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October 3

More firefighting Q's...

1) Are Novec 1230 fire extinguishers likely to be found in airport terminals?

2) How much heat can 1 mole of Novec absorb from a burning object at 800 C, and how many moles of it does a typical fire extinguisher contain?

3) Suppose I substitute a Novec extinguisher for the CO2 one in my previous scenario (trying to extinguish a burning office cubicle at 800 C and cool it down to 100 C) -- how much Novec must be expended to achieve this (assuming the cooling is rapid enough that heat transfer from the rest of the room, which is also at red heat, is negligible), and is this even possible with Novec?

2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 01:08, 3 October 2017 (UTC)

They're used, but in flood systems, so not in human-occupied spaces. You find them in server rooms or machinery spaces. The regulations are very tight on mixing these flood systems with humans - you either have to disable the flood system when humans are in there, or the humans have loud warnings to evacuate before it goes off - and those systems are only used where there's a risk of explosion that would destroy the building (it's worth the risk of suffocating people if they'd be killed by an explosion anyway).

Again, these materials are used to extinguish a fire chemically, by blanketing or by chemical reaction. They're not intended for use by simple cooling.

They're used in three main scenarios:

• Expensive equipment. So it's a safe blanket that's easy to clean up and doesn't react with warm materials. You can flood a room full of money and only damage the one rack that was actually on fire. Note that cold gases can cause damage by thermal shock.
• Dangerous materials. They're a fast knock-down to energetic materials that you really don't want on fire. An installed flood system is deployed far faster than a human team reaction, or bringing extinguishers to it.
• Difficult to extinguish materials. The ability to block the chemistry of the fire reaction can be useful to extinguish things that can't otherwise be extinguished by simple cooling or blanketing. Note the difference between inert sodium bicarbonate powder extinguishers for BC fires and ammonium phosphate that is acidic, reactive and can extinguish ABC fires (but will leave a corrosive residue). Fluids like Novec (I know nothing of Novec itself) are inert at low temperatures, limiting cleanup damage, but reactive at high temperatures.

You don't need to extinguish such a fire by cooling it, because you had installed an expensive flood system with an expensive fluid, which extinguished the fire before it became so hot that its simple total heat was a problem. Hot fires (as total heat in a volume, not temperature) are extinguished with water, because nothing else is available in the quantities needed to deal with a big fire.

If you're on site, you can extinguish potentially serious fires with a tiny CO₂ extinguisher, just because you were quick on the scene. Even better when is automatic.

If you're not on site, and have to travel to it, serious fires will be big by the time you get there. That's why it's nearly always time for water.

To answer your specific questions needs textbook figures that I just don't have handy. But I don't think they're even needed here, because your basic premises - that these fluids operate only by cooling - aren't correct. Andy Dingley (talk) 11:56, 3 October 2017 (UTC)

The article Fire extinguisher clearly states that Novec works by cooling as well as by blanketing/chemical reaction -- and your assertion that hot fires always require water is not correct, because if there's live electrical equipment in there (as in the cubicle farm I described), then water cannot be used. 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 12:27, 3 October 2017 (UTC)

Dat is not exactly correct. A water spray can and is often used were there is live electrical equipment. What is important is the voltage of that equipment. A water spray, even on three phase mains at 480V does not create a conductive path back to the fire fighter when performed correctly. The resulting steam then dilutes the atmospheric oxygen available and once again breaks the triangle. Don't try it however, unless you have been on a basic industrial first responders fire fighting course. Get to know your extinguishers long before you may ever need to use them. If it can spray, it should show dielectric test approval rating for use on electrical equipment. Aspro (talk) 16:39, 4 October 2017 (UTC)

Not gonna try it myself -- I was thinking about a fictional scenario I encountered (to be exact, an episode from American Airport Firefighter Simulator, toward the end of the "Headache" level), and trying to figure out what kind of extinguisher John (the player's character, a firefighter trapped in a burning airport terminal and trying to escape) uses. (Of course, you can say that he's using fictional extinguishers, but that doesn't cut it for me -- I like to keep things as close to real life as possible. BTW, that's also why I asked about the highest survivable temperature -- in that room, the walls are literally glowing red-hot, and I had my doubts that John could actually survive that -- correctly, as I suspected! And that is why the cooling effect is so important -- before he can even enter the office space, he must first use the extinguisher to carve out a survivable zone just inside the entrance, and to do that he must not only put out the fires in that area, but also cool down all objects in it to no more than 100-200 C -- while everything else in the room is still at red heat!) So right now I'm down to 2 options (now that CO2 has been ruled out) -- Novec or Halon/Halotron. Which brings up a 4th question: Do Halon or Halotron fire extinguishers have a significant cooling effect, or do they work entirely by disrupting the chemistry?2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 04:38, 5 October 2017 (UTC)

Efficiency of jet engine

Suppose a jet passes $r$ kg/s of matter at a velocity $v$ m/s. Then the force on the jet is $F=rv$ N (I think). Now, suppose you want to configure $r$ and $v$ so that the engine is "efficient" in the sense of using a small amount of power for the given force $F$. Basically, is it better to have small $r$ and large $v$, or large $r$ and small $v$? My guess is that the power used to pass the propellant is ${\frac {1}{2}}rv^{2}$ W, because each second, you're passing matter which has kinetic energy of ${\frac {1}{2}}rv^{2}$ J: that means you have to give the propellant ${\frac {1}{2}}rv^{2}$ Joules every second, or expend ${\frac {1}{2}}rv^{2}$ watts. Substituting my first equation, that would equate to a power of either ${\frac {1}{2}}{\frac {F^{2}}{r}}$ or ${\frac {1}{2}}Fv$ watts. That would suggest that it's better to have large $r$ and small $v$ if you want to minimize power. Is this logic sound? PeterPresent (talk) 02:53, 3 October 2017 (UTC)

Nope! It's really hard to compute the relation between the thrust (force) and the power for a jet engine. In fact, it's as hard as doing rocket science. You can try to deduce a relation from first principles of kinematics, but your equation is bound to be incredibly inaccurate because it fails to account for all the complications of airflow.

