Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

December 16

Statistics: What causes what distribution?

I get that if you throw a handful of dice, you'll end up with a normal distribution. Could someone suggest literature matching process/phenomenon to expected distribution? (not only how to statistically analyze the resulting distribution) --C est moi anton (talk) 06:20, 16 December 2019 (UTC)[reply]

A book that will give you lots of real world examples of distributions is "Statistical Procedures for Engineering, Management, and Science" by Leland Blank. It has a section called "Level Two: Distributions and Their Uses". The section contains several chapters, each on a different distribution, and several examples within each chapter. The examples are fairly specific, rather than general phenomena, so it might not be exactly what you are looking for.--Wikimedes (talk) 07:46, 16 December 2019 (UTC)[reply]

A fair traditional die thrown once provides a Univariate distribution of its 6 discrete settling positions, each with probability 1/6 = 0.166... . A true normal or Gaussian distribution can only be approximated by dice throws due to the Central limit theorem that states that the average of many throws with finite mean and variance is itself a random variable whose distribution converges to a normal distribution as the number of throws increases. DroneB (talk) 15:43, 16 December 2019 (UTC)[reply]

If every throw is done precisely the same way, wouldn't the same face of the die turn up nearly all if not all the time? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:03, 16 December 2019 (UTC)[reply]

No, because the system is highly sensitive to initial conditions. A rolled die is not a perfect random system (studies have shown that there is are small effects that skew statistics ever so slightly one way or the other over many rolls) but insofar as it is a random system, a rolled die and the results of rolling thereof is akin to the double pendulum problem, in the sense that the tolerances for resetting the system are much larger than the differences in outcomes based on those differences. In other words, it isn't physically possible to recreate the initial conditions given that your level of uncertainty over those initial conditions is large enough that variations within those unknowables produces unpredictably different results. This is the basis for studies like chaos theory, which is a powerful tool making meaningful conclusions about such systems without resorting to the clockwork universe requirements of Newtonian physics. --Jayron 32 21:06, 16 December 2019 (UTC)[reply]

Presumably, using some sort of machine to roll a die or toss a coin would negate the presumed "randomness" of it - and we also assume those objects are "fair", i.e. that they are weight-balanced. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:10, 16 December 2019 (UTC)[reply]

If presumption could make things work then a Brownian ratchet sort-of-machine promises free power. DroneB (talk)

Refs to Coin_flipping#Physics say coin flip probabilities can be derandomized in real conditions (e.g. an illusionist performing a trick). Dice rolls is not in our article, a bit of searching finds [1] and it's more complicated: basically, if you can limit the die to a few bounces it falls on the initially-up face way more often, but if not, it's pretty much "random" (chaotic). Tigraan^{Click here to contact me} 15:50, 17 December 2019 (UTC)[reply]

If you're interested in the applications to physics: Wikipedia has compiled a list of textbooks in thermodynamics and statistical mechanics. Of these, I can personally recommend Landau and Lifshitz; Kittel; Stowe.

It is fair to say that the whole art of modern physics is the qualitative process of matching a physical phenomenon to the statistical distribution that accurately models it. The more unexplored parts of modern physics are those phenomena for which scientists still debate which model is appropriate - or even if any statistical model is appropriate at all.

Nimur (talk) 16:04, 16 December 2019 (UTC)[reply]

December 18

Mean maximum (temperature) versus average high

At San_Juan,_Puerto_Rico#Climate, what is the difference between the "mean maximum" and the "average high"? It seems to me like they should be the same thing. Bubba73 ^{You talkin' to me?} 04:49, 18 December 2019 (UTC)[reply]

Literally, it means about the same, but there's more than one way to define an average maximum. I guess that for "mean maximum" you take the highest temperature measured in January, February, ... or the entire year and average that over 30 years. For "average high" you take the highest temperature measured on each day in a particular month, then average that over the entire month, then over 30 years. Note that the mean maximum of the entire year is higher than that of each month, but the average high of the entire year is the mean of the monthly average highs. The same for the average low and the mean minimum. PiusImpavidus (talk) 09:43, 18 December 2019 (UTC)[reply]

OK, the mean maximum must be taking the highest temperature that month, not the highest temperature of each day in the month. Bubba73 ^{You talkin' to me?} 19:50, 22 December 2019 (UTC) [reply]

Resolved

Condensation and flatulence

On a cold day when one breathes out, you may see a puff of water vapour or condensation. I am curious if it is possible to see flatulence on such a day? Would it be possible to see a puff of vapour and thus alert a victim that the pin has been pulled before the grenade goes off? Please assume good faith. Thanks. Anton 81.131.40.58 (talk) 13:56, 17 December 2019 (UTC)

