know much about this subject, but Zero_point_energy#Levitation_and_inertia looks relevant. --Allen (talk) 05:35, 28 May 2008 (UTC)

There's no such thing as a zero-point-energy force. The Casimir force is just an ordinary electromagnetic attraction between closely spaced neutral conducting plates. It's unusual in that you can compute its magnitude approximately from an argument involving zero-point fluctuations, but you can also compute its magnitude (more accurately) in the same way as any other electromagnetic force. See this paper. That said, you can levitate macroscopic objects electromagnetically—see magnetic levitation—so in effect the answer to your question is yes. -- BenRG (talk) 13:03, 28 May 2008 (UTC)

I find it interesting that the paper above contradicts the implications in the articles Zero_point_energy and Casimir_force that the Casimir force is strong evidence for the existence of zero point energy. Is it possible those two articles need to be rewritten to de-emphasize Casmir forces as being linked to zero point energy?

Also Ben commented above that there is no such thing as a zero point energy force. My understanding is that you can't extract work out of zero point energy, since it is the lowest possible energy state, but that zero point energy itself does exist as a strictly positive amount of minimal energy. So while you presumably can't extract work from zero point energy, the random quantum fluctuations of zero point energy will prevent any system from reaching an absolute zero energy state. Am I understanding all this correctly? 63.95.36.13 (talk) 20:44, 28 May 2008 (UTC)

Can BritaTM Containters Leach BPA?

Can BritaTM Containters Leach Bisphenol A? Are they made of polycarbonate? Are they made of a plastic that can leach BPA?68.148.164.166 (talk) 21:40, 21 May 2008 (UTC)

Can you find the plastic number marking on the container? 2 and 3 are safe, I think. Imagine Reason (talk) 00:43, 28 May 2008 (UTC)

I could not find the plastic number marking on the container.68.148.164.166 (talk) 06:55, 28 May 2008 (UTC)

Ask the manufacturer. Coincidentally, my brother forwarded this email from P&G: "PUR dispenser bodies are manufactured from an acrylic-based polymer classified as recycling code #7. PUR dispenser lids are manufactured from polystyrene, code #6. PUR dispenser filters are made from polypropylene, code #5, and also contain no BPA." I still won't use it, however, because it no longer filters flouride or even chlorine. Imagine Reason (talk) 02:38, 28 May 2008 (UTC)

height and alcohol

sir i want to know about can alcohol drink related with height increases. if yes how it work and if no so how some body heavy drinke and they become very tall and stong. —Preceding unsigned comment added by Dss sakti (talk • contribs) 09:40, 28 May 2008 (UTC) for any sugesion u mail me plz {e-mail removed)

I'm not aware of any study or claim saying drinking alcohol increases height. As to the second part of your question, if they drink beer they get a lot of calories. If they get enough exercise to burn those calories they'll get strong. If they don't burn the calories they get obese and may develop health problems.

We don't respond by e-mail, please don't include your e-mail on this desk. (You never know who might use it.) --71.236.23.111 (talk) 10:14, 28 May 2008 (UTC)

Are you referring to children (who haven't stopped growing) being heavy drinkers? I would expect it to reduce their final height, although I have no references for that. Also, drinking while pregnant can reduce the height of the baby - see Fetal alcohol syndrome. Drinking as an adult shouldn't have any effect on height - you've stopped growing by then. --Tango (talk) 10:17, 28 May 2008 (UTC)

Glow Sticks

I have two questions about Glow Sticks. 1. On the article, it says that the ester oxidizes. But, I don't quite understand how it oxidizes on a molecular level. Could you please show me the equation. So far, I only know the LEO and GER. 2. How do glow sticks manage to stay bright for long periods of time? In videos/ demonstrations, they only stay bright for a few seconds.

Thanks. 121energy (talk) 09:46, 28 May 2008 (UTC)

Glow stick and Cyalume give the chemical equations going from oxalylic ester to carbondioxide. --Stone (talk) 15:20, 28 May 2008 (UTC)

Re: Wheel diameter

(Moved up to join the original question.)

Subtance that increases sex drive?

I'm doing some research for a script. I wonder if there is any drug that makes people... well... more horny? Preferably without any elaborate side effects. It should be used as a kind of "love potion", meaning it should help one character persuade another to have sex with him. I realize there's probably no substance that makes you go crazy for sex without any other side effects, but anything even remotely close to that would be enough, it's not a scientific script so I can make things up a bit to make it fit. It would be nice to just have the name of a substance that is remotely close, to make it a touch more realistic. Thanks! 81.236.199.5 (talk) 11:12, 28 May 2008 (UTC)

The word you're looking for is aphrodisiac. There's a good list of alleged aphrodisiacs in the article. -- Coneslayer (talk) 11:27, 28 May 2008 (UTC)

For fiction you might also find the human portion of Pheromones interesting. Or you could spin an idea off this [22]--71.236.23.111 (talk) 14:39, 28 May 2008 (UTC)

Some dopaminergic drugs have alot of anecdotal evidence supporting 'horniness'. MDPV, methamphetamine#Sexual_behaviour, yohimbine and GHB are the most common ones I can think from the top of my head. --Mark PEA (talk) 19:36, 28 May 2008 (UTC)

Testosterone is well-known to increase libido. --Sean 15:34, 29 May 2008 (UTC)

Cleaning a dog skull part two

Here is the dog skull that I cleaned using the advice you gave here. What article can we enhance with this image?--Lenticel ^(talk) 12:08, 28 May 2008 (UTC)

How about Dog anatomy or Skull? Only thing is there are many pictures there already. Yours is a good pic, though. Fribbler (talk) 12:26, 28 May 2008 (UTC)

Good picture - I'd add it to dog anatomy, there are lots of pictures there, but none of a dog's skull! --Tango (talk) 12:55, 28 May 2008 (UTC)

Survivable?

I went to see this film a couple of days ago. In it, the hero hides in a metal box which is thrown through the air for several miles by an explosion, before it comes crashing to the ground, tumbles end-over-end, and eventually coming to rest. The door bursts open and our hero rolls out of the box apparently unscathed by his high-speed journey. Assuming the box is strong enough to retain it's shape, would a man actually be able to such a violent journey? Astronaut (talk) 12:13, 28 May 2008 (UTC)

I doubt it. I would expect him to be crushed by the g-forces on both take off and landing. To propel a person several miles would require massive acceleration. According to projectile motion, the maximum range is ${\frac {v^{2}}{g}}$, assuming he travelled 5km, that gives a minimal initial velocity of about 224m/s (higher if he wasn't launched at exactly 45 degrees), assuming the explosion provides all of that speed in 1 second, that corresponds to an acceleration of about 22g. He'd probably lose conciousness, but may survive that. However, that same amount of speed needs to be lost when it lands, and that will be done in a fraction of a section (if the box retains it's shape, it means it didn't absorb the impact and would have stopped dead), resulting in much greater accelerations, almost certainly killing to occupant. (Imagine a car crash at 500mph with none of a car's usual safety features - not likely to walk away from that!) NB: I'm ignoring air resistance - for a heavy, compact box, it's negligable. --Tango (talk) 12:49, 28 May 2008 (UTC)

In the film, the box bounced across the ground several times before finally stopping; and I suppose there could have been some minor deformation of the outside of the box (ie. it didn't change the inside shape of the box, but could have been quite dented on the outside). Could the deceleration have been such that each bounce removed some of the velocity so our hero didn't get crushed on landing? Astronaut (talk) 13:34, 28 May 2008 (UTC)

Reality would have made for a really short movie. --LarryMac | Talk 13:26, 28 May 2008 (UTC)

