Wikipedia:Reference desk/Archives/Science/2010 September 28

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September 28

Through-glass photography

I would like to take photographs of my fish and assorted gastropods with my 7D 780 digital ELPH but find that the flash wipes out the object because of the glass and it's all way too dark without the flash. I tried taking a video and then taking pause shots from it, but they are not so clear. Any suggestions? DRosenbach ^{(Talk | Contribs)} 00:45, 28 September 2010 (UTC)

You could experiment with a polarization filter. To get rid of the reflection you need to look at the object from about 50° angle from the normal. It's explained in the Brewster's angle article. You could also try to put a polarization filter in front of the flash light to get even beter results. Count Iblis (talk) 01:06, 28 September 2010 (UTC)

(edit conflict) Sounds like a polarizer might help: Polarizing filter (photography). WikiDao ☯ (talk) 01:08, 28 September 2010 (UTC)

It seems to me much simpler to get some light pointing inside the aquarium and using a tripod, and no flash at all. The tripod allows you to shoot at slower shutter speeds, presumably the fish are not moving so fast that you cannot get shots that way. They might blur if they are moving faster than they usually do, but should be all right if they aren't. You will need to be careful not to just get reflections and glare from whatever light you point inside the aquarium, of course, and you may need to use faster "film speed" or whatever they call it in this digital age...

rc (talk) 01:49, 28 September 2010 (UTC)

If you need flash to take photos it'd be way too dark to use polarisers (-2-3 stops just by itself). Plus polarisers are not perfect and the extra flash power needed for the same exposure will offset any gains you get from a polariser. Get your lens right next to the glass surface to get rid of all reflections, then you can use flash all you want (unless it's prohibited). But yea, I second Ralphcook. Flash is no match to proper lighting inside the aquarium. --antilived^{T | C | G} 10:21, 28 September 2010 (UTC)

A remote flash will change the angle of the flash, so that it will be less visible to the camera. Covering it in thin white gauze will reduce the peak brightness and also reduce the reflection. Can't you use studio lights so that you don't need a flash? CS Miller (talk) 10:31, 28 September 2010 (UTC)

You can also sometimes avoid flash by opening up the aperture and increasing the ISO and slowing down the shutter. I dislike flash, so I typically push all three of these close to the limit. I get a lot of blurry or grainy pictures, but some of them come out looking nice, even in relatively low light. Paul (Stansifer) 14:03, 28 September 2010 (UTC)

Sorry to say, but if you ever thought of needing a flash it's not a job for a compact camera (at least, not right now). Built-in flash is out of question for fish photo - even if polarizers would work, the horizontal light will flood the scene in a most unpleasant way. The normal colours of the fish will be washed out in reflections from their scales, etc... Beef up your normal, top-mounted light. The amount of light recommended for intensive plant growth usually allows decent no-flash exposure times at low ISOs - assuming, of course, that the water is clear and the fish aren't too agile. East of Borschov 02:50, 29 September 2010 (UTC)

Earth's surface

After recalling something I heard years ago regarding a gyroscope so perfectly round that if it was scaled to the size of the earth, the tallest mountains and deepest ocean trench would measure only 2.4 m high (from here), I got to thinking about going the other way. That is, how rough/smooth would the earth be if it was scaled to the size of a tennis ball? Any ideas? Thanks, Mark 150.49.180.199 (talk) 01:11, 28 September 2010 (UTC)

Earth's radius: 6371 km

Mt. Everest: 8848 m

Tennis ball radius: 66 mm

"mini-Everest": ((66 mm) * (8848 m)) / (6371 km) = 92 microns

WikiDao ☯ (talk) 01:25, 28 September 2010 (UTC)

you'd have to include the mariana trench which is deeper (11km) then Everest is tall,so the total delta of earth surface is about 20000m, which makes the above about 200 microns, or 0.2mm. A similar anecdote I heard was that to scale, the earth is smoother then a billiard ball. Vespine (talk) 01:42, 28 September 2010 (UTC)

I just did a quick google and it looks like the billiard ball thing isn't quite true but it isn't far off. Vespine (talk) 01:44, 28 September 2010 (UTC)

Of course, if you want to consider how far the Earth is from being spherical rather than how rough its surface is, then you have to account for the variation between the equatorial and polar radius, which is about 0.35%. Your tennis ball with radius 66 mm would be nearly half a millimeter wider at the equator than through the poles. --Anonymous, 04:40 UTC, September 28, 2010.

