Wikipedia:Reference desk/Archives/Science/2007 March 19

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March 19

CO2 recovery and reuse

How difficult would it be to create a mechanical or chemical process to take CO2 out of the exhaled breath and reuse it to make soda water? —The preceding unsigned comment was added by 71.100.1.200 (talk) 02:35, 19 March 2007 (UTC).

Bubbling CO2 through solutions will cause it to dissolve, this can be observed by exhaling through a straw into a solution of bromothymol blue in a neutral solution of water. (do not do this without the aid of someone experienced in chemistry) This process isn't very complete though, rebreathers rely on a scrubber to remove the CO2 from the breathing gas, typically soda lime. Once it's bound chemically, there is probably some path that would convert it into relatively pure HCO3 sol'n, but it would cost way more than creating soda water the ol' fashioned way. -- atropos235 ✄ (blah blah, my past) 04:39, 19 March 2007 (UTC)

Sub-Lightspeed Craft

If a spacecraft where built and had the capabilities to travel at half the speed of light how much shieling would it need? For example in the Project Daedalus article there is a link that describes how Daedalus would need an erosion shield for travelling at twelve to sixteen percent the speed of light, they go further to say it would probably be made out of Berillium. So to restate the question how thick would a berillium shield have to be for a craft traveling at 50 percent the speed of Light? —The preceding unsigned comment was added by 68.120.225.214 (talk) 04:18, 19 March 2007 (UTC).68.120.225.214 04:19, 19 March 2007 (UTC)

Simply put, Project Daedalus is a fictitious foray by a non-technical group of space enthusiasts. The engineering and scientific claims are not necessarily realistic. To give a straightforward answer like "30 cm of beryllium shield" would be silly - it would assume that somebody has gone through the difficult engineering and design process for a non-existent spacecraft, making the necessary tradeoffs and compensating for a minimum level of safety. In a practical sense, it is impossible to make engineering assessments about technologies which are so distant from the present state of the art. (Present craft do not travel at even a remote fraction of that speed, so there is no way we could compare our designs against it in a meaningful way). Nobody can possibly forsee the actual required specs for a craft which is many many generations beyond present-day space vehicles. In the mean-time, you might look at the Atmospheric reentry to learn about real shielding on actual spacecraft. On a more philosophical note, some of these scientific studies, such as SETI, are not meant to actually yield conclusive answers about anything, but are more of a way to stretch our way of thinking. They shouldn't be taken at face value - in fact, any level of scientific analysis that goes into them makes it blisteringly self-evident that such projects are impossible (in the foreseeable future). Nimur 08:53, 19 March 2007 (UTC)

Granting Nimur's comments as true for actually building such a craft, it can still be fun and informative to do back-of-the-envelope calculations for this kind of thing. For example, you could take the density of matter in the interstellar medium, and calculate the explosive power of each of those atoms hitting your craft at at 1/2 c and see how far you can get with a given shield. --TotoBaggins 13:12, 19 March 2007 (UTC)

My idea is to clamp onto an metallic asteroid or even a small moon, and keep that in front of the spacecraft both as a shield and a source of material for a linear accelerator (which would eject particles at the speed of light for propulsion). It might not be as effective per meter as beryllium, but you would have many kilometers of this material between the occupants and particles. StuRat 15:52, 19 March 2007 (UTC)

in the Discovery channel they had a episode (cant remember the name of the show) in which they show a forcefeild generator. yes its a real one however the only problem with it is that it takes a machine the size of a bedroom to generate the energy to protect a can of soda. its acctually more like a plasma shield and had a blueish green look to it it was pretty awsome. Maverick423 17:05, 19 March 2007 (UTC)

Thank You all for the answers you have given me but I think it is sad to say that Daedalus is out of our time reach. I look at the rapid progress of technology and doubt almost nothing as far as how far technology can progress.67.127.164.153 03:04, 20 March 2007 (UTC)

direction of rotation for IC engine

What is the convention for the direction of rotation for an internal combustion engine?

And is it only the direction of rotation of the starting (electric starter motor, pull start or other) that determines this?