Heh. Anybody see "Air America" with Mel Gibson, where the C130 (I think?) crashes in the jungle, and begins a long skid for about a mile over a couple of minutes before stopping, with (to me) pretty funny reaction from those on board? (It was a comedy, btw, I'm not being sociopathic). Gzuckier (talk) 15:11, 28 May 2008 (UTC)

Bouncing would require some temporary deformation - it works by deforming the object and storing some of the kinetic energy as elastic potential energy and then that elastic energy turns back into kinetic energy and the deformation rebounds. I'm not sure what that would do to the person inside - the total change in velocity is actually greater, since you go from +224m/s to -10m/s, say, which is a change of 234, rather than the change of 224 if you stop dead. That change probably takes place over more time, though, so the acceleration (which is what's important) would be less. --Tango (talk) 14:13, 28 May 2008 (UTC)

Stranger things have happened. WilyD 13:35, 28 May 2008 (UTC)

That's a lot less strange. He would have been falling about four times slower, plus his fall was cushioned by a handy glass roof, rather than being inside an unyielding metal object. Algebraist 13:42, 28 May 2008 (UTC)

A metal box is better then? Or sitting comfortably in a chair? WilyD 13:57, 28 May 2008 (UTC)

Actually, you make an interesting point - I neglected air resistance, since it's usually negligible for a box, but at those kind of velocities, it probably isn't any more. Terminal velocity for the box would probably be less than 500 mph, would would improve his chances, but only to the chance of surviving a fall from a plane without a parachute and not landing on anything soft, which is still pretty much zero. Falling while still in a plane (which seems to be the case with most of these miracle stories) would give you a much lower terminal velocity - there's far more drag on a large plane (even after breaking up) than on a person. --Tango (talk) 14:13, 28 May 2008 (UTC)

The plane weighs a lot more, though. Your terminal velocity is just a function of your density and cross-sectional area. At high speeds, drag is going to go like r²v² and gravity will go like ρr³. If you're roughly spherical, your terminal velocity scales like v_t ~ ρ^½r^½ ... density's probably irrelevent (you're 1, a plane with lots of airspace is probably ~1. So person strapped to a chair = person, person in aircraft depends on chunk size, but they're falling faster. WilyD 14:26, 28 May 2008 (UTC)

My very rough calculations say that the density of a fully laden 747 is about 200 50 Note to self: Diameter and radius aren't the same thing! times less than that of a person (based on Boeing 747#Specifications). They are designed to be a light as possible, otherwise they wouldn't be able to fly. Even broken up into a few pieces, it's going to be significantly less than a person, and terminal velocity will be significantly reduced. (Unless you're unlucky enough to end up in a nose dive, perhaps.) --Tango (talk) 15:01, 28 May 2008 (UTC)

Yeah, deceleration by a long series of bumps, rolls, disintegration, etc. looks spectacular, but will keep peak G forces down to survivable levels. Look for the various Youtube videos of the Michael Mcdowell Texas Nascar Crash from a couple of months back. Since the OP's guy in a box is not strapped in, he has to avoid impact with the inside wall of the box, but if it's spinning, centrifugal force could keep him "strapped down" figuratively and prevent him from fracturing his skull. Kids: don't try this at home. Gzuckier (talk) 15:08, 28 May 2008 (UTC)

I doubt it would spin reliably enough while bouncing. If it's small enough, he could wedge himself inside so he doesn't get shaken around. Even with all the bouncing, landing at terminal velocity in a metal box doesn't sound survivable to me without something to absorb the impact. --Tango (talk) 15:12, 28 May 2008 (UTC)

But if you are Indiana Jones, cinematic rules override kinematic rules! --Stephan Schulz (talk) 15:16, 28 May 2008 (UTC)

It's also probably worth noting that the amount of lead in a lead refrigerator would not have protected the hero in question from the thing in question that tossed him. Even if he had, improbably, survived he'd have probably gotten quick sick. --98.217.8.46 (talk) 19:34, 28 May 2008 (UTC)

I think the original poster is wrong to assume the metal box was thrown "several miles". As I understood the scene, it didn't move particularly far; it's just that the same thing that put it in motion also damaged the surrounding area, so it may have looked different. You don't see it flying through the air or anything. --Anonymous, somewhere in the real world, 00:01 UTC, May 29, 2008.

Actually, it was shown flying through the air. In fact, from what I remember, its first bounce was just in front of the army car which was driving away from the explosion. The car didn't make it, but the fridge carried on bouncing. Jdrewitt (talk) 08:50, 29 May 2008 (UTC)

Oh. Perhaps I remembered seeing what I expected to see, then. --Anon, 23:49 UTC, May 29.

you all seem to be forgetting that each time the box experiences a collision, its passenger is going to experience an internal collision. Our hero would've been broken and bloody after that trip, even if the box stayed closed and intact. Which it wouldn't have. --Shaggorama (talk) 03:41, 29 May 2008 (UTC)

I think the most ridiculous thing that has been lost in all of this (having just returned from a showing of said movie) is that he stands in the immediate aftermath of (what one can only assume is) a fairly dirty uranium-fission explosion, what looks like less than a mile from ground zero, with no long- or short-term effects on his health. The physics of that whole movie was (were?) shall we say, less than intelligent. -RunningOnBrains 05:38, 29 May 2008 (UTC)

I bet his hair was perfectly styled when he stood up too. That always happens to me when I get caught in nuclear explosions :) And I always get clean clothes in the next scene. Franamax (talk) 08:18, 29 May 2008 (UTC)

He was rinsed off afterwards though to remove any radioactive particles on the outside of his body. As long as he didn't ingest any of these particles then he would be ok. The largest fraction of gamma radiation is emitted in the very first milliseconds of a nuclear explosion, during which time he was in the lead lined fridge (why was the fridge lead lined?) which would have reduced the dose. Jdrewitt (talk) 08:31, 29 May 2008 (UTC)

Homing distance of snails

Sorry - I didn't check responses to my question: How far can snails travel back to their usual habitat if you remove them from this? within the 4 days. Please would anyone who knows the answer repeat it for me? Thank you. Ruth 555Ruth555 (talk) 12:38, 28 May 2008 (UTC)

The previous question is archived here. No-one knew a distance, they suggested marking the shells before releasing them so you can tell if they come back. --Tango (talk) 12:52, 28 May 2008 (UTC)

Original Research is frowned upon here, but it is allowed if no one can come up with a reference. Why not find out and tell us? On day one, pull each snail off, mark it with a red X and gently relocate it 100m away. On day 2, if any snails have a red X you know they can go 100m, so use a green marker and try 200m. If none have made it back, try 50m. Anyway, you have to use different colors and symbols so that on day 3 you know whether the returnees were from day 1 or day 2, etc. Once you have run out of colors use a circle, etc. Ensure that the marks are non-toxic because the experiment ends when you get tired of it and eat them. -SandyJax (talk) 16:01, 28 May 2008 (UTC)

http://upload.wikimedia.org/wikipedia/commons/8/8a/Musical_instrument_classification_by_physics-based_organology.png

What is the instrument with the guy with his fingers in those beer glasses?68.148.164.166 (talk) 12:39, 28 May 2008 (UTC)

It's known as a Glass harp. --Tango (talk) 12:54, 28 May 2008 (UTC)

It's not clear why it is shown under the heading Plasmaphone though. Pfly (talk) 21:03, 28 May 2008 (UTC)

(edit conflict) That is NOT a glass harp. A glass harp is played by running your finger around the rim of the glass. In that picture, the musician clearly has his fingers in the water. Moreover, the water level is the same in each glass, so there would be no difference in pitch. My guess is the cords connected to the glasses aren't just lighting them up: I'm betting those fluids are charged. I can only speculate how the instrument works, but maybe by sticking his fingers in the liquid, he changes its conductance properties, or cause a current to pass through his body changing the conductance of the system....I can only guess. In any event, it's probably some sort of fancy electronic instrument or user interface -- Shaggorama (talk) 03:26, 29 May 2008 (UTC)

Good point. I'd assumed his fingers were inside the glasses simply because he was getting them wet, and he wasn't actually playing at that instant. I hadn't noticed the water levels were all the same - there must be something more going on (presumably to do with the wires, as you say). --Tango (talk) 13:38, 29 May 2008 (UTC)

Current, volts, Ohm's law...