OOB/Armaments question - NATO choppers and recent airstrikes into Pakistan

Read an interesting article today about NATO air assets based in Afghanistan flying into Pakistani airspace to return fire after receiving "direct small arms fire" from ground forces there. This left me with two questions, unfortunately neither of which were answered in the article - (1) What sort of helicopters are we talking about? (2) What is the risk of "direct small arms fire" to modern attack/assault gunships? I'm assuming they're firing AK-47s or other variants? The Masked Booby (talk) 01:23, 28 September 2010 (UTC)

Here's a list of military aircraft that have crashed in Afghanistan, which gives a general sense of what's being used over there (and how often different things get shot down, as opposed to just crashing; no comment on specific tactical vulnerabilities;). WikiDao ☯ (talk) 02:05, 28 September 2010 (UTC)

Articles I have read identified them as Apache helicopters - and while all the articles made a point of never identifying their national owners, one article pointed out that only the U.S. uses Apaches. [1] —Preceding unsigned comment added by 75.41.110.200 (talk) 13:03, 28 September 2010 (UTC)

On a side note, NATO later backpedaled and said that the helicopters hadn't actually entered Pakistani airspace, only their rockets had. :) --Sean 15:19, 28 September 2010 (UTC)

The AH-64 Apache article says it is designed to remain flyable after taking fire from one of these, which is well beyond small arms fire. --Sean 15:25, 28 September 2010 (UTC)

Cigarettes

Do cigarettes cause gynecomastia —Preceding unsigned comment added by Kj650 (talk • contribs) 02:00, 28 September 2010 (UTC)

It appears that it is commonly believed that smoking marijuana may be positively correlated with the development of gynecomastia ([2]). I found one small study that failed to find any correlation, though the sample size was tiny, so I wouldn't read to much into it ([3]). I have seen no evidence that smoking tobacco is correlated with gynecomastia. Buddy431 (talk) 03:12, 28 September 2010 (UTC)

How proteins really work

I've learned that a protein's function is tied to its specific shape, but looking at models of proteins, they just look like coils of twine. If I take several coils of twine and put them in a box and shake them up, they'd all just be a big mess of knots, with each piece of coiled twine being no more or less jumbled, regardless of how I bent it at the outset. So, how the heck do proteins function as a result of their shape? What am I missing?

Are there any dynamic models out there, showing protein interaction, as it happens? ☯  Zenwhat (talk) 02:22, 28 September 2010 (UTC)

Wow. What you are missing is the very complex way they are "knotted" up. That is, while, say, myoglobin is a very complex, knotty looking structure, all myoglobin looks like all other myoglobins, and they all work the same. Also remember that in any given sample of a protein, you have billions of billions of billions of molecules, so imagine taking your long bit of twine, knotting it up to a very specific set of instructions, and then doing it again several billion times, exactly the same way. THAT is how proteins work. It is complex, but that's not the same thing as random. Articles you want to read to give you an overview are Protein tertiary structure and Protein quaternary structure and follow the blue links from there. The basic principle is that the folding of the protein you describe is actually predetermined by the exact amino-acid order (the protein primary structure). Specific amino acids cause certain types of folds and kinks in the chain. For example, proline has a ring structure which forces a very specific kind of bend, while cysteine will form disulfide bridges with other cysteines, which causes very specific kinds of folds. There are also acid-base effects based on local pH, for example Histidine is very sensitive to small changes in pH near physicological pH, and so its effect on the overall shape will change depending on the pH. This is just a very basic overview, what you are looking at is the way in which chains of hundreds of units, selected from among 22 or so building blocks, can not only be organized, but also how they interact with each other and their environment.--Jayron32 03:13, 28 September 2010 (UTC)

