Science desk
< March 15	<< Feb \| March \| Apr >>	March 17 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 16[edit]

What is the difference between magnitude and amplitude? (in physics)[edit]

93.126.95.68 (talk) 00:42, 16 March 2016 (UTC)[reply]

Suggest you read the articles you linked then come back for any clarification need.--31.109.183.147 (talk) 01:02, 16 March 2016 (UTC)[reply]

Diameter and length[edit]

What determines the diameter and length of the human stool?--31.109.183.147 (talk) 01:10, 16 March 2016 (UTC)[reply]

The design choices of the carpenter who built it, or the customer who commissioned it Iapetus (talk) 11:24, 16 March 2016 (UTC)[reply]

Diet, metabolism, health, and anatomy. 109.150.174.93 (talk) 11:35, 16 March 2016 (UTC)[reply]

When was the first known vivisection as a part of the anatomy study?[edit]

According to what I read "the first of use of human cadavers for anatomical reaserch occured later in the 4th century BCE when Herophilos and Erasistratus gained permission to perform live dissections or vivisection on criminals in Alexandria under the aouspices of the Ptolemaic dynasty." Is that true? I always knew that the first anatomy dissection was by Andreas Vesalius 93.126.95.68 (talk) 02:24, 16 March 2016 (UTC)[reply]

It's obviouse that this has been done long befor, for example in Ancient Egypt, because you need this knownledge to perform a Mummification successful. --Kharon (talk) 12:45, 16 March 2016 (UTC)[reply]

The sentence doesn't even make sense. "Vivisection" means dissection of a living animal. Cadavers are not living. Regarding the comment by Kharon, the knowledge required for mummification does not require working with living animals. Looie496 (talk) 13:48, 16 March 2016 (UTC)[reply]

I suggest re-posting this on the Humanities Ref Desk, where the historians might provide an answer. Carbon Caryatid (talk) 10:20, 18 March 2016 (UTC)[reply]

sun's power[edit]

how long can 1 second of the sun's power provide for the whole world? — Preceding unsigned comment added by Money is tight (talk • contribs) 04:49, 16 March 2016 (UTC)[reply]

Do you mean the total power output of the sun in one second, or the fraction of it that reaches Earth? If the latter, then the answer is one second if you include the requirements of all life on Earth, but perhaps you mean the artificial power used by humans? Dbfirs 08:17, 16 March 2016 (UTC)[reply]

No - that's not exactly true, the Earth is powered by the sun PLUS the stored energy from past sunlight (oil, natural gas, coal) PLUS energy that didn't come from the sun at all (eg nuclear power) PLUS the stored energy from the Earth's core (geothermal energy, heat from volcano's). So if you're counting all of the energy from the sun that strikes the earth versus all of the energy that's consumed by the processes on the earth, then it's very slightly more than the sun provides. But the Earth also radiates energy out into space - so talking about this in exact terms gets a bit ugly. SteveBaker (talk) 15:30, 17 March 2016 (UTC)[reply]

Assuming you mean how long would 1 second of sun power last if it all fell on the earth at the same rate as present rather than anythig to do with human power, the number of seconds is approximately given by the area of a sphere at the earth's radius from the sun divided by the area the earth presents to the sun, i.e in kilometers (4π × 149600000²) / (π 6371²) or about 2.2 billion seconds, about 70 years. Dmcq (talk) 11:00, 16 March 2016 (UTC)[reply]

Except a) the sun doesn't strike the whole earth during that 1 second (it would strike about half of it) and b) the sun doesn't illuminate all parts of the earth equally, because it is a sphere, the sun strikes obliquely at those places further from the line between the center of the sun and earth. All of the actual calculations for figuring out the amount of light striking the earth are covered at Solar irradiance. --Jayron 32 11:11, 16 March 2016 (UTC)[reply]

That's why Dmcq's calculation used the area of a circle, not a sphere. - Lindert (talk) 11:33, 16 March 2016 (UTC)[reply]

And if you're asking about energy consumed by humans versus total energy production of the Sun, here's an estimate: the world population consumes about 20 TW, i.e. 2 * 10¹³ J/s, and the Sun produces 3.8 * 10²⁶ J in one second, so in that time provides 1.9 * 10¹³ seconds worth of energy, equivalent to about 600,000 years. - Lindert (talk) 11:33, 16 March 2016 (UTC)[reply]

Let me just add that these numbers can be found, with sources, in our article Orders of magnitude (energy). Looie496 (talk) 17:05, 16 March 2016 (UTC)[reply]

If you're talking about the total energy output by the sun - consider that from the perspective of the sun, the earth is a tiny, tiny dot. So the percentage of the sun's total power output that hits the earth is very, very tiny indeed. That's why you get such large answers. SteveBaker (talk) 15:32, 17 March 2016 (UTC)[reply]

What a coincidence you should ask this!

