(Besides modern humans, obviously.) --Romanophile (talk) 05:41, 26 October 2015 (UTC)[reply]

Dr Marina Davila-Ross certainly seems to think so. Vespine (talk) 05:54, 26 October 2015 (UTC)[reply]

From Koko "Koko has also been reported to use language deceptively, and to use counterfactual statements for humorous effects, suggesting an underlying theory of other minds.[18]" with reference. --Jayron32 15:13, 26 October 2015 (UTC)[reply]

I would expect that most types of humor, like puns, would be impossible for other great apes to understand. Slapstick might work on them, though, like slipping on a banana peel. And perhaps hiding something so somebody looking for it can't find it might qualify as humor to them. Schadenfreude is another possibility. I can picture a great ape being amused by another that is too fat to climb a tree. StuRat (talk) 00:00, 28 October 2015 (UTC)[reply]

Of course they do. I believe there was even talk of this chimp replacing Letterman. Unfortunately he struggled to learn English to a sufficent standard. Hillbillyholiday ^talk 00:16, 28 October 2015 (UTC)[reply]

I'm pretty sure my dog has a sense of humor - it would be really surprising if the great apes did not. SteveBaker (talk) 15:52, 28 October 2015 (UTC)[reply]

• If we can believe YouTube videos of Koko, she liked Robin Williams and also liked being tickled. Whether this can be extended to "having a sense of humour"? I don't know.

Off topic, but another video alleged to show that another gorilla (Quiqley) had been 'taught' the concept of death, and understood that he would die. He was not enthusiastic about the idea. I'm now fairly sure certain that was a hoax. However, this in the NY Times makes interesting reading.

• Back on topic, Do animals have a sense of humour? from Slate via New Scientist, seems relevant. Koko gets a mention,:

"...once tied her trainer’s shoelaces together and signed “chase”.

• That sounds like humour (and slapstick) to me! (IANAP-I Am Not A Primatologist) - 220 of ^Borg 10:17, 29 October 2015 (UTC)[reply]

Do testosterone boosting activities like masturbation and anaerobic exercises like intense weight lifting and pushups etc... increase DHT and accelerate hair loss ? Does Minoxidil 5% in such a case block DHT at the follicles or become helpless ? What about Finasteride 1mg ? Does it become helpless if testosterone is too high ? — Preceding unsigned comment added by 175.101.24.136 (talk) 13:02, 26 October 2015 (UTC)[reply]

We do have the articles Dimoxinil and Finasteride. The first works by increasing the growth of blood vessels, not by counteracting DHT directly. The second has hormonal effects not limited to the scalp. μηδείς (talk) 16:41, 26 October 2015 (UTC)[reply]

How is there a watertight seal between the wheel wells and the drive shaft while still allowing the axle to spin in most amphibious automobiles? 20.137.7.64 (talk) 13:22, 26 October 2015 (UTC)[reply]

Stuffing_box#Gland 196.213.35.146 (talk) 14:00, 26 October 2015 (UTC)[reply]

Automobiles have many rotating seals that inhibit leakage of water e.g. at the coolant pump, or of oil from the crankshaft bearing. Instead of a stuffing box filled with string, seals now often use O-rings and elastomer materials as noted in the article Radial shaft seal. The amphibious cars shown have at their rear a drive shaft with seal for a propeller (the Schwimmwagen lacks reverse propulsion and can reverse only slowly by spinning its land tyres). Bestfaith (talk) 19:50, 26 October 2015 (UTC)[reply]

There was also the DUKW, a military issue amphibious vehicles which have been repurposed in many cities to give Duck tours. --Jayron32 21:37, 26 October 2015 (UTC)[reply]

Am puzzled by the above explanations. If you look at the right hand image. The drive shaft joins the gearbox above. The water line. Thus one doesn’t need a seal. Seals course friction and lower the milage per gallon. OK perhaps, in military vehicles, because the tax payer pays, but for a civilian vehicles ! They were designed so that water didn't ingress into the floor pan (via foot pedals, gear lever etc.) by making sure these ports where 'above' the water line.--Aspro (talk) 20:55, 27 October 2015 (UTC)[reply]