Ok, I think after all this time I still do not really have a good grasp of what current is (and I've read the articles).

We normally rate batteries by their voltage. So a battery might have 1.5 Volts, say. If we connect a resistor across the battery's terminals, a current goes through it. That current can be calculated by Ohm's Law: I = V/R. So if we have a 10 ohm resistor, we have 0.15 Amps coming out of the battery, right?

If we have a resistor which is 0.1 ohms, we have 150 amps going through the resistor. So I guess we can keep going up to nearly infinity if we keep making the resistance smaller, is that right? (Except eventually the battery will run out.)

However, when I look at solar cells, they give both a voltage and a current (or sometimes they just give a current). So I might have a cell that says it provides 1 amp. So if I connect a resistor across it, is the voltage of the cell going to change? The current? I assume that Ohm's law has to be maintained?

Why are solar cells and batteries different? Can batteries produce any current they want, and cells can only produce a fixed current? Or is it a maximum current? What happens if I have a 5V solar cell connected across an 0.001 Ohm resistor? What is the current?

Thanks! — Sam 14:48, 28 May 2008 (UTC)

Ah; the catch is (there's always a catch) that batteries and solar cells are not ideal voltage sources, nothing being ideal, the way they are often simplified as. In the real world, of course the battery/solar cell has its own internal resistance; everything does. So, if your 1.5 volt battery has a 1 ohm internal resistance, then even if it is short circuited, it's not going to deliver any more than 1.5 amps. Same for the solar cell. Same for transformers, anything in the real world; there's always an internal resistance which needs to be factored in in some cases. Of course, also there's internal capacitance and inductance which may need to be accounted for under some conditions; that's why electronic engineers who understand real things not just ideal things do a better job. Gzuckier (talk) 15:01, 28 May 2008 (UTC)

(See also internal resistance). TenOfAllTrades(talk) 15:23, 28 May 2008 (UTC)

If you'll allow me to expand on Gzuckier's point, we normally design electronics so that our "voltage sources" are operating pretty close to the regime of being an "ideal" voltage source. That is, while a battery might deliver (say) 5 amps into a dead short, it's commonly used in equipment that's drawing far less current, say 0.25 Amps. There are three reasons for this:

1. It makes the circuitry a lot easier to design if you can mostly ignore the internal resistance of the voltage source (battery).
2. It would be wasteful if the battery were internally dissipating a large share of the total power that was being consumed from it. To a first approximation, if you tried to operate our hypothetical "5 amp" battery with a 2.5 Amp load, roughly half the power being produced from the battery's chemical reaction is being dissipated in the load and half the power within the battery itself. The power dissipated within the battery does no useful work.
3. The internal resistance of a battery rises as it ages. If you design your circuit to consume a lot less current than a new battery is capable of, an old, decrepit battery may still be capable of powering the circuit.

Hydraulic analogies are often useful in this case. A 1.5 volt battery might be compared to a water tank 1.5 metres off the ground. That tiny AAA cell represents a tank of 1 litre capacity. That big D cell represents a tank of 20 litres capacity. The bigger tank also has a proportionally-larger shut-off valve on the tank's discharge connection. Now, connect a drainage pipe to the tank. For a very skinny pipe, both tanks will provide adequate water pressure but the AAA-sized tank will run out of water twenty times as fast as the D-size tank. Now connect a bigger discharge tube to the tanks. For the tiny tank, the tank's discharge valve will limit water flow into the big pipe and there'll be very little pressure in the discharge pipe. But for the D-sized tank, its larger discharge valve can still provide full water flow into the discharge pipe and full water pressure. Batteries (and solar cells and most other voltage sources) work just like this.

Atlant (talk) 17:28, 28 May 2008 (UTC)

Ok, that makes a little sense. However, I still don't quite understand why solar panels are rated just by their amperage. Is a "one amp" panel describing the current that would be delivered into a short? — Sam 20:49, 28 May 2008 (UTC) —Preceding unsigned comment added by 63.138.152.238 (talk)

It's more likely a roughly defined point at which the internal resistance can be considered negligible, and thus at which the cell is suitable for powering a given application. As Atlant notes in the 5-amp (short current) battery example, it wouldn't make sense to use it in a 2.5 amp application, either. — Lomn 21:57, 28 May 2008 (UTC)

I don't know about the case of solar cells, but normally when both a voltage and an amperage are quoted the voltage is an estimate while the amperage is a maximum. E.g. a 240V 13A wall socket will maintain a potential difference of about 240 volts and you shouldn't try to draw more than 13 amps from it or something bad will happen (in this case a tripped circuit breaker). -- BenRG (talk) 23:27, 28 May 2008 (UTC)

A battery or solar cell could be characterized by the open circuit (no load voltage), which will be the highest possible output voltage, higher than seen when it is supplying current, and the short circuit current, which is quite high (several amps) even for an AA alkaline cell. But such a high current would limit the useful life to a very short period for a battery, and the voltage would drop dramatically. Another rating system would be so many amps (or milliamps) at a certain output voltage for normal or optimal operation. For example, a 200 Watt Kyocera solar panel [23] specifies that for max power output, the current should be 7.61 amps and the voltage should be 26.3 volts, the product of current times voltage equalling 200.61 Watts,which implies a total external circuit resistance including the load of 3.46 Ohms. but says the short circuit current is 8.21 amps and the open circuit voltage is 32.9 volts. The power under short circuit conditions would be 8.21 amps times zero volts, or zero Watts. The power for open circuit conditions would be 32.9 volts times zero amps, or zero Watts. For conditions close to short circuit or open circuit, the output power would be nonzero but far smaller than the 200 Watt maximum. Edison (talk) 02:41, 29 May 2008 (UTC)

solar power

i want get the details of solar power process and its panel types with photo graph & the details of batterys used to store power with maximum capacity and its configration details

if provide.any source or call center to discuss about said details —Preceding unsigned comment added by 124.125.42.50 (talk) 15:11, 28 May 2008 (UTC)

I would think that solar energy would be a good place to start and then, when you have specific questions, ask again. -- kainaw™ 19:08, 28 May 2008 (UTC)

Homing Instinct of snails.

Thank you for responding to my latest enquiry. The idea of nail varnish is a good one. Please be patient with my lack of expertise on this site. I'm aware that this is a response, rather than another question, but am not sure how to slot this comment into the correct place! As a newcomer, I'm enjoying the site immensely! What a variety of different subjects - I've spent hours reading through the topics instead of getting on with my own work - I'm in process of writing a novel. Ruth555Ruth555 (talk) 15:21, 28 May 2008 (UTC)

I answered the question above. -SandyJax (talk) 16:13, 28 May 2008 (UTC)

Hello Ruth - we're glad you're enjoying yourself. When you want to add to an existing section, just click on the "edit" link on the right side of the line that contains the section title. --LarryMac | Talk 16:19, 28 May 2008 (UTC)

Chemistry: What exactly is produced by immersing steel in salt water?

I know that rust is produced, but what gas is created?