Thanks 139.163.138.10 04:53, 19 March 2007 (UTC)

You can't spin an ICE in a different direction than it was designed for, the cams will not open and close the valves at the correct time, nor will any of the devices (alternator, coolant pump, oil pump) connected to the engine with the fan belt work correctly when spun backwards. I'm not sure if there's a convention to the direction, but my Corolla's engine spins counter-clockwise when viewing it from the flywheel side of the engine. -- atropos235 ✄ (blah blah, my past) 05:40, 19 March 2007 (UTC)

Given that there are IC engines that will run backwards perfectly well then I think you might need to qualify your answer. Almost all would rotate backwards, they just wouldn't run. In a 4 stroke the valve events would be all wrong, you'd be unlikely to get it to run backwards, unless it had special timing gear and a special oil pump.

For car engines most run anticlockwise from the flyweel end, but historically many manufacturers have ignored it, including Honda for many years. Greglocock 06:46, 19 March 2007 (UTC)

Right, there's nothing fundamental about internal combustion engines (encompassing a very broad range of machine designs) that prevents them from rotating or even operating in either direction (nor anything that requires them to have a rotating shaft, for that matter). Many specific rotating-shaft ICE designs are built to only run in one direction, but I've seen (older) diesels that will actually run in reverse, though poorly. Sometimes the reason that the engine only runs in one direction is because it is optimized for efficiency that way. Of course the reasons for choosing any ICE design feature will vary depending on the application and the specific type of engine under consideration. -- mattb @ 2007-03-19T07:09Z

It seems to me that the sorts of IC engines used in model airplanes (those engines having no valves) would probably be perfectly happy to run backwards, although they wouldn't be of much use while operating in that mode. And, BTW, with the exception that its cooling fan probably would be less efficient, the alternator on a modern car engine would work perfectly fine running backwards.

Atlant 12:50, 19 March 2007 (UTC)

More PSU Shocks

I recently reported that I received an electric shock while simultaneously touching my PSU and a radiator, even though the PC was off. Today, I touched a PSU from a completely different (and two week old) computer and another radiator in the same house, and while the PSU was unplugged from the mains no less, I received a similar shock (although slighltly lesser in intensity), to that which I received a few weeks ago. What is going on? --Seans Potato Business 06:05, 19 March 2007 (UTC)

I would guess that it was you that shocked the computer in this case, not vice versa. -- mattb @ 2007-03-19T06:08Z

Maybe it's a recurring phenomenon with you because of some behavior or environmental circumstance. What sort of shoes are you wearing when working on computers? Do you drag your feet on carpeted floors (this can build a lot of charge!) Do you properly ground yourself to the chassis (at least by discharging yourself to the case, or if you really want to be a nerd, you can actually use a ground bracelet). This might prevent shocks in the future, it seems like you are particularly susceptible. Nimur 09:00, 19 March 2007 (UTC)

Putting aside the issue of shocks from static electricity, you need to know that PSUs have substantial electrical filters to prevent the egress and ingress of radio frequency interference (RFI) from/to the computer. These filters connect substantial capacitors from the chassis of the computer (and the "ground"/"earthed" terminal of the line cord) to both the hot/live power line wire and the neutral/return power line wires. The end result is that if you don't properly ground/earth the computer, the case will be floating at about 1/2 the line voltage and yes, you'll get shocked every time you connect yourself between the computer's case and something that is earther (such as your radiator). You may also get shocks from the monitor or any other part connected to the computer's case.

Properly ground/earth your computer.

Atlant 12:55, 19 March 2007 (UTC)

Can I improvise an earth by connecting the case to the radiator with a peice of wire/jumper cable? I dont want to go through the rigmarole of trying (and failing) to get the house properly wired since it's apparently not a legal requirement where I'm living. It's apparently not uncommon in the Netherlands. I rent one room and will be out of there in a few months tops, to go to university. Thanks for the advice so far. :) Seans Potato Business 16:12, 19 March 2007 (UTC)

It's probably a bad idea to have exposed wiring (grounded or otherwise) randomly attached between your computer and the radiator. I think the safest course is to have a professional electrician (or your landlord) take a look at the problem. Barring that, you should probably close up your computer case entirely and try not to touch it. You might have a serious issue at hand, you should avoid adding stray wires. Nimur 18:54, 19 March 2007 (UTC)