Just this very day, I borrowed out a book called a bee in a cathedral, which provides a lot of scientific analogies. Here is one page.

The sun burns through matter at a rate equivalent to a million elephants every second.

This is 4 million tonnes of hydrogen, or the mass of a large supertanker.

Converting 1 kilogram (2.2 pounds) of hydrogen into 1 kilogram of helium (through fusion reactions) releases a million times more energy than burning 1 kilogram of coal.

This is equivalent to the same energy as a a 1-megatonne hydrogen bomb.

Solar flares (a release of magnetic energy built up in the solar atmosphere) release the energy equivalent to up to 1 billion megatonnes of TNT.

I would highly recommend the book if you should chance upon it!

JoshMuirWikipedia (talk) 11:46, 18 March 2016 (UTC)[reply]

Sintering[edit]

What is the relation between melting point and sintering temperature? 2601:646:8E01:515D:4C67:A04A:3241:D896 (talk) 11:07, 16 March 2016 (UTC)[reply]

Melting and sintering are timedependent processes. When your Furnace or sintering form reaches some temperature that does not mean everything inside reached the same. On Top this transition from solid State of matter to fluid, what we commonly call "melting", needs extra energy for what in physics is called Phase transition. So you have some state inbetween like Semi-solid metal casting for some time, dependent on how much heat you keep adding or not and thus how long you hold that "middle state", which is exactly what is used for sintering and its advanced twins Thixoforming, Thixocasting, Thixomolding etc. --Kharon (talk) 12:13, 16 March 2016 (UTC)[reply]

Maybe I should have been more clear: Is it possible to calculate the sintering temperature of a material if you only know its melting point? And what if you want to sinter 2 different materials with vastly different melting points? 2601:646:8E01:515D:E5BA:3C96:3120:9204 (talk) 00:42, 17 March 2016 (UTC)[reply]

You can calculate such processes ofcourse, even when they are complex, but there is no general formular or factor and no guarantee your calculated result fits the real thing. Sintering 2 different materials with vastly different melting points is near impossible and its obvious why. However, there are always tricks to achieve things initially assumed as impossible and this was and is mothing less than the high art of science and engeneering. But you want an easy sollution for something very difficult, right? Sorry, things rarely work that way. --Kharon (talk) 05:22, 17 March 2016 (UTC)[reply]

So, let's say I heat up the mixture so that the lower-melting component melts while the higher-melting component remains solid -- what would you call a process like this? It's not really sintering, but not really melting either -- what would be the right word? And am I correct that in this system the liquid phase will readily react with the solid phase if the chemistry is right, like I'm sure it would? 2601:646:8E01:515D:11AE:5E92:64F:4F12 (talk) 08:12, 17 March 2016 (UTC)[reply]

I doubt that works in sintering because you will have a weight difference and once one component becomes partly fluid the other elements will start to sink down or swim up. Additionally this will become a structually weak sponge with an expensive filling? Phases are another thing because this is usually used to discribe melting multiple components together that make an Eutectic system. In science and industry socalled Phase diagrams like the picture i added are used for common Alloy compositions. You have to learn some material science basics to understand all this and answer most questions around that. --Kharon (talk) 16:05, 17 March 2016 (UTC)[reply]

This is for chemistry, not for material science -- my goal is not to make a sintered composite, but to turn 2 salts with different melting points into a compound salt. 2601:646:8E01:515D:A1F1:E1A7:1FE3:7191 (talk) 00:42, 18 March 2016 (UTC)[reply]

Please take safety precaution which includes learn basic chemistry befor you start melting materials that are known to be able to inflict very agressive chemical reactions - like melted salts. Also you may want to correct your conception of material science. Chemistry has always been an essential part of it. Please avoid becoming another Icarus tru skipping the basics. --Kharon (talk) 12:54, 18 March 2016 (UTC)[reply]