I've noticed bubbles continually forming. Is it chlorine? —Preceding unsigned comment added by 24.81.198.165 (talk) 20:11, 28 May 2008 (UTC)

It's got to be hydrogen. Rust is a mix of iron oxides. Since there isn't enough dissolved oxygen in water to rust things very fast, the water must be dissociating into hydrogen and oxygen. The oxygen combines with the iron in steel to form rust, and the leftover hydrogen atoms combine to form hydrogen gas. --Carnildo (talk) 20:45, 28 May 2008 (UTC)

Ethyl Alcohol

Hello. Is C₂H₅OH a hydrocarbon? When burning, is the chemical equation: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O? Can this reaction possibly be double displacement? Thanks in advance. --Mayfare (talk) 21:21, 28 May 2008 (UTC)

Have a look at Ethanol, Alcohol and Metathesis reaction (double displacement). Jkasd 21:41, 28 May 2008 (UTC)

You should also take a look at combustion. bibliomaniac15 04:02, 29 May 2008 (UTC)

Terminal Velocity

This French guy has just recently failed in an attempt to float his helium balloon at 40,000m and then jump out, free-falling for around 15 minutes before opening his parachute. In every article I have read about this, it says at 35,000m he would have been expected to break the sound barrier. Is this possible? I know at that height the air is relatively thinner and there would therefore be less friction, but surely his terminal velocity would not rise from c. 150mph (nearer the ground) to over 750mph? Also, would there be a sonic boom and what effect would this have on him, considering he wouldn't be in the safety of a jet-plane?--ChokinBako (talk) 21:26, 28 May 2008 (UTC)

I can't comment on the specifics, but one thing people sometimes forget is: the only reason a falling object has a terminal velocity at all is air resistance. So, if the air resistance almost goes away, the resulting speeds could be very high. Friday (talk) 21:30, 28 May 2008 (UTC)

Also, the speed of sound varies with temperature. Lower temperatures at high altitude decrease the speed of sound. See sound speed gradient for a discussion of this phenomenon. — Lomn 21:47, 28 May 2008 (UTC)

Indeed 150mph is not an accurate terminal velocity near the ground. According to Terminal velocity an experienced skydiver can achieve about 200 mph by optimising body position (of course an experienced skydiver wouldn't want to be at that speed to near the ground, but hopefully people get what I mean). According to [24] the record is 321MPH without any special equipment and Joseph W. Kittinger achieved 619mph Nil Einne (talk) 23:08, 28 May 2008 (UTC)

TECHIE COOLIE

Who is a TECHIE COOLIE & Why are they so called?117.197.240.153 (talk) 21:44, 28 May 2008 (UTC)

It could be a racial slur about someone who is a "techie". See techie and coolie. Friday (talk) 21:50, 28 May 2008 (UTC)

Alternatively, it may derive from the use of "coolie" to indicate a brute-force laborer. That would still leave it a derogatory remark, though perhaps not an outright slur. In any event, Google shows very little use of the phrase, so there's not likely a definitive answer. — Lomn 21:54, 28 May 2008 (UTC)

It could be a derogatory remark about the techie's employer, saying that they treat their workers like coolies. That seems the most likely interpretation to me, but of course I'm guessing. --Anonymous, 00:05 UTC, May 29, 2008.

Perhaps he works next door to the Code monkey. Edison (talk) 02:22, 29 May 2008 (UTC)

Water + grease fire: Why so much energy released?

RE: http://www.youtube.com/v/kS9inNW4KS8 -- Why is so much energy released when water is added to a grease fire? I'm wondering whether the combustion of the fuel in an internal combustion engine could be similarly augmented, by injecting some water into the cylinder, either with the fuel or separately, before or immediately after ignition. --Nonlocal (talk) 21:58, 28 May 2008 (UTC)Nonlocal

All that's happening is that the water is (very quickly) brought to a boil by the hot oil. So, it bubbles and expands and the hot grease goes everywhere, and the fire spreads. There is such a thing as water injection in automotive technology (see Water injection (engines), but it's about cooling, not getting energy out of the water. Friday (talk) 22:24, 28 May 2008 (UTC)

Man, what is it with the British and their very disturbing PSAs! Yikes! --98.217.8.46 (talk) 01:23, 29 May 2008 (UTC)

Disturbing = unlikely to be forgotten Theresa Knott | The otter sank 06:35, 29 May 2008 (UTC)

I think my main confusion is that the British seem to think their PSAs should actually be useful rather than just hollow ad campaigns used to write-off a tax deduction or something along those lines. ;-) American PSAs are almost always totally toothless, laughable, poorly designed and poorly executed. --98.217.8.46 (talk) 15:27, 29 May 2008 (UTC)

That's a pretty awesome demonstration in that video. I think the fire grows so rapidly because the explosive boiling of the water conitnually throws up grease because it's contained in the pot (and there's also probably an unusual amount of grease in the pot). Normally, grease fires don't result from pots of grease like that; usually, the flaming grease is in a pan and there is less of it. In that scenario, adding water spreads the fire around instead of making it grow like that. But in any event, don't put water on a grease fire! --Shaggorama (talk) 03:13, 29 May 2008 (UTC)

A kilogram of TNT releases less enery than a candle of 1kg, but it looks different, becaus the candle takes hours and the TNT far less than a second for the reaction.--Stone (talk) 05:25, 29 May 2008 (UTC)

The paper, On the interaction of a liquid droplet with a pool of hot cooking oil, Short communications, by S.L. Manzello, J.C. Yang and T.G. Cleary (Fire Safety J 38 7 (2003), pp. 651–659), notes that such occurrences of rapid boiling of water "have been termed vapor explosions, explosive boiling, or rapid vapor explosions." --Nonlocal (talk) 16:39, 29 May 2008 (UTC)

Conservation laws and space-time symmetry

As I understand the modern conception of physics, conservation laws arise because of symmetries in the laws of physics (Noether's theorem, I think). Conservation of momentum is the result of the universe being symmetric under spatial translation, conservation of angular momentum is due to spatial rotational symmetry, and the conservation of energy is due to time translational symmetry. However, we also have the concept of space-time, where there is no distinction between space and time (after accounting for a few -1's, i's, and c's). So if we have conservation of angular momentum due to rotational symmetry in the x-y plane (a rotation that occurs between two spatial axises), is there a conservation law for rotation in the x-t plane? (That is, a rotation that occurs between a spatial axis and the time axis.) - How about for rotations and translations involving the other 6+ dimensions proposed by string theory? -- 128.104.112.147 (talk) 22:32, 28 May 2008 (UTC)

The best way to think about it is to consider the metric. It will be a function of your coordinates, (t,x,y,z), say. If it doesn't depend on one of them, you have a conserved quantity (momentum in that direction, roughly speaking - see Killing field for more details). If you use different co-ordinates, for example, spherical coordinates, you may find that the metric doesn't depend on one of the angles, that gives you conservation of momentum in the direction of that angle - angular momentum, in other words. If you choose a coordinate system in which one of the coordinates is a rotation in the x-t plane, I imagine you would find that the metric does depend on that coordinate (those -1's, i's and c's do need to be accounted for!), so you don't get a conserved quantity. I'd have to find pen and paper to work it out for sure. The extra dimensions of string theory would definitely allow for extra conserved quantities, but if you ever actually have Killing fields in those directions, I don't know. --Tango (talk) 23:01, 28 May 2008 (UTC)

The conserved quantity associated with rotation around the origin in the xy plane is x p_y − y p_x, i.e. the angular momentum around the origin in the xy plane. This holds for any pair of perpendicular axes, even if one of them is timelike. So the conserved quantity associated with rotation in the xt plane is x E − t p_x. I'll let you work out what that represents. Note that it depends explicitly on t, unlike the conserved quantities people normally talk about, but that's not a deep difference—you just plug in different values of t at different times.