The math you used might apply to some toy problems in continuum mechanics like computing the energy budget for a chain falling off a table, or for bulk material getting accelerated as you continuously pour it onto a conveyor belt... this is the sort of problem that is concocted to torture physics graduate students, but it's not a practical equation, and it's not particularly useful as a practical approximation to real-world aerodynamics.

You might want to read our article on specific impulse; thrust; and jet engine.

For a practical overview of how this works, read Chapter 5 of the Pilot's Handbook of Aeronautical Knowledge; for a theoretical overview, Aerodynamics for Navy Aviators (Required Thrust and Power, pg. 96; and principles of propulsion, pp. 104-112). The latter reference actually starts with your exact equation and develops it into an equation more familiar to the engineers who build jet engines. They do so by introducing η (eta).

Our Wikipedia article used to have this great picture, two airplanes tied to a tree; it's not a wonderfully sound explanation; but the metaphor is potent - the relationship between power expended by the engine, and thrust that actually develops, is subject to aerodynamic inefficiency. The aerodynamic effieciency-factor can range all the way down to 0% - so it's not something you can casually neglect!

This is exactly why engineers use the specific impulse to examine engine efficiency; and they use the drag coefficient and the lift-to-drag ratio to examine the aerodynamic efficiency. For large jet engines, there are many separate types of efficiency losses, and many distinct regimes of operation; so you can't summarize all of engine efficiency into a single parameter.

I might observe, for example, the recent trend toward high bypass turbofans. That trend seems to indicate that on the whole, it's more efficient to move more air at subsonic speeds, than to try to move a small jet of air at hypervelocity. But on more thorough consideration, this is not a generalizable rule; it's easy to find counter-examples. For example, one of the first maneuvers taught to aviators is slow flight - the regime of "reversed command," in which slowing down the aircraft requires adding engine power. More fuel is spent, and the aircraft goes slower! Aerodynamics - it's not intuitive!

Nimur (talk) 04:32, 3 October 2017 (UTC)

The OP might find this explanation to be helpful: Why Planes Don't Fly Faster. --Guy Macon (talk) 08:08, 3 October 2017 (UTC)

The formula $f=rv$ is quite accurate for a rocket engine in a vacuum, but for a jet engine you have add a slightly lower mass flow of gas flowing in at a lower speed at the front end of your engine, in addition to the other difficulties of fluid dynamics which make finding analytical solutions impossible most of the time. I'd say that jet engines are much harder than rocket science. But qualitatively, it's quite easy to see that a larger flow at a lower speed gives a more efficient engine: you put less kinetic energy in the jet for the same momentum. The momentum of the jet is what gives you thrust. The high bypass ratios of modern jet engines are there to increase efficiency. PiusImpavidus (talk) 11:02, 3 October 2017 (UTC)

But, lower speed means flow that is less laminar, so less of the momentum you impart is in a useful direction. When you measure thermodynamic energy budgets for a jet engine, is it useful to consider the work output if the work is spent moving turbulence, instead of the vehicle? Nimur (talk) 13:49, 3 October 2017 (UTC)

The OP may find the Ramjet article interesting. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:54, 3 October 2017 (UTC)

combustion engine efficiency is a complicated combination of multiple processes and their own efficiencies. So its much more a task of balancing all these parameters while they have to work under a wide range of conditions. Just imagine the volume of water a jet engine has to handle in bad weather or the temperature range from the ground of a desert airport to the 30,000 feet traveling height. There are some general formulas used in engineering to approach the forces that are much more complicated then your 3 parameter formula but these are already very limited use. Your approach is frankly useless. --Kharon (talk) 19:01, 3 October 2017 (UTC)

How does the Portuguese man o' war eat

Our article has lots of info about how it stings and tons about the gas filled sail, but doesn't explain how it actually eats the things it stings. Presumably, they'd normally float away, so do the tentacles grab them and pull them to some kind of mouth or do they grab them and eating parts of the tentacles get to work? --84.19.47.96 (talk) 09:06, 3 October 2017 (UTC)

This National Geographic video shows the process. -- ToE 09:29, 3 October 2017 (UTC)

Complex roots by numerical methods

Which numerical method is best for finding the complex roots of a given algebraic equation? 14.139.241.85 (talk) 16:21, 3 October 2017 (UTC)

Most math software suites use lots of Parametric equation now i think. --Kharon (talk) 19:16, 3 October 2017 (UTC)

Root-finding algorithm#Finding roots of polynomials, and some of the articles it links to, may be helpful. Loraof (talk) 21:18, 3 October 2017 (UTC)

Refilling Glycogen Stores

According to various sources (although somewhat lacking in the Wikipedia article) the liver can store ~100 grams of glycogen and the muscles can store ~400 grams. As each gram of glycogen has 4 calories, this means in total a hypothetical persons body can store ~2,000 calories in glycogen.

Lets say that hypothetical person has a daily total caloric expenditure of 2,000 calories to maintain their weight (ignore water weight here since 1 gram of glycogen binds to 4 grams of water so water weight will fluctuate by 2 kilograms).

If they depleted their liver and muscle glycogen through exercise, a ketogenic diet, or starvation and then ingest 4,000 calories of carbohydrates in a single day, does that mean that 2,000 calories of the ingested carbohydrates will go directly to glycogen stores and the remaining 2,000 will be used by the bodies metabolism? Meaning in effect that despite consuming double their required daily intake, they do not put on any fat? 209.40.170.84 (talk) 16:42, 3 October 2017 (UTC)

I'm not sure if you will find any studies on that, but it seems unlikely that fat production would be 100% shut down. I could believe it would be reduced somewhat, yes, but entirely stopped, no. However, if stored fat is also turned into glycogen by some method, then effectively, this could be the case. StuRat (talk) 17:14, 3 October 2017 (UTC)

Anti-biotics questions.

1. Some anti-biotics advertise as killing gram-negative bacteria as good as gram-positive bacteria. Are there any anti-biotics that advertise as killing gram-negative better than gram-positive? Or should I say, what % of anti-biotics kills gram-positive better, what % both equally, and what % kill gram-negative better.