No. Moisture in outgoing breath originates in the Respiratory epithelium mucosa lining of the airways of the Respiratory tract while Flatulence is invisible gas accumulated in the gastrointestinal (GI) tract, especially the colon. DroneB (talk) 14:29, 17 December 2019 (UTC)

Could flatulence not contain elements of water in a gaseous form? How about if someone were to "shart". Thanks. Anton 81.131.40.58 (talk) 14:41, 17 December 2019 (UTC)

Did you used to have a user ID called "Light current"? ←Baseball Bugs What's up, Doc? carrots→ 15:10, 17 December 2019 (UTC)

No. Anton 81.131.40.58 (talk) 14:41, 17 December 2019 (UTC)

Can Baseball Bugs kindly cease and desist from deleting other people's posts. It has been requested that we assume good faith. Your editing in this regard is not wanted, needed or appreciated! Anton. 81.131.40.58 (talk) 10:50, 18 December 2019 (UTC)[reply]

I didn't delete it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:06, 18 December 2019 (UTC)[reply]

In which case I apologise, and refer to whoever did. Anton 81.131.40.58 (talk) —Preceding undated comment added 13:50, 18 December 2019 (UTC)[reply]

If I read the history correctly, it seems user:nimur did [2]. Probably a mistake and no malfeasance meant. --Lgriot (talk) 15:33, 18 December 2019 (UTC)[reply]

Probably not, because the large intestine is good at absorbing water. By contrast, the respiratory passages don't absorb water in large amounts. Rather, they keep the inhaled air moist, and will lose water to the air to do so, which is what leads to nosebleeds in dry conditions. This is to protect the delicate alveoli from damage. --47.146.63.87 (talk) 12:57, 19 December 2019 (UTC)[reply]

Thank you very much 47.146.63.87. Anton. 81.131.40.58 (talk) 13:56, 19 December 2019 (UTC)[reply]

Emily L.B. Forster

Can anyone kindly supply info (and sources) on the author and chemist Emily L.B. Forster (Q79050883), such as birth/death dates and a full name? I have a list of her works, and this article; her VIAF is 18750511. Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 20:41, 18 December 2019 (UTC)[reply]

Not finding much except "Little is known about her", from Chemistry was Their Life: Pioneering British Women Chemists, 1880-1949 (p. 112) . Alansplodge (talk) 15:39, 20 December 2019 (UTC)[reply]

December 19

Ion exchange membranes and electrochemical compressors

Can gases like nitrogen and/or chlorine be compressed by using anion exchange membranes in electrochemical gas compressors? Thanks!--109.166.131.155 (talk) 11:29, 19 December 2019 (UTC)[reply]

Cool idea. Not my area of expertise but, I found a 2017 paper which shows it can be used for compressing ammonia. It says that it has previously only been used for hydrogen. They also seem to have a newer paper showing that it works with CO2 too. I don't know why it wouldn't work with N2 or Cl2 in principle. Pelirojopajaro (talk) 15:57, 19 December 2019 (UTC)[reply]

N2 may be easier than Cl2; Cl2 is much more reactive with a broader range of substances and I would be concerned about such unintended side reactions. N2 is basically inert though. --Jayron 32 17:36, 19 December 2019 (UTC)[reply]

Water, water everywhere...

Nor any drop to drink. How do salt-water aquatic animals acquire "fresh" water (essential for all life as we know it). Is it somehow absorbed through the skin, leaving salt behind? Is salt water consumed and the salt somehow excreted? Or, ... (?) Is the mechanism different for fish (eg: sharks) as opposed to mammals (eg: whales)? 107.15.157.44 (talk) 21:55, 19 December 2019 (UTC)[reply]

See Surviving in Salt Water from the American Museum of Natural History. Alansplodge (talk) 22:36, 19 December 2019 (UTC)[reply]

And How can sea mammals drink saltwater? which answers the question for manatees, seals and sea lions, but "For most whales and dolphins, however, we simply do not know how they get their water, because it is difficult to observe these animals". Alansplodge (talk) 22:39, 19 December 2019 (UTC)[reply]

For more detail on mammals, see Osmoregulation in Marine Mammals. Alansplodge (talk) 22:49, 19 December 2019 (UTC)[reply]

Thanks, Alansplodge (am reading). From the 1st link: "A gland in the shark's digestive system gets rid of excess salt". I cannot find that gland's name or any mention in the Shark article. 107.15.157.44 (talk) 23:31, 19 December 2019 (UTC) -- P.s. found it here: "Shark". Animal Digestion.[reply]

