Wikipedia:Reference desk/Archives/Science/2013 February 11

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February 11

Anodisation of Aluminium

Ive read numerous stories of iphone 5s being scuffed from the moment they opened the box. Ive also heard similar stories with other anodized aluminium products. This leads me to wonder, is anodisation a process which is difficult to achieve without causing small scuffs or marks? Clover345 (talk) 00:13, 11 February 2013 (UTC)

Not at all, but aluminum is a relatively soft metal, compared to say, stainless steel which I think was used on some of the earlier iPhone models. Metals of high hardness scratch less easily (and a scuff is basically just a scratch as I understand the term). 202.155.85.18 (talk) 00:17, 11 February 2013 (UTC)

One of the advantages of traditional anodising done with electric current per standards is that it provides a surface significantly harder than the base aluminium. However, it is a porus surface, further treatment (eg varnish) is usually done if the device is to be handled. See http://en.wikipedia.org/wiki/Anodizing. There could be a production problem with the further treatment. Also, there are various non-electric processes that result in what looks like an undyed anodised surface - these are not as tough. A substitute finish used by a company I once worked for used the following (much cheaper) process: Step 1 - clean with detergent and air blower dry. Step 2 - dip in dilute caustic soda. Step 3 - clean again with citrus solvent (slightly acidic). Step 4 - water rinse and air blower dry. Step 5 light spray with thinned marine varnish. The result looks identical with genuine anodising, but has no where near the toughness and durability - and usually the product left the shop with marks already on it. Ratbone 121.215.57.135 (talk) 01:06, 11 February 2013 (UTC)

Aluminum is relatively soft, but an anodized surface on aluminum is very, very hard. this page claims that apple uses something called "soft anodizing" which I am unfamilar with. --Guy Macon (talk)

Betretta M9 hammer hole

What is the purpose of the hole in the hammer spur of the M9 Baretta?

202.155.85.18 (talk) 02:42, 11 February 2013 (UTC)

Having less weight on the hammer means it can move faster, reducing the time between pulling the trigger having the gun fire. I think it is also done for aesthetic reasons. --T H F S W (T · C · E) 04:54, 11 February 2013 (UTC)

Maybe it's a design feature to match the seemingly useless hole at the bottom of the handle. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:09, 11 February 2013 (UTC)

The "useless hole" at the bottom is for a lanyard Bugs. Shadowjams (talk) 05:35, 12 February 2013 (UTC)

Not necessarily useless - ISTR some soldiers (or rather, officers) used to have a piece of string attaching their handgun to their belt (or holster, or similar). The hole at the bottom of the handle is in the perfect place for doing this. --Demiurge1000 (talk) 12:48, 11 February 2013 (UTC)

See Lanyard#Origins. No idea on the hammer spur, though. --Dweller (talk) 14:55, 11 February 2013 (UTC)

Nobody in their right mind puts a lanyard on a hammer. Shadowjams (talk) 05:34, 12 February 2013 (UTC)

I was replying to a comment that read "The hole at the bottom of the handle is in the perfect place for doing this". If there had been any doubt that was what I meant, the second of my two brief sentences should have addressed it. --Dweller (talk) 09:06, 12 February 2013 (UTC)

And you apparently take indents a bit too personal. Shadowjams (talk) 10:31, 12 February 2013 (UTC)

As Demiurge was also clearly talking about the hole at the bottom of the handle, your impersonal comment seems to have been aimed at no-one at all. --Dweller (talk) 11:11, 12 February 2013 (UTC)

It's called a "skeletonized hammer". This means the gun has the same hammer geometry as it would with a solid hammer, but the hammer is lighter. Beretta themselves say here that this "can improve cycle time because of the lighter weight." Alternatively, as the hammer is lighter, you can replace the hammer spring with a weaker one (a lighter hammer is less mass for the spring to accelerate). This gives the gun a lower "pull weight" (the amount of force needed to pull the trigger); a smaller shooter (with weaker fingers) might opt for a lower pull weight, so they can still operate the gun easily. Naturally a lower pull weight isn't without issue, as a more sensitive trigger can make it more likely that the gun is fired accidentally. One can also get skeletonized triggers, which again lower the mass of the moving trigger system. -- Finlay McWalterჷTalk 16:23, 11 February 2013 (UTC)

Interestingly, I've never come across this question before, but it's a good one. The common theme is that most match hammers are milled like this... compare most standard 1911s to a match-grade 1911, and you'll see similar milled out hammers. My guess is it has to do with weight. It doesn't have to do with trigger pull... that's easily adjustable through other means, and the weight of the hammer matters almost nothing for that. Yes that gun's a DA, but you see this on single action guns all the time. The factory 92FS hammer is not referred to as "skeletonized" either, as the link clearly indicates. The hammer in the link is very different than the textured hammer in the picture.