2. If something is both an anti-biotic and a anti-viral, what would it foremost be classified as? I just asked a chemistry professor who worked in the pharmaceutical industry, designing drugs, he say he never heard of a medicinal drug that can do both, so I guess I should instead ask, are there any drugs that are both anti-viral and anti-biotic at the same time? I note that Wikipedia's antiviral article says most anti-virals unlike anti-biotics, are used for killing/treating 1 virus at a time. But it wouldn't surprise me if some anti-viral are also have some anti-biotic. The anti-biotic article, says that "A limited number of antibiotics also possess antiprotozoal activity," so. Thanks. 12.239.13.143 (talk) 17:46, 3 October 2017 (UTC).

See list of antibiotics regarding to your first question and antimicrobial for your second. 208.90.213.186 (talk) 19:58, 3 October 2017 (UTC)

For your second question, it would be classified as both, if both are chief uses. I also am not aware of any drug that is both an antiviral and an antibiotic. It's possible in theory, but unlikely because antivirals and antibacterial drugs work via different mechanisms. In addition, there are practical constraints such as cost and side effects that limit the applicability of drugs. C0617470r (talk) 19:31, 4 October 2017 (UTC)

Generally majority of antibiotics kill gram-positive bacteria better or equal to gram-negative. Counter examples include, for example, first generation fluoroquinolones and second and third generation cephalosporins. Ruslik_Zero 08:56, 5 October 2017 (UTC)

Big science equipment - rolled on wooden trunks?

• 

Does anybody know the story behind this picture? It shows a large magnet of the Mirror Fusion Test Facility in 1981, probably prepared for transportation on a road made out of logs. Was is really transported so low-tech? At those times SPMTs were already known.

Thanks for any help.— Preceding question restored by Spmt6 (talk • contribs) 18:03, 3 October 2017 (UTC)

Looks like somebody went over budget and had to make due. :-)

One thought is that it won't do much bouncing around, this way. If the equipment is extremely sensitive, and time is no object, and perhaps the money involved in a more high tech solution is an issue, this approach might make sense. StuRat (talk) 17:00, 2 October 2017 (UTC)

I've taken over this question, since I don't believe in any coincidence.--Spmt6 (talk) 18:03, 3 October 2017 (UTC)

• Remember that this is Secret Alien Technology, after all: http://www.thelivingmoon.com/42stargate/04images/Machine/steigerphoto.jpg The Rainbow Conspiracy. ISBN 0786000651.

(and why wouldn't you move it on logs? Logs are great. Cheap, reliable, non-sparking, non-magnetic) Andy Dingley (talk) 19:19, 3 October 2017 (UTC)

It was a giant magnet, not a satellite or electron microscop. Industrial parts of such size are usually transported alike "naked". It was just an experiment. If you like you can read all about it here. --Kharon (talk) 19:42, 3 October 2017 (UTC)

I really can't see what advantage an SPMT has in this case. Entire ships are moved around on wooden rollers, not just little magnets. The logs use much more of the width of the roadway to support the weight than wheels would (although an air cushion/skirt system would be even better). Greglocock (talk) 19:54, 3 October 2017 (UTC)

What is the name for this method of transport? Log rolling refers to many thing, but apparently not this. -- ToE 15:00, 4 October 2017 (UTC)

You might think that we would have an article for this type of machine system, but our Roller (disambiguation) page suggests that the closest is roller bearing. Alansplodge (talk) 10:24, 5 October 2017 (UTC)

There's a brief mention in Bearing_(mechanical)#History; it uses the terms "rolling bearing" and "roller bearing". Alansplodge (talk) 10:28, 5 October 2017 (UTC)

Atmosphere and gravity

Just a thought experiment; I've got some conflicting ideas in my head, and I'm wondering which of them, if any, is correct.

Earth mass is approximately 5.9722 × 10²⁴ kg. The mass of the atmosphere of Earth is 5.15 × 10¹⁸ kg. If we lost our atmosphere suddenly, would the weight of a non-pressurised object indoors (as measured by scales) be affected? [Presumably the loss of pressure would cause problems for pressurised objects.] As we're indoors, wind wouldn't be a significant factor with atmosphere, and thus losing the atmosphere wouldn't affect the total mass that's acting on our scales. On one hand, the atmosphere's vaguely 0.0000863% of Earth's mass, so the reduction in mass being cubed in the gravitational constant would be absolutely tiny, and we'd have to have an extremely sensitive measuring device in order to notice any change. On the other hand, in the final section of Wikipedia:Reference desk/Archives/Science/2016 January 21 I learnt that the basic gravitational constant breaks down once you're inside the massive object. Obviously someone on Earth's surface is just barely "inside" the entire massive object, the atmosphere being only a thin skin on the regolith, but still I'm wondering if having mass above us has an effect on our weight.

So...what is it? Does the presence of the atmosphere have any effects on the net gravitational force being experienced by an object on the ground, or does it not? Nyttend (talk) 23:58, 3 October 2017 (UTC)

The atmosphere is essentially a spherical shell, and one of the astonishing facts about gravity that Newton proved is that a spherical shell exerts no gravitational force on anything inside it; see shell theorem. In other words, if you are beneath the atmosphere, the atmosphere's gravity does not affect you (except for small perturbations due to the fact that the atmosphere isn't really perfectly spherical). Looie496 (talk) 00:09, 4 October 2017 (UTC)

Balsa wood weighs about 160 kilograms per cubic meter. Air weighs about 1 kilo per cubic meter. Without the bouyancy of air that wood might now weigh 161 kilograms. There's likely less dense things that could survive both air and depressurization without the density changing (unlike say marshmallows). A giant hollow titanium sphere perhaps? Those would increase weight a higher percentage upon depressurization. Sagittarian Milky Way (talk) 00:34, 4 October 2017 (UTC)

Nothing "weighs X kilograms" because kilogram is a unit of mass, not of weight. A block of balsa will not gain mass, as per conservation of mass.

