Wikipedia:Reference desk/Archives/Science/2008 January 30

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January 30

dissapation of light

seriously how come if you were to put a candle in the middle of a dark place(room,ally hallway) it would not illuminate the entire area is it simply because the light is not powerfull enough or is it because it really dissapates,but i always thought that matter can't be destroyed just changed —Preceding unsigned comment added by Gotnse (talk • contribs) 00:01, 30 January 2008 (UTC)

Who says it doesn't illuminate the entire area? Try these experiments:

1. Place a lit candle at one end of a dark hallway. Stand at the other. Can you see the candle flame? If so, photons from the candle flame are making it all the way down the hallway.
2. Place a bicycle reflector on the wall at the other end of the hallway from the candle. Stand next to the candle. Can you see red glints from the reflector at the other end? If so, photons are making it down and back.
3. Stand at the other end of the hall from the candle, with your back to the candle. With your eyes completely adjusted to the dark, stare intently at the (ideally white) wall. Have an assistant block the light from the candle at some point, without telling you. Can you see a change?
4. Again at the other end of the hall from the candle, and with your eyes completely adjusted, see if you can see the shadow of your hand on the wall.

I'm not sure if numbers 2, 3, or 4 will work, but I can assure you that the candle does "illuminate" the whole room, even if it's not enough illumination to, say, read by.

See also this previous question. —Steve Summit (talk) 00:31, 30 January 2008 (UTC)

Well, it will only "illuminate" things it hits and bounces back off of into your eye. So although it looks like the light it dissipating its jut not bouncing off shit. —Preceding unsigned comment added by 69.159.193.94 (talk) 04:53, 30 January 2008 (UTC)

In re matter can't be destroyed just changed - light isn't matter. --Ouro (blah blah) 08:57, 30 January 2008 (UTC)

And besides, matter can be destroyed: e=mc² and all that. As far as the primary question, though "isn't powerful enough or dissipates" is a bad use of "or". The candle isn't powerful enough (for a specific application, such as reading a book) because its intensity dissipates as a function of the cube square of distance (surface area of a sphere). Other respondents will note that "because" isn't exactly the right word, but I hope it conveys that your two criteria are not exclusive and in fact are quite related. — Lomn 14:10, 30 January 2008 (UTC)

You mean square of distance, right? Algebraist 16:34, 30 January 2008 (UTC)

Oops, yes. Typed SA, thought volume. — Lomn 19:19, 30 January 2008 (UTC)

What's interesting is how the fourth power of distance is relevant in some cases and senses. If you have a diffuse reflector of a fixed size, and you're near the source of the light (e.g., a building being illuminated by your car's headlights), then the total light you see reflected by the object is inverse quartic. But since the apparent size of the object drops as the inverse square, the brightness falls off only quadratically as well. See also Lambert's cosine law, where cosines and distance interact in a similar fashion. --Tardis (talk) 17:28, 30 January 2008 (UTC)

Best way to destroy an old, (almost) non functional hard drive?

I replaced one of my drives today. The old drive was giving me lots of read/write errors and was making a grinding noise all the time and I was unable to securely erase the contents before I removed it. What's the best way to render it completely non-functional and/or make the contents non-recoverable to your average bin-raiding identity thief, given that there is quite a bit of personal information/private correspondence stored on it and it does occasionally still sort-of-work.

I'm not going to blast it with a shotgun and I don't have the facilities to melt the thing, before anyone suggests that... --Kurt Shaped Box (talk) 00:10, 30 January 2008 (UTC)

If it's in the middle of a head crash, you don't have all that much to worry about; why not just let it keep ruuning until it totally trashes itself? But if you like here are two other possibilities:

• Take your Torx screwdriver, disassemble the drive, and turn the platters into ornaments or throw it all in the metal recycling bin at your local dump/landfill/tip.

• Take your electric drill and about 3/4 of an inch out from the center of the spindle, drill a hole straight through the drive. If anyone attempts to run the drive, the hole will rip all the read-write heads off of their gimbals.

Other folks have suggested other creative means in past Reference Desk posts.