I don't have a satisfactory answer for the OP, wish I did, because it's a good question. I can dispel, however, a few obviously wrong answers. Shadowjams (talk) 05:32, 12 February 2013 (UTC)

hair drier off lithium batteries?

can a hairdryer (very high draw device) be run off of any common, relatively light-weight batteries? The usage case would be that it is OK to charge for a long time, but then a very high drain hairdrier should deplete it in just a minute or two... are any battery technologies appropriate? If the battery would get warm, the hairdrier can actually draw air from over it (preheating the air) so maybe this helps a bit. The application is actually on an RC helicopter that is supposed to work in a very new way. The battery for the hairdrier can be separate. Note: this is just about a special application, like an rc helicopter that can help glue sheet paneling. Thanks! 91.120.48.242 (talk) 12:32, 11 February 2013 (UTC)

Google [battery operated hair dryer] and a number of entries turn up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:42, 11 February 2013 (UTC)

Uh, this is a pretty resounding "no". Anyway, nobody uses a hairdrier for "just a few seconds" so I'm wondering if you can answer my quesiton more directly. (The hairdrier was a stand-in anyway.) Can a battery release 1600 watts for, say 30 seconds at a time, without damage or terrible overheating? I mean, long-charge, fast-discharge batteries... does that describe the profile of existing, compact, light-weight batteries? thanks... 91.120.48.242 (talk) 13:33, 11 February 2013 (UTC)

Probably not; a hair drier pulls an intense amount of current, and there's just not enough electrons at a high enough energy in a small, compact lithium ion battery to power such a devise for a meaningful amount of time. Battery-operated hair driers could possibly run off of the sorts of rechargable batteries used for cordless drills and tools like that, but only if you were just running a powerful fan motor. The heating element is the real energy hog in the hair drier, and you really need a huge amount of electrical power to run such a heating element effectively. The chemistry just doesn't work out given the amount of material available in any compact chemical battery. --Jayron32 16:41, 11 February 2013 (UTC)

Try googling the subject further and see what you find. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:42, 11 February 2013 (UTC)

RC hobbyists sometimes want fairly high discharge rates and they usually rely on lithium polymer batteries for the purpose although what you're asking for seems a bit extreme to me. It may be barely doable but it depends greatly on what you mean by 'relatively lightweight'. For example our article mentions some batteries managing up to 65C [1] continuous. As an example it links to [2]. If the specs are correct, this battery can handle up to 292.5A continuous discharge. With the nominal voltage of 37V (it's 10S) this means it should be able to supply 10,822.5W although given the rate of 65C this will be for less then a minute. However the battery itself is over 1.3kg so may not be considered lightweight. (I have to admit I wonder if the cabling and battery is really capable of handling 292.5A but perhaps it can.) Of course you don't need quite that level of power. So if we look under the category and sort by weight, you can find [3] which is 2200 mAh which given the rate of 65C can handle up to 143A continuous discharge. With the nominal voltage of 11.1V (it's 3S), this will be 1,587.3W so may fit your purposes. The battery is 266g. Of course you don't really need such a high discharge rate, more cells in series with a lower discharge rate would be fine. For example you could also use [4] which at 6S and 40C is supposed to be able to handle up to 72A continuous discharge so should be able to supply 1,598.4W for slightly longer then a minute although it's heavier at 385g. Probably one problem is generally for RC purposes, if you want a high voltage it's generally for a bigger device so a heavier battery isn't such a big deal. Of course the other point is even at 10S, you're still going to need about 43A. Personally I wouldn't want a lithium polymer battery supplying 43A near me (and if it's supplying 43A to a hair dryer it's likely to be near me) or I may find my hair getting dry a lot fast then I intended, along with the rest of my body. (While RC batteries are subject to shocks a hairdryer hopefully won't be, there are plenty of videos showing what can go wrong.) Nil Einne (talk) 17:00, 11 February 2013 (UTC)

