Wikipedia:Reference desk/Archives/Science/2009 January 5

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January 5

Possible Meteorite strike

Looking at Southern Russia on google earth Two round lakes caught my eye.North 52.44'58.11" East 78.37'05.37" Bolshove lake The other lake not sure the name but its @ North 54.35'17.46" East 71.45'21.10"Nasa has an icon in the area called KULUNDA STEPPE Could these lakes be Craters from meteorites? They are almost prefect circles.My email is <removed to prevent spam> Thanks. —Preceding unsigned comment added by 5544mik (talk • contribs) 01:02, 5 January 2009 (UTC)

Not answering the question, but here's a quick link to the location: 52.749475°N 78.618158°E / 52.749475; 78.618158. [ cycle~ ] (talk), 02:01, 5 January 2009 (UTC)

I'm no expert - but wouldn't there be raised edges if they were craters? Where did all of the ejected material go? The agriculture around these lakes appears to go right up to the edge of the lakes without interruption - which seems unlikely unless the edges of the lakes are dead flat...but I could easily be wrong. SteveBaker (talk) 04:07, 5 January 2009 (UTC)

While it's certainly plausible, I wouldn't say its the most likely, or even one of the top 3 most likely methods of formation for these lakes. Just because a lake is circular does not mean that it is a crater lake; I'm sure most lakes in flat-terrain areas are roughly circular in shape. They appear similar to Kettle ponds, although I doubt glaciers would reach that far south in recent eras. It could be an old shaft mine which has filled with water (although this is unlikely given the flatness of the nearby terrain). It could be a man-made reservoir or irrigation lake. It could also just be a natural dip in the terrain which is below the current water table. Without knowing the depth of the lake, it is hard to make a judgment in any case. -RunningOnBrains 20:40, 5 January 2009 (UTC)

The maximum extension of the Wisconsin glaciation, about 21,000 years ago, terminated roughly at that latitude in that region (though in North America it extended quite a bit further, to about 40°N). I'm not an earth scientist of any kind, but I would have to agree that these are probably Kettle ponds. In fact, they're very similar to Lake Ronkonkoma (the lake, not the hamlet), which isn't far from where I live. – ClockworkSoul 16:45, 6 January 2009 (UTC)

An old eroded crater may not have a raised rim. —Tamfang (talk) 20:31, 5 January 2009 (UTC)

I don't see anything round enough to scream 'crater'. —Tamfang (talk) 20:31, 5 January 2009 (UTC)

See the Earth Impact Database. Under Criteria (for determining if a geological feature is an impact structure) there is a note under #4 Morphology that states "a circular structure alone is not sufficient to claim impact structure status" due to other processes on the earth that can cause circular features. It is possible that it is an impact, but the only way to distinguish between other causes is to examine the geology on the ground and look for evidence such as Shatter cones or Planar deformation features. --mikeu ^talk 15:38, 7 January 2009 (UTC)

Ray that stops internal-combustion engines

I was browsing through an old newspaper online and found an article about supposed Nazi secret weapons. The article (Hurt Doberer, "New Reich Weapon May Be Dust Bomb, New York Times, 15 October 1939, p. 36). went over some things that th Nazis had claimed to invent in the 1930s, and points out that none of them are that spectacular or were original to the Germans. The last entry was:

Ray Z—the ray that could stop an internal combustion engine. (This secret also was shared. And, anyway, the ray, though effective when dealing with a near-by motor-car engine, ha never been effective against an airplane.)