Atlant (talk) 00:20, 30 January 2008 (UTC)

I've found smashing it with a large hammer to be both effective and enjoyable. Someguy1221 (talk) 00:26, 30 January 2008 (UTC)

Like Someguy1221, I used a sledge hammer on an old drive from a school (containing both staff and pupil records). I can recommend this as a stress-relieving activity.dbfirs 16:08, 30 January 2008 (UTC)

after edcon

Open it up (using screwdriver, spanners, pliers etc), take out the platters,(made of aluminium) and

a)Put them through a bulk degmagnetizer that they use to have for magnetic tapes (could also try a hand held head demagnetizer).

Or, b) you could try putting the platters in the microwave oven (CAUTION: I dont know what gases might be given off so perform at your own risk).

Or, c) you could take out the platters and sand them down with emery cloth etc (esp using a sanding attachment to an electric drill). That should make 'em pretty hard to read!

Or,d) you could put the platters individually into your lathe, and cut off the magnetic coating with your tool.

Or,e) you could take the platters and just cut them into pieces with your hacksaw or tin snips.

Or f)you could just file across the platters with your big file.

Or g) maybe you could just torch the platters with your blowtorch (gas warning again)

Or.......--TreeSmiler (talk) 00:29, 30 January 2008 (UTC)

(ec) How resistant to heat is the magnetic stuff? Maybe bake it in a hot oven? DuncanHill (talk) 00:30, 30 January 2008 (UTC)

It will lose its magnetism beyond the Curie temperature but magnetism will then return when the magnetic material cools down. Whether the data will still be there is a very interesting question.--TreeSmiler (talk) 00:37, 30 January 2008 (UTC)

Definitely open it up. Supposedly those platters are quite pretty. (I've got a drive I've been meaning to do this with, containing tens of thousands of imperfectly-erased customer records, including credit card numbers 'n' stuff.) —Steve Summit (talk) 00:48, 30 January 2008 (UTC)

They are very flat and very reflective (if uncrashed). For people like me (who are easily amused), you can have a lot of fun just sticking two platters together and peeling them apart; because of their amazing flatness, that can be surprisingly hard to do.

If they're crashed, they can still be attractive but in a "surface ground" sort of way. But crashed disks can also be very dusty and the very fine dust can be as annoyingly hard to remove as toner.

By the way, most disk drives will still spin up and run, at least for a little while, once opened up. But if they're in the midst of crashing, please beware of high-speed flying ejecta (such as the heads!) from the disk drives.

Atlant (talk) 12:56, 30 January 2008 (UTC)

1. Smash it with a hammer a couple of time's 2. Drive to the nearest lake 3. Weigh it down and throw it as far as you can 4. ??? 5. PROFIT! 2. w —Preceding unsigned comment added by 69.159.193.94 (talk) 04:55, 30 January 2008 (UTC)

Put them on gravel and drive over them a few times? No car? ask a friend. Julia Rossi (talk) 07:20, 30 January 2008 (UTC)

Wouldn't it be enough to take out the platters and fly over them with a permanent magnet a few times (so as not to damage the platters visually, because they are nice)? —Preceding unsigned comment added by Ouro (talk • contribs) 08:18, 30 January 2008 (UTC)

Yeah, I forgot to sign, sorry. --Ouro (blah blah) 08:21, 30 January 2008 (UTC)

I think the only question this posting has demonstrated is, "How do I not destroy my hard drive?" x42bn6 Talk Mess 13:09, 30 January 2008 (UTC)

Bruce Schneier's classic book Applied Cryptography begins "There are two kinds of cryptography in this world: cryptography that will stop your kid sister from reading your files, and cryptography that will stop major governments from reading your files. This book is about the latter". But let's be honest here, Gull Man: you just need to keep out your kid sister. I'd say if you were to just poop on it and throw it in the trash, there is almost surely no chance of it ever being touched again. --Sean 14:18, 30 January 2008 (UTC)

Open the drive, remove the disks and file them down by scratching them on concrete or the road.--155.144.251.120 (talk) 22:57, 30 January 2008 (UTC)

Nuke it from orbit, it's the only way to be sure. Cheers, WilyD 23:05, 30 January 2008 (UTC)

(after edit conflict) Wow. This is a busy thread. Who knew that gratuitous violence against electrical devices was so popular these days? ;) Thanks muchly for all the tips. However I end up disposing of it (the prospect of getting to use poo for a useful purpose is an intriguing one), I think I'll open the thing up to take a look inside first. I always just figured that the contents were a thicker version of the matter you'd see inside a floppy disc. --Kurt Shaped Box (talk) 23:11, 30 January 2008 (UTC)