The rewiring suggestion is not applicable to my situation. I don't wish to go into why. It's surely a better idea to have an exposed earth connection than none at all. Seans Potato Business 21:30, 19 March 2007 (UTC)

Do not ever test for electricity by seeing when you get a shock, since electrocution is possible. Hardware stores and Radio Shack sell inexpensive digital voltmeters. The radiator would normally be grounded (earthed) through the cold water pipe to this planet most of us inhabit. But that is not guaranteed. There can be insulating fittings in pipe connections, and water meters insulate the building pipes from the water main ground unless an electrician has properly made a substantial and solid ground jumper around the water meter. Electric water heaters often leak AC to the water pipes and water supply. I saw a case where a bathtub was electrically energized by a thermostat wire which was exposed and touching a drain pipe. So it is possible that the couputer is somehow grounded, through a modem or phone line or broadband cable ground, and the current is going from an energized radiator to the ground on the computer chassis. Or as you assume the computer could be what is energized, through the power system or from an energized signal wire ground. Have someone knowledgable about electricity test with a voltmeter. A piece of metal pipe going into the ground is a pretty good reference groung for testing purposes. I have learned to doubt the solidness of various supposed grounds you find inside a structure, since there are an infinite number of ways for homeowners and hacks to miswire things. Running a "ground wire" from a computer to a radiator is not recommended, since you have no solid assurance that the radiator is actually grounded. Edison 14:22, 20 March 2007 (UTC)

If I use my voltmeter to compare the red wire from my PSU with the radiator, and it reads 5v, then must the radiator be earthed? --Seans Potato Business 01:29, 21 March 2007 (UTC)

Perhaps, but the trouble is that it's very hard to evaluate the "quality" of the earth that the radiator is providing. A good earth connection (ground) today might turn into a poor connection as things corrode or the plumbing is modified. Another concern is that if you flow any substantial electrical current (even the leakage current from your computer's PSU) into the radiator, over time, galvanic corrosion can occur elsewhere in your plumbing. It's less of a problem with ordinary AC mains current than with DC, but it's still bad practice. Edison gave the best advice: provide a real earth ground connected to a grounding rod. Failing that, you might be able to obtain an "isolation transformer" or isolating UPS and operate your computer from that.

Atlant 12:40, 21 March 2007 (UTC)

molecular vibrations

I may be the expert you are looking for (Author "Vibrating Molecules, 1971) This is a very large field, so I will welcome any guidance that can be offered. Peter Gans e-mail as userer name at hyperquad dot co dot uk Retired lecturer, Leeds University, UK petergansPetergans 07:59, 19 March 2007 (UTC)

Welcome! I see you've created an account already. If you'd like to contribute, you can edit any page by clicking the "EDIT" tab at the top. You might want to look at Molecular vibration to start. Feel free to hang around the Reference Desk as well. I've added a standard greeting at your user talk page so you can find some quick links to introductory material (how to contribute, how to edit, etc). Nimur 09:10, 19 March 2007 (UTC)

reticular fibers

is it possible for reticular fibers to have parenchymal function?

According to the article on reticular fibers, "Networks of these fibers make up [... the] parenchyma of liver, testis and lung." I'm not a med student, so I don't have a good grasp on what that means. -- atropos235 ✄ (blah blah, my past) 16:26, 19 March 2007 (UTC)

yeah i saw that but have doubts since i haven't read anything like that elsewhere...

Quick comment, if you don't want your IP address shown (as you keep removing the automatic {unsigned} tag from each post you write), you can create an account which will hide it. -- atropos235 ✄ (blah blah, my past) 21:58, 19 March 2007 (UTC)

Liquid conversion

Many drinks on the internet are posted in CL and I was wondering what that is converted into on 1 OZ ? It certainly cannot be 1-1 can it or maybe it is? —The preceding unsigned comment was added by 70.50.185.202 (talk) 16:06, 19 March 2007 (UTC).