It sounds like you don't actually want a hairdryer for heating hair but even so I'd suggest that even if it's theoretically possible, it's not practical for your purposes. These sort of things are at the bleeding edge (particularly when pushed close to the limits of the specs) and are targeted at a hard core group of hobbyists willing to take the associated risks (and as I said, there are plenty of videos and forums posts to show it). And in fact given your purposes it sounds like you will be in the group where 'rough handling' does come in to play. And since it sounds like this has some sort of industrial purpose, I quite doubt OSH and the fire brigade or the equivalent in your jurisdiction will be happy about the occasional exploding battery while charging, landing or storage (after a crash for example). Nil Einne (talk) 17:22, 11 February 2013 (UTC)

A look in RC forums suggest most 'C' ratings are, shall we say, optimistic, particularly when coming from HK and Chinese sellers. However this rather old post [5] suggests 40C may be possible or even 46C (120A in the case in point) although that was only with a single cell of a 3S battery. Of course even if all 3 could supply that at the same time you'd still be about 400W short, you'd need 4S. I didn't find the weight but it was suggested to be typical given the capacity (3S, 2600mAh) so from what I saw earlier it'll probably be under 400g.

In any case, I'd note you only seem to be considering this 'hair dryer' load. If you're planning some sort of RC helicopter, you'd also need power to lift the helicopter itself along with the battery and !hair dryer, take it to the destination, stay there while you glue the boards and then land again. It sounds quite unlikely 30s will be enough for this, so you'd need to adjust your demands and requirements. Presuming you come up with something like 3-5 minutes total flying time and you don't need more then say 300 watts for the helicopter (including all loads), from what I've already seen from over 1.5 years ago, it does sound likely it may be possible. I still think it isn't practical for anything other then demonstration/we can do this purposes. Edit: And I also question what you'll actually achieve if you only heat the glue for 30 seconds and then need to charge your helicopter or send a new one. Notice also the comments on cycle life and heat.

Nil Einne (talk) 18:19, 11 February 2013 (UTC)

A discharge rate that fast might be closer to the capabilities of a capacitor than a battery, specifically a motor capacitor. Note that such devices are dangerous, as the voltages produced may match or exceed mains voltage. StuRat (talk) 16:33, 11 February 2013 (UTC)

Sturat, this is very good/interesting. I didn't know this before. Do you think it's possible to have one that is really very much "capped" (hehe) at 1600Watts, and will discharge for, say, a full 1 minute, if it has 1 minute * 1600 Watts in it for the voltage that's being drawn? Thanks. 91.120.48.242 (talk) 16:43, 11 February 2013 (UTC)

Stu is correct that a capacitor would provide a large current for a short time, but you are very unlikely to find a capacitor that you can afford with enough capacity to run a hair dryer heating element for more than a second or two. A very big capacitor might run a small DC fan motor for a minute or so, but would gradually reduce in speed as the capacitor discharged. I'd advise running a 12v hair dryer from a car booster battery, not lithium. Dbfirs 17:09, 11 February 2013 (UTC)

Nil's suggestion above, of a lithium polymer battery, sounds like it suits your purposes better than a capacitor, although it's still dangerous. StuRat (talk) 17:32, 11 February 2013 (UTC)

It would help if you could describe the purpose of this device more. Are you trying to dry paint on an high wall ? If so, perhaps shining lots of heat lamps at it from the ground might be a better approach. StuRat (talk) 17:38, 11 February 2013 (UTC)

I think you need to channel the antimatter emitter directly into the output stream... no, really, what I'd wonder is, is there a way that you can store the energy chemically in the glue itself, rather than electrically? But I like the direction of your mind. :) Wnt (talk) 17:40, 11 February 2013 (UTC)

From the OP's previous posts, I do wonder the state of the OPs mind when they had this idea. Nil Einne (talk) 18:21, 11 February 2013 (UTC)

To get your heat it could be easier to burn a liquid fuel like kerosene. Your storage can be much lighter weight. Graeme Bartlett (talk) 21:02, 12 February 2013 (UTC)

Exactly. We've run up against the reason we're not all driving electric cars, despite their numerous advantages, and why electric airplanes are restricted to model planes; which is that a tank of hydrocarbons holds so much more energy than the best battery of similar weight and/or size as to make it no contest. For this application, note that one of the interchangable tips on my little butane soldering pencil (from radio shack, so many years ago) is a catalytic tip which generates a nice flow of hot air, suitable for heatshrink tubing etc., without the dangers of a flame. Gzuckier (talk) 05:12, 13 February 2013 (UTC)

I strongly suspect that our OP - having been defeated in his efforts to come up with a way of having an R/C plane transform into a helium balloon when it's batteries run down (see previous questions) - is now trying to transform it into a hot air balloon. Still not going to work - still going to be blown so far off-course while it's batteries recharge that it'll never get back on course before they run down again...etc, etc. 21:47, 12 February 2013 (UTC)

Resonant frequency of an aluminium bar.