But the laws of physics are not symmetric with respect to ordinary rotation in the xt plane; you need a Lorentz transformation instead. I'll let someone else figure out what the corresponding conserved quantity is, though. —Ilmari Karonen (talk) 22:16, 29 May 2008 (UTC)

The Lorentz symmetries give rise to conservation of four-momentum, surely? Algebraist 22:26, 29 May 2008 (UTC)

I don't know whether the Calabi-Yau manifolds that describe the extra six dimensions in string theory have any symmetries that lead to conserved quantities. In Kaluza-Klein theory I think that the conserved quantity associated with translation in the fifth dimension is the electric charge. -- BenRG (talk) 00:19, 29 May 2008 (UTC)

May 29

electrons and perpetual motion

To start off, I am a 17 year old high school student that has just completed his first year of high school-level physics. I'm pretty smart (at least I like to think so), but if this question can't be answered with vocabulary and ideas that someone of my edjucation level will be able to understand, that's ok. The answer to this question is probably in Wikipedia somewhere, but in my reading I've only seen equations and explanations that I don't think I'll ever understand until sometime through college.

Question: If there is no such thing as perpetual motion, how can electrons keep moving around the nucleus of an atom? My guess is that at the level we're talking about, there's not really anything like friction in the common sense, so there's nothing to act against the electrons after they are moving, but then where does the energy come from to move them in the first place?Hypershadow647 (talk) 00:03, 29 May 2008 (UTC)

The motion of electrons in an atom is perpetual motion in the ordinary English sense but not in the technical sense used in physics. A "perpetual motion machine" in physics is a system that violates the first law of thermodynamics (a "free energy machine" or "perpetual motion machine of the first kind") or the second law of thermodynamics (a "perpetual motion machine of the second kind"). The electrons in an atom don't gain or lose energy or entropy (at least not without interacting with the outside world), so they don't violate either of those laws. -- BenRG (talk) 00:39, 29 May 2008 (UTC)

You'll be happy to know that it's not a dumb question at all—in fact, it was a major objection to the original Rutherford atomic model, that the electrons seemed to whip around without losing energy, and if you imagine them behaving like any other gravitating object (like a planet) you'd expect that not to work out. Bohr's great insight, the insight which set off quantum mechanics (as distinct from the original quantum theory by Planck and Einstein), was that if you take for granted that the electrons can do that in specific orbitals, that they are not in "motion" in the same way that we understand it to be on a macroscopic level, then it all works out perfectly well mathematically and according to experiment, even if it doesn't make as much conceptual sense (this is the kernel of what would become the Copenhagen interpretation of Bohr and Heisenberg). Einstein thought this approach to physics was repulsive—to come up with answers that didn't make any intuitive sense, as he saw it—but Bohr's method won out in the end, and much of quantum mechanics is about taking for granted certain properties of the quantum world which are not shared by the macroscopic world. Why don't electrons behave like billiard balls, is essentially your question, and the answer is simply because the laws that govern billiard balls don't apply on that scale. --98.217.8.46 (talk) 01:10, 29 May 2008 (UTC)

Whoa, whoa, whoa. Bohr's atomic model did help inspire quantum theory, but it was completely wrong. Real electrons are nothing like the electrons in Bohr's model. They don't even have the angular momenta that Bohr thought they did. Bohr thought the angular momenta were 1, 2, 3, ..., but in fact they're 0, ${\sqrt {2}}$, ${\sqrt {6}}$, .... I think it was little more than dumb luck that his model gave the right values for the hydrogen spectrum (which could be measured to confirm it) despite having the wrong values for the angular momenta (which couldn't be measured). And quantum mechanics does explain the quantization of the orbits, it doesn't simply assume it the way Bohr's model did. Schroedinger's equation doesn't have any quantization built in; you have to solve it before you discover that the electron orbits are quantized.

There are two things that keep the electrons from dropping into a state of zero energy: the uncertainty principle and the exclusion principle. They're both hard to explain. The electron can't just fall into the nucleus because the nucleus is very small; that would give the electron a well defined position, which would mean that it would have to have a very uncertain momentum, which would quickly propel it out of the nucleus again. The "ground state" is a compromise between position uncertainty and momentum uncertainty. The exclusion principle comes into play when there's more than one electron in the atom. Without the exclusion principle they would all fall into the ground state, since systems "like" to have the lowest energy possible. With the exclusion principle you can only have one electron in each state, so some of them have to be in higher-energy states with larger angular momenta (meaning they're actually orbiting the atom, unlike the ground state electrons which have an angular momentum of zero and could be said to not be moving at all). -- BenRG (talk) 04:00, 29 May 2008 (UTC)

If the electron were a ball bearing circling inside a hemispherical bowl, or a weight tied to a string circling around the point of suspension, friction and air resistance would cause it to drop gradually to lower and lower levels. The reason electrons do not show such a gradual decay of energy level, as it was explained to me back when, is that even taking it as a sort of standing wave, it might be expected to bleed off energy like an electromagnetic wave circling on a loop of conductor. The quantum effect is the theory or observation that it cannot drop gradually to imperceptibly lower energy energy levels as the circling weights could in the mechanical analogies. Only a quantum of energy can be absorbed or emitted, changing it to a higher or lower energy level, thus no slight gradual decay of energy level is possible.Edison (talk) 02:20, 29 May 2008 (UTC)

It's true that only a quantum of energy (a photon) can be absorbed or emitted, but the energy of a photon can be arbitrarily small, so in effect the energy that can be emitted isn't quantized at all. So this can't explain why the electron orbit doesn't decay. -- BenRG (talk) 04:00, 29 May 2008 (UTC)

However, the stable energy states around a nucleus are quantized as well, and this imposes the appropriate restriction on the possible photons that can be emitted. Confusing Manifestation(Say hi!) 04:12, 29 May 2008 (UTC)

I don't know about our 17 year old OP, but reading through this thread I'd feel confused (and not just in manifestation). So can we explain it in understandable terms without sacrificing enough to run into my favorite Feynman quote?--71.236.23.111 (talk) 16:57, 29 May 2008 (UTC)

antioxidants to delay ageing and damage of cells

what combinations work and do they¿ i know you cant give medical advice, but what does science say so far about the effectivity of them¨¿thnx guys —Preceding unsigned comment added by 75.69.26.8 (talk) 03:20, 29 May 2008 (UTC)

The empirical evidence to date has been quite disappointing; the benefits are largely theoretical rather than demonstrated. - Nunh-huh 05:07, 29 May 2008 (UTC)

While antioxidants are great at scavenging damaging free radicals generated via metabolism, which can denature proteins and injury other macromolecules such as nucleic acids and lipids, there is no conclusive evidence that they prevent general cellular senescence. See telomeres. Wisdom89 _{(T / ^C)} 06:45, 29 May 2008 (UTC)

Career

What jobs and career options are there in relation with animation? —Preceding unsigned comment added by 117.194.225.94 (talk) 03:55, 29 May 2008 (UTC)

If I had to surmise, I'd say a viable option would be 3D video game development. Wisdom89 _{(T / ^C)} 06:42, 29 May 2008 (UTC)

There are tons of video animation companies for everything from bad car commercials to popular children's movies. -- kainaw™ 12:57, 29 May 2008 (UTC)

There are quite a few unique ones, too. If you like kids you can run animation workshops at museums or fair events, for one. What job you can find and end up in might not be the same as the "standard" job description. And even that can differ from one place to another. --71.236.23.111 (talk) 16:35, 29 May 2008 (UTC)

Thermo Pond Epoxy

Hi. I saw a '3rd Rock From the Sun' episode where mary albright puts this chemical on dick solomon's desk, because earlier they had been playing impractical jokes on one another. Dick comes in and sits at his desk. as soon as he puts his hands on the desk, they are instantly stuck. Then he uses too much force to get his hands off and he accidently puts his head on the desk and then is stuck to this position. My question is: Can this chemical really do that sort of thing, paste objects together that quickly?Jwking (talk) 05:32, 29 May 2008 (UTC)