The Amphicar transmission has a rear-mounted hypoid differential and 4-speed gearbox built by Porsche (shown here) that are filled with oil, and so require rotating seals regardless of possible use in water. Drive to the twin three-blade screws is taken through a separate water transmission controlled by a transfer lever with forward and reverse positions, located next to the conventional gearshift on the center console. Special seals around the doors and their hinges contribute to keeping the footwell dry below the water line. Bestfaith (talk) 18:55, 28 October 2015 (UTC)[reply]

Who would win in a 50 mile race; a man on a bicycle or a man on a horse? 202.20.99.196 (talk) 16:21, 26 October 2015 (UTC)[reply]

See Man versus Horse Marathon, which has both on foot, and which sometimes the man wins. Given the greater speeds of a bicycle, the man on the bike would win 100% of the time, even if not a professional-class racer. Horses cannot keep full speed for more than a few miles, so over 50 miles, the man in the bike should win always. --Jayron32 16:49, 26 October 2015 (UTC)[reply]

Might depend a bit on the track. Something somewhat rough and narrow may favor a horse more, but I certainly agree with your assessment if the roads are paved (although I don't think it would be safe for the horse to run 50 miles over pavement).

Century_rides for cyclists on paved roads can usually be done in under 12 hours by most people fit enough to attempt the task. Obviously dirt trails would be slower. Average time for the 100 mile Tevis_Cup is a little under 14 hours. These are both 100 mile races but perhaps over a 50 mile length the horse's lack of endurance may be less of an issue than in a 100 mile race. So maybe a very good horse could beat a merely decent cyclist for some 50 mile journeys. SemanticMantis (talk) 16:58, 26 October 2015 (UTC)[reply]

Note that per the article, the Man versus Horse Marathon had a female champion cyclist lose to the horse in 1985. However the first victory to a human was to a cyclist by over 3 minutes in 1989. The article doesn't seem have other details of cyclists competing. These is some additional discussion in the article talk page suggesting a big reason for the failure of cyclists to win until 1989 was due to the lack of cyclists experienced in that type of terrain competing. Of course, the distance is a lot shorter than 50 miles, still I agree with SemanticMantis and wouldn't be sure that a non professional will always win depeding on the type of terrain. BTW, Endurance riding suggests 50 miles is a common distance for such horse racing, so if you'll look around you'll probably find completion times for such distances. However times are likely to depend significantly on the terrain so it'll probably be difficult to compare them to human times over such distances. Nil Einne (talk) 17:59, 26 October 2015 (UTC)[reply]

Everyone seems to have assumed the Q is about a champion bike racer. What happens when we put an average man on the bike, instead ? StuRat (talk) 22:02, 26 October 2015 (UTC)[reply]

Well, it depends on whether the couch potato brought along his handgun. Wnt (talk) 14:11, 28 October 2015 (UTC)[reply]

No, I mentioned 12 hours for century is the common goal for people who think themselves fit enough to attempt it, that's not an estimate for champion racers - a recent record for 100 miles cycling was set in 2003 at 3hr 23min 33sec [1]. Likewise, many if not most horses cannot travel 100 miles at high speed. What's an "average man" anyway? Maybe you can try a century ride and let us know your time. Maybe I'll do it too, and we'll have an average for n=2 :) SemanticMantis (talk) 22:23, 26 October 2015 (UTC)[reply]

Yeah and I specifically mentioned, "wouldn't be sure that a non professional will always win depeding on the type of terrain". Which was of course in response to what you said, and also what Jayron said "even if not a professional-class racer". So it doesn't seem anyone who responded assumed the question was about a champion bike race....

As for average, we need to assume median rather than mean here, since mean makes little sense. Although I know the traditional stereotype of people from China is that they all cycle, when we consider all the people from Africa and Asia (the later particularly China and India) who make up a big percentage of the world's population, I wouldn't be surprised if the median person has never cycled before (remembering also that quite a big percentage of the world's population is fairly young). So if you were to put them on a bike you get something like this [2].

Speaking personally, I cycle to shops around my neighbourhood (perhaps 2 km or so distance tops) sometimes, and have perhaps 10 times over the past 10 years gone further afield (10-20 km) but I'm not particularly fit and don't fancy my ability to make a 50 mile ride in one day (let alone a Century). However if I bring enough food, water and supplies (which will slow me down more but still) I guess I could make it within a few days (perhaps longer depending on the terrain). Probably the biggest barrier is I'm still not that good at fixing many problems that may arise with my bike, and I'm not sure I'll be that good at finding some place safe to sleep. But I definitely don't fancy myself making it there ever given my current ability, on a horse.