I've never heard of such a thing. I googled "Ray Z" and "Z-Ray" and found, well, nothing relevant. Anybody have a clue what this refers to? --98.217.8.46 (talk) 01:59, 5 January 2009 (UTC)

Electromagnetic pulse? Did they know how to generate one by non-nuclear means back then? I dunno. --Kurt Shaped Box (talk) 02:17, 5 January 2009 (UTC)

I figure that everyone who ever went to school to learn to work on radars (the big ones that track aircraft) will have heard a story about a radar killing engines or catching a camera shop on fire. The claim is that the electromagnetic radiation from the radar will cause all spark plugs to fire at once - killing the engine. I never attempted anything of the sort. However, I have seen fluorescent bulbs light up only through the power of the radar flowing through the air. Come to think of it, it also caused my radio to turn on and faintly play some music as the radar sweep passed by. I had it sitting on top of the cabinets above my work desk, so it was above the safe altitude. -- kainaw™ 02:53, 5 January 2009 (UTC)

There's no need to worry. If the Nazis do indeed invent such a weapon, our esteemed scientist Nikola Tesla has already invented a death ray capable of shooting planes out of the sky and annialating entire armys. [1] 216.239.234.196 (talk) 13:27, 5 January 2009 (UTC)

---

So the answer is, basically, nobody knows, really? Except maybe radar or EMP, neither of which existed at energies in which this would be possible (much less a routine thing) in 1939? What impresses me about the article is the smug way the author shrugs off this idea as something both the Nazis developed and that many other people developed. Obviously law enforcement agencies today would be pretty interested in something that could easily stop car engines (it would make car chases a thing of the past, at no risk to the officer or the public). --98.217.8.46 (talk) 19:20, 5 January 2009 (UTC)

Could this have been written by the same NYT ignoramus who mocked Robert Goddard? Moral: never ever fully trust what you read in the papers about science. Clarityfiend (talk) 20:54, 5 January 2009 (UTC)

The cops are interested in the idea. See "Stopping Cars with Radiation" (2007). --Heron (talk) 21:37, 5 January 2009 (UTC)

That device attacks the microprocessors controlling modern cars, which weren't around during the second World War. I doubt even an EMP could have much of an effect on an old-fashioned internal combustion engine; EMPs affect tiny sensitive circuits used in computers and such, not levers and pistons and other mechanical components.

I don't know what "near-by motor-car engine" is supposed to mean, but I'd say any device that can stop a vehicle reliably is tremendously useful, unless "near-by" means going up to the car with hand tools and disassembling the engine. --Bowlhover (talk) 05:35, 6 January 2009 (UTC)

There was a TV show recently ("Prototype this" IIRC) which was somewhat successful in stopping cars by releasing a large cloud of an inert gas (I think they were using CO2) right in front of them to briefly cut off the oxygen flow to the engine. But I agree - using an EMP to try to stop a WWII-era car would be fruitless. Even my '71 VW bug has no significant electronics in it - an EMP might take out the radio - but it's not gonna stop the engine. It really wasn't until about the 1980's or so that EMP-sensitive electronics started to appear in most cars. Perhaps a really large induction coil - buried under the road and set off by the weight of the car pushing down on a switch could make the sparkplugs fire prematurely - or maybe do something nasty to the alternator - but a car moving at speed would recover from that and restart almost immediately. A bunch of tyre spikes would have been far more practical. But an induction coil would have been in reach of German science & engineering of the 1940's...but it's hardly a "ray" that you could selectively aim from a long-ish distance. The inverse square law is a harsh mistress! If they could have done that - then sticking it on an aircraft to take out incoming fighters would be much more interesting to them than taking out cars. SteveBaker (talk) 15:51, 6 January 2009 (UTC)

Are there any Nobel winning scientists in baseball?

Seems a bit far fetched, believe it or not, - not all jocks are stupid. I figured at least one of them cured the cancer of a teammate or two. Has anyone ever abandoned our beloved game of baseball and followed a noble scientific pursuit? Has any big leaguer ever broke out a chemistry set in the locker room?--Baseball and and and Popcorn Fanatic (talk) 02:29, 5 January 2009 (UTC)

Frank Sherwood Rowland played at College level (for Ohio Wesleyan University), but the Laureate who is was the best baseball player is probably Lester Pearson (who wasn't a scientist, but won the Nobel Peace Prize in '57). He was a semi-pro who played for the Guelph Maple Leafs. Rockpocket 03:32, 5 January 2009 (UTC)