If you are looking for another useful purpose for poo, you may be interested in humanure. DuncanHill (talk) 23:20, 30 January 2008 (UTC)

I've always considered flinging poo to be the earliest (and most basic) debating technique. --Kurt Shaped Box (talk) 23:34, 30 January 2008 (UTC)

The best way to destroy a hard drive beyond repair is to save the only copy of your most important file on it. Second best is any of the following: smashing it with a stress-relief device, covering the disk in a pretty substance, running it through a shredder, or throwing it in an Aperture Science Emergency Intelligence Incinerator.-RunningOnBrains 10:29, 1 February 2008 (UTC)

Open it up. Plug it in. Turn it on. Wait. Repeat as necessary. If this fails touch drive with whatever you feel like. —Preceding unsigned comment added by Shniken1 (talk • contribs) 15:22, 1 February 2008 (UTC)

Put it in a plain box, store somewhere safe, and wait for entropy to run its course. SpinningSpark 22:52, 1 February 2008 (UTC)

(undent)However original you all think you have been . . . YouTube was there first [1], done it, filmed it. I particulary liked the comment "thermite is always the answer", but then again, YouTube is not trying to answer such a wide range of questions as the Science Desk. SpinningSpark 23:14, 1 February 2008 (UTC)

I've always just writen over every sector, taken the drive apart, taken out the neodymium magnets, wiped them across the platters then scored them up with a screw driver or something abrasive. I have read that with modern harddrives just over writing the data is enough to make recovery very difficult. I guess the word "difficult" depends on who you and a little mindless violence towards technology is great therapy for the frustrated modern day man. A word of warning, the smaller 2.5inch disks used in laptops that I have destroyed contained glass platters yet look metallic - if you pry them or treat them too rough they will "energetically disassemble" into small sharp pieces! —Preceding unsigned comment added by 78.32.138.240 (talk) 19:08, 2 February 2008 (UTC)

Magnet, Hammer, Drill, Saw, or (if you feel like a bit of fun) Microwave. Two words: "Tesla Coil" Ilikefood (talk) 22:07, 6 February 2008 (UTC)

It's not as fun, but I suggest recycling it. There are local computer recycling places that take that sort of thing and either re-use it or strip it into components and recycle it. It would be worth looking into.

Of course, you could always remove the neodymium magnets and then give it to the recyclers. —Remember the dot ^(talk) 22:11, 6 February 2008 (UTC)

s z qasim

who is s z qasim?Zikrullah (talk) 11:35, 30 January 2008 (UTC)

My Googling tells me he is supposed to be a scholar devoted to studying ocean ecosystems, the Indian Ocean in particular. We don't have an article on him, though. --Ouro (blah blah) 12:49, 30 January 2008 (UTC)

CPR

Is is possible for a person perform CPR on them self to jump start their heart? —Preceding unsigned comment added by Hyper Girl (talk • contribs) 11:42, 30 January 2008 (UTC)

How would you go about moving your arms and applying force to your own chest while unconscious? --Ouro (blah blah) 12:45, 30 January 2008 (UTC)

Apparently, by coughing: Cpr#Self-CPR jeffjon (talk) 13:48, 30 January 2008 (UTC)

I don't see how you can even cough... Your heart can beat without you breathing (although not for long), but you can't breathe if your heart isn't pumping. Once your heart stops pumping, or goes into fibrillation, you go unconscious within a matter of seconds. -- MacAddct  1984 ^{(talk • contribs)} 15:10, 30 January 2008 (UTC)

The CPR article briefly mentions the idea of self-cpr, but says it's largely hoax and myth. CPR#Self-CPR APL (talk) 13:53, 30 January 2008 (UTC)

But you can give yourself the Heimlich Maneuver, so if you're on your own it's advisable to choke on something rather than have a heart attack. --Sean 14:20, 30 January 2008 (UTC)

Surely this is a very nice paradox. If you can perform CPR on yourself you don't need it. Can I claim this as "Avery's Paradox" Richard Avery (talk) 16:21, 30 January 2008 (UTC)

It's like when someone tells you they're choking, they're not really choking. I think Mr. Liar already beat you to it, calling it the Liar paradox. -- MacAddct  1984 ^{(talk • contribs)} 16:51, 30 January 2008 (UTC)

.. with a touch of Catch-22 AndrewWTaylor (talk) 18:15, 30 January 2008 (UTC)