I suspect you'll find the same for the median person, since while I'm not totally certain the median person has never cycled, I am sure they've never riden a horse. In other words, the average person on a bike will surely either beat the average person on a horse or it will be a tie since neither of them make it to 50 miles. Doesn't seem particularly meaningful though....

Now technically the OP mentioned "man" not human, so perhaps they only mean adult males. This would if anything seem to push the trend in favour of the bicycle.

Either way, it makes sense to restrict ourselves to people with some level of ability on either. This is what I was doing, it sounds like what SemanticMantis was doing and I think was what Jayron32 was doing. This doesn't mean they have to be champions on either, but probably means at a minimum they have to be able to make it 50 miles without either killing themselves or the horse.

Possibly it's easier to train someone to be able to successfully ride a horse 50 miles than it is to train them to ride a bicycle 50 miles, since the horse will be doing a lot of the work (although as SemanticMantis said, why average person but not average horse?), but I'm not sure. After all, a lot of people are going to be very uncomfortable riding the horse since they just don't trust it, and it'll get even worse if the terrain is challenging. And most races over that distance seem to involve vet checks. While this may be mostly for humane reasons, it still implies the need for the rider to have some understanding of the horse. I guess if they aim for 2 or even 3 days, they may be a bit better off.

Nil Einne (talk) 07:57, 27 October 2015 (UTC)[reply]

If the ground is not ideal or bikes, such as damp, marshy or muddy dirt,or having to leap over fences, hedges and ditches, or swim across deep but slow-moving creeks the horse would be at a great advantage.I have ridden a horse across a creek when the horse was swimming, and I was not much of a rider. I could not have waded the creek carrying a bike. In wartime, cavalry often crossed 50 mile stretches which would have been a nightmare for bicyclists. Edison (talk) 03:50, 27 October 2015 (UTC)[reply]

You can always design a course that will favor one over the other. Consider this: "Which is faster, a racehorse or a snail?" Well, if the first hurdle on the track is a 50 foot high, foot-thick wall with a row of 2" tall holes at the base - then the snail will definitely win. Does that make it "faster"? Even if you're talking about an absolutely flat, uniform running track - then the winner depends on the distance over which the event is run, the temperature and probably a whole bunch of other stuff. SteveBaker (talk) 15:51, 28 October 2015 (UTC)[reply]

If I put both positive and negative points of battery to a bulb it will work. But if I put bulb's one point, the one that should be with battery's -ve, and the battery's -ve to earth I don't think it will light up. Why? 124.253.251.169 (talk) 17:02, 26 October 2015 (UTC)[reply]

The reason is works with a plug is that they connect the generator to the ground. If they didn't then you would not get a shock when you touched a plug. (Which sounds pretty nice, but there are historical reasons making that impossible.) If you go out and check you will find wires down the sides of telephone poles that connect the ground to the transformer up on top. Also every house has a connection to the ground. So when you get a shock power flows through you, into the ground, up one of those wires, then back to the transformer, and finally the generator. If you wanted you could do the same with the battery - connect one side to the ground, and see if you can get power to flow through the ground and light the bulb (it might be tough because of the low voltage, wet earth will be easier). Ariel. (talk) 18:06, 26 October 2015 (UTC)[reply]

Do I understand this correctly? You have connected one side of the bulb to battery positive. The other side of the bulb and battery negative are connected to two different earth connections, right? How good are your earth connections? Are you even talking about the soil, or something commonly referred to as 'earth' such as a vehicle body? Do you mean the earth wiring of a dwelling? If the latter, I suggest that you immediately stop testing and have the house wiring checked by a competent certified electrician, as it seems there is a discontinuity in the house's earth wiring that is hazardous to human life. Please be more specific. Akld guy (talk) 01:50, 27 October 2015 (UTC)[reply]