For the record, I know basic chemistry (which includes chemical safety), and will definitely use proper equipment for this experiment -- you don't have to remind me! As for material science, I don't care about it -- this experiment has nothing to do with material science! Also, learn the meaning of the word "phase" -- it has meanings FAR BEYOND eutectic systems! 2601:646:8E01:515D:20BD:80F6:2385:C378 (talk) 00:21, 19 March 2016 (UTC)[reply]

Im not an expert on chemistry or metallurgy but i think i answered your Question about Sintering professional enough. Also i have to disagree! Its very important to warn People who ask Questions here that imply they may be planning some unsave experiments. Just to make shure. Stay save. --Kharon (talk) 16:38, 19 March 2016 (UTC)[reply]

Getting acid[edit]

In the USA, what regulations govern the purchase of sulfuric acid and hydrochloric acid (if any)? 2601:646:8E01:515D:4C67:A04A:3241:D896 (talk) 11:13, 16 March 2016 (UTC)[reply]

Our DEA list of chemicals which was recently changed [1] remains a bit confusing as does this unofficial list provided by the DEA which includes both hydrocholoric acid and sulfuric acid [2]. But this 2016 list [3] seems to imply hydrochloric acid and sulfuric acid are only type II listed for large exports to South America and Panama. However hydrochloric gas is type II listed for domestic purposes but I'm not sure what the threshold is. [4] has what I think are the main regulations covering purchases for listed chemicals but there may be others as well as additional regulations not directly relating to purchases. There are likely additional regulations concerning storage, transport etc unrelated to them being listed chemicals [5] [6]. While this isn't directly what you asked, any purchaser will potentially need to ensure they comply. The seller too may in some cases be expected to make some attempt to vet purchasers to ensure they are likely to comply with the storage, transport etc regulations and/or report possible violations seen during delivery. Nil Einne (talk) 11:57, 16 March 2016 (UTC)[reply]

There are probably thousands of applicable Federal, state, and local regulations that pertain to the purchase of these materials. Just for fun, I used the eCFR search engine to scour just the 2016 edition of the Code of Federal Regulations and I found over 500 hits. Regarding corrosive substances: There are laws about safety, about trade, about commerce, about tax; there are laws about labeling, about pollution, about food; about railroads, about highways, about ships at sea in Territorial waters; about use on farmland, about use on Federal land, about use on Indian lands, about the use in aerospace vessels in the National Airspace System; about treaty compliance when using in international waters inside the Economic Exclusivity Zone; about labor effects, about health effects, about health effects on laborers; there are laws about liability, about postal mail, about paperwork, about everything. The whole raison-d'être of an attorney is that their professional expertise is to accurately and correctly identify which of the thousands of possibly relevant laws are actually applicable to your specific circumstance. If the answer to your question actually matters, you need to consult an attorney.

If you like recreationally reading law, the best way to start is to read some meta-discussion about how law works in the United States. Federal law is often the most well-written and least contradictory stuff; local laws are often a lot more vague, but they tend to be written in less "academic" language. I enjoy the CFRs, because they read like computer-code: everything is defined. That makes the rules exceptionally clear, but some people find their language difficult to parse.

CFRs are administrative law, and arguably they are where you will probably find the majority of specific boring details about specific boring laws for specific boring corrosive substances. But, there are also codified laws in the form of the United States Code; there are also Acts of Congress, executive orders, and various court decision precedents; there are memoranda of understanding (official letters written between members of Government that carry legal weight); ... and of course, the United States Constitution! ...and all this only pertains to Federal laws! And if you've watched the news lately, you might have heard about the All Writs Act (28 U.S.C. § 1651). Broadly interpreted, that law is the proverbial Government sudo command: according to some interpretations of that law, anything that any Federal judge writes down is automatically Federal law. This can be problematic if a judge writes something contradictory to other laws!

You can read the regulations online. The official eCFR website is actually pretty abysmal (although it is our Federal government's authoritative electronic source). You can also get official PDF versions from the Government Publishing Office website. You can also buy legal extracts in book form; for example, the FARs [7] are published by several commercial vendors, with commentary. You can even buy the entire CFRs and US Code in encyclopedia form. Such books are usually sold at immense mark-up to overly-wealthy law students (Bernan and Co. will sell you beautiful hardcover copy at around $7500 for the set, and it'll be obsolete next year - but it'll look great on the bookshelf in your law office or living room!) You can also get paperback copies for cheap, and official Government PDFs on the web at zero cost.