The effect of buoyancy on weight is not straightforward, as weight can mean apparent weight or true weight (mass times local gravitational acceleration) -- depends on which you mean. The article on weight discusses buoyancy. A helium balloon will float up in Earth's atmosphere, but not in a vacuum. Its mass and true weight remain constant, while its apparent weight changes. 91.155.192.188 (talk) 10:32, 4 October 2017 (UTC)

To be fair, the kilogram as a force unit is a real unit, just not part of the modern metric system (the SI). --69.159.60.147 (talk) 18:47, 4 October 2017 (UTC)

That's why I said (as measured by scales) when defining my meaning of "weight". Nyttend (talk) 21:23, 4 October 2017 (UTC)

Scales don't measure weight (as a spring balance does) they measure mass more directly. As scales work by balancing two masses, they're self-compensating for the effects of change in a local gravitational field (provided that there still is one). Unlike a spring balance or load cell, they don't have to be re-caibrated for lattitude or local gravimetric variations.

The pan weights do float in the air though, due to buoyancy (a tiny effect, but it's there). If you remove the atmosphere, this effect would disappear, for both the spring balance pans. As the balance weights are usually denser than the thing being weighed (they're solid and made of dense stuff), they were less buoyant in atmosphere and so the scales were previously reading very slightly heavy beforehand, which will no longer be the case without an atmosphere. Andy Dingley (talk) 22:24, 4 October 2017 (UTC)

The distinction between the two kinds of scales is perfectly correct, but it is unusual and confusing to use the name "scale" only for balance scales and not for spring scales. --69.159.60.147 (talk) 08:37, 5 October 2017 (UTC)

But who was using scales to refer to a spring balance or made a distinction between two kinds of scales? Andy Dingley clearly wasn't. Instead they said a similar thing to you namely that a spring balance is not a scale and so effectively made a distinction between a balance scale and a spring balance; although only barely as needed for their main point namely that since the OP referred to "scales" these would measure mass, not weight, and how this all affects the OP's original question. Nil Einne (talk) 13:31, 5 October 2017 (UTC)Sorry misread 69's comment. Nil Einne (talk) 13:33, 5 October 2017 (UTC)

October 4

Website showing heavens appearance at a given date

Hello! Is there a website that tells me where the sun and the planets were at a given moment in the past? I only know http://www.heavens-above.com, but there you cannot go very far in the past.

Thanks!

Megalexandros (talk) 02:16, 4 October 2017 (UTC)

In Wolfram Alpha, you can type "Sky map for [place] [time] [date]" and get a sky chart for then. For instance, "sky map for London 1 AM 4 October 1800" gives you this. Smurrayinchester 09:47, 4 October 2017 (UTC)

• Stellarium is usually favoured for this. It's a downloadable program, but it's free and it's cross-platform. There are several others, and a list at that article. Andy Dingley (talk) 10:00, 4 October 2017 (UTC)

It's all carefully worked out [1]. 82.12.63.55 (talk) 11:16, 4 October 2017 (UTC)

Muscle and liver glycogen, which refills first?

When a person has fully depleted both their muscle and liver glycogen stores and then ingests carbohydrates, which refills first; muscle glycogen or liver glycogen? My understanding is that all carbohydrates will pass through the liver first because the blood vessels from the intestines go directly to the liver. However I have also read that the liver will not actually replenish its glycogen stores if blood sugar is low. Also, StuRat, as much as I love you (seriously, I do like reading your comments) I am looking for referenced answers to this question not just idle speculation :) Thanks for your time. 109.62.183.116 (talk) 15:46, 4 October 2017 (UTC)

That's fine, but why did you repost ? Is this a different Q from the one above ? Even if it is, I'd put it right after that one. StuRat (talk) 16:01, 4 October 2017 (UTC)

It's a different question. The other one was about both liver and muscle glycogen stores together acting as a cabohydrate sink during excessive ingestion. This one is specifically asking which of the two refills first. 109.62.183.116 (talk) 16:21, 4 October 2017 (UTC)

To simplify, the liver stores glycogen, the muscles use it. When I prepped for bariatric surgery last January I had to go on a strict three-week diet for the purpose of shrinking my liver's size by 75%. The doctor said the liver would shrink, making access to my stomach easier, but the muscles would have enough glucose as long as my blood sugar remained over 80.

I had to test three times a day, because your heart and lungs (and brain) have to have glucose at a sufficient level, while your liver will simply cut back on non-essential functions. No, that's not an RS, but I lived through it. I threw out the pre-op documentation, but it's easy enough to get if you google pre-op bariatric diet. 22:24, 4 October 2017 (UTC)

Shoot, if a person can diet well enough to keep blood sugar under 80 for three weeks and shrink their liver, why do they need bariatric surgery? Wnt (talk) 06:16, 6 October 2017 (UTC)

How old are you, exactly, Wnt?

Because it's an otherwise unhealthy starvation liquid diet, requires the use of very expensive, unsatisfying, and diarrhea and nausea inducing protein drinks, risks ketoacidosis, a potentially fatal condition, does not address the issue on the long term, and is not comfortable or cost effective?

Having had the laparoscopic over-night stay gastric sleeve surgery (which cost ~$10,000), I am off diabetes meds that had cost ~$12,000 year, am not on a starvation diet, and have lost over 50% of my pre-treatment body weight? And actuarial tables show I have added about 30 years to my expected life span. I am in better shape now than I was 25 years ago, and am unlikely to die or suffer amputations due to diabetic complications like about 1/2 of the people on my father's side of the family.

I'd give you the research, but I see no reason to humour medical conspiracy theorists. I feel, look, and test great. μηδείς (talk) 19:24, 6 October 2017 (UTC)

October 5

What is this thing?

What is this thing?