Some personal experience/original research: When installing ground rods at transformers it was straightforward in my locale to achieve a ground impedance of under 10 ohms via a 10 to 30 foot driven ground. So draw your circuit with the bulb connected to "ground" through a 10 ohm impedance and a battery terminal also connected to the same ground through 10 a ohm impedance. This is similar to a 20 ohm resistor connecting the bulb to the battery, with a wire connection of the other bulb terminal to the battery. Work out the voltage across the bulb and the current through it. If the bulb does not light, then you could increase the battery voltage, or select a different bulb, or decrease the ground impedance in two ways: drive the ground rod deeper, or add more ground rods several feet away from the initial ones and electrically connected to them. Four 10 ohm grounds located 6 feet apart and bonded together typically gave a 2.5 ohm combined ground impedance. I found that there might also be a slight stray voltage, both AC and DC, between the ground rods, as a complication to the thought experiment. Do not try this in real life without a utility locate process to make sure there are no buried lines or pipes where you drive ground rods.Edison (talk) 03:41, 27 October 2015 (UTC)[reply]

Resistance is discussed at length in electrical ground. Some specialty systems like Counterpoise (ground system) are used when it is high; of course, in your example, that basically means having two nets of wires that touch each other, or come close. The notion of perfectly zero ground is an approximation; that's often OK though, because the potential of the battery or AC connection is often kind of up in the air also, and it's only the difference that matters, so there's no need to have one better than the other. The question here is whether the ground resistance is comparable to the resistance of your lightbulb; resistors in series is relevant. A key thing to remember (though I think you know this) is that electrons aren't coming out of a battery unless they're also coming in, because even a tiny excess would create enormous voltages to drive them away. Wnt (talk) 14:06, 28 October 2015 (UTC)[reply]

It is said photons are massless particles that are force carriers. They are quantum of electromagnetic energy. If photons don't have mass, why are they called particles? The standard definition of particle is that particles are smallest units that constitute matter. Could anyone please explain in simple language how we conceptualize energy particles? What is quantum of energy? --IEditEncyclopedia (talk) 16:03, 27 October 2015 (UTC)[reply]

Someone can try to break it down for you in simple language, but in the meantime, see Elementary_particle and Wave–particle_duality. Also photon, which explains that they have zero rest mass, but positive relativistic mass. This is explained a bit in the section Mass–energy_equivalence#Massless_particles. SemanticMantis (talk) 16:12, 27 October 2015 (UTC)[reply]

(editconflict):I see SemanticMantis has mentioned Wave–particle duality already: in some circumstances, light behaves as waves, in others it behaves as particles: Interference for example is a wave property, the Photoelectric effect can be explained when we consider light as particles. It's similar to electrons, these are seen as particles, but will also behave as waves (will also show interference in a double slit experiment).

I'm not sure if "particle as the smallest unit of matter" is a standard definition, as the particle article says, it's rather general and would be further defined depending on the scientific field in which it is used. Elementary particle and List of particles gives more info: there are two fundamental classes of particles, the fermions and the bosons. Fermions are "matter" particles and bosons are "force" particles. It's quantum mechanics, and I think someone once said, if you're not shocked then you haven't understood it. Ssscienccce (talk) 16:30, 27 October 2015 (UTC)[reply]

Here it is written that photons are energy packets. These energy packets flow in a stream. What does it mean by energy packet? What is the distance between two energy packets. If light consists of a stream of photons, then there must be a difference between two photons. What is that distance? --IEditEncyclopedia (talk) 16:34, 27 October 2015 (UTC)[reply]

Not necessarily. Photons are bosons, which means that they can have the same exact set of quantum numbers. That means that you can literally have multiple photons occupy the exact same location in space and time. It's important to remember that photons are the way we model light behavior when it behaves as particles would (for example, during the photoelectric effect or during certain kinds of nuclear decay, or in the Bohr model of the atom). That is, sometimes light behaves in a way that a particle would, and when it does, we model that behavior as a photon, which is like a little ball or packet. Except this ball is not like a ball in all ways, just in the ways we need it to to represent what is happening during phenomena when light behaves like particles. --Jayron32 16:41, 27 October 2015 (UTC)[reply]

There's no particularly good reason photons are called "particles". I wouldn't read anything into it. Photons aren't really even "things". It's more accurate to say that light can only be emitted or absorbed in discrete amounts, at a single point, but when it's not being emitted or absorbed it obeys Maxwell's equations. Between emission and absorption, you don't have N "pieces" of light, you just have light. -- BenRG (talk) 08:25, 28 October 2015 (UTC)[reply]