I have to say, screw things like "exact amino acid order" in these explanations -- that doesn't help people understand protein structure. You can reverse the amino acid order sometimes and it won't make a difference (sometimes amino acids are essentially just filler, meant to separate structures, etc.). But substituting a hydrophobic amino acid in the middle of a hydrophilic chain can drastically change things of course. John Riemann Soong (talk) 03:20, 28 September 2010 (UTC)

The secret lies in organic chemistry. If you want to talk about enzymes, the other amino acids provide a skeleton against which the active site amino acids can do their work -- act as acid, base, nucleophilic catalysts in a concerted reaction in a smoother transition state. Some proteins are very water-soluble don't have a shape until induced that way by another protein (these proteins are really hard to crystallise). Also, don't forget the proteins we know about tend to be proteins we've crystallised -- so we have a bias already. The coils are arranged in a very specific way sometimes -- determining how they can open up become a receptor, or fit snugly inside another protein.

But they are not in fact rigid structures and this is often key to their structure. John Riemann Soong (talk) 03:20, 28 September 2010 (UTC)

Another thing with proteins is that it's like they have little "magnets" inside them, and the proteins will only stick together if the magnets match up exactly with the magnets on the receiving protein. The complicated shape, plus the positioning of the magnets means that proteins will only lock together with exactly the right target. So it's not like random coils of twine, it's carefully matched sets. Ariel. (talk) 03:26, 28 September 2010 (UTC)

We have an article, protein folding, that ought to be helpful here. Looie496 (talk) 03:28, 28 September 2010 (UTC)

You may want to check out the article on sickle cell anemia, or more specifically, the 3rd paragraph of the genetics section. It's written with too much scientific gobble-de-gook, but in essence, it's stating how a single point mutation that causes a single amino acid change can lead to such drastic results because of the so called "sticky patch" that it causes when two regions of hydrophobic amino acids are now able to be exposed to each other. DRosenbach ^{(Talk | Contribs)} 04:12, 28 September 2010 (UTC)

I think that the answer to your question is that proteins don't act like twine; they're too "slippery" to really "knot" in a macroscopic sense. For example, I've never heard of one end of a carbon chain getting shoved through the hole in a benzene ring and getting snagged in there - it just doesn't work like that. Effects like "quantum tunneling" and the Heisenberg uncertainty principle mean that with enough energy one thing can slip right past or right through another if it has to, though I don't think the covalent chains actually cross through one another with any appreciable frequency.

Also bear in mind that molecules move really, really, really fast relative to one another. Of course, that's because it's actually a very small distance. But to consider the kind of witchcraft molecules are capable of, you can take a little oligonucleotide primer and put it in with an entire 3 billion base human genome, give it two minutes or so to "anneal", and there it is: stuck fast to the one exact complementary sequence in the entire freaking human genome. (Well, at least, that's the theory... generally some repetitions and tinkerings of the experiment are required to get this to work the way it's supposed to... see PCR) Now imagine that oligonucleotide flipping around in the breeze, jumping along this strand and that strand to and fro, gently tagging onto one nucleotide here and four nucleotides there and so forth until it gets hooked up to all 20 or so exactly matching so that it's so tightly bound that it hopefully doesn't pop back off the DNA again.

Between these two things, the point is that an ordinary protein gets the chance to flip around a bazillion different ways, until finally it happens to ball up in a shape so perfectly comfortable that it mostly stays that way. Wnt (talk) 06:56, 28 September 2010 (UTC)

At least related to the question is a statement of Levinthal's paradox: the number of possible conformational states for a protein (different ways to jumble up the 'coils of twine') means that sampling even a small fraction of the possible states would take longer than the age of the universe, so why do proteins fold at all (sometimes in fractions of a second)?