The shark article says they don't need one:Shark#Osmoregulation

basically, it says that sharks are salty Rmvandijk (talk) 10:44, 20 December 2019 (UTC)[reply]

Shark article may be wrong (perish the thought): "A special gland near the end of the intestine, called the rectal gland, absorbs extra salt from the blood and passes it into the intestine to be excreted. These two adaptations function together to ensure that sharks do not dehydrate". From Sharks - Water And Salt Balance. More reliable sources are:

THE SHARK RECTAL GLAND MODEL: A CHAMPION OF RECEPTOR MEDIATED CHLORIDE SECRETION THROUGH CFTR and
Mechanism of active chloride secretion by shark rectal gland: and
Function of the rectal gland in the spiny dogfish (a dogfish, is a small type of shark), also
The rectal gland of Squalus acanthias: A model for the transport of chloride.

Alansplodge (talk) 15:18, 20 December 2019 (UTC)[reply]

Plenty of animals, notably a number of herps, manage with salt or brackish water by drinking it, then having some additional mechanism or "salt gland" to excrete the excess salt. Even some seabirds do this. The gland is usually either a modified tear duct or gland in the nose. They can appear to "cry" tears of brine, or even to sneeze out salt crystals. Most such animals also have kidneys which can tolerate a high salt diet and help by losing less water during urination, and they may be able to recover more water through their bladder walls (reptile urine is practically solid). This may be a re-use of an adaption for desert life, then enabling life in a wet but salty environment. Andy Dingley (talk) 00:22, 20 December 2019 (UTC)[reply]
There's a nice video of marine iguanas doing just that at Video on YouTube. Bazza (talk) 11:09, 20 December 2019 (UTC)[reply]

December 20

Do pigs enjoy music or other sounds?

If given levers which they can nudge to choose type and loudness, will they prefer some sounds over silence and pick out types to make louder?Rich (talk) 23:38, 20 December 2019 (UTC)[reply]

A simple websearch on "+pigs+music" returns (to me, at least) many hits suggesting that they do. Whether or not these reflect peer-reviewed studies rather than wishful lay thinking is a study I leave to you as an exercise. {The poster formerly known as 87.81.230.195} 90.199.211.222 (talk) 09:27, 21 December 2019 (UTC)[reply]

Definition of the derived quantity electrostatic potential as a function of base quantities like electric current

What is the algebraic relation (and how is obtained) for a derived quantity like electrostatic potential (a state quantity) as a function of only base quantities in SI like electric current which is a process quantity? Thanks!--109.166.135.195 (talk) 23:54, 20 December 2019 (UTC)[reply]

I am not so sure what you are asking. Process quantity does not appear to be what you want. Did you read Volt#Definition? The simplest definition along your text would be watts per ampere. If you want to integrate along a path, with an electric potential between the two ends, it will be simplest to assume that the current is going on that path. If this is not the case and you are dealing with current in a 3D solid, the you had better consider electric current density. Graeme Bartlett (talk) 11:42, 22 December 2019 (UTC)[reply]

1 volt = 1 joule per coulomb if I remember correctly. 173.228.123.190 (talk) 12:00, 22 December 2019 (UTC)[reply]

December 22

Chemical reactions.

What are some examples of reactions that take place below room temperature? And if so, that would mean the colder the temp is, the faster the reaction? 67.175.224.138 (talk) 17:34, 22 December 2019 (UTC).[reply]

See reaction rate and Arrhenius equation

In general, reactions continue at any temperature, but their rate will increase with increasing temperature. They don't suddenly "stop" (although this dependency on temperature can be exponential, so it might look like it!). Also many reactions will be exothermic (or even endothermic) and so their reaction may itself change the ambient temperature. This leads to the fairly common situation of a reaction undergoing some form of thermal runaway. It's hard to start it, but once started it quickly accelerates under its own influence. Andy Dingley (talk) 17:47, 22 December 2019 (UTC)[reply]

Okay look at the Haber process, the probability of it happening at room temperature, is like less than 1%? So imagine the equilibrium being at really cold temperatures, doesn't that mean at room temperature, it is almost 0%, and therefore, as we get colder, the reaction speeds up? Say a equilibrium is at -50 C, so at -70 C, the rate is slow, and as it gets warmer, towards -50 C, the rate gets faster, but doesn't that mean as we go past -50 C towards room temp, the reaction slows down again? 67.175.224.138 (talk) 20:00, 22 December 2019 (UTC).[reply]