BenRG is on to the most important thing to understand about this sort of physics. All we have, empirically, is data. We know that if you perform X experiment, you get Y results. Everything else we create to explain those results is theory, in the sense of Scientific theory, which is an experimentally verifiable explanation of events. Which is to say, that light does what light does. It isn't a particle, it isn't a wave, it's light, and its behavior is not governed by our expectations of what it should do. That we have those expectations is merely a product of our stubborn psychology, and not an issue with physical phenomenon. Back at the idea of a photon. A photon is a model of light, and a model which doesn't work all the time. That's what meant by wave-particle duality. That sometimes the photon model of light is necessary to explain a behavior (that is, to explain an observation we make about light) and sometimes the wave model of light is necessary. "But what is it really?" many people say. The answer is "light". It's just what it is. To fit its behavior into our paradigm of the world, that is into the set of expectations we have about how the world should work, we've invented these concepts like photons as "particles" of light. But, like any model, all models are wrong, but some are useful. The photon, it turns out, has been quite useful for explaining many of the observations we have made about light's behavior. --Jayron32 11:10, 28 October 2015 (UTC)[reply]

Photons do have mass - they carry energy, and mass and energy are two sides of the same coin. The complicating factor is relativity. Photons travel at the speed of light. If an ordinary piece of matter (a rock, say) were to travel at the speed of light, you'd need an infinite amount of energy to get it moving that quickly, and it would have infinite mass. Any number for the mass of the rock when stationary would be multiplied by infinity and would result in infinite mass. So if the photon could be stopped dead in it's tracks, what mass would it have? That's called it's "rest mass". What its mass would be if it weren't moving. The answer would have to be zero - since that's the only number you can multiply by infinity and still get a non-infinite answer. Zero times infinity can be any number - and so the photon has a nice, reasonable mass when it's zipping along at the speed of light - and zero mass if it were ever to be stationary. Weird, eh? SteveBaker (talk) 16:52, 27 October 2015 (UTC)[reply]

@IEditEncyclopedia: Steve's answer is a decent intuitive way to think about it, but be a little careful. What Steve is calling "mass" is technically relativistic mass, a concept that I am given to understand is somewhat out of fashion with physicists.

When I say "out of fashion", I don't mean wrong. You can define it precisely, predict how it behaves, and express your equations in terms of relativistic mass, and it works just fine. You can also express your equations without ever using relativistic mass, and it also works just fine. Physicists seem to have decided that the latter approach is, I don't know, more convenient, more perspicuous, a "better" conceptualization in some regard. I don't know whether they're right or wrong; I see some downsides to their preferred approach, but then I'm a bystander and don't really get to "vote". The important thing is that you need to be aware that when a physicist says "photons have zero mass" and Steve says "photons do have (presumably nonzero) mass", they're not really contradicting each other, just using different terminology. --Trovatore (talk) 17:15, 27 October 2015 (UTC)[reply]

One big problem with "relativistic mass" is that we already have a perfectly good name for it: energy. There's no good reason to give different names to the same quantity in different units, and relativistic mass is just another (redundant) name for the energy when it's divided by c^2 to put it into units of mass. --Amble (talk) 20:29, 27 October 2015 (UTC)[reply]

Well, it behaves like mass in a number of ways, and it is additive, whereas invariant mass is not. In several ways it more closely matches our intuitions about mass than either rest mass or invariant mass. There may be no need to have more than one name for the same thing, but there's also no great harm, and there are times it comes in handy. But in any case our personal preferences are of secondary importance here; the "facts on the ground" are that readers may encounter both systems of nomenclature, and need to avoid getting confused by what boils down to just two different bookkeeping methodologies. --Trovatore (talk) 21:02, 27 October 2015 (UTC)[reply]

I'm not describing my personal preference, I'm trying to help you understand the reasons why physicists generally do not use "relativistic mass" and instead simply talk about "mass" and "energy". Relativistic mass doesn't behave at all like mass in Newtonian physics: it changes with velocity, whereas invariant mass is a property of the object. (And neither is additive in GR). These aren't even two different bookkeeping methodologies, just a needlessly confusing historical terminology that has no currency in the field but for some reason continues to be brought out to dazzle the uninitiated by making relativity seem more bizarre than it really is. --Amble (talk) 22:04, 27 October 2015 (UTC)[reply]