Hi! I'm trying to get a rough idea of the resonant frequency of an aluminium bar that's 1400 x 40 x 40mm and can probably be considered to be "unclamped" - in the plane that I'm expecting the vibration to occur.

I don't need an exact answer - I'm just trying to find out whether it's likely to have a resonant frequency somewhere between 10 and 20Hz.

SteveBaker (talk) 14:03, 11 February 2013 (UTC)

Hmmm. Looks like the speed of sound in aluminum is roughly 5100 m/s. So sound travelling 1.4 m and back should take 2.8 m / 5100 m/s = 1800 Hz. The other directions should be higher. Acoustic resonance says more about this. My perception is that such disturbing "infra"sound can come from ducts less than twice this diameter, but this is presumably because of some lengthwise geometry, that the speed of sound in air is 15 times slower and perhaps because for some reason the formula for a closed tube is /4L instead of 2L. Wnt (talk) 15:50, 11 February 2013 (UTC)

The bending vibrations of the bar will be at a much lower frequency, http://hyperphysics.phy-astr.gsu.edu/hbase/music/barres.html may be helpful (I haven't checked it thoroughly). Note that when you clamp a free free bar the first bending mode drops in frequency. The reason is subtle. Greglocock (talk) 01:57, 12 February 2013 (UTC)

Atom Volume

I can't seem to find any references for the assertion that "approx. 99.9% of an atom's volume is empty space". Can someone please provide some references, or is this assertion not verified? Thanks.165.212.189.187 (talk) 16:55, 11 February 2013 (UTC)

Which article says that? Dmcq (talk) 17:58, 11 February 2013 (UTC)

I don't think any do.165.212.189.187 (talk) 18:02, 11 February 2013 (UTC)

I googled 99.9% of an atom's volume is empty space and got a lot of hits, some of which at a glance seem to be legit. Duoduoduo (talk) 18:23, 11 February 2013 (UTC)

Anywhere in Wikipedia?165.212.189.187 (talk) 18:36, 11 February 2013 (UTC)

It depends on what is meant by "empty space". If you consider electrons to be point particles, like little tiny infinitesimal balls, and the nucleus to be another tiny, solid ball, then I suppose the claim could be made. But that's a rather primitive and not-very-accurate view of what an atom is. Instead, if you consider an atom to be a nucleus surrounded by the probability space which contains the electrons, then it's as solid as anything; if by solid you mean "impenetrable little hard nugget", then an atom is essentially solid, and none of it is "empty". The entire volume of any given atom is essentially all made up of the electron cloud, which is essentially impenetrable by other atoms. So the "claim" that atoms are "empty space" is based on some rather silly leaps of logic from a non-too-accurate view of what an atom is. It sounds all profound and all, but its basically bullshit. --Jayron32 18:41, 11 February 2013 (UTC)

You can take it the other way too. At atom can be considered 100% empty space. The electrons are point like particles with no size, the nucleons are in turn made up of quarks which are also point like. So in some way an atom is 100% empty space. Of course in the real world atoms interact not by their location, but by the forces acting on them and those forces have ranges. So the forces acting on the electrons certainly reach the nucleon, and the entire area in between can be considered to be "filled in" with that force. Same for the strong force holding the nucleons together and also for the force in between the quarks. The interesting conclusion is that the "size" of particle depends on what force you want to use to measure it with. Ariel. (talk) 18:51, 11 February 2013 (UTC)

That's why any visualization you can conceive of to represent the atom or its parts always falls woefully short of how it actually behaves. See the discussion a few days ago regarding this very topic. --Jayron32 19:29, 11 February 2013 (UTC)

One sense in which you can say they're mostly empty is mass/energy density. -- BenRG (talk) 22:11, 11 February 2013 (UTC)