Not a Nobel winner, but Kerry Ligtenberg (formerly of the Atlanta Braves, among others) has a degree in chemical engineering: http://mlb.mlb.com/team/player.jsp?player_id=117763 —Preceding unsigned comment added by 24.98.239.50 (talk) 03:44, 5 January 2009 (UTC)

Dr. Bobby Brown was an all-star third baseman for the New York Yankees, and studied medicine while still an active player. He became a cardiologist and surgeon with a successful practice for several decades, then returned to baseball after retiring from medicine as President of the American League. — Michael J 23:27, 5 January 2009 (UTC)

Titanium Knives vs. Stainless Steel

I saw some Titanium kitchen knives on sale at a houseware store this weekend. They were rather expensive, but very nice looking. Are there any pros or cons of using titanium for knives? Do they hold their edge longer than normal stainless steel? Are they sharper? --71.158.216.23 (talk) 06:24, 5 January 2009 (UTC)

This blog post seems to have some good points. Dismas|^(talk) 07:00, 5 January 2009 (UTC)

Aside from the points mentioned there, titanium is also not as dense as steel; according to titanium and iron, its density is only 4.5 g/cm^3, compared to iron's 7.9 g/cm^3. (Stainless steel's density is similar to that of iron since it is only a few percent carbon.) For that reason, it's sometimes used for mountain equipment. See the camping utensils here, for example. Of course, I doubt your houseware store was targeting mountaineers, but titanium offers a much greater advantage in mountain equipment than it does in a regular kitchen. --Bowlhover (talk) 09:08, 5 January 2009 (UTC)

According to our article on Mohs scale of mineral hardness, hardened steel is quite a bit harder than titanium (2-3 times harder on the scale of absolute hardness). I'm not a materials scientist, but I believe blade hardness would be directly correlated with how well it holds its edge. --Bmk (talk) 13:44, 5 January 2009 (UTC)

Harder materials are less likely to wear down, but more likely to chip or crack. Japanese swords often combine harder steel for the cutting edge with softer supporting steel, to get the best benefits of both. StuRat (talk) 18:06, 5 January 2009 (UTC)

I don't think I'll be using any Samurai swords in the kitchen! --71.158.216.23 (talk) 03:02, 6 January 2009 (UTC)

Not even a Ginsu ? But what if you need to cut a can in half and then slice tomatoes with the same knife ? StuRat (talk) 05:06, 6 January 2009 (UTC)

Daytime Conflict with clock time

The day time is not exactly equal to 24 hours .It is short of 4 mints a day .But th eclock shows exactly 24 hours then how will this difference keep correct. —Preceding unsigned comment added by 123.237.213.65 (talk) 07:54, 5 January 2009 (UTC)

See sidereal day. The clocks are based on the Sun's apparent movement; every 24 hours, the Sun returns to approximately the same place in the sky. Because Earth is also orbiting the Sun, it only takes 23 hours and 56 minutes for a star to return to the same position. That's why a sidereal day is 23 hours and 56 minutes. To see how this works, look at the diagram in the article I linked; it explains the concept much more concisely than I can using words. --Bowlhover (talk) 09:34, 5 January 2009 (UTC)

Headphones jack or line out?

I am going to record the audio signal from a reel-to-reel tape recorder. It offers both a headphones jack and some kind of line out DIN connectors (and arc of 5 pins or so) on the back. Which option would give me the best result?