And even April Fools Day - it seems to be one of those weird questions I might have posted on APril 1. I would never do anything to the articles, but this seems like the best place to pul a funny little joke and asking a paradoxical question like that would be the way to do it. —Preceding unsigned comment added by DTF955 (talk • contribs) 21:47, 30 January 2008 (UTC)

Destroying matter

Is antimatter the only way matter can be destroyed and release energy (aka e=mc^2)? 64.236.121.129 (talk) 16:38, 30 January 2008 (UTC)

I guess theoretically. From antimatter: "mixing of matter and antimatter would lead to the annihilation of both in the same way that mixing of antiparticles and particles does, thus giving rise to high-energy photons (gamma rays) or other particle–antiparticle pairs. The particles resulting from matter-antimatter annihilation are endowed with energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original matter-antimatter pair, which is often quite large." -- MacAddct  1984 ^{(talk • contribs)} 17:28, 30 January 2008 (UTC)

No, both nuclear fission and nuclear fusion convert mass to energy. (Also, television destroys brain matter without any energy release.) Clarityfiend (talk) 19:16, 30 January 2008 (UTC)

No (with a possible yes). Nuclear fusion, nuclear fission, and even your generic chemical reaction all exchange energy for mass. If it's exothermic, then the mass of the end product is less than what you started with, and vice versa if endothermic. All of these can be accomplished without an antimatter reagent. As for the possible yes, it may be that at some quantum level all this is accomplished by short-lived antimatter particles -- I have no understanding either way, so I don't want to rule it out -- but I don't think this is the core of what you're asking. — Lomn 19:17, 30 January 2008 (UTC)

It's also probably the only way to get complete annihilation of matter - all the other methods have the energy release as part of a bigger process that produces more matter as well. Confusing Manifestation(Say hi!) 21:41, 30 January 2008 (UTC)

Fission and fusion don't create more matter—they end up with less matter, overall, in the end. "Annihilation" doesn't really get rid of matter, it just converts it totally into (various forms of) energy. So the answer is "no", but matter-antimatter mixing is certainly the most efficient way to convert matter into energy. --24.147.69.31 (talk) 23:36, 30 January 2008 (UTC)

Once fusion reaches iron, it requires an energy input and thus produces mass. As far as I know, though, you're correct about fission. — Lomn 06:02, 31 January 2008 (UTC)

How can that be so? Aren't fusion and fission inverse processes? Wouldn't the fission of elements lighter than iron also require energy input and produce mass? --NorwegianBlue ^talk 15:50, 31 January 2008 (UTC)

Beats me, though that sounds reasonable. I'm only aware of fission in the context of heavy elements, but perhaps this is why. — Lomn 16:55, 31 January 2008 (UTC)

Yes, that's correct. If you hit a light nucleus with a very energetic neutron you can fission it into even lighter nuclei, but the sum of the products' masses will be greater than the mass of the original particles. TenOfAllTrades(talk) 17:15, 31 January 2008 (UTC)

More generally, each kind of nucleus has a binding energy which you can think of as the energy released if you could start with all the component protons and neutrons, and "assemble" the nucleus from the pieces. Here is a graph. Note that the general trend of the curve is increasing towards the middle where iron is. That means in general, fusion of light elements and fission of heavy elements will yield energy (and lose mass). But note that the curve is bumpy in places, so the general rule doesn't always hold. JohnAspinall (talk) 21:31, 31 January 2008 (UTC)

Potential other ways to destroy matter are the black hole, the Big Crunch, the Big Rip. Graeme Bartlett (talk) 03:17, 31 January 2008 (UTC)

Auderiense

What could the name Leptictidium auderiense refer to? I have though of the possibility of it being a reference to the Aude department in France, but it's highly improbable due to the fact that this animal has been found only in Germany. Also, if it was the Aude, it would be something more like "audiensis", wouldn't it? What could it be? Thanks. -- Leptictidium (mammal talk!) 17:24, 30 January 2008 (UTC)

While I don't wouldn't to encourage crossposting, you may actually be better off posting on the Language Reference desk. -- MacAddct  1984 ^{(talk • contribs)} 17:31, 30 January 2008 (UTC)

Thanks, I will do that. I was hoping some expert in paleontology could give me an answer here. -- Leptictidium (mammal talk!) 19:51, 30 January 2008 (UTC)

How far into the ear canal is the ear drum located?