Uploader has a local name for the bug. Claims a local discovered it. What is it? Magog the Ogre (t • c) 01:31, 5 October 2017 (UTC)

It's a caterpillar. Someone would probably need a location to get more precise than that.--Jayron32 01:34, 5 October 2017 (UTC)

The file description page on commons has some clues, including a precise location in Kenya. Jahoe (talk) 09:17, 5 October 2017 (UTC)

Description says it's a centipede, but it looks suspiciously similar to a Saturniid moth larva to me O_o Dr Dima (talk) 20:07, 5 October 2017 (UTC)

It is certainly not a centipede. μηδείς (talk) 23:51, 5 October 2017 (UTC)

Slide-fire adapter

In the reports and commentary about the latest (at time of writing) American celebration of the Second Amendment mass-murder there are many mentons of bump stocks and slide-fire adapters. Bump stock is a redirect to an article which has some information about them (as well as lots of hints for anyone wishing to murder lots of people). We do not appear to have anything about slide-fire adapters. What are they? DuncanHill (talk) 21:00, 5 October 2017 (UTC)

More or less the same thing. "Slidefire" (the company) are one of the main makers of bump stocks.

One difference, in historical terminology, is that a bump stock requires a semi-automatic (self-loading) weapon. A "slide fire" technique was originally applied to manually-loaded weapons, particularly pump-action shotguns, with a poorly-designed, faulty or modified trigger disconnector. Holding the trigger down on these and racking them (working the loading slide) they would fire the trigger mechanism as soon as the breech went back into battery. Andy Dingley (talk) 21:58, 5 October 2017 (UTC)

Thank you, DuncanHill (talk) 22:18, 5 October 2017 (UTC)

The shotguns are also sometimes called slam fire. Here is a video that compares how fast you can fire the two types: https://www.youtube.com/watch?v=0-csrQ_VP5Y --Guy Macon (talk) 22:32, 5 October 2017 (UTC)

Off-topic: I find the little jabs in your question a bit insulting to a lot of people, especially when you say you really have no clue about what you're talking about. Please refrain from the superfluous comments in the future. Justin15w (talk) 14:40, 6 October 2017 (UTC)

Has anyone seen any other notable uses of bump stocks this week? I think defensive gun use claimed there were something like 33 million of them. Jimbo forfend that we would offend anyone using one! Andy Dingley (talk) 14:57, 6 October 2017 (UTC)

One doesn't need to have an extensive technical knowledge of firearms to have a valid opinion about mass murder and its enablers. DuncanHill (talk) 15:21, 6 October 2017 (UTC)

October 6

Can electron quantum tunnel out of a black hole?

If a single hydrogen atom is just at the event horizon of a black hole. Can it's electron quantum tunnel from inside the event horizon to outside it. After all, its location is just a wave function and half of the wave is inside the event horizon and half of the wave is outside the event horizon. 110.22.20.252 (talk) 01:56, 6 October 2017 (UTC)

Hawking radiation is at least a bit relevant. Sagittarian Milky Way (talk) 02:15, 6 October 2017 (UTC)

Yes, there are generally theories that quantum mechanical effects will allow particles to escape from black holes, albeit with a very low probability. However, as we lack a comprehensive theory of quantum gravity or any direct experimental access to black holes, I would suggest such ideas are rather speculative at present. I would note though that unless you have some magic way of suspending matter right at the event horizon, then the atom is likely to be falling into the black hole at very high speeds. The amount of time that any atom might be considered half-in/half-out of the black hole is likely to be extremely small for any normal black hole. The situation is more interesting in the case of microscopic black holes, if such entities actually exist. It is possible to imagine, at least in theory, black holes so tiny that particles like electrons are essentially too large to fit in the black hole and even after being eaten there is an appreciable chance that they leak back out again. Again though, this all rather speculative and untested. Dragons flight (talk) 02:55, 6 October 2017 (UTC)

• Jak skazal SMW, see Hawking Radiation. μηδείς (talk) 00:50, 7 October 2017 (UTC)

What does jak skazal mean? Sagittarian Milky Way (talk) 01:18, 7 October 2017 (UTC)

Limit of temperature generated by electricity

Hi again ref desk, another impossible to Google question. I heard on a podcast about converting the world to renewables, that creating steel requires around 3000°F and they claimed that using electricity alone, you can't get to those temperatures. So, is this true? If so, given an infinite amount of power, is it a law of diminishing returns? I was thinking they could just turn large chunks of iron into filaments (however impractical) to accomplish this. Anywho, thanks in advance. Drewmutt (^ᴥ^) talk 04:35, 6 October 2017 (UTC)

No, not true at all. Our article on electric arc furnaces says that they can reach temperatures of 3,000 °C (5,432 °F). 2601:646:C101:C8A2:34D5:864B:CE64:F9CD (talk) 05:46, 6 October 2017 (UTC)

That just the furnace. The actual arc is hotter.

• "Electrical arcs produce some of the highest temperatures known to occur on earth, up to 35,000°F (19,426°C). This is 4 times the temperature of the surface of the sun which is about 9000°F (4982°C)."[2]

BTW, it took me roughly a minute on Google to find the answer to this "another impossible to Google question". I'm just saying. --Guy Macon (talk) 06:53, 6 October 2017 (UTC)

(ec)Maybe we should also mention that many high-quality steels are routinely produced in electric arc furnaces (and have been for at least decades), because they offer more control over the chemical composition of the steel (there is no coal to introduce carbon, or other undesirable impurities coming with coal, like sulphur and phosphorous), and they also make the physical process easier to control. Of course there also is a red herring - just because it is hard to replace some fossil fuel applications does not mean that we cannot reduce carbon emissions to a sustainable level - most carbon emitting processes can be replaced or improved. --Stephan Schulz (talk) 10:00, 6 October 2017 (UTC)

• As pointed to above, the problem is not the maximum temperature. But a key consideration is that coal is used to bring not only heat but also carbon content to the steel in blast furnaces (historical note: Wootz steel), which can help the economics of coal vs. electricity - you would need a source of carbon if you heated by electricity.