Another great web link is the Legal Information Institute from Cornell: here's 49 CFR Part 171 from their very well-maintained website. It's a really nice webpage to browse, but it is an unofficial non-Government source. So, depending on why you need to be reading about laws that pertain to hydrochloric acid, keep that in mind!

49 CFR §171-180 specify the Federal Hazardous Material regulations, which relate to transportation and packaging of material including corrosive substances. That's just one area of Federal law I happen to know about - but I bring it up because it demonstrates that there are so many different places to check for the rules. You could try your luck running a search engine over various legal sources... but the results would be an awful, spastic disjoint set of word-matches with no coherency!

An even better idea is to work with somebody who has experience doing whatever it is you plan to do with these strong acids. They can mentor you about the safety and legal requirements that are most relevant.

Nimur (talk) 15:40, 16 March 2016 (UTC)[reply]

Here in Michigan, you can buy gallon containers of muriatic acid (HCL) at hardware stores. I believe it's used to break up clogs in pipes. So, presumably that means it is legal here. StuRat (talk) 18:03, 16 March 2016 (UTC)[reply]

HCl is often used for swimming pools, and for cleaning masonry. Relatively cheap, and useful. For pipes, however, lye is the most often used chemical, with sulfuric acid also in use (but not at the same time!). HCl is not corrosive enough <g>. Collect (talk) 12:35, 17 March 2016 (UTC)[reply]

Note also that our stomachs contain a .05–0.1 M solution of HCl. SteveBaker (talk) 15:25, 17 March 2016 (UTC)[reply]

Sulfuric acid is used in car batteries, and so can be purchased at a place that maintains lead acid batteries. It is diluted and not pure however. Graeme Bartlett (talk) 22:23, 17 March 2016 (UTC)[reply]

Natural Disasters and the Environment[edit]

What have natural disasters got to do with the environment? Bonupton (talk) 20:47, 16 March 2016 (UTC)[reply]

They can damage the environment, short term, and potentially improve it, long term. For example, a fire is bad to begin with, but by clearing out all the dead underbrush and trees, can be a boon for new life later on. The interaction between nature and people can make natural disasters far worse, as when people build homes in unsafe areas and fill in swamps which would absorb the impact of hurricanes if left intact. StuRat (talk) 21:14, 16 March 2016 (UTC)[reply]

Degradation of the environment can make "natural" disasters more likely and more severe. Climate change leads to glacier retreat, which reduces summer run-off, which would make the effects of a drought more severe. Damming and canalising rivers can lead to concentration of floods, making them more severe if they overwhelm river control structures. Deforestation has many negative effects, and can e.g. make avalanches and landslides more likely and more severe. And so on... --Stephan Schulz (talk) 21:29, 16 March 2016 (UTC)[reply]

For an example, read about the impacts of the Mount Saint Helens eruption of 1980. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:27, 17 March 2016 (UTC)[reply]

All organisms on Earth have evolved in an environment where these "natural disasters" happen. Some organisms manage to survive despite them, others benefit from them, others don't survive at all - but often the reduction in their numbers helps other species to survive. This makes labeling these dramatic, large-scale events as "disasters" somewhat iffy.

For example - a meteor the size of a mountain whacking into our planet seems like a highly dramatic "natural disaster". But the one that was so utterly disastrous for the dinosaurs turned out to be the only reason that mammals went from being tiny, rather strange oddities to being the species that 'Rules The Earth'. So was that event a "natural disaster" or was it the joyous event that birthed the whole human race - that caused the invention of art, science, music, poetry, Wikipedia and all manner of other "good" things? The answer to that question depends on whether you're a warm-blooded furry creature that feeds it's young from milk - or a large hairless, egg-laying reptile.

Conversely, if you take the view of a passenger pigeon or a dodo (both descendants of the few who survived the meteor) - the entire human race is a "natural disaster" unlike any other your species has ever suffered - and all of that art, science, music, poetry and Wikipedia-ing nonsense is just a part of a cataclysmic disaster that was triggered by that meteor.

Everything depends on your viewpoint.