Yes, some types of superglue can. There are loads of documented cases of people putting it on toilet seats, glasses etc. Not a very sociable think to do. If you put it on a non-porous surface skin will bond almost instantly. There have also been eyeball to eyelid and similar in accidents. I'd stick to clingfilm for jokes... --BozMo talk 06:22, 29 May 2008 (UTC)

Since detaching the stuck human can require medical assistance this way exceeds funny. The doctors and lawyers will laugh all the way to the bank, though. (Neither legal nor medical advice)--71.236.23.111 (talk) 16:21, 29 May 2008 (UTC)

Brain + Sex

What part of the brain becomes more active during sexual arousal? Or at least, what part controls that. --68.90.143.120 (talk) 06:30, 29 May 2008 (UTC)

The Raphe nucleus and serotonin are thought to be involved. Wisdom89 _{(T / ^C)} 06:35, 29 May 2008 (UTC)

Well, speaking as a guy, it's pretty clear your entire brain goes on vacation. Gzuckier (talk) 20:47, 29 May 2008 (UTC)

Under a burning night sky

I'm curious why the sky is orange during nighttime. First of all it was 10 pm so I discount the sun. It is relatively cloudy and rainy during the night and the clouds are actually the ones that is a dull orange. I live in Manila so the air pollution is strong but I can't account fo r the orange hue as we use fluorescent lamps here rather than oil or fires.--Lenticel ^(talk) 06:58, 29 May 2008 (UTC)

Sodium street lamps? (See the section on light pollution) 81.174.226.229 (talk) 08:41, 29 May 2008 (UTC)

Also the article on Light pollution Jdrewitt (talk) 12:00, 29 May 2008 (UTC)

hmm... I think you're right. It is Skyglow. No wonder this never happens when I'm in the provinces. --Lenticel ^(talk) 12:38, 29 May 2008 (UTC)

Power Generators

I was wondering how efficient generators are at converting mechanical energy from the rotating magnet to electrical energy? 61.69.132.119 (talk) 07:32, 29 May 2008 (UTC)

I think it's about 80-85%, which is from actual, but half-remembered, research. If someone doesn't give the definitive answer, I'll try and get back to you. It's definitely quite high, because the overall efficiency is about 40%, with most of the losses at an early stage, I think in the production of steam. 130.95.106.128 (talk) 11:25, 29 May 2008 (UTC)

I second the 80-85%, but can't quote a good source either. I know the figure from adding up losses for overall systems in which case it would be stated as a 15-20% loss. --71.236.23.111 (talk) 17:05, 29 May 2008 (UTC)

Surely it is higher than 80 to 85%, given that in 1879 Thomas Edison's "Long legged Mary Ann" generator achieved 82% mechanical to electrical efficiency, a sizeable increase from the 40% of earlier generators, with his reasearch team over the next decade achieving 90% efficiency [25] . If present day 1000 megawatt utility baseload generator were 15% to 80 20 % inefficient, it would get heated up by 150 to 200 megawatts, which seems unlikely. [26] cites 93% to 97% efficiency for small hydro generators. [27] says a wind generator has achieved 98% efficiency. [28] cites an 800 megawatt generator's efficiency being increased from 98.93% to 99.01% efficiency via stator rewinding and other improvements. I wonder if the lower efficiency deducts the auxiliary equipment such as coal handling, plant lighting, pumps etc? Edison (talk) 19:12, 29 May 2008 (UTC)

I guess not all your losses are heat. You lose quite a bit to vibration. I've seen the 80-85% ballpark used in wind turbine and cogeneration setups. (And I've usually seen those come out on the low end rather than overshoot the target.) It should be straightforward enough Joules in Watt out, but there's a lot of leeway in who measures what where as usual. If you look at steam temperature/wind energy to power output you get a different number than if you look at torque to output. 71.236.23.111 (talk) 22:43, 29 May 2008 (UTC)

Mortality rates expressed as hazard rates

Does anyone know where I could find mortality rates calculated as hazard rates? I'm trying to answer questions like, if a Canadian man makes it to the age of 93, what are his odds of surviving to 94? If an American baby reaches the age of 6 months, what are the odds of her surviving the remainder of her childhood? Thanks. moink (talk) 12:36, 29 May 2008 (UTC)

I once did a similar analysis on South African mortality rates and I used Statistics South Africa for the data so I would presume that the United States Census Bureau would be able to help you for US data. Do you know how to calculate the probabilities you need from actuarial tables? Also, see force of mortality which is the hazard rate in survival analysis with respect to mortality. Zain Ebrahim (talk) 13:20, 29 May 2008 (UTC)

Thank you! I think I just needed the term to search for. moink (talk) 16:45, 29 May 2008 (UTC)

You're welcome. All the best with your work. Zain Ebrahim (talk) 18:08, 29 May 2008 (UTC)

Horrible plastic smell!

I bought some plimsolls online from River Island, but they stink of plastic like they're from some crappy discount shoe warehouse.. I've put them outside to air but they still smell awful. I thought I'd ask you clever lot for some advice. Whack on the Febreze? Air tight container with some Bicarbonate of soda? Thanks in advance! 79.78.46.84 (talk) 12:57, 29 May 2008 (UTC)

You bought some "lines painted on the hull of a ship to help determine displacement and draft"? Where are you planning on using them? There has got to be another definition for that word.... -SandyJax (talk) 15:01, 29 May 2008 (UTC)

Um yes? plimsolls Nil Einne (talk) 15:05, 29 May 2008 (UTC)

(after edit conflict) Plimsoll shoes have a very pungent smell of rubber, I've always found, but not plastic which doesn't really smell much. Theres not much you can do about it. It fades with with time, I find. Fribbler (talk) 15:07, 29 May 2008 (UTC)

Also see wiktionary:plimsoll Nil Einne (talk) 15:08, 29 May 2008 (UTC)

My guess would be that this is the culprit Thiourea. Vulcanization makes rubber usable, but sulfur is known to combine into truly stinky substances. The thing is that you want to avoid the rubber drying out (which would ruin it.) So the baking soda will eat the smell, but in an airtight container will also desiccate the rubber which will make it brittle. Fragrance oil might cover the smell, and you could use some activated charcoal insoles. 71.236.23.111 (talk) 16:10, 29 May 2008 (UTC)

A doubt

How does one cite matter from a chapter in a book that has contributors that are different from the editors mentioned on the cover and elsewhere? Which all authors are to be included in the citation?

Kindly help me with this doubt.

Thanks in advance.

Regards.

PS: Have posted the same query on the talk page of citations, but am not expecting a quick reply. Thanks.

—KetanPanchal^taLK 13:30, 29 May 2008 (UTC)

I would err on the side of more information, listing both the chapter's editors as well as the editors of the entire book. Roughly working from the MLA guidelines, "Works with Multiple Authors" should list the individual author first, followed by the group:

Heller, Steven, ed. The Education of an E-Designer.
Heller, Steven and Karen Pomeroy. Design Literacy: Understanding Graphic Design.

Hopefully this example helps. Nimur (talk) 14:23, 29 May 2008 (UTC)

Incidentally, that's not how you cite chapter authors. Chapters are cited separately and then in the same citation you cite the main work and note the editors. E.g. Paul, Diane B. (2003), "Darwin, social Darwinism and eugenics", in Hodge, Jonathan and Radick, Gregory, eds., The Cambridge Companion to Darwin, Cambridge University Press, 214–239--98.217.8.46 (talk) 15:23, 29 May 2008 (UTC)

Thanks Nimur, for your reply. But, my doubt was more about the technical aspect since I'd never seen the {{cite book}} in its expanded form, had only seen its abbreviated form at WP:Citation templates. Surprisingly, I got my doubt cleared at the talk page of citations itself! Bye. Take care. —KetanPanchal^taLK 14:54, 29 May 2008 (UTC)

Optimal nap/sleep time

I've read somewhere that if you're not having a full night's sleep, or if you're just taking a nap, certain sleep durations are better than others because you'll not be waking up during the "wrong" part of the sleep cycle. I think two recommended durations were given in the article I read, one for short naps and the other for longer sleep.