For AD-conversion, I'm thinking about using a gramophone, which connects to a computer via USB, and which has a connector for taking in an external audio signal. If it makes my question easier to answer, we can assume that I'll connect the reel-to-reel directly to the simple sound card of the computer instead of to the gramphone. —Bromskloss (talk) 09:50, 5 January 2009 (UTC)

Probably the LINE connections would give the best impedance match - but IMHO, you should try both and see what gives you the best results - you won't break anything by doing that. Old tape recorders tend to be pretty well-behaved. The things that are a pain to interface to is old record players...but I guess you've already solved that one! SteveBaker (talk) 14:51, 5 January 2009 (UTC)

Thanks for taking the time. Impedance matching, does it really matter? The input impedance of the receiving equipment is supposed to be "very high" anyway, isn't it? As for the "pain", do you refer to RIAA equalization? It's convenient not having to fiddle with that. —Bromskloss (talk) 15:06, 5 January 2009 (UTC)

I would use the line out thereby bypassing the headphone amp (which may introduce some distortion). Impedances do not have to be matched as long as you are not overloading the output of the tape recorder. Direct input to the sound card should not be a problem.--79.75.49.50 (talk) 16:56, 5 January 2009 (UTC)

We seek to load up an output. The input impedance of the thing you are connecting to should be as high as or higher than the output impedance of the source, and never lower, to avoid distortion and damage. What does a gramophone to do with electronic audio? That is a British term for a wind up disc phonograph with purely acoustic output. Edison (talk) 04:07, 6 January 2009 (UTC)

Ah, I did have my doubts I was using the right word. So, phonograph it is. —Bromskloss (talk) 10:03, 6 January 2009 (UTC)

Brit's wouldn't say "phonograph" either - "Record Player" or "Turntable". But it's OK - most of us speak American fairly fluently. SteveBaker (talk) 15:41, 6 January 2009 (UTC)

Thanks. I strive to follow British conventions unless I am speaking only with Americans so this is useful information to me. —Bromskloss (talk) 19:34, 6 January 2009 (UTC)

How long will it take for Pluto to clear its neighborhood?

I was just wondering if anyone's ever tried to figure out how long (persumably, millions or billions?) of years for Pluto (through collisions with meteors, comets, asteroids, etc.) to clear its neighborhood and become a "planet"? —Preceding unsigned comment added by 216.239.234.196 (talk) 13:19, 5 January 2009 (UTC)

I don't know the answer to your question - but I'm not sure that this would ever happen. Clearing the neighborhood would be a major deal - as our article on Pluto points out, Pluto's mass is only 7% of the mass of the other objects in its orbit. Earth's mass, by contrast, is 1.7 million times the remaining mass in its own orbit. So Pluto would have to get something like 14 times bigger before it could be considered to be a planet under the present rules. Of course that would depend on whether Charon would gain mass proportionately or disproportionately to Pluto - and whether that large weight gain would cause their orbits to misbehave and one to collide with the other or break apart and form yet more debris to be swept up. Worse still - Pluto/Charon's orbit around the sun is retrograde and tilted at a crazy angle - if much of the debris turns out to be in the plane of the ecliptic (as one might expect) then Pluto's rare intersections with the ecliptic (just once every 120 years!) would make the opportunities for it to pull in rocks in orbits that intersect somewhat unlikely. So my gut feel is that the answer has to be "a very long time" - possibly longer than the predicted life of the Sun. SteveBaker (talk) 14:44, 5 January 2009 (UTC)

While it may be possible for Pluto's orbit to be cleared (although unlikely for the reasons Steve gives), it wouldn't contain anything we recognise as Pluto by the end of it. Pluto would have to merge with lots of other objects (including ones of comparable size), so only part of the remaining object would be Pluto. Alternatively, lots of objects could be thrown into different orbits, but if that happens there is no reason to believe it would be Pluto that remained, it may well be thrown into a different orbit itself. --Tango (talk) 22:19, 6 January 2009 (UTC)

We need to take into account more than just the mass of pluto. Pluto is in a region of the solar system where neptune dominates. Orbital resonance is an exception to clearing the neighborhood where a number of objects can be trapped in a resonant orbit. [2] But, also see [3] for information about how pluto does influence nearby objects. --mikeu ^talk 16:04, 7 January 2009 (UTC)

how many horsepower can a horse pull with?

how mnay horsepower can a horse pull with? 1? —Preceding unsigned comment added by 79.122.29.166 (talk) 16:03, 5 January 2009 (UTC)