"CL" could mean centiliter, though it would properly appear as "cL" or "cl". According to Google:

one centiliter = 0.338140226 US fluid ounces

one US fluid ounce = 2.95735297 centiliters

-- atropos235 ✄ (blah blah, my past) 16:15, 19 March 2007 (UTC)

Yes, they mean centiliter. Conveniently, one cL is almost exactly 1/3 fl. oz.; there are three centiliters to the fluid ounce. TenOfAllTrades(talk) 16:21, 19 March 2007 (UTC)

Or of course if you mean Imperial fluid ounces (which are a bit smaller than US), it's 0.35195008 fl.oz. --Anon, March 20, 2007, 22:15 (Imperial), um, (UTC).

Ear bleeding

(NOTE: This is a medical question, but I am not asking for medical advice; merely curiosity.) A number of the more fantastic TV shows and films I've seen show bleeding ears (from the canal, not the lobe) as part of particularly gruesome death scenes. However, I've never actually heard of it being a symptom of any disease, and my fairly in depth first-aid book carries no mention of bleeding ears, while the only mention on Wikipedia is ear bleeding caused by over vigourous ear-wax removal. So, are there any diseases or accidents, other than direct damage to the ear itself, which would cause this? Laïka 16:59, 19 March 2007 (UTC)

I'm guessing some kind of trauma to the brain or a burst eardrum might cause ear-bleeding. Otherwise TV shows would be a bit strange. "What happened to him, doc?" "Vigourous ear-wax removal, the silent killer." "Dear God!" -GhostPirate 17:09, 19 March 2007 (UTC)

When I had an infected tooth I bled from my ear. Anchoress 17:23, 19 March 2007 (UTC)

Wonderful soundbite! ---Sluzzelin talk 17:26, 19 March 2007 (UTC)

Thanks. My cat's breath smells like cat food. Anchoress 21:26, 19 March 2007 (UTC)

• Our article on Bleeding states "Externalised bleeding from the ear may indicate brain trauma if there has been a serious head injury...". Bleeding from the ear is also mentioned in Cholesteatoma. Johntex\^talk 20:00, 19 March 2007 (UTC)

In most TV shows, bleeding from the ear is meant to represent a posterior basal skull fracture. Leaking CSF from the ear would represent an anterior basal skull fracture, but doesn't look as dramatic.... - Nunh-huh 03:35, 20 March 2007 (UTC)

Ok, thanks for that! Laïka 08:13, 20 March 2007 (UTC)

I suspect (without evidence) that the movie makers like it because it's easier to trickle some fake blood out of someone's ear/nose/mouth and produce the impression of serious injury than it is to have their makeup people produce a really convincing external wound and tie the actor up in makeup for hours while they apply it. SteveBaker 14:38, 20 March 2007 (UTC)

Treadmills

While in the gym yesterday, I spent a half hour on a treadmill and it very apparent that the effort (which equates, I guess, to "work done" or calories burned) running X miles on a treadmill appears to be much less than for an equal distance running on a pavement. Discounting variation in terrain on road running, what I would like to know is, what is the major contributing reason for comparative ease of running on a treadmill? I can think of four significant possibilities:

• Enforced pace maintenance when running on the treadmill
• Cushioned running surface on the treadmill
• Lack of wind resistance when running on the treadmill
• Lack of leg energy used to "push forward" on the treadmill

I would guess that these are listed in order of least to most influential, but would welcome any pointers to expert analysis, particulary regarding the actual difference in leg energy expended in running on the spot compared with running forwards. Finally, is there any data available on the total amount of calories I would burn per mile of treadmill running v road running. Thanks. Rockpocket 19:16, 19 March 2007 (UTC)

Those are good possibilities, and if you were holding the handlebars of the treadmill, I will also propose reduced arm movement on the treadmill. − Twas Now ( talk • contribs • e-mail ) 19:36, 19 March 2007 (UTC)

• I would suggest that outside, no ground is perfectly level. You are going up and down hills or at least slight gradients. Not true on a treadmill. —The preceding unsigned comment was added by 74.134.146.52 (talk) 19:54, 19 March 2007 (UTC).