Duo, anywhere in wikipedia??165.212.189.187 (talk) 20:08, 11 February 2013 (UTC)

So is it true or not??165.212.189.187 (talk) 15:20, 12 February 2013 (UTC)

The best answer we can give you is it isn't even wrong. The premise upon which it is built: that you can reliably model an atom as a collection of relatively solid parts, with the balance being empty space, isn't correct in any way. So, there's not a simple "yes or no" answer; though if you want to know about some of the common models of the atom, and want to know why it is so hard for us to give you a straight answer, read the responses in detail with the understanding that concepts like "empty space" and "particle" and the like don't make sense on this scale, and instead you need to very carefully define your terms before the question becomes meaningful. --Jayron32 18:48, 12 February 2013 (UTC)

Even if you focus soley on the location of the electron and disregard the momentum so that you "find" its location?165.212.189.187 (talk) 19:14, 12 February 2013 (UTC)

Logic

Is this a true statement?: Things that don't exist have the same quantum state.165.212.189.187 (talk) 17:00, 11 February 2013 (UTC)

If coded in Predicate logic and following its usual axioms then that would evaluate as true. Basically what we'd be asking is whether the statement for all x and y, do x does not exist and y does not exist imply property 'quantum state the same', is that falsifiable ie can we find x and y so it is provably false? However this is an empty meaningless statement and the answer I gave is one more suited to the maths reference desk. Dmcq (talk) 17:49, 11 February 2013 (UTC)

More concisely: Everything exists, so any sentence starting with things that don't exist have... is vacuously true. Falisfiability and provability are unnecessary distractions. --Trovatore (talk) 18:59, 11 February 2013 (UTC)

Yes, that's the heart of it. We can also have fun with the vacuous truth of conditionals that have false antecedants. For example this sentence: "If this question is posted in January, then Wikipedia is an invisible pink unicorn" -- is true. SemanticMantis (talk) 19:22, 11 February 2013 (UTC)

Yes, good one, I can't wait until next year. or, since EVERYTHING exists then so does an Invisible Pink Unicorn.68.36.148.100 (talk) 01:54, 12 February 2013 (UTC)

No, you're missing the point. Everything exists. That's a true statement, but a less interesting one than it appears — it's actually a sort of tautology, because every thing is a thing, and things, by virtue of being things, must exist.

On the other hand, "a square circle exists" is a false statement. But there is no contradiction, because to conclude from "everything exists" that a square circle exists, you would first have to have a square circle to instantiate the universal quantifier "everything". --Trovatore (talk) 03:23, 12 February 2013 (UTC)

Still can't wait til next year. So no thing doesn't exist, but does nothing exist also?68.36.148.100 (talk) 04:10, 12 February 2013 (UTC)

Nothing doesn't exist. There's nothing you can do that can't be done. There's nothing you can sing that can't be sung. --Trovatore (talk) 04:15, 12 February 2013 (UTC)

The electron and positron existED once then annihilated each other getting just close enough to not exist forever? Then we must qualify what things exist with a time coordinate in order to be true or false right?68.36.148.100 (talk) 04:31, 12 February 2013 (UTC)

All very interesting thanks for your honest input. Does Empty space exist?165.212.189.187 (talk) 19:36, 11 February 2013 (UTC)

Yes, at least conceptually. So you can make meaningful statements about it. --Stephan Schulz (talk) 19:45, 11 February 2013 (UTC)

Interesting, I thought the current most correct answer to the question "does empty space exist?" was NO. Vespine (talk) 21:46, 11 February 2013 (UTC)

Thanks vespine, even more of a reason to include vacuum space as a critical component of the atom. There might be more going on in there than doesn't meet the eye. No?68.36.148.100 (talk) 01:18, 12 February 2013 (UTC)

• No, the statement is neither true nor false, but ambiguous. The correct statement is that "things that don't exist have no quantum state." μηδείς (talk) 03:09, 12 February 2013 (UTC)
  • Because it's the empty set; and while there are endless ways of grouping elements into different sets, there is only one set that contains no elements - namely, the empty set. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:22, 12 February 2013 (UTC)
    • Actually, ambiguous is probably too weak a term. Could you specify the quantum state of an atom with an atomic number of 500, and claim it has the same quantum state as a hydrogen atom inside a flask which contains only oxygen molecules? They'd both be descriptions of non-existent things. Things that don't exist don't have any identity at all--you can't then claim they do have the same identity. My not being a fire breathing dragon does not in any way make me the same as subtracting 37 from 51 while underwater or the dress size of last night's bad dream which are also not fire breathing dragons. μηδείς (talk) 04:35, 12 February 2013 (UTC)