SteveBaker (talk) 15:20, 17 March 2016 (UTC)[reply]

To be a bit more precise, humans would be considered invasive species and apex predators and ecosystem engineers. "Natural disaster" tends to be associated with abiotic processes, and our article mostly supports this, though wildfire is in some sense biotic. Some people might consider the outbreak of Mountain_pine_beetle to be a "natural disaster", but the scientists involved usually class it as an epidemic (e.g. USFS [8]), though our article doesn't currently cover the sense of an insect infestation. SemanticMantis (talk) 16:27, 17 March 2016 (UTC)[reply]

To be fairer to furry mammals, they took old man Jonathan from the Seychelles one year before the country was hit by a tsunami, caused by the 1883 eruption of Krakatoa. 133 years later, human progress is still helping a reptilian brother out (though it also wiped out the Seychelles tortoises). InedibleHulk (talk) 17:22, 17 March 2016 (UTC)[reply]

Note also the similarities (and differences) between Lonesome George and Chief Dan George. InedibleHulk (talk) 20:12, 17 March 2016 (UTC) [reply]

You might be interested in reading about Disturbance_(ecology). When a forest burns down, it releases carbon in to the atmosphere (carbon cycle), and so deforestation is a positive Climate_change_feedback, because warmer and drier areas are also more likely to burn [9]. Climate change can lead to increased incidence of other natural disasters like floods [10] and hurricanes [11]. SemanticMantis (talk) 16:27, 17 March 2016 (UTC)[reply]

Odd that the question so quickly became, "good" for the environment or "bad". There's no such thing, unless you specify "good for what?" An environment that's good for humans may be bad for manatees or mosquitoes. We call an event "disaster" if it causes our environment to be bad for people, for example drowns or burns us or knocks down our buildings. So, working from that definition, a natural disaster is always "bad for the environment" because it is bad for people. Other definitions, other values, will give other answers for various short term or long term changes in environment. Jim.henderson (talk) 17:22, 17 March 2016 (UTC)[reply]

What's bad for humans is also good for humans. Hurricanes create construction jobs, firestorms end unhappy marriages and pandemics deal with bullies. Man-made disasters also open up new doors. Pretty much anytime someone dies, that's one less competitor in whatever field. InedibleHulk (talk) 17:29, 17 March 2016 (UTC)[reply]

Fruit ID[edit]

Are these yellow fruits on a Roman fresco apples or something other? I'm not sure, 'cause they look quite strange for apples. Thanks. 93.174.25.12 (talk) 22:03, 16 March 2016 (UTC)[reply]

They look rather like quinces to me. DuncanHill (talk) 22:19, 16 March 2016 (UTC)[reply]

The shape and the colour both look closer to a quince than an apple - though it is difficult to be sure exactly what apples looked like 2000 years ago. Modern breeding has given us a particular shape, which may not always have been so common as it is now. 109.150.174.93 (talk) 22:26, 16 March 2016 (UTC)[reply]

That reminds me -- I once tried to eat a raw quince because I mistook it for an apple :-/ 2601:646:8E01:515D:E5BA:3C96:3120:9204 (talk) 00:58, 17 March 2016 (UTC)[reply]

Did you wince at the quince ? StuRat (talk) 02:54, 18 March 2016 (UTC) [reply]

Is that an ancient Roman fresco? The clear glass fruit bowl looks rather modern to me. Regarding the fruits, they look like kakis, but those were only introduced to southern Europe in the 19th century. - Lindert (talk) 22:28, 16 March 2016 (UTC)[reply]

Yes, it's from Oplontis. See this article. Tevildo (talk) 22:54, 16 March 2016 (UTC)[reply]

Thanks Tevildo and Looie496. - Lindert (talk) 23:03, 16 March 2016 (UTC)[reply]

I don't think we should rule out peaches. Richard Avery (talk) 07:49, 17 March 2016 (UTC)[reply]

Given the five sections and five points at the top, I think quince is a good bet. Crataegus azarolus works too. They come in yellow, were Roman fruits, and have the five pointed tops. EvergreenFir (talk) Please {{re}} 08:10, 17 March 2016 (UTC)[reply]

I've never seen a Crataegus azarolus, but if they resemble the Crataegus monogyna (common hawthorn) in any way, then the fruits will be much smaller than a grape,[12] making it a very small bowl indeed. Alansplodge (talk) 22:36, 17 March 2016 (UTC)[reply]

Apologies, I've just seen this image of azarole fruits in the article; they're bigger than hawthorn fruits ("haws") but still on the small side - the purple-grey sloes at the bottom of the picture are about the same size as a grape. Alansplodge (talk) 08:51, 18 March 2016 (UTC)[reply]