Scientifically, the main reason may be the treadmill base acting as a linear spring. There has been tons of studies looking at how to make springy running shoes, but they all flopped... --Zeizmic 20:13, 19 March 2007 (UTC)

• Pure speculation on my part, but I wonder if some treadmill manufacturers deliberately miscalibrate the system to make you feel happier about how much work you have done? Johntex\^talk 20:15, 19 March 2007 (UTC)
• I think Zeizmic's explanation is the correct one. The baseboard of a treadmill (the surface underneath the moving belt) is generally a rather springy plywood board. This gives a lower-shock impact (which is easier on the tendons of the ankle and knee) and gives a bit of energy return. That lower impact is the design goal - it cuts injuries, and makes the treadmill suitable for those recovering from injury (it's common for athletes who are recovering from injury to be told to walk or run on a treadmill, but forbidden from running on an asphalt or concrete surface). The energy return (the bounce-back from that springy surface) is a side effect of that, and indeed it will lessen the effort of a given run (although by how much I'm not sure). A very similar effect (with the same underlying design-goal) will be experienced when running on a nice rubber-crumb running-track. Darryl Revok 11:22, 20 March 2007 (UTC)

Incidentally, the energy usage of a treadmill can be increased by using an inclined treadmill, or by just increasing the pace. StuRat 13:09, 20 March 2007 (UTC)

forget the treadmill grab a bike. i lost 50 pounds in one month by bike riding every day for about 5 hours (not all at once) and i still ate like a pig =) but maybe the mountains had something to do with that. so if thats the case just make your treadmill incline to its highest point and trust me you will get a pretty good work out. Maverick423 15:19, 20 March 2007 (UTC)

Speaker wiring question

This weekend I helped my friend set up a home theatre system. The reciever is a Yamaha RX-V2500 like this one. We hooked up seven Definitive Technology speakers for the main room, no problem. On the "B speaker" connections, we rigged up a pair of Infinity outrigger speakers like these out in the back-yard. They also work fine, except that they don't provide enough coverage for the whole back-yard. We would like to add a second pair of speakers to the back-yard.

The question is, can we hook up a second set of these outdoor speakers in series to the first set? Thanks for your help. Johntex\^talk 19:55, 19 March 2007 (UTC)

If you meant in parallel, then yes, you can. However, the same power will be distributed over the speakers so each one might not be as loud. --Wirbelwindヴィルヴェルヴィント (talk) 22:54, 19 March 2007 (UTC)

Thanks for your reply. I actually did mean in series. Because of the way the wiring runs, it would be convenient to run the wire from the receiver to the first set of speakers (as they are wired currently) and then to take wire from each of the first speakers to the second pair. Would that work?

Part of the problem is just that the Infinity speakers are quieter than the Definitive Technology speakers. What my friend wants to do is to have both A + B on a once, so that the same music can be playing in the house and outside on the patio. However, the receiver does not have a seperate volume for A vs B. A volume that is good for the B speakers is deafeningly loud for the A speakers. We thought about putting a seperate volume control onto the B speakers, and we shopped for one. However, all the ones we saw at our Radio Shack would not accomodate the size wire we are using. I don't remember the gauge, but the wire itself is pretty thick and it is well protected for outdoor use. Having already purchased and run the thick wire, we are reluctant to replace it with cheaper, thinner wire that would fit into one of these volume control boxes.

So, is it possible to connect speakers in series, or is there a better solution? Johntex\^talk 23:04, 19 March 2007 (UTC)

Please check the specifications in the manual for the amp, and see if the series impedance (the sum of the individual impedances) is within the allowance for the amp. The amp is more of a concern than the speakers or the wire. Edison 04:45, 20 March 2007 (UTC)

First up, putting a second set of speakers in series is /safer/ than in parallel, so far as your amp goes. BUT you will make the original set quieter, in fact there is a very good chance that you'll end up with less noise outside than before. I wouldn't recommend putting speakers in parallel unless you understand the specs very well, or your amp has good output circuit protection. I wouldn't risk it. Really the best thing is to go and find another amp, then T the input to the first amp into the second amp, or take the line out signal from the first amp into the second one. Greglocock 07:36, 20 March 2007 (UTC)

Affordable solar panels

I'm an eco-conscious individual who rents his appartment (in Boston, MA) and whose wallet isn't too fat. I'm thinking of sticking a small solar panel on my roof to generate electricity, probably to sell it back to the grid. Is this feasable nowadays? And how much initial investment would such a thing (both the panel and hooking up to the grid, however you do that) cost?