I can't find the article and don't remember what the recommended durations are. Can someone point me to some good articles/resources on the subject? —Preceding unsigned comment added by 71.162.242.15 (talk) 16:53, 29 May 2008 (UTC)

Power nap doesn't state a duration, but you might get that in the original NIMH study cited. --71.236.23.111 (talk) 17:11, 29 May 2008 (UTC)

Shindo earthquake scale

When measuring earthquakes there are different sclaes, like Mercalli intensity scale and Richter magnitude scale. Why did the Japanese invent their own scale "shindo" (Japan Meteorological Agency seismic intensity scale) (In Japanese called 震度)? Moberg (talk) 16:57, 29 May 2008 (UTC)

As the article's lede notes, the Japanese scale serves a function distinct from that of the Richter scale (and, for that matter, it predates the Richter). The Mercalli scale serves a similar purpose, but again postdates the Japanese scale (1902 vs 1884). — Lomn 17:21, 29 May 2008 (UTC)

("lede", what does it mean?) Ah okey, predates, thanks! But why is the Japanese the ones who made their own scale and not China or Australia or some other country? Moberg (talk) 18:55, 29 May 2008 (UTC)

(lede is an alternative spelling of lead and refers to the beginning of an article) --Tango (talk) 19:03, 29 May 2008 (UTC)

(ok! :)) Follow-up-question: I think that Taiwan uses this scale or a similar one. Is there any other other countries that uses the shindo- (or a from the shindo-scale derived) scale? And if so, why? Moberg (talk) 19:24, 29 May 2008 (UTC)

Original rotation of solar system.

Under the Nebular Hypothesis, the rotation of the solar system is caused by the contraction of the original cloud and, as it condensed, the rotation went from perhaps once every million years to that which it is today. The principle of the conservation of angular momentum is applied. The question is, however, what caused the original rotation? Any generally accepted reasons for the cause under this hypothesis, or are we still guessing?Boblaw1 (talk) 17:52, 29 May 2008 (UTC)

I don't think you need anything to cause it - chances are, when you add together the angular momenta of all the particles in the cloud, you're going to get something non-zero, the chance of all the random movements cancelling out exactly is vanishingly small. That tiny, but non-zero, value is then increased dramatically when the cloud collapses. --Tango (talk) 18:16, 29 May 2008 (UTC)

Nuclear reactors and fissile materials

What distinguishes the following technologies?

• Uranium enrichment
• Plutonium reprocessing
• Graphite reactor
• Light water reactor
• Heavy water reactor

--141.161.98.180 (talk) 18:12, 29 May 2008 (UTC)

Might they all be distinguished by being the subject of homework questions? Edison (talk) 19:13, 29 May 2008 (UTC)

We have Wikipedia articles on each of those. Uranium enrichment, nuclear reprocessing, graphite moderated reactor, light water reactor, heavy water reactor. The different reactor types use different neutron moderators (which has different implications for what type of fuel you put in them and what types of products you get out in the end), uranium enrichment is about increasing the percentage of U-235 in a given sample of uranium, reprocessing is about taking spent fuel and getting out certain materials created by the fission reactions (such as plutonium). For more details, read the articles. --Captain Ref Desk (talk) 19:34, 29 May 2008 (UTC)

Diodes

what exactly will happen when we short two terminals of a common type of diode ,does there be any charge movement and a resulting effect on depletion region202.125.143.75 (talk) 19:25, 29 May 2008 (UTC)

Presuming that the diode was not connected to a circuit then probably nothing since unlike say a capacitor, I'm pretty sure a diode doesn't keep a charge. If the diode is connected to a circuit, then I believe shorting it will basically remove any potential affect the diode may have Nil Einne (talk) 19:51, 29 May 2008 (UTC)

A reverse-biased diode does effectively act like a small capacitor, storing a tiny amount of charge. I don't suppose most diodes have enough capacitance for it to have any measurable effect in practice, but apparently some do: see varicap. —Ilmari Karonen (talk) 21:48, 29 May 2008 (UTC)

I am guessing that the questioner is thinking that shorting the ends of a diode together will have some effect of connecting the P-type side of the diode to the N-type side. However, they are already connected in the P-N junction inside the diode. Connecting them again will have no effect. By bringing up the depletion region, the questioner is implying that the diode is in a circuit and has current passing through it. Shorting out the terminals in that case will mean that you have a parallel circuit. The short has a resistance of nearly 0 ohms. The diode is commonly treated as having 0 ohm resistance, but that is not true. The good ones are 300 ohms (if my memory from circuit design 15 years ago is correct). So, until the current surpasses the capability of the short, there will be basically no current in the diode. The depletion region will quickly dissipate. If you take a good electronics course, this is the type of problem you'll see on a final: At 0.02 seconds after shorting out the diode, what is the potential difference between the terminals? -- kainaw™ 21:49, 29 May 2008 (UTC)

Electronics home project

Well I would like to build a switch which is switched on and off by clapping your hands twice. What do I need, and how do I do it? Bastard Soap (talk) 20:29, 29 May 2008 (UTC)

You can order a kit to build a sound-activated switch (which seems to cost exactly the same as The Clapper). This page also has a link to a PDF version of the assembly manual which includes a theory of operation section. --LarryMac | Talk 20:41, 29 May 2008 (UTC)

Or order everything separately [29] (This doesn't have to be cheaper in the end. I've had a couple of DIY projects that added up to more in parts than the thing off the shelf. Less fun buying it, though.) Be sure to follow local code in all projects involving home installations! Have a licensed electrician check any circuit before connecting to your house electricity. (No advice, but if you burn down the house your insurance won't pay and your spouse will never shut up about it.)--71.236.23.111 (talk) 22:55, 29 May 2008 (UTC)

Nuclear Power Plant on "automatic mode"

In the event of a hypothetical doomsday scenario how long would a modern nuclear power plant be able to supply electricity before it shuts down? I know an that nuclear power plant's have some kind of dead man's handle mechanism as a failsafe but let's assume that it was turned off. How long could a modern nuclear power plant work on it's own? For hours, days, weeks or years? Mieciu K (talk) 21:57, 29 May 2008 (UTC)

Hours would be easy, and days would be likely. Weeks would be a stretch. This assumes that the system has some sort of automatic load following, or that the load on the generator remains constant. so it just has to do steady-state operation. If "doomsday" meant that the load dropped abruptly or that it dropped gradually and there was no load following, the generator would trip followed by the shutdown of the reactor. Edison (talk) 23:34, 29 May 2008 (UTC)

List of Physics equations

We have a page which lists lots of trigonmetric equations. Is there a similar page for physics equations. In particular "v = u + at", "s = ut + 0.5at^2", "F = ma", etc. Maybe also for electrical equations "V = IR" "Q = VC" etc. If it does exist you can't find it by searching for "v=u+at". -- SGBailey (talk) 22:24, 29 May 2008 (UTC)

We have list of equations (not all Physics), list of relativistic equations and list of equations in classical mechanics (this one has the constant acceleration equations, but I think the TeX stops search working). Algebraist 22:42, 29 May 2008 (UTC)