The response comes in two parts: Anfinsen's dogma, which says something about the likely stability and accessibility of properly-folded states; and the idea of a folding funnel, which suggests that the energy landscape in conformational space is funnel-like — meaning, very roughly speaking, that early steps towards the correct folded shape tend to favor a further collapse of the protein down to its final fully-folded state. TenOfAllTrades(talk) 16:21, 28 September 2010 (UTC)

My opinion is that this "paradox" is a bit overwrought — as you point out, it's based on the absurd idea that a whole protein receives no feedback from potential energy changes until it finds its final perfect form. In practice the protein secondary structure (alpha helix and beta-pleated sheet) is fairly predictable from the amino acid sequence and can be obtained by an exploration of the landscape at a fairly local level. Additionally, proteins tend to be composed of conserved protein domains which have evolved stable folds independently and don't mix very much. Of course, none of these things are absolute... Wnt (talk) 17:41, 28 September 2010 (UTC)

I'm pretty sure that even Levinthal didn't really believe his naive observation to be genuinely paradoxical. He simply used it as a jumping-off point to discuss why the protein folding process must be cooperative. (Think of it as a proof by contradiction — if we first assume that proteins fold by an unbiased random walk through conformational space, we quickly reach the conclusion that folding cannot happen within the age of the universe; therefore folding must be cooperative; QED.) TenOfAllTrades(talk) 21:13, 28 September 2010 (UTC)

Sorry, I didn't mean to suggest Levinthal didn't know better — it's just that sometimes when people talk about it they seem to treat this as a serious contradiction rather than a strawman. Wnt (talk) 15:29, 1 October 2010 (UTC)

Dichlorocarbenes and water

I've yet to use this reaction practically in real life...but, dichlorocarbene organic reactions can be performed in water? How is this possible? Don't you want an inert solvent that won't attack your carbene? John Riemann Soong (talk) 03:55, 28 September 2010 (UTC)

Thinking through your proposal, you are suggesting that oxygen attacks the vacant orbital of the carbene...which would give a carbanion? Not so stable--the carbene was originally formed when a similar carbanion spontaneously and easily did alpha-elimination (ejecting halide). Carbenes aren't really stable stable, you don't usually isolate a flask of them and then continue with another step, but make them in situ where they react promptly with something else (our article suggests they are formed in an organic layer so there are lots of the organic reactant but little of the water present). DMacks (talk) 05:22, 28 September 2010 (UTC)

Are carbenes soft Lewis acids/bases? Well yes, it would give a carbanion, but you can have a proton shift which effectively gives HCCl2-O-H (dichloromethanol) -- which readily becomes formyl chloride + HCl and then formic acid. John Riemann Soong (talk) 05:27, 28 September 2010 (UTC)

My point is that the immediate reaction that forms them is approximately the reverse, and is in an organic solvent (tends to exclude water--biphasic, just like the article states) that contains some other reactive component. DMacks (talk) 05:46, 28 September 2010 (UTC)

When people mix bleach and acetone for cleaning purposes....they say they form chloroform...but do they risk forming carbon monoxide in the process? John Riemann Soong (talk) 06:15, 28 September 2010 (UTC)

No, I am pretty sure the major problem in the mixture of bleach and acetone would be Phosgene, Diphosgene, and other analogs. Chlorine + carbonyl = nasty stuff. --Jayron32 06:20, 28 September 2010 (UTC)

On the other hand, the reaction of bleach (at normal "laundry" strength) and acetone is fairly slow compared to bleach oxidation of other materials. Acetone is a popular (co)solvent for bleach oxidation of some secondary alcohols (I think acetic acid is also added). DMacks (talk) 06:50, 28 September 2010 (UTC)