Thanks,
Mike, 19:58, 19 March 2007 (UTC)

• It is feasible, but how feasible it is depends on many things. Climate is one, government rebates are another. The time to pay-back an investment in solar energy is typically 4-10 years, depending primarily on these fators. Our article on Solar power has a lot of info. Johntex\^talk 20:03, 19 March 2007 (UTC)

• And also see Deployment of solar power to energy grids. Johntex\^talk 20:06, 19 March 2007 (UTC)

If you're in Boston, you're probably getting energy from NSTAR, and as far as I can tell, they don't really do green energy :/ - that is, I don't think they don't have any programs to encourage or enable environmentally minded people like yourself to take initiative. Good luck though - I know you can connect solar systems into your house mains, but I wouldn't expect to get paid for it - could be wrong though. --18.214.0.135 04:14, 20 March 2007 (UTC)

Buying power back may be automatic. That is, the present meter might run backwards when you provide power. I'd aim to meet, but not exceed, the total power needs of the tenant. This means you would produce excess power on sunny days but not enough on cloudy days and at night. On the other hand, even if they don't buy back the excess, you can still provide it to your tenants as a plus ("reduced electricity bills during the day, due to solar cells on the roof") and possibly charge higher rent, as a result. This would be particularly valuable if you live in an area with insufficient power availability which has brown-outs or black-outs when all the air conditioners are on in summer. It does take quite a bit of power to run A/C, though, so you would need large solar panels. If not, at least they can run a fan when the A/C dies during a power outage. You might also want to consider passive solar heating. For example, conventional or vertical blinds, facing the Sun, which are white on one side and black on the other would allow the tenant to use the solar heating, but only when they want it. StuRat 13:03, 20 March 2007 (UTC)

Not particularly sure what the climate is like in Boston but if you use a fair amount of hot water, you may also want to consider a solar heated hot water system. Such systems tend to be more efficient then just generating electricity for obvious reasons. Of course, this would require plumbing and the like so may be too expensive for you Nil Einne 14:17, 20 March 2007 (UTC)

Electronics Express and walmart have the lowest prices on solar panels. walmart sells a panel that generates 12 volts for 9.99 and electronic express sells a 2X2 grid for 150.00 think that grid generates 240 volts. just rechecked *its been a while since i checked the site* no more 2x2 grids but they got a 18 volt panel for 16.00. however none of that wont do you any good if you got not light =P here is the link to the prices [1] and the link to the site[2] hope this helps you out with what your looking forMaverick423 15:24, 20 March 2007 (UTC)

Ok, thanks for the replies everyone! -Mike, 17:02, 20 March 2007 (UTC)

Mutation in nectariens

can someone explain how the mutation in the nectarines happens? why?—Preceding unsigned comment added by 83.135.36.133 (talk • contribs) 12:34, 2007 March 19

Well, the nectarine article says the fruit was grown in England as early as 1616, but that the history is "unclear". This source suggests they "probably originated in China over 2,000 years ago and were cultivated in ancient Persia, Greece and Rome." A few more details emerge here. -- MarcoTolo 23:10, 19 March 2007 (UTC)

The mutation is in the peach gene g (glabrous, "without hairs, smooth.") The mutation appears to be spontaneous, singular (i.e. just one mutation is all it takes), and is recessive (perhaps in Blake MA, "The JH Hale peach as a parent in peach crosses" Proc Am Soc Hortic Sci, 1933). -- MarcoTolo 23:23, 19 March 2007 (UTC)

earth and space science

fraction of difference between two fixed temperatures is called what?

${\cfrac {\Delta T}{T}}$ ? This sounds like carnot engine efficiency, but I might be misinterpreting your question fragment. Nimur 23:15, 19 March 2007 (UTC)

Or it could be just ${\Delta T}$, from ${\Delta T}={\cfrac {T_{1}}{T_{2}}}$ [Mαc Δαvιs] (How's my driving?) ❖ 05:45, 20 March 2007 (UTC)

$\Delta T$ would generally indicate a difference, not a fraction: $T_{2}-T_{1}$. -- mattb @ 2007-03-20T13:19Z

What is the complete breakdown for X55 Cr Mo V14?