I don't think your last point is relevant.68.36.148.100 (talk) 05:34, 12 February 2013 (UTC)

But what about things that once did exist but now don't, that is categorically different than "never proved to have ever existed", or "figment of your imagination" because you can describe it as having existed prior to X time, which is part of its identity forever, is it not? Once you designate "existing-thing-to-non-existent-'thing'" the description is precisely and only that, and it is exactly the same for all things that exist then cease to exist.165.212.189.187 (talk) 15:15, 12 February 2013 (UTC)

The passage of time doesn't "erase" existence as if something never had existed. You just have to keep your tenses straight, and you'll notice that the language I just used is perfectly common English. But you cannot say that the current King of France is the same as a three-inch flying unicorn because they both don't exist. μηδείς (talk) 02:02, 13 February 2013 (UTC)

This: The passage of time doesn't "erase" existence as if something never had existed. is MY point. But to further my point notice the "used-to-exist" vs. "figment of imagination" argument. You said yourself that a detailed description of non-existent things don't define those "things". I would liken your use of current king of France and the 3 inch unicorn to gibberish and then say that they are both categorized as such. 165.212.189.187 (talk) 15:37, 13 February 2013 (UTC)

If that's a question, I don't understand it. μηδείς (talk) 04:36, 15 February 2013 (UTC)

What if its a statement? then would you understand it?165.212.189.187 (talk) 21:15, 15 February 2013 (UTC)

Geological change in recorded history

It is a known fact that Earth has undergone continuous geological changes throughout its history and the process is ongoing. I'm wondering whether there have been any visible geological change in recorded history? --PlanetEditor (talk) 17:04, 11 February 2013 (UTC)

I saw a documentary a while ago about post-glacial rebound. They interviewed an old woman, who had lived her whole life in the same place (it was either in northern Sweden or in Finland). They went to the house she had lived in as a child; she said that then the family rowing boat was tied up right outside the window. Now the ground had risen such that the water's edge was about 10 metres (horizontally) from the house. This paper gives the rate of rebound in Skellefteå at nearly 1cm/year; given that there was maybe 80 years between the woman's early recollection and the documentary being made, that's consistent with the land on which her house stood being maybe 80cm higher than when she was a little girl. This is a geological (and not just a local) phenomenon, as all of Britain and Fennoscandia is tilting in this manner (the woman just lived somewhere where the effect was particularly high, and particularly evident). So that's not just recorded history, that's living memory. -- Finlay McWalterჷTalk 17:30, 11 February 2013 (UTC)

Changes due to Earthquakes and Volcanoes qualify, don't they? Mingmingla (talk) 17:44, 11 February 2013 (UTC)

I don't think so. Volcanoes, for example, have only limited effect in a limited region without significant and large-scale stratigraphcal change. In that sense, mining activities by humans will also count as geological change. --PlanetEditor (talk) 18:01, 11 February 2013 (UTC)

Geological change happens at all scales from planetary to atomic. Sean.hoyland - talk 18:09, 11 February 2013 (UTC)

Will 1964 Alaska earthquake qualify? The earthquake was accompanied by vertical displacement over an area of about 520,000 square kilometers. .... Vertical displacements ranged from about 11.5 meters of uplift to 2.3 meters of subsidence relative to sea level. Off the southwest end of Montague Island, there was absolute vertical displacement of about 13 - 15 meters. .... This zone of subsidence covered about 285,000 square kilometers, including the north and west parts of Prince William Sound, the west part of the Chugach Mountains, most of Kenai Peninsula, and almost all the Kodiak Island group. [6] Ruslik_Zero 19:00, 11 February 2013 (UTC)

Even more dramatic, and more recent, was 2004 Indian Ocean earthquake and tsunami. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:51, 12 February 2013 (UTC)

Thank you guys for clearing my misconception. --PlanetEditor (talk) 02:37, 12 February 2013 (UTC)