The reaction of bleach and acetone is an example of the haloform reaction. It forms chloroform and acetic acid, not carbon monoxide, nor phosgene. Physchim62 (talk) 12:53, 28 September 2010 (UTC)

That is the primary pathway yes. But I believe chloroform may go on to react in hypochlorite solutions to cause all sorts of mess! John Riemann Soong (talk) 18:27, 28 September 2010 (UTC)

Microfin

what is a microfin used in heat transfer applications —Preceding unsigned comment added by 115.111.61.66 (talk) 04:41, 28 September 2010 (UTC)

See Heat sink, which explains the use of fins in this regard. See also Fin (extended surface), which also deals with heat transfer properties of fins. Keep in mind that microfin just means "really small fin". --Jayron32 05:26, 28 September 2010 (UTC)

slow combustion

Are there any strategies being investigated to say, effectively burn something at -20C? Maybe by microwaving a dry ice bath full of organic material and some oxidant like perchloric acid? The idea is to track combustion pathways and maybe identify "weak points" in flammability. John Riemann Soong (talk) 05:33, 28 September 2010 (UTC)

Define combustion... After all, technically rust is a combustion product, just a really slow moving combustion. --Jayron32 05:38, 28 September 2010 (UTC)

Combustion tends to be autocatalytic, yes? But I don't want it to be too autocatalytic. John Riemann Soong (talk) 06:13, 28 September 2010 (UTC)

Combustion is autocatalytic over the flash point or Fire point temperature; if the rate of heat dissipation is great enough, due to low ambient temperature, then it won't sustain a burn because the local temperature stays too low to overcome the activation energy. This is a major problem when dealing with internal combustion engines in very low temperatures, in very low temperature the gasoline will not sustain combustion. It's even more pronounced with diesel, which is why diesel fuel is sold in winter and summer formulations. --Jayron32 06:26, 28 September 2010 (UTC)

Is it possible to engineer an experiment where the reaction is just slightly over the self-sufficiency rate? I'm thinking if black body equilibrium can be established at a lower temperature, but at say, 273K where the reaction is not so "crazy", then maybe combustion could be more easily studied. John Riemann Soong (talk) 07:14, 28 September 2010 (UTC)

• I'm not well versed in this chemistry, but I think that (as explained in combustion) a key detail is that triplet oxygen carries a spin angular momentum. This momentum needs to go somewhere (conservation of spin quantum number) when the reaction takes place. Since the fuel and/or product is usually some ordinary hydrogen or carbon containing compound, not a weird diradical like O2, that means that either the other reactant has to carry an opposite angular momentum (a free radical) to cancel it out, or else the oxygen needs to be energized up to singlet oxygen, whose spin is balanced out, before interacting. (As we just covered recently, the exact amount of angular momentum needed to do that comes from the photon, no matter what its frequency!) Either takes energy. This energy can come from a highly reactive fuel (pyrophoric) - Wikipedia gives triethylborane as an example of something that burns at -20 C. I don't know what temperatures are needed for various other compounds listed in pyrophoric. I also don't know how stable singlet oxygen is, which would be interesting, since as I understand you should be able to expose anything to the stuff, no matter how cold it is, and have slow oxidation with production of heat. Your call on whether that's cheating... Wnt (talk) 07:49, 28 September 2010 (UTC)

What about an alternate oxidant like perchloric acid? John Riemann Soong (talk) 13:13, 28 September 2010 (UTC)

The flame would be much hotter, but what about methane ice? ~AH1^(TCU) 20:30, 1 October 2010 (UTC)

Operators in QM

Why does :${\bigg (}\langle \phi |A{\bigg )}\;|\psi \rangle =\langle \phi |\;{\bigg (}A|\psi \rangle {\bigg )}$? Are we just forcing operators to have this property, or is this the result a more basic mathematical property? Why would we force operators to behave this way? Thanks. 74.15.136.172 (talk) 10:52, 28 September 2010 (UTC)