Blast_furnace#Iron_blast_furnaces says that there have been electrical blast furnaces in Sweden but I cannot track down a source. I found this report considering switching to biomass (which counts as "renewable" by most standards). Tigraan^{Click here to contact me} 09:46, 6 October 2017 (UTC)

Global warming

So when people think global warming is made up, what is their reasoning for why they think scientist would just make it up? Is it just random conspiracy nuts? CTF83! 09:30, 6 October 2017 (UTC)

It's very much not random - it's carefully seeded by people and organisations that profit from the old-school carbon-based economy and want to reduce or delay changes. A modern classic on the topic is Merchants of Doubt, but you will find plenty of additional sources via Google Scholar. --Stephan Schulz (talk) 09:40, 6 October 2017 (UTC)

There are not many global warming denialists. Temperature is quite easy to measure after all. Denialists mostly deny it's man-made, and hence, believe nothing should be done.

They normally explain the consensus as a result of aggressive activism, as a Chinese invention, or whatever. See Global warming conspiracy theory for the whole story. --B8-tome (talk) 11:45, 6 October 2017 (UTC)

To be fair, those of us who grew up in the 1960s and 1970s were regularly served up gloomy scientific predictions; the world would run out of food or water (or both) at some time in the 1970s, we could be thrown back into the stone age by a power cut, we would completely run out of oil in 1984 and millions would die when the next ice age arrived early in the 21st century. So although I agree fully with what Stephan Schulz says above, there has been an awful lot of crying wolf beforehand, so some scepticism is understandable. Alansplodge (talk) 12:06, 6 October 2017 (UTC)

The reason I've heard is funding, that if global warming wasn't real, climatologists risk losing their funding. A Quest For Knowledge (talk) 12:15, 6 October 2017 (UTC)

Because as a rule scientists are motivated by money and choose their profession because scientific careers pay so well? Or because there is a hive mind controlling all scientists? Note that anyone who puts a serious dent into a widely accepted theory would be set for life - compare Albert Einstein (who killed Newtonian mechanics), or Barry Marshall and Robin Warren, who showed that most gastric ulcers are caused by infections, and not (directly) by stress and diet. --Stephan Schulz (talk) 13:37, 6 October 2017 (UTC)

It isn't just because it is in the interest of some very big companies, there is also a desire in people to not believe they are doing any wrong by driving cars or taking holidays by plane or any of the other countless good things of modern life that need fuel to be burnt. And in particular in America it basically says you can't be altogether free to do whatever you like which is one of the beliefs the country was built on. So lots of people are quite happy to engage in what psychologists call denial. Dmcq (talk) 13:55, 6 October 2017 (UTC)

As hinted above, there is a habit of grouping anyone and everyone who disagrees with anything at all about global warming into the "stupid denier" section. If I were to point out a prediction from Gore's Inconvenient Truth that didn't happen, I would immediately be as much of a denier as some guy who claims that it is all made up by the illuminati. 209.149.113.5 (talk) 17:25, 6 October 2017 (UTC)

Ok thanks all! CTF83! 17:30, 6 October 2017 (UTC)

Is there a wikipedia article debunking the "Never Adjust for Curvature of Earth" claim of Flat Earth?

Is there a wikipedia article debunking the "Never Adjust for Curvature of Earth" claim of Flat Earth? Basically the stupid argument of flat earthers is that an aeroplane flying level on a spherical earth would fly off into space. Since the pilot of the plane NEVER adjust for curvature of the earth, the only conclusion a sane person can draw (with his kindergarten crayon) is an earth that is as flat as a pancake.

I know how to debunk it, it involves the vector from the centre of mass of the aeroplane to the centre of the earth. The aeroplane naturally balances itself on the centre of the mass, in the direction of the centre of the earth. So just imagine the aeroplane like a see saw with the pivot being the centre of mass of the plane. However it takes too much words, diagrams and effort to explain the idea to the Flat Earthers. So I am looking for a wikipedia article to explain this concept so that I can just direct them to the article. 110.22.20.252 (talk) 10:21, 6 October 2017 (UTC)

Gravity adjusts the plane for curvature of earth. That's like Earth is longeing the plane.

PS: I hope you don't meet many flat-earthers in your day to day. I have some just through the internet, and thought they were a parody of creationists. This was a classical case of Poe's law. --B8-tome (talk) 12:01, 6 October 2017 (UTC)

If those flat-Earthers admit the existence of gravity anomaly, it might be a starting point to argue that "gravity is not always vertical" (or rather, that if by definition vertical = in the direction of gravity, all verticals on Earth are not parallel), and the plane goes perpendicular to the gravity field, etc. But I am not sure of what is causing g in their world model, so... Tigraan^{Click here to contact me} 12:11, 6 October 2017 (UTC)

The Handley Page Gugnunc, flying very slowly downwards, whilst pointing clearly upwards

• There are a few effects here. Conservation of energy is one, things just don't change their gravitational potential energy unless there is some trade of energy going on. So planes don't change altitude against gravity unless they're either driven by their engines, they perform a zoom climb and trade speed for altitude, or light gliders might climb in a thermal.

Then there's the classic balance between lift and weight, thrust and drag. When these are balanced, there's no vertical movement (Note to Newton - there's no vertical acceleration because they're balanced. But there's also no vertical speed because of the work against the gravitational field).

Finally there's the angle of attack issue. Aircraft move vertically because of the lift/weight imbalance. But flat earthers think aircraft "go where they're pointed" and so presume that any aircraft pointing "up" flies in that same direction.

Underlying all of this though, is the flat earth refusal of either gravity (at all) or their belief that gravity acts parallel and perpendicular to a flerf, rather than symmetrically and radially. Andy Dingley (talk) 12:15, 6 October 2017 (UTC)

Wikipedia has an article Flat Earth but does not as far as I know address this claim. If you get a reliable source discussing it then you could try adding it somewhere I guess. However I don't see the point of the question. No flat-earther is going to be convinced by some rational scientific argument about what a plane does or gravity or whatnot if they think pictures of the earth from space are part of some conspiracy theory. Dmcq (talk) 13:48, 6 October 2017 (UTC)

Flight instruments#Altimeter would appear to be relevant. The pilot will use his instrumentation to ensure his craft is an appropriate distance above the ground. This is important because aircraft are segregated laterally and vertically. 92.8.220.234 (talk) 15:19, 6 October 2017 (UTC)

So do you follow the flat earth claim here? That aircraft only maintain altitude, rather than flying straight above an Earth curving away beneath them and so heading off into space, because the pilots are deliberately steering them downwards?