I can find Cr (Chromium) and Mo (Molybdenum). These are used in selling knives as the materials the knife is made of.

Thanks,

Chris

V could be vanadium, which is used in some high-temperature stainless steels. From preliminary search, this means that the Chromium + Molybdenum + Vanadium total percentage is 14%. I can't find information on the X55. See our steel article or Stainless_steel#Types_of_stainless_steel... there's similar nomenclature in the latter article. It seems that steel standards are proprietary and expensive: this handbook costs >$500US! Nimur 23:08, 19 March 2007 (UTC)

out feet

Was wondering what may cause feet to be facing to the sides with respect to the movement of the person and what effects may this bring

—The preceding unsigned comment was added by Bastard Soap (talk • contribs) 21:39, 19 March 2007 (UTC).

No idea what causes it but my mum used to tell me off if she saw me walking at "ten to two". I happen to notice that the majority of people who walk like this have a rather 'lazy' looking posture, whereas I tend to walk a little more forest-gump like (???). ny156uk 21:56, 19 March 2007 (UTC)

Could be for stability. When I took fencing lessons, I was taught that my feet should be at 90 degrees to each other. Clarityfiend 22:35, 19 March 2007 (UTC)

This is called pronation of the feet, and may be due to flat feet. Here is a web article about it. If you are a runner, you should try to avoid this, as it has negative ergonomic effects and can adversely affect your speed. Nimur 22:55, 19 March 2007 (UTC)

(Insert standard medical disclaimer here). The illustration looks more like femoral retroversion to me. What effects this may have depends largely upon the age of the individual in question (i.e. its normal in infants, but may be somewhat concerning in adults). There is a good review of lower limb issues in children in the journal American Family Physician from August of 2003 (link). -- MarcoTolo 23:02, 19 March 2007 (UTC)

I heard an aunt describing a course to improve elderly people's balance in which they were told to walk like this for the improved stability. Aaadddaaammm 08:06, 20 March 2007 (UTC)

Also, I personally seem to have my feet attached to my legs in such a way that I either walk with my feet facing slightly outwards, or my knees facing slightly in. Seriously, if I extend my legs straight out with my knees facing up, my feet face out. Since, like Ny156uk, my mum told me off for walking with my feet facing outwards, I walk with my knees facing in. It hasn't seemed to lead to any problems, other than shoes wearing out in an uneven pattern, but I would advice anyone else in this situation to consult with an appropriate doctor to determine which manner of walking would be best before they settle into a pattern and their bones form to accomodate it! I assume this can't be too uncommon. <OT>I suppose I got a slight wiggle to my walk for my troubles, which is no bad thing, but I also got mocked by PE teachers for my running style.</OT> Skittle 17:22, 20 March 2007 (UTC)

Some martial arts and yoga often have you place your feet parallel rather than like the illustration. This always seemed unnatural to me. Any thoughts on this? —Pengo 13:28, 23 March 2007 (UTC)

science

What is the chemical symbol for sodium chloride and what is its compound's molecular weight?24.148.188.8 23:20, 19 March 2007 (UTC)

Did you look at our article on sodium chloride? --Wirbelwindヴィルヴェルヴィント (talk) 23:26, 19 March 2007 (UTC)

Focal point of an earthquake

What is the point on Earth's surface directly above the focus of an earthquake?

The epicenter. Did you check earthquake? Nimur 23:34, 19 March 2007 (UTC)

I'm not familiar with "focus," I learned it was "origin" or "hypocenter." [Mαc Δαvιs] (How's my driving?) ❖ 05:44, 20 March 2007 (UTC)

All three terms mean the same thing in this context. Note that this contrasts with the popular use of "epicenter" (of some other sort of phenomenon) to mean its origin or focus, and also with the use of "hypocenter" to mean the point on the Earth's surface directly below a nuclear explosion (otherwise called "ground zero"). --Anonymous, March 20, 2007, 22:19 (UTC).