I already understand their reasons. I don't necessarily find them compelling. But it doesn't matter whether I do or I don't. The terminology exists, and that's not going to change, so we need to help "the uninitiated" navigate the possibly-apparently-contradictory things that they may encounter. --Trovatore (talk) 22:06, 27 October 2015 (UTC)[reply]

That's the thing, the terminology "relativistic mass" scarcely does exist except in a historical context and in needlessly confusing explanations given to laymen. It's as though every time someone asked about how a thermostat works we started by telling them all about the galvanic and caloric fluids. We don't usually keep outdated terminology around just for the purpose of confusing people, and there's no good reason why we should do it here. --Amble (talk) 22:27, 27 October 2015 (UTC)[reply]

No, sorry, I don't agree. It may be true that the concept is not really used in present-day research physics. But it has a plenty big footprint in writings that are still relevant and useful for learners. The thing to do is just explain what's going on, not try to excise Tolman because he doesn't follow your preferred language reform. I see that as "tidy-mindedness" as I think the British say (it's not a compliment). --Trovatore (talk) 23:49, 27 October 2015 (UTC)[reply]

I might be way off, but I find "relativistic mass" to be a semi-intuitive term, and I'm fully happy to have similar things have different names, especially when their units and scaling are different. The main drawback in my opinion is that you also have to talk about "mass energy equivalence", which was easy enough for me to mention in my first response. But maybe Trovatore and I share some biases - I think sometimes it's useful to talk about antiderivatives, and sometimes it's useful to talk about indefinite integrals :) SemanticMantis (talk) 00:59, 28 October 2015 (UTC)[reply]

I think we should usually follow the relatively clear terminology used in physics research and education. If that makes me a tidy-minded language reformer, so be it. Talking about relativistic mass is fine where there's an actual use for it, but there's no good reason why it should be presented to learners as the mass in relativity. --Amble (talk) 01:07, 28 October 2015 (UTC)[reply]

Certainly you can rearrange words and concepts to avoid talking about the relativistic mass of the photon - but then you get into deeper complications with explaining that light has momentum...which classically, is mass times velocity. It is certainly convenient to separate out the concepts of rest mass from relativistic mass. But there are times when that's less convenient. SteveBaker (talk) 15:46, 28 October 2015 (UTC)[reply]

It remains a concept that is difficult to understand, even for physicists: see the 2008 book The Nature of Light: What is a Photon?. A photon is the smallest energy packet that can be measured or emitted for a given wavelength/color of light. In that sense it is somewhat similar to an atom being the smallest amount of any given element. However, the trouble with photons is that you cannot really measure them without destroying them, so you can't really 'follow' their behavior. - Lindert (talk) 16:55, 27 October 2015 (UTC)[reply]

Today I found that Ruthenium has oxidation state -4. Who knows where is Ru(-4) published?129.132.90.77 (talk) 16:15, 27 October 2015 (UTC)[reply]

This mentions the existence of Ru^-2 in Ru(CO)₄^-2 complex ions as the lowest known oxidation state of Ruthenium. Several other sites note the existence of this complex ion. I can't find any confirmation of a -4 Ruthenium, at least as yet. --Jayron32 16:34, 27 October 2015 (UTC)[reply]

doi:10.1016/j.solidstatesciences.2007.12.001 seems to have Ru as –4. I would be interested to know where the questioner found it noted, in case there are other leads there for references (or other interesting info). DMacks (talk) 02:04, 28 October 2015 (UTC)[reply]

List of oxidation states of the elements gives Ru(−4) in metal-rich compounds containing the octahedral complex [RuIn_6−xSn_x] (the Fe and Os homologues are also known). The two sources given are [3] and [4]. Double sharp (talk) 14:58, 29 October 2015 (UTC)[reply]

Those are the same two links, and also the same ref as the one I posted. The List article does have a second ref for Ru, but it does not appear to be about the –4 oxidation state. DMacks (talk) 15:33, 29 October 2015 (UTC)[reply]

I noticed the label says it's good for gargling, but doesn't list washing hands as a use. Is this because it would dry them out ? StuRat (talk) 01:30, 28 October 2015 (UTC)[reply]