See Horsepower from a horse. Echinoidea (talk) 16:27, 5 January 2009 (UTC)

Ah, that explains it. I've often wondered why a 50 horsepower car has difficulty going up a steep hill, when 50 horses would have no trouble pulling the same car up the same hill. StuRat (talk) 18:00, 5 January 2009 (UTC)

No, that's not the reason. A car is not designed to climb a steep hill. A small tractor has a lot less power, but it can climb the hill because it has a much lower gear ratio and it has cleats on the tires. Similarly, horses can "gear down," and they have adaptive traction control (loosely speaking.) You can raise a large car up a steep incline, or even a vertical cliff, using a 1Hp winch, given the proper gearing. -Arch dude (talk) 02:19, 6 January 2009 (UTC)

I saw a comic once, which clearly stated that one horsepower is defined as the power of the prototype horse in a Parisian archive. ——Bromskloss (talk) 16:22, 5 January 2009 (UTC)

Note that there is a difference between horsepower and torque. --Russoc4 (talk) 02:25, 6 January 2009 (UTC)

When early steam engines were rated in "horse-power" the steam engine promoters were very conservative in rating the engines. Thus a factory owner or mine owner who replaced a horse driving a sweep arm around with a 1 "horsepower" steam engine was pleasantly surprised, and advised his friends to also buy steam engines. Edison (talk) 04:04, 6 January 2009 (UTC)

J/k then when everyone was hooked on steam engines, they began to find their new 1 'horsepower' engines were less and less powerful until they couldn't even pull 1 horse! j/k Nil Einne (talk) 12:10, 8 January 2009 (UTC)

Racemates/racemic mixtures

In my exam specification we know that we have to learn about optical isomers, with dextroenantiomers and laevoentantiomers and why reactions tend to produce racemic mixtures.

I understand these terms, but I do not know why racemic mixtures are formed. Why is one enantiomer not formed more than the other? Note this isn't homework, it's revision. Cheers :) —Cyclonenim (talk · contribs · email) 16:04, 5 January 2009 (UTC)

In many cases, the production may go via an SN1 reaction or similar, in which the intermediate molecule in the reaction actually loses a functional group temporarily - as the carbon center, for a brief moment, only has 3 other groups attached to it any existing chirality at that centre is lost. Even in the case of a bimolecular reaction (such as an SN2 reaction) there is often no real factor that causes the attacking group to come in from one side in preference to another. ~ mazca ^t|c 17:54, 5 January 2009 (UTC)

Er, in a normal S_N2 reaction, there is usually a nearly complete preference for the atacking group to come in opposite to where the leaving group is. That type of reaction usually gives clean inversion of configuration, completely not racemization. DMacks (talk) 04:29, 6 January 2009 (UTC)

You're right, my bad. My chemistry degree is evidently rapidly vacating my brain. :D ~ mazca ^t|c 18:29, 6 January 2009 (UTC)

Genetics

Some traits come in two varieties( for example Mendel's round and wrinkled peas with green and yellow colors)Do all traits for all species come in only two varieties?Justify the answer by explaining the relationship between genes and traits. —Preceding unsigned comment added by Shadnasa (talk • contribs) 17:35, 5 January 2009 (UTC)

This really sounds as if it breaks the "The reference desk will not do your homework for you" rule. -- Aeluwas (talk) 17:43, 5 January 2009 (UTC)

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

All traits come in just two states, such as "blue eyes" and "not blue eyes". :-) StuRat (talk) 17:55, 5 January 2009 (UTC)

You could start by reading the Genetics article. The Quantitative trait article will at least give you the "yes/no" part of your answer. The rest of the question is going to require some basic understanding of genes/proteins and sounds like a good essay to work on. You will find sections on "multifactorial inheritance", "complex traits", "polygenic traits", etc. in any good genetics textbook. As a general rule, if the question says "all", you should automatically suspect that the answer is "NO". The goal here is for you to understand why not. --- Medical geneticist (talk) 19:06, 5 January 2009 (UTC)