More volcanic changes: 1883 eruption of Krakatoa, check the map in the infobox. Surtsey didn't exist before 1963. Today it's the size of a small village. The 1980 eruption of Mount St. Helens took out the top and one face of the mountain. There's some nice before-and-after pictures in the article. The Minoan eruption of Santorini is a likely source of the Atlantis legend. Look at the map: That used to be one complete island, similar to Krakatoa. Look at the Hawaiian Islands. Those are merely a string of islands created by the Pacific plate dragging across a giant volcano which has been erupting more-or-less constantly for millions of years. The Big Island's shape has changed considerably over the past few millenia. --Jayron32 04:46, 12 February 2013 (UTC)

In fact, the crater at Halemaumau has changed its shape in the last thirty years. We have photographic evidence of it being a different shape prior to volcanic activity in the 1970s and 1980s. And we have drawings and records from the previous century that describe and depict even more dramatic shape-changes. Perhaps some of the most stunning video-recordings are the eruptions of the 1950s, culminating with the 1959 eruption in which thousand-foot-tall mountains of lava burst out of the ground. We also have an article on the former island Jolnir, and on the cornfield-volcano Parícutin; and even non-seismic geological events like the subsidence of California's central valley... and the list goes on. There's no shortage of geological change that has happened fast enough for humans to watch and photograph and record it! Nimur (talk) 06:05, 12 February 2013 (UTC)

• The course of the Nile has changed over the centuries and its navigable mouths have had to be resurveyed and charted.
• The Tigris and Euphrates used to flow separately into a much longer Gulf of Arabia which has silted up over the millennia.
• The course of various rivers such as the Mississippi River have changed so much in recent centuries that bits of land from various states have ended up on the other side of the river from their mainland. See New Madrid Earthquake.
• Iceland when the Vikings arrived and much of the Levant even during Roman times was green or forested until goats got to them.
• According to the oral history of the Nivkh people, Sakhalin Island was a peninsula until well after the founding of the Chinese Empire, when rising sea-level broke through at the Amur River outlet, severing it from the Eurasian mainland.
• The town of Calais used to be English til the French had it towed to the other side of the Channel by Napoleon.

μηδείς (talk) 02:56, 12 February 2013 (UTC)

Is the last one really true? Sagittarian Milky Way (talk) 04:31, 12 February 2013 (UTC)

Is your lack of a sense of humor real? --Jayron32 04:38, 12 February 2013 (UTC)

Of course it's nonsense! Everyone knows that Napoleon lived in the 18th and 19th century, while Calais was towed over to France under Henry II in 1558. France didn't even have real galleys for the towing around 1800. But you can still see where Calais broke off. --Stephan Schulz (talk) 11:05, 12 February 2013 (UTC)

Jist wannit a make sher youse guys was payin a tension. μηδείς (talk) 21:00, 12 February 2013 (UTC)

There was a hell of a lot going on in Chile in 1960 (don't be fooled by the title, it was way more than just one event). I still remember news reports, saying the entire Chilean coast would have to be redrawn. -- Jack of Oz ^[Talk] 02:10, 13 February 2013 (UTC)

Splitting water with a vacuum

Suppose you have a small icy asteroid you'd like to terraform. You wrap it securely in a watertight membrane that reflects infrared light, you put a large tinfoil dish at the L2 point behind it to focus the sunlight, and the chunk of ice and rock turns into a mini planet with a warm water ocean, maybe some ammonia. Great, except... no air, only some water vapor. So you fenestrate your membrane with little holes that let hydrogen seep through freely, and do anything you can to make the membrane kinetically catalyze the equilibrium 2H2+O2 <-->>>>> 2H2O and the same for ammonia (but easier for that, I should think). Logically, the hydrogen should go out through the holes and never be seen again.

Now, I can read from electrolysis of water that it takes "286 kJ of electrical energy input to dissociate each mole", i.e. 16 kJ per gram of water (MW 18). Work done by pushing water through a pressure differential should be delta P * V, i.e. for one cc (gram) of boiling water (1 atm = 100 kPa to 0 atm) it would be 100000 kg/ms^2 * 0.000001 m^3 = 0.1 kgm^2/s^2 = 0.1 J. Harrumph. If I'm right, that's amazingly disappointing!

Yet my feeling is that it should happen anyway - that there should be some equilibrium value for hydrogen pressure outside the membrane. If it were encapsulated by a second membrane, then it would build up to some miniscule value and eagerly react and reenter. But it's not - the moment one molecule of H2 gets free it should head for deep space and never be heard of again. Which is weird - it's as if I expect some additional work to be done on the water by "extracting" the lack of entropy from deep space.