^topic 64.236.121.129 (talk) 20:55, 30 January 2008 (UTC)

The ear canal is approximately 26 mm long, with the ear drum located at the end of that, as discussed in the ledes of the articles. — Lomn 21:11, 30 January 2008 (UTC)

Actually only the ear canal article says "approximately 26 mm", thus immediately showing that the number is untrustworthy. The other one doesn't say.

The old edition of Gray's Anatomy available at bartleby.com says here that the distance along the ear canal (external acoustic meatus) from the bottom of the concha (the central cavity of the external ear) to the tympanic membrane (eardrum) is about 2.5 cm (25 mm), or from the tragus (the little flap you can press on to "close" your ears) to the eardrum, about 4 cm (40 mm).

--Anonymous, 00:18 UTC, January 31, 2008.

I fail to see how no discussion equates to "untrustworthy". The eardrum article doesn't mention earwax either (ear canal mentions it in the context of the eardrum); is its existence likewise in doubt? Nonsense. Now if one article said 26mm and the other said 1cm, there might be a trust concern -- but they don't, so there isn't, particularly when Gray's agrees to within 1 millimeter -- a number I suspect is well within the range of normal human variation. — Lomn 05:59, 31 January 2008 (UTC)

No, it's "approximately 26" that implies untrustworthiness. It's an obvious case of false precision and therefore implies that the passage was written carelessly. --Anon, 23:48 UTC, Jan. 31.

I would disagree that two significant digits are an obvious case of false precision. Perhaps the text can be more clear, but that does not throw its veracity into doubt. — Lomn 22:39, 1 February 2008 (UTC)

Pet Parrots need 12 hours or more sleep a night?

Is this true? The internet seems to think so. My macaw (hyacinth) doesn't get anywhere near that. She lives with me in a one room flat, so she's pretty much awake when I am (she's usually awake before me, I guess when she hears the birds singing outside). Will this be affecting her health? I've had her for many years and she seems okay. Thanks for the tips about macaw training by the way (the question I asked a few days ago). --84.66.26.102 (talk) 23:51, 30 January 2008 (UTC)

I would think that parrots are like humans in that they probably need so many hours of sleep (8 for us) but many people get by fine with less. I haven't had a good 8 hours sleep in absolutly ages. Could it be that she is sleeping at times other than whenshe normally sleeps as well? TheGreatZorko (talk) 08:46, 31 January 2008 (UTC)

It seems this may explain it. One part of the brain can sleep while the other is awake. TheGreatZorko (talk) 08:54, 31 January 2008 (UTC)

(after edit conflict) 12 hours seems like a lot. I don't know how accurate that is - there's a lot of birdcare advice on the internet that's not really worth much. My experience with parrots tells me that they'll sleep when they're tired. If she's alert and wanting to play/hang out, then she's not tired. --Kurt Shaped Box (talk) 09:08, 31 January 2008 (UTC)

Pet carrot = Parrot? LOL - reminds me of a personal joke where Bone marrow = Barrow. Sandman30s (talk) 11:30, 31 January 2008 (UTC)

Looks like an annon user went and changed the title. I put it back.

Easily confused: see Robert W. Wood's How to tell the Birds from the Flowers (specifically, HOWTO05.GIF). --ColinFine (talk) 00:24, 4 February 2008 (UTC)

feel like crap

What causes the really bad feeling while being sick, such as having the flu or common cold? You know when you get out of bed to take your medicine and you go "ugh... I feel like crap!" and take your meds and go back to sleep. I hope someone know's what I'm talking about. schyler (talk) 23:54, 30 January 2008 (UTC)

Ah, malaise! - Carbon ^[Nyan?] 23:58, 30 January 2008 (UTC)

I have the notion that it's interferon that makes you feel like that, and that the reason it makes you feel like that is precisely so that you will go back to sleep, conserving energy for the immune response. But I'm not really sure about either part. --Trovatore (talk) 00:02, 31 January 2008 (UTC)

Yep. That's it. Thanks. schyler (talk) 00:36, 31 January 2008 (UTC)

It is prostaglandins, that's also the reason why non-steroidal anti-inflammatory drugs help against that sicky feeling. Prostaglandins are probably downstream of interferon. Сасусlе 04:30, 31 January 2008 (UTC)