$|\psi \rangle$ is basically just a column vector, $\langle \phi |$ is a row vector, and A is a linear transformation, which can be thought of as a matrix. Then $\langle \phi |A|\psi \rangle$ is matrix multiplication in the usual sense, which is associative. Rckrone (talk) 12:38, 28 September 2010 (UTC)

The equation is actually the definition of $\langle \phi |A$. Looie496 (talk) 21:42, 28 September 2010 (UTC)

Crackle or hiss from radio

When I tune a radio so that it is not recieving any broadcast, where does the noise come from? Is it an echo of the big bang? Thanks 92.28.249.130 (talk) 13:15, 28 September 2010 (UTC)

Technically there's some component of the remnants of the Big Bang in white noise, but in practice, it's a non-factor which is dwarfed by solar or terrestrial (or even other cosmic noise) sources. Lightning and electrical equipment are prime sources of the noise heard on a consumer radio. — Lomn 13:50, 28 September 2010 (UTC)

Citation please? As a layman, I have to say this sounds doubtful. Comet Tuttle (talk) 18:36, 28 September 2010 (UTC)

As a former EE I share your doubts. East of Borschov 02:39, 29 September 2010 (UTC)

A realtime map of worldwide lightning strikes can be produced by analyzing the 'static' picked up by a handful of antennas scattered worldwide. IIR they settled on a 100KHz standard frequency which was low enough to contain lots of atmospheric static, yet high enough so that lightning signals at that frequency don't travel all the way around the earth. (The extra 'echo' would mess up their algorithm.) 128.95.172.173 (talk) 08:56, 29 September 2010 (UTC)

Any idea what the proportions are? Thanks 92.28.249.130 (talk) 14:22, 28 September 2010 (UTC)

Cosmic noise makes it sound like it is exceedingly small. --Mr.98 (talk) 15:39, 28 September 2010 (UTC)

Big Bang (book) by Simon Singh says that, if you were to observe static on a television screen then 1% of that would be background radiation from the horrendous space kablooie. Brammers (talk/c) 16:43, 28 September 2010 (UTC)

Wikipedia used to have an article on the horrendous space kablooie, but it now redirects to Calvin and Hobbes. -- BenRG (talk) 20:35, 28 September 2010 (UTC)

Particularly for an AM radio, we hear atmospheric lightning discharges, crackle due to electrical discharges from switching of power, and corona from high voltage transmission towers. In addition, we hear fish tank thermostats, and electric blankets and other electrical devices switching on and off. We also hear ham radio transmissions, defective doorbells, pizza ovens, medical diatheremy devices, relays in vintage pinball machines, and car ignition systems. Edison (talk) 04:59, 29 September 2010 (UTC)

On the FM band most of the noise would come from the transisters in the earliest stages of the receiver. There will always be some kind of noise floor. If your radio was not making this there is also thermal radio emissions from anything above absolute zero, including the earth, and sun. Graeme Bartlett (talk) 12:33, 29 September 2010 (UTC)

Why does the M16 have a higher muzzle velocity?

On the XM8 article it says that the XM8 uses polygonal rifling which would allow the rifle to have a higher muzzle velocity than the M4 or the M16. But it says that using a 20 inch barrel, it's muzzle velocity is only 916 m/s while the M16 rifle with a 20 inch barrel has a muzzle velocity of 948 m/s. Why does the M16 have a higher muzzle velocity, especially when the XM8 is supposed to have polygonal rifling. ScienceApe (talk) 14:32, 28 September 2010 (UTC)

I have to run quickly, but I will provide an answer based on what I know to be fact and my memory (which is often faulty). From memory, the XM8 is optimized to use a 24" barrel. So, optimal muzzle velocity is at 24". The fact... polygonal rifling is not designed to produce faster muzzle velocity in general. It is designed to reduce muzzle velocity loss when the barrel is shortened below optimal length. So, both riflings will produce similar muzzle velocities when barrels are the same length (on the same rifle). When you cut the barrel length in half, the standard rifling will take more of a hit on velocity than the polygonal rifling. The comparison you are looking at is using the optimal length M16 barrel and a 4" short XM8 barrel. You should expect a hit on muzzle velocity with a shortened barrel. -- kainaw™ 15:06, 28 September 2010 (UTC)

Conventional rifling on the left; polygonal rifling on the right.