Logic gates

I was mulling over how to make demonstration logic gates using many different technologies. Obviously a mechanical AND gate can be made with two input levers which can be up or down pushing on opposite ends of a floating pivoted beam where the central pivot holds a flagpole. If both are down, the pole is down, if only one is up the the beam pivots and the pole is down, if both are up then the beam itself is raised and hence the pole is up. What other technologies are there and how might they be demonstrated? Hydraulic (liquid pressure?); Pneumatic (flow (or not)); electromechanical (relays); electronic (transistors and voltages); Pure optical (no idea how); Magnetic (how?), etc etc. Suggestions and advice on a postcard please... -- SGBailey (talk) 22:35, 29 May 2008 (UTC)

Our school used to have a cool board with chutes, marbles and switches that switched LEDs on/off. --71.236.23.111 (talk) 23:02, 29 May 2008 (UTC)

Here's an idea for an optical OR gate. Light shines down both tubes, but each one may be blocked by a piece of cardboard. Where the tubes combine is some sort of prism/two-way mirror set-up that combines the two beams together and sends it down the bottom tube. If one tube or the other is open, or if both are, then there will be light coming out the bottom.

     |    |         |    |
     |    |         |    |
    -+----+-       -+----+-
     |    |         |    |
     |    |_________|    |
      \     *     *     /
       \    *     *    /
        \   *     *   /
         \  *     *  /
          \ *     * /
           \*     */
            |     |
            |     |

I think that perhaps to make a XOR gate you could consider how to make a NOT XNOR gate first - pick a medium that involves something flowing (like water, or sand), and let each switch divert the flow in opposite directions somehow. So having neither, or both on, lets the flow continue as it was, while having just one diverts it (into a secondary channel, say). You can then turn that all around, and make that secondary channel the primary one, and you've got a XOR. Confusing Manifestation(Say hi!) 23:38, 29 May 2008 (UTC)

Hmm. Yes. Remember that all logic operations can be built from NAND or NOR if you are really desperate. --Prestidigitator (talk) 01:04, 30 May 2008 (UTC)

How to calculate minimum wind speed to cause white caps on ocean

Wiklearn (talk) 23:42, 29 May 2008 (UTC)How is wind speed related to the height of ocean waves? At what wind speed would white caps appear? Wiklearn (talk) 23:42, 29 May 2008 (UTC)

Definition for trompe on wikipedia please

Trompes are simple devices that use the power of falling water to compress air. Trompes were used widely in the 19th century. They were used to provide the air for mines, blast furnaces pneumatic tools for alpine tunnel making, etc. The town of Cobalt in Ontario, Canada claims to have the only hydraulic air compressor (Trompe) left in the world http://www.cobalt.ca/ragged_chutes.htm Researchers in England have tried to use low pressure trompes (attached to an enclosed wind turbine and electric generator) to extract energy from the water running over weirs in a cost effective way. (Pdf is available if required). I believe that a dedfinition of trompe would help show people in poor countrys that energy is available from low grade (low head) hydro sources without the huge investment in machinery that is currently a barrier to using these (often high volume) sources of energy. —Preceding unsigned comment added by Gaiatechnician (talk • contribs) 23:46, 29 May 2008 (UTC) Gaiatechnician (talk) 23:47, 29 May 2008 (UTC)

Not sure what you're driving at, but have you looked at "Trompe"? --Milkbreath (talk) 01:25, 30 May 2008 (UTC)

May 30

Adipocere smell

Hello, My question is about Adipocere aka, grave wax.

http://en.wikipedia.org/wiki/Adipocere

A friend of mine sent me a hunk of it, part of a woodchuck that had been trapped in an old well. It was in a zip-lock bag, which sat on a of table of hats and gloves waiting to be put away after a long Alaskan winter.

The smell of the Adipocers seeped out of the zip-lock bag, and stuck to the hat and gloves. It washed out, but how/why can it get though plastic. And stick to anything, including my hands, and some how I could not get the smell of it out of my nose for a long time. Why? Thank you for your time.

Art4u (talk) 02:24, 30 May 2008 (UTC)

The larger question is why a "friend" would send someone a hunk of dead woodchuck. It seems of little use, other than for pranks I described then thought better of per WP:BEANS and did not post. Serial killers have had similar problems when they leave their victims in the crawlspace of their home. Perhaps you should have covered the plastic bag of dead woodchuck with six feet of earth or a layer of concrete. If you had left it outside during the Alaskan winter, would it have more likely attracted or repelled Grizzly bears when they emerged from hibernation? Crime novels and some forensic sources [30] describe police and pathologists placing a bit of Vicks#VapoRub under theis nostrils when dealing with stinky corpses, and some sources also say it helps with adipocere [31] [32] but we do not offer medical advice. Edison (talk) 03:28, 30 May 2008 (UTC)

COOLING TOWER EVAPORATION

WHAT IS THE BASIS OF EVAPORATION CALCULATION IN COUNTER FLOW COOLING TOWERS ? WHAT ARE THE UNITS USED FOR LATENT HEAT OF EVAPORATION? —Preceding unsigned comment added by 59.182.38.14 (talk) 03:23, 30 May 2008 (UTC)

We don't do your homework here. Chris M. (talk) 04:54, 30 May 2008 (UTC)

CHEMISTRY

PLEASE EXPLAIN THE INDUSTRIAL PREPARATION OF THE FOLLOWING ORGANIC COMPOUND (a). Ethene (b). Propene —Preceding unsigned comment added by Frankdinero (talk • contribs) 03:30, 30 May 2008 (UTC)

You might want to check out Ethene and Propene. Paragon12321 (talk) 03:54, 30 May 2008 (UTC)

Burning stomach fat with an ab machine

I recently saw a commercial for one of those ab machines, the kind that facilitates crunches. Naturally, it included before-and-after pictures of people who lost lots of fat around their stomachs in "just 30 days!"

Of course doing crunches would strengthen and define one's abdominal muscles. But in regard to burning fat in specifically the area around the stomach—does the body burn fat stored in a certain area faster if the muscles around that area are exercised? In other words, say that two identical people each expended a certain amount of energy during workouts, but one did crunches and one did, say, cardio. Would the first person's body burn more fat around the stomach than the second person's, or does the body have its own set order as to which fat deposits it burns? --zenohockey (talk) 04:15, 30 May 2008 (UTC)

Theres no such thing as spot fat reduction unfortunately. So the only way to get abs is have a really low body fat % (for most people). 61.69.132.119 (talk) 04:55, 30 May 2008 (UTC)

Battery question, part II

Thanks to everyone who answered my question earlier, your comments were very helpful. So (in summary) the main consideration with batteries, in terms of the electronics that use them, is the voltage they produce. And now, operating on this premise, I am going to raise a few eyebrows. What would be the feasibility of using a series of common batteries (e.g., C or AA) to power my laptop? Bare question there, again hypothetical. For reference, the power adapter for my laptop says it gives the laptop 20v at 3.5A and 70W. 63.224.79.202 (talk) 04:24, 30 May 2008 (UTC)

Possible, but not really feasible. Let's take AAs. It'll take 13 in series to make 20v. The AAs I have sitting around list at just under 3000 mAh, which means those batteries will run that laptop (at peak power) for about an hour. Supposing that the laptop's standard battery lasts 4 hours, that means you need 52 AAs to duplicate its functionality. Those are the single-use ones. Go to rechargeables and the mAh rating drops to about 2000, which means you're looking at about 75 AAs to replace the laptop battery. Larger batteries (say, D cells) will have a higher mAh rating -- about 10000 mAh for rechargeables, or 16000 for single-use. That means you'd only need 13 single-use D-cells instead of the 52 AAs, though Ds cost about 4 times as much (if not more) per battery. — Lomn 05:02, 30 May 2008 (UTC)

Wow. How would one hook that up? (Now I'm asking for trouble) 63.224.79.202 (talk) 05:09, 30 May 2008 (UTC)

hens eggs

is it possible to freeze eggsand for how long —Preceding unsigned comment added by 84.48.90.44 (talk) 04:49, 30 May 2008 (UTC)