Where am I going wrong here? And, yes, can we actually make comfy little planets this way? Wnt (talk) 17:31, 11 February 2013 (UTC)

Wouldn't it get colder? You are essentially allowing a gas to expand which will get colder, and eventually stop the hydrogen escaping. The sun heats it up though, so that's your energy source. Ariel. (talk) 18:56, 11 February 2013 (UTC)

Hmmm, I was thinking the hydrogen could get cold "out in space" and not affect the inside of the membrane, at least conceptually, though I don't actually know if that is possible even in theory. On second thought though, I suppose that the "very rare molecules" that would somehow manage to spontaneously split in equilibrium must be at the very highest energies present in the Boltzmann distribution - and that kinetic energy would be the source of the energy to break the chemical bonds. Once removed, the liquid as a whole gets cooler. Yes, I think that might just be the answer - I'm actually using the heat, not the pressure, to split the water. Wnt (talk) 05:28, 12 February 2013 (UTC)

Can you elaborate on your calculation? As stated it makes no sense to me. What are you calculating? Dauto (talk) 21:20, 11 February 2013 (UTC)

I was calculating the amount of energy needed to split a gram of water, versus the amount of energy that should be produced if the gram = cc of water is pushed out under pressure. True, only the hydrogen actually is supposed to be pushed out ... but it was such a low number I didn't try to figure out that detail. I'm not sure it's the right way to do that calculation anyway... Wnt (talk) 05:24, 12 February 2013 (UTC)

tube amplifers

looking for information on how to build a simple tube amplifer — Preceding unsigned comment added by 98.235.151.172 (talk) 18:12, 11 February 2013 (UTC)

D-d-d-danger! High Voltage! [7][8][9] don't come crying to us when you electrocute yourself to death ;) ---- _nonsense ferret 18:27, 11 February 2013 (UTC)

I suggest you google it or visit your local library. Ratbone 120.145.64.230 (talk) 01:21, 12 February 2013 (UTC)

The "Bear Scout" handbook (US Cub Scouts) in the 1950's had a schematic for a simple 1 vacuum tube radio for children to build, which used a tube intended for portable radios powered by dry cell batteries. I doubt that it used a very high plate voltage. I have used several 9 volt batteries connected in series for the plate supply to run an amplifier using early tubes such as the UX201A . If I recall correctly it was designed to run on a 90 volt plate supply but would also work as low as 45 volts. Note that even these voltages can cause dangerous shock. Some tube will provide some amplification down to 22 volts of plate voltage, though the amplification may be low. Most schematics on the internet seem to be for "modern" 1960's high power-high fidelity amplifiers, with very high plate voltages, Libraries might have "Radio physics course" by Alfred Ghirardi (1933) which includes diagrams for simple low power low fidelity inefficient amplifiers with early tube types (which can be bought on Ebay). Edison (talk) 04:20, 12 February 2013 (UTC)

Depending on your focus; if you are more interested in the amp part than the building part (i.e. if you just want to try "tube sound" or something) the easy way is to get an old tube type radio and feed signal in to the volume control, via a capacitor. Gzuckier (talk) 06:19, 12 February 2013 (UTC)

Ah the good old days when I converted a television into a monitor with sound and without the need for the UHF stage. Seriously though even when you switch off and unlug the power you can get a nasty shock because of capacitors, if you have to fiddle with it while switched on make sure you keep one hand behind your back and keep insulated - and don't blame us if you use high voltages and kill yourself. BTW a concrete floor can conduct, use rubber shoes or a rubber mat to stand on. Dmcq (talk) 10:23, 12 February 2013 (UTC)

And of course those ubiquitous 5 tube table radios had the chassis connected directly to one side of the AC plug; and zillions of them were made for decades before the polarized AC plug/socket appeared (in the US anyway). Well, that's a 50/50 chance, anyway.Gzuckier (talk) 15:50, 12 February 2013 (UTC)

If you Google "tube amplifier kit" there are lots of them available for a few hundred dollars. To build a basic 1 tube audio amp circuit as a demonstration, the 1T4 pentode is popular, with a 1.5 volt filament and a typical plate voltage of 45 volts (still a dangerous voltage, so caution is required). The tube itself is readily available for a few dollars. Googling "1t4 tube amplifier" will show many example circuits. Edison (talk) 15:14, 12 February 2013 (UTC)