Perhaps we need an article on the legal fallacy of riding two horses as well? Globe Earth aircraft maintain a constant altitude as an equilibrium, because of gravity. The same gravity shapes the form of the Earth too, so we end up with a constant gravitational height approximating a constant altitude over a plain. This is the same case for both globe and flat earth models.

The fallacy of flat earthers claims about aircraft depend on two underlying fallacies. Firstly that aircraft climb "by pointing upwards", rather than by having an excess of lift. Secondly, a flat earth aircraft would fly straight and level above a flat earth, and a globe earth aircraft would follow the same altitude around a globe Earth. The fallacy is to claim that a flat earth aircraft, following flat earth physics, would somehow be above a globe Earth, dropping away beneath it! Aircraft over a globe Earth are flying by globe Earth physics. Andy Dingley (talk) 15:50, 6 October 2017 (UTC)

This is serious. This is NOT A LAUGHING MATTER. THIS IS SO SERIOUS THAT a man took a spirit level on an airplane to prove that the earth is flat. [Man takes spirit level on an airplane]. 110.22.20.252 (talk) 16:42, 6 October 2017 (UTC)

The easiest way to understand why a plane does not fly off the Earth is to consider the frame of reference fixed with respect to that plane. In such a frame the plane is not moving at all but instead the Earth rotates beneath it. The air follows the Earth and moves relative to the plane creating a lift that balances the total gravity force. So, it is not surprising that plane stays bound to the Earth. Such a frame is, of course, generally non-inertial save one special case. However one of the two inertial forces – centrifugal force – is just added to the true gravity forming the total gravity force and is essentially unobservable. The second inertial force – Coriolis force – is small (depending on velocity relative to the plane) although it will readily reveal itself once you conduct a Foucault pendulum test. Ruslik_Zero 18:26, 6 October 2017 (UTC)

You are not going to convince a flat-earther with rational argument. See Duty calls for what I think about your capital letters about that this is so serious. Dmcq (talk) 18:49, 6 October 2017 (UTC)

Flat-earthers don't believe in gravity; they believe that the earth is accelerating upwards at the rate of gravity. If you think the Earth is a globe because you can see the curvature of the horizon, try this: take a long pole that you know to be perfectly straight from sighting along it. Grasp it at its centre with one hand; hold that arm out in front of you at full arm's length so that the pole is horizontal and level with your eyes. Look at the hand. Do you see anything unusual about the pole in your peripheral vision? Explain that. Akld guy (talk) 21:15, 6 October 2017 (UTC)

Talk about the amount of ignorance of physics. 99% of the youtube videos explaining why the plane does not fly off the earth in a level flight is COMPLETELY WRONG. Right result but wrong explanations.

• The air get more rare as the altitude increases, Therefore the plane must curve with the shape of the earth. CORRECT STATEMENT but wrong explanation, I can prove this if you replace the plane with a rocket and take away all the air by moving it to the moon. A rocket with thrust (directed towards the centre of the moon) that perfectly balance out the force of gravity over the moon, will still curve with the shape of the moon. The air get more rare explanation is wrong.

• Gravity makes the plane confined to a certain altitude above the earth. TRUE but how?

• The autopilot of the plane keeps it curving with the earth. WRONG. The plane will still curve even with no autopilot.

The true answer is that the plane is like a (weighing) scale which naturally balances itself by the centre of mass located at the centre of the aircraft by the wings. As the airplane travels an infinitesimal distance to the right, the front of the plane dips down an infinitesimal amount and the tail of the plane rises up an infinitesimal amount. This is because the plane is like a (weighing) scale or a see saw. As it moves to the right, the vector from the centre of mass of the plane to the centre of the earth changes. So the plane becomes "unbalanced" and like a scale or a see saw, it will naturally rebalances itself to make it level according to the new gravitational field. You can say the plane ALWAYS forms a right angle triangle from the front of the plane to the centre of the plan to the centre of the earth. You don't need autopilot and you don't need any other explanation. 110.22.20.252 (talk) 04:09, 7 October 2017 (UTC)

Name of 'Bill Gates just walked in the room effect'

How would you call the statistical effect on income/personal wealth colloquially called 'when Bill Gates just walked in a room'?--B8-tome (talk) 11:41, 6 October 2017 (UTC)

?? [3]? Andy Dingley (talk) 12:04, 6 October 2017 (UTC)

• This is related to the Ecological fallacy - the mistake of making assumptions about individual members of a group based on group averages. That article discusses a similar effect where the average wealth of US states is distorted by the super-rich. Smurrayinchester 12:09, 6 October 2017 (UTC)

• Don't know the name, but this is used to show the importance of using median incomes instead of average incomes. If you have a billionaire in a room with a thousand homeless men, their average income makes them millionaires, but saying "the room contains a thousand people, who, on average, are millionaires", is highly misleading. Yacht salesmen would be advised to look elsewhere. The median income correctly shows that most people in the room are dirt poor. StuRat (talk) 14:21, 6 October 2017 (UTC)

This effect might work out to the benefit of Paddock's victims, given his supposedly high net worth, as long as they take Hamlet's advice on the lawyers. μηδείς (talk) 19:32, 6 October 2017 (UTC)

Skin moisturizer as universal solvent ?