You're confusing chemical kinetics with chemical thermodynamics. In the Haber process, it is thermodynamically favored at low temperatures, but kinetically favored at higher temperatures. --Jayron 32 20:25, 22 December 2019 (UTC)[reply]

So can some reaction be both thermodynamically favored at low temperature and kinetically favored at cold temperature? As well as something for hot for both. 67.175.224.138 (talk) 02:27, 23 December 2019 (UTC).[reply]

Depends on your definition of "reaction". For instance, certain fuels exhibit a "negative temperature coefficient" domain where an increase in temperature causes an increase in the autoignition delay (example), but that is because the "reaction" of combustion is actually a multitude of elementary reactions (i.e. reactions that cannot be broken down any further and involve very few molecules), and some of these compete for reactants so that the whole process becomes slower (there is no notable change in the thermodynamic equilibrium state). I would expect^{[citation needed]} that any elementary reaction must have its reaction rate increase with temperature (that is at least the case for any reaction that follows one of the two common models: Arrhenius equation with a constant prefactor or Eyring equation). Tigraan^{Click here to contact me} 09:58, 23 December 2019 (UTC)[reply]

There are times where lowered temperatures are desired for a reaction to prevent your product from decomposing or engaging in a secondary reaction, or to achieve a higher yield of your product by limiting competing side reactions. Rmhermen (talk) 19:16, 22 December 2019 (UTC)[reply]

December 23

Artifact on old TV - dark area around a bright area

In the screenshot from TV at Mercury-Atlas_6#Launch, there is a dark area around the bright flames. This is very common in TV of the area. What caused this artifact? Something about the TV camera? Videotape? Kinescope? Bubba73 ^{You talkin' to me?} 03:43, 23 December 2019 (UTC)[reply]

I think you mean in this image, Bubba73. But I don't know the answer to the question. Bus stop (talk) 03:48, 23 December 2019 (UTC)[reply]

Yes, the one from TV. Bubba73 ^{You talkin' to me?} 04:59, 23 December 2019 (UTC)[reply]

It looks a bit like lens flare to my eye. You may find some answers at the TV Tropes and Lens flare articles. MarnetteD|Talk 03:58, 23 December 2019 (UTC)[reply]

I don't think it is lens flare - lens flare doesn't look like that. I've seen it in a lot of old TV surrounding a bright area. Bubba73 ^{You talkin' to me?} 04:59, 23 December 2019 (UTC)[reply]

You can see this effect in other places too, for instance this infrared video. The video system can be adjusted so that hot objects are white, or flipped to the negative, as in this screenshot. Bubba73 ^{You talkin' to me?} 05:34, 23 December 2019 (UTC)[reply]

Running Rail Trains on Roads

Could it be possible to replace train wheels with tires and drive on roads? — Preceding unsigned comment added by 91.159.43.14 (talk) 13:39, 23 December 2019 (UTC)[reply]

[OP, I have added a heading to your question to set it off from the previous one. In future, please create a new query by clicking the 'New Section' tab at the top of the page and filling in a suitable 'Subject/Headline'.]

To answer your queastion: No, this would generally not be possible.

Firstly, train vehicles designed to run on steel rails are usually much heavier than road vehicles, and their weight typically exerts a pressure of several tons per (solid steel) wheel (see Adhesion railway); such pressures would be unsustainable for a pneumatic-tyred wheel of similar dimensions, and would also damage the road. Steel wheels without rubber tyres would simply sink into the road immediately.

Secondly, rail-trains work because the rolling friction of steel wheels on steel rails is very low, enabling a comparatively weak motive force to move the train. The rolling resistence of rubber-tyred road vehicles is much higher, requiring a combination of lighter vehicle weight and a more powerful engine relative to that weight. On a road, with rubber wheels, a train designed for rails would be able to propel itself barely if at all.

Thirdly, rail vehicles are not steered, since they are guided by the rails. Such vehicles would have to be modified extensively with steering mechanisms.

Fourthly, such a converted rail train would cause huge inconvenience to other road users in most circumstances, although in some isolated circumstances road trains are a thing.

Of course tramways, where a light rail train runs on tracks alongside or set into a road, are commonplace, but they cannot, of course, deviate from the fixed rails. Also, passenger road vehicles have sometimes been adapted to run on rails (usually on narrow-gauge railways), so it would be possible to design a dual use vehicle and even to couple two or more together thus forming a train, but there not many contexts in which this would be both feasible and more economical than the currently used solutions. {The poster formerly known as 87.81.230.195} 90.199.211.222 (talk) 14:47, 23 December 2019 (UTC)[reply]