It's a good point, though. All else being equal, polygonal rifling should give a higher muzzle velocity (except possibly in the case of lead bullets, see Lead bullets and polygonal rifling). The information at XM8 is poorly cited. WikiDao ☯ (talk) 17:51, 28 September 2010 (UTC)

The manufacturer says the M16 has a muzzle velocity of 948 m/s; the Federation of American Scientists says it's 853 m/s. Who are ya gonna believe...? ;) WikiDao ☯ (talk) 21:48, 28 September 2010 (UTC)

Wait, since when was the XM8 optimized for a 24" barrel? As far as I know, there isn't even a configuration for the XM8 that uses a 24" barrel. ScienceApe (talk) 23:06, 28 September 2010 (UTC)

Note kainaw's caveats. :) The XM8 comes in flavors of Sharpshooter/AR, Assault, and Compact (20, 12.5, and 9 inch barrels, respectively). WikiDao ☯ (talk) 23:39, 28 September 2010 (UTC)

And the articles now read: 916 m/s for 20" XM8, 853 m/s for the M16 but then there's the AR-15 article... WikiDao ☯ (talk) 23:43, 28 September 2010 (UTC)

Acceleration of rocket

what is the acceleration of a rocket —Preceding unsigned comment added by 41.221.209.5 (talk) 16:30, 28 September 2010 (UTC)

You'll need to be a little more specific. Do you want the minimum acceleration and velocity required for any rocket to escape Earth's gravity, or do you want information on a specific rocket or system like the Space Shuttle? Regards, --—Cyclonenim | Chat  16:46, 28 September 2010 (UTC)

Not all rockets escape Earth's gravity; see model rocket. Nyttend (talk) 17:21, 28 September 2010 (UTC)

Sorry that is correct, I just made the assumption the OP meant those which escape Earth's gravity. Not sure why. Regards, --—Cyclonenim | Chat  17:54, 28 September 2010 (UTC)

Also see skyrocket. We need to know what sort of rocket you mean.--Shantavira|^{feed me} 18:40, 28 September 2010 (UTC)

A rocket accelerates because of Newtons laws - for every action, there is an equal and opposite reaction. When exhaust is expelled out of the back of the rocket, in order to balance the motion the rocket must move in the other direction. See also Conservation of momentum. Ariel. (talk) 18:56, 28 September 2010 (UTC)

irrelevant pedantry
The following discussion has been closed. Please do not modify it.
Ariel, a minor point of pedantry. A rocket doesn't accelerate because of Newton's Laws. I suspect the earliest Chinese rockets powered by black powder were accelerating centuries before Newton was born. Rockets (and other bodies) accelerate in accordance with Newton's Laws, but they don't require Newton's Laws in order to change their velocity. Dolphin (t) 22:45, 28 September 2010 (UTC) Yah, that was pretty pedantic. I can understand "in accordance with", but what do you mean by "they don't require Newton's laws"? Of course they do - if they didn't have them, they couldn't move. And the laws existed before Newton was around of course - he just named them, he didn't create them. Ariel. (talk) 02:15, 29 September 2010 (UTC) I disagree. I think our Scientific law article makes it pretty clear that a law is merely a human summarization of how the underlying principles behave. I think it'd be more appropriate to say that rockets behave according to the principles that are embodied (and approximated) in Newton's laws. But at this point we've drifted far afield of the original question. Buddy431 (talk) 02:27, 29 September 2010 (UTC)