The first 4 ingredients in my skin moisturizer are water, mineral oil, stearic acid, and cetyl alcohol. So, it should dissolve substances which are water-soluble, oil-soluble, acid-soluble, and alcohol-soluble, right ? Is there some reason this is an important attribute in a skin moisturizer, or is this just a coincidence ? StuRat (talk) 14:29, 6 October 2017 (UTC)

Err yes & no. These are just the ingredients for making a Cream (pharmaceutical) which can be washed off. If you have a liquidizer in the kitchen you can make your own – and even eat what's left over. The important omega 3 fatty acids are left out of commercial products as they go rancid quickly and start to smell off. Aspro (talk) 15:37, 6 October 2017 (UTC)

That article says that water and oil are essential ingredients, and certainly for a moisturizer the goal is to add water to the skin, and oil is needed to hold it in and prevent immediate evaporation. That article also says an emulsifier and thickening agent are needed. Do the acid and alcohol serve those purposes ? If not, what do they do ? StuRat (talk) 16:38, 6 October 2017 (UTC)

From the stearic acid article: its primary use is as a "surfactant and softening agent" SemanticMantis (talk) 17:33, 6 October 2017 (UTC)

As I understand it oil & water are necessary to make a cream rather than a greasy ointment. The 'goal' of the moisturizer which one buys, is to generate profits for the share holders of the company. Any water can only affect the upper lays of the skin File:Skinlayers.png; like if one stays in the bath too long and ones fingers turn white and fingerprints expand, unlike bathing in sea water. No moisturizer on Earth will reach down to the lower layer where wrinkles form. Proprietary products use emulsifiers in order to combine oil & water (like egg yolks are used to combine the fat of dairy cream to make ice-cream and mayonnaise etc). See a dermatologist, for to find out what skin-care (note: I did not say treatment)suits your skin. If he says you have very thick skin – just point out to him, that as a WP editor -it is a necessity ;-) Aspro (talk) 17:54, 6 October 2017 (UTC)

I'm not looking for any medical advice, I only use skin moisturizer on my dry feet. Just wondered why it seems important for a it to be able to dissolve everything. StuRat (talk) 22:11, 6 October 2017 (UTC)

Conductive fingernail decoration strip?

Is the metallic form of this nail strip (for decorating fingernails) liable to be conductive or is that a stupid thing to hope? I find myself in need of a conductive material that is adhesive, very narrow (~ 1mm) and aesthetically pleasing/decorative and it would be great if this was, even if the resistance is high for a conductor. --185.216.49.78 (talk) 17:01, 6 October 2017 (UTC)

Have you tried the fingernail tips for touch-screens? 209.149.113.5 (talk) 17:16, 6 October 2017 (UTC)

They also make gloves with those built in. I own a pair. StuRat (talk) 17:20, 6 October 2017 (UTC)

Very high impedance. Too high to power LEDs etc. Andy Dingley (talk) 17:24, 6 October 2017 (UTC)

• No, it's a plastic (often polyester) with an aluminium metallisation deposited onto it. As the metallisation is so thin, resistance is high.

You might find conductive thread to be more useful. Also kitchen aluminium foil can be used like this, so long as you glue it down. I usually stick it to double sided tape, with the backing tape still in place, then guillotine that into narrow strips. Copper is better than aluminium for some tasks, as the oxide layer is less troublesome. Andy Dingley (talk) 17:24, 6 October 2017 (UTC)

It's not impossible that it's conductive enough for your purpose. But I wouldn't bet on it. I suppose for 0.99 you don't have much to lose, except your time, but I think you'll be frustrated.

Alternatives are conductive ink, copper tape, or conductive thread.

Good luck with your project. ApLundell (talk) 18:01, 6 October 2017 (UTC)

Carbon fibre is good for this though hard to find. I was given threads from a place selling fibreglass etc. for boat repairs.Polypipe Wrangler (talk) 23:14, 6 October 2017 (UTC)

Those human-looking robots

You know each year they have those AI things where people make robots that are like people? Last I saw, they just stare off into space but talk like people. Can they now detect eyes and make eye contact and follow your eyes around? That would be well-spooky. Anna Frodesiak (talk) 23:59, 6 October 2017 (UTC)

This is nearly ten years ago https://www.youtube.com/watch?feature=player_embedded&v=hCsEFaInYlQ

For serious research, look at 'Kismet' at MIT Andy Dingley (talk) 00:07, 7 October 2017 (UTC)

Darn. YouTube is blocked in China. :( Would that have show the eyes thing? Anna Frodesiak (talk) 00:16, 7 October 2017 (UTC)

http://jarkman.co.uk/catalog/robots/theeyestheeyes.htm

http://www.jarkman.co.uk/catalog/robots/giantstaringeye.htm

Andy Dingley (talk) 00:43, 7 October 2017 (UTC)

That's a good start. Anna Frodesiak (talk) 00:56, 7 October 2017 (UTC)

This certainly is doable. We have other technologies that tracks eye movements to determine what the user wants. See eye tracking. The more subtle part would be in getting it to know when not to track eyes. For example, if I hand you a file and say "Here's the Johnson report" and you keep looking at my eyes instead of the report, I'd think there was something wrong with you. And then there's people on the autism spectrum, who often don't like people staring them in the eyes. This would upset them, especially if it wouldn't stop, when asked to do so. StuRat (talk) 00:25, 7 October 2017 (UTC)

That makes sense. Maybe it could track the nearest person, or the one emitting the most sound (the one talking). And that "Here's the Johnson report" thing reminds me of someone. Maybe he's a robot. I'm going to pour water on him to find out. :) Anna Frodesiak (talk) 00:31, 7 October 2017 (UTC)

Good thinking. That will also work if he's the Wicked Witch of the West, in disguise. :-) StuRat (talk) 00:36, 7 October 2017 (UTC)

Or one of those aliens from Signs (film). In fact, I think we should hire a hit man with a Super Soaker (we really do have an article on everything, don't we?) to hose down the top management of the WMF and see if they melt. You can't be too careful. --Guy Macon (talk) 01:24, 7 October 2017 (UTC)

Yes, water-soluble evil aliens without the sense to wear raincoats, on a planet where it rains regularly, really gave me a good laugh. StuRat (talk) 01:45, 7 October 2017 (UTC)

There could be multiple people talking. Also, whether they are looking at you should figure into whether you look at them, and also how well you know them, should. Then there are some cultures where servants aren't supposed to look their "masters" in the eyes, which would be important to know, if those robots are to be servants. StuRat (talk) 00:39, 7 October 2017 (UTC)

Well, for now, if it just stared at the nearest/loudest that would be pretty impressive, I think. Anna Frodesiak (talk) 00:55, 7 October 2017 (UTC)

Not just the loudest, that would mean always looking at Trump. :-) StuRat (talk) 01:49, 7 October 2017 (UTC)

October 7