Volume controller

I got a fancy new radio for christmas and would like to listen to it at work, however it does not have a headphone jack, only a "line out" jack. The volume knob on the radio does not affect the "line out" signal, and when I plug my headphones in it is super loud. My headphones do have their own volume knob, but the control is not fine enough and I have to turn it to its lowest setting just so it doesn't hurt my ears. So currently I have to choose between super loud, kinda loud, and off. I'm wondering if there is a device I can stick between the radio's line-out jack and my headphones which would allow me to have greater control over the volume, or is there another solution? — jwillbur 18:05, 5 January 2009 (UTC)

Considering how cheap headphones are, you could just buy a set with more precise volume controls. Specifically, look for a volume slider or knob, not a separate "up" and "down" buttons, as that type never seems to have much precision. If you want a free solution, put something between the headphones and your ears which will absorb most of the sound. StuRat (talk) 18:44, 5 January 2009 (UTC)

A volume control is just a variable resistor - if you have any construction skills you could buy a 'potentiometer' (aka: a 'variable resistor' or a 'pot') and wire it up in series with your headphones. That would give you another volume control that you could use to cut the volume from the radio before sending it to the headphones - and the headphone volume control would still operate after that to adjust to personal preference. Sadly, I can't think of any devices that you can just go out and buy that'll do the job. Some radios have either a switch or a menu option to switch the output jack between 'LINE' and 'Headphone' levels - but I guess you've already checked that. SteveBaker (talk) 18:49, 5 January 2009 (UTC)

I would expect a headphone amplifier, like this one, to be an off-the-shelf solution. -- Coneslayer (talk) 20:47, 5 January 2009 (UTC)

Cheap off the shelf solution: [4]--GreenSpigot (talk) 01:29, 6 January 2009 (UTC)

"Line out" outputs should, in general, not be connected to a load (like low impedance headphones) of low impedance. Headphones vary in their electrical characteristics. Excess current might be drawn, and distortion might occur. Manufacturers might have taken this into consideration and used a hardy output stage. A headphone amplifier can solve this problem if it has a high input impedance and a low output impedance, as well as providing a volume control. Some modern audio devices provide equalization to boost the bass to compensate for poor low frequency response by headphones, and this might also be a feature to look for in a separate headphone amp. For a Powerbook G4 audio system, for instance, the headphone impedance is 32 ohms, and the headphone jack (the output) has 10 ohm impedance. The line out or "audio output " jack has a recommended minimum of 1000 ohms impedance for the load connected to it.[5]. Your radio instruction book might state the minimum load for the line out. Edison (talk) 20:45, 6 January 2009 (UTC)

Artificial Gravity

I heard a idea in a sci-fi book one time to create artificial gravity in a space station all you have to do is spin the space station at the right speed so that the Centripetal force pushing you into the outer edge of the space station matches that of gravity on earth. If this is indeed possible, how fast would it have to spin to simulate Earth’s gravity? I suppose it'd be a function of the diameter? Would it be possible to spin fast enough that it would rip anything apart that happen to be in the center? Now that I think about it, this all seems wrong to me since if we choose the station to be the reference point it as the station is stationary and the universe is spinning around it so no force should even be created. Am I thinking about that wrong? Thanks. Anythingapplied (talk) 19:12, 5 January 2009 (UTC)

All this and more is covered in Artificial_gravity#Rotation. Except maybe the bit about tearing something apart in the center, which doesn't seem all that likely to me unless you were spinning it at ridiculously fast rates and the thing in the center was especially prone to being ripped apart (you'd have to spin it at a rate that would be much much much more powerful than any simulated earth gravity, yes? You'd be essentially just creating a giant centrifuge). --98.217.8.46 (talk) 19:13, 5 January 2009 (UTC)

Centripetal force can work to provide artificial gravity. However, there are some reasons why it hasn't been done so far:

1) Since the force of gravity reduces to nothing at the center, that means the apparent force of gravity changes when you move toward or away from the center. Also, for a small station, the distance between your head and feet causes a significant change in apparent gravity. This causes nausea.