Acceleration is the force from the engine divided by the mass of the rocket. All else is byplay, vanity, and folly. Edison (talk) 04:52, 29 September 2010 (UTC)

Acceleration is the net force on the rocket, including the engine force, the force due to gravity, and air resistance (if in the atmosphere). It's most certainly not just a function of engine force and mass. Buddy431 (talk) 16:11, 29 September 2010 (UTC)

The questioner did not specify it was starting from a launchpad on Earth, as you assume. I could assume it was starting in space. Or someone could assume it was clamped down in a test stand, such that it does not move relative to the test stand. Edison (talk) 16:29, 29 September 2010 (UTC)

Does science yet have an explanation for how bees can fly?

It's one of those common knowledge "facts" that people quote at you, that science says that bees should be unable to fly because their wings are far too small for the size/weight of their bodies and that no-one can come up with a convincing explanation as to how they manage to get airborne at all. Is that still true? If so, are there any promising theories? --95.148.108.177 (talk) 22:29, 28 September 2010 (UTC)

It isn't true to say science says that bees should be unable to fly because their wings are far too small for the size/weight of their bodies. It is equally untrue to say no-one can come up with a convincing explanation as to how they manage to get airborne at all.

It is easy to come up with a very simple model of flight, and then show that this simple model does not allow bees (or birds or bats or fish) to fly. But the fact that bees do engage in flight just shows that the very simple model of flight is inadequate.

Science makes observations of the natural world and sets out to explain these observations, and how all observations are part of an orderly universe. Science does not develop theories and then set out to determine which parts of the natural world conform to scientific theories and which parts don't. Dolphin (t) 22:38, 28 September 2010 (UTC)

@95.148.108.177: You are quoting folklore, not "fact". Have a look at our article: Bumblebee#Flight. --- Medical geneticist (talk) 22:45, 28 September 2010 (UTC)

@Dolphin51: Some "science" develops theories and sets out to conform discoveries to scientific theories. You should get what I mean. --Chemicalinterest (talk) 00:21, 29 September 2010 (UTC)

Are you willing to reveal which science you have in mind? If you reveal some details, others can comment on whether they agree. Dolphin (t) 01:36, 29 September 2010 (UTC)

I'm pretty sure from his history CI is referring to evolution. His claims have been discussed many times before, I see no need for a rehash Nil Einne (talk) 02:18, 29 September 2010 (UTC)

http://www.sciencedaily.com/releases/2006/01/060111082100.htm "We're no longer allowed to use this story about not understanding bee flight as an example of where science has failed, because it is just not true," Dickinson says. Hcobb (talk) 01:51, 29 September 2010 (UTC)

Footage of the behavior in question. WikiDao ☯ (talk) 02:29, 29 September 2010 (UTC)

See also Insect_flight#Basic_aerodynamics and the final paragraph of List_of_common_misconceptions#Biology 92.24.186.80 (talk) 15:18, 3 October 2010 (UTC)

Why are muscle cells multinucleated

Everywhere on the internet where someone asks this question they get the answer "Because embryonic muscle cells fuse", which doesn't really explain anything- what purpose does this fusion have? 149.169.249.172 (talk) 23:45, 28 September 2010 (UTC)

Because it works. Nature does not have purpose, other than "it works." If the cells were individual, normal cell sized, muscle fibers would be very short. Having long, undifferentiated fibers, without definitave cell membranes between them, works better for what muscles do, which is to contract along their length. If you want to make a rope, you want long fibers, not short little ones. --Jayron32 23:50, 28 September 2010 (UTC)

Multinucleate cells don't have multiple nuclei because it's useful, it's just a byproduct of cell fusion. Take two individual myotubes, each with one nucleus. They then fuse together, so that there are now two nuclei in the combined cell. It doesn't harm the cell to have two or more nuclei, so there is no evolutionary pressure to remove this feature. Regards, --—Cyclonenim | Chat  13:51, 29 September 2010 (UTC)