2) A rotating station is more difficult to use for docking. Generally, docking would only be possible at the axis, allowing two ships at most, and they would still need to match the station's rotation to dock, which is difficult, but not impossible.

3) Items like solar panels and antennae, which need to point in one direction, either need to be moving constantly relative to the station, which makes for many moving parts to break down, or they would need alternative designs. For the antennae, you could have a separate, nearby, non-rotating antenna ship that always points toward the target, and uses a low-power signal to communicate with the rotating ship with the people on board. The rotating ship could use an omni-directional antenna. For solar panels, you could put them on all sides of the rotating ship, so some are always pointed towards the Sun. This would, of course, increase weight relative to energy produced, but would also provide for redundancy, eliminate the need to use energy to aim them at the Sun and would reduce complexity which would be likely to cause failures.

4) Space walks away from the axis wouldn't work, as the astronauts would be pushed away from the ship. Thus, you would need to stop the space station's rotation to do exterior maintenance. StuRat (talk) 19:30, 5 January 2009 (UTC)

I think the major reason we have not done this yet is that we have not put anything bigger than a large truck worth of manned station up into orbit. Especially to overcome problem 1 above, you need a big station. For our small stations with small, highly trained crews that only stay up for a few weeks or months, the price for artificial rotation is not worth it. If we ever get to build real habitats, rotation will likely be the means if providing simulated gravity. Von Braun's space station design was a torus with a diameter of 76m, i.e. with similar outer proportions to the ISS, but much much more livable space and a much larger crew. --Stephan Schulz (talk) 20:03, 5 January 2009 (UTC)

That's partly true, but I think the main reason is that we want to study all the negative effects of microgravity on the human body and how to combat it. Lose of muscle mass and bone strength are major issues. If the ISS was built as a rotating wheel, we lose an opportunity to figure out a cure/treatment. 67.184.14.87 (talk) 23:54, 5 January 2009 (UTC)

That sounds rather unethical: "Let's damage the health of some astronauts so we can collect data". StuRat (talk) 23:58, 5 January 2009 (UTC)

Not really. The point of space travel is learn more about the universe and our place in it. If we cannot overcome the health issues of space travel, that severely limits our ability to explore it. Besides, astronauts already know that space travel is dangerous. I'm not sure if this is still true but in at least the early days, astronauts were recruited from test pilots where risking your life with each flight is a basic part of the job. 216.239.234.196 (talk) 15:19, 6 January 2009 (UTC)

This one doesn't quite fit in with the other's: Microgravity (say 1% of normal gravity) is actually the best for getting work done, as massive objects (like satellites) can be moved easily and yet your tools don't float away. This might mean you want to spin the station slowly, instead of at the 1g speed. StuRat (talk) 20:12, 5 January 2009 (UTC)

The force doesnt dissapear when you change reference frames because the artificial gravity is due to the centripetal acceleration. This means that the spinning frame is non-inertial (as spinning frames always would be), and so the force is maintained when the transformations between reference frames occurs.

Certainly 'spin gravity' works. There is absolutely no doubt about that. The problem is that (as already noted) the station has to be large enough that you don't notice significant difference between gravity at your feet and your head - but remember that once you are spinning the thing - these outer sections of the station are going to be pulling on the central 'hub' with the full force of gravity. So instead of the station being a typical lightweight construction - it's suddenly got to be built with all of the structural strength of something like a bridge on earth. Since we've already agreed that it also has to be large - you have something that's physically huge and has to be strong - so it's chunky too. That's going to make for a pretty major launch weight. The suggestion to use fractional 'g' is a good one - but it's essentially impossible to determine what fraction of a 'g' is enough to counteract the alarming dangers of staying up there for prolonged amounts of time. We know that zero 'g' is incredibly harmful - both to health while aboard the craft - and (more worrying) to the long-term health of the astronauts once the mission is over. We know that 1g is good...but what happens if you spend a year on the moon at 1/6th g? We really don't know because short of building a moon-base or an actual spinning space station - we can't do the experiment. It might be sufficient (for example) to have a pair of small cabins (each the size of a phone booth - say) attached to opposite ends of a long cable so that they are able to spin. The astronauts take turns to eat, sleep and exercise in 1g while they do all of their daily work activities in zero 'g'. That might be enough to keep them healthy - and it would be vastly cheaper than spinning the entire station. But we don't know. As for the issue of performing maintenance on a spinning space station - you'd have to use ladders and safety lines and all of the other apparatus that you need for doing that kind of thing down here on earth. That at least is something we understand! Alternatively - you could always have a large flywheel for storing the rotational inertia while the station (or perhaps just the two phone-booths) is spun down to normal speeds. That would consume relatively little energy - so altering the amount of artificial gravity and allowing transfers from the non-spinning parts of the station. Docking could be handled the same way - turning off the spin for however many days the docking is going on - and putting spin back on again once the shuttle departs. SteveBaker (talk) 21:57, 5 January 2009 (UTC)

Not only the gravity gradient (difference between feet and head) is of concern, but also the Coriolis effect. For constant apparent gravitational acceleration, Coriolis effect is proportional to ${\frac {1}{\sqrt {r}}}$ and gravity gradient is proportional to ${\frac {1}{r}}$.

The tension in a rotating ring or the maximal tension in a rotating rod is both $\rho \cdot a\cdot r$, where $\rho$ is the density of the material, $a$ is the pseudo-gravitational acceleration (9.80665 m/s² is one standard gravity ('g')) and $r$ is the radius. This and the article on tensile strength gives you an estimate how large you can build the structure - with steel it would be a few kilometers.

If there is only 1 rotating wheel-like space habitat, then it's a problem to change the orientation due to gyroscopic effects - it's better to have 2 counter-rotating wheels on one axle. To prevent bending of the axle during re-orientation one could build opposing magnets at the rims of the wheels where the forces due to the torques are smaller than at the axle.

Icek (talk) 23:12, 5 January 2009 (UTC)

I'll just make two points relating to the fact that artificial "gravity" due to rotation of a structure diminishes as you get nearer the center. First, this could be useful. If it's found that say a level equal to say 60% or 100% Earth gravity is necessary to maintain the health of the station occupants, but 1% is better for some kinds of work area, then all that has to be done is to place those work areas near the center of the station and the living quarters farther out. This might involve an elongated station rather than a wheel-shaped one that would put most of the usable space around the rim.

And second, the original poster asked if the station might come apart at the center. While a flaw anywhere in the structure could cause its destruction, this would be more likely to happen near the rim, where the forces are greatest. But such a thing isn't a major risk: the forces are well understood, just as gravity is on Earth, and it's only a matter of properly engineering the structure to resist them reliably. It might be harder than doing it on Earth because the costs of lifting materials into space are large, but it's basically just a matter of engineering. And while ordinary structures sometimes do fail here on Earth, it's a pretty rare event. --Anonymous, 00:00 UTC, January 6, 2009.

A Zebra Finch as a pet?

Does anyone here have one? What are they like as pets? My impression from seeing them is that they don't really do much, have no interest in interacting with people and are a bit like just having a sparrow in a cage. Whenever I've seen them, they just seem to jump from perch to perch, tweet, eat, drink and back away if a person gets too close. Am I wrong? --84.67.67.100 (talk) 23:14, 5 January 2009 (UTC)

The article on Zebra finches mentions a bit about their behaviour and taming them. Mattopaedia (talk) 00:37, 6 January 2009 (UTC)

Have you only seen them? You must hear them before you ever consider them as pets. Zebra finch vocalizations can be very loud and, to some people, very, very annoying. Make sure you like what you hear first ;) --Dr Dima (talk) 01:20, 6 January 2009 (UTC)