H2O2 can oxidize surface skin cells and leave white spots on your skin. Doesn't usually happen with 3% if you wash it off promptly, but if you leave it on, it will. I certainly wouldn't gargle with undiluted 3% H2O2 — surely it says to dilute it first? --Trovatore (talk) 01:53, 28 October 2015 (UTC)[reply]

Actually, now I see that our article claims that the white spots are due to "a local capillary embolism", whatever that means. I'm a little skeptical; my impression is that the whitening is more superficial than that. I'd be interested to see a specific reference either way (the citation in the article points to a page that has four separate articles; doesn't say which article or page). --Trovatore (talk) 02:10, 28 October 2015 (UTC)[reply]

It's very strange that gargling is recommended. Our own article on hydrogen peroxide says, Large oral doses of hydrogen peroxide at a 3% concentration may cause irritation and blistering to the mouth, throat, and abdomen as well as abdominal pain, vomiting, and diarrhea. Intravenous injection of hydrogen peroxide has been linked to several deaths. Akld guy (talk) 02:02, 28 October 2015 (UTC)[reply]

Yes, vomiting, diarrhea, etc. are expected for an "oral dose", i.e. ingestion, but I think gargling is not a dose or ingestion. SemanticMantis (talk) 02:08, 28 October 2015 (UTC)[reply]

But if it can blister your mouth if you swallow it, I don't see why it wouldn't also blister your mouth if you rinse with it. Someone please check the bottle — I'm pretty sure the "gargling" usage is diluted, not full 3%. I don't think I'm likely to try it even diluted. --Trovatore (talk) 02:17, 28 October 2015 (UTC)[reply]

The bottle says to dilute with an equal quantity of water, so 1.5% concentration. StuRat (talk) 16:54, 28 October 2015 (UTC)[reply]

You made no mention of dilution in your original post. We have all been commenting on the basis that the concentration was 3%, which is what you did state. Akld guy (talk) 19:03, 28 October 2015 (UTC)[reply]

Well, my Q was about hand washing, which isn't mentioned at all on the label, so obviously there's no mention of concentration either. StuRat (talk) 01:58, 29 October 2015 (UTC)[reply]

Not only that, but if gargling were recommended with a strict admonition that it must always be spat out and not swallowed, it would only be a matter of time before someone would swallow a mouthful. Any instance where a product is intended to be placed in the mouth must cater for the fact that it will eventually be swallowed. The makers of chewing gum are mindful of that. Akld guy (talk) 05:33, 28 October 2015 (UTC)[reply]

A few drops, yes, but if somebody drinks a gallon of a gargle, they can't blame the manufacturer. A few drops should be nicely diluted and not pose any problem in the stomach. StuRat (talk) 06:05, 28 October 2015 (UTC)[reply]

Lots of websites seem to recommend diluting OTC H2O2 3% down to 1.5% or 1% for gargling and other oral care, but that other products equivalent to 3% or stronger is not uncommon for tooth whitening. A capillary embolism is fun, if your idea of fun is an embolism in your capillaries (tiny bubbles of oxygen under your skin). DMacks (talk) 02:19, 28 October 2015 (UTC)[reply]

Is that for real though? The spots seem very superficial, not deep enough that a cut that deep would bleed. Maybe they're sort of disused capillaries, passages where red cells used to travel back when that part of your skin was alive? --Trovatore (talk) 02:24, 28 October 2015 (UTC)[reply]

I am similarly skeptical. The epidermis doesn't have blood vessels (as our article says). The living parts obtain nutrients through diffusion, as do other avascular tissues like the cornea. --71.119.131.184 (talk) 04:59, 28 October 2015 (UTC)[reply]

Plenty of sources say the same, although some call it micro-embolisms Ssscienccce (talk) 10:08, 28 October 2015 (UTC)[reply]

Australian Dental Association study reports[5] long-term oral use of ≤3% was generally safe. DMacks (talk) 02:31, 28 October 2015 (UTC)[reply]

Say you had a large parabolic reflector aimed at a lens designed to focus the light into a beam. How much light could you send through the lens before the lens itself started overheating? Cpergielx (talk) 02:21, 28 October 2015 (UTC)[reply]

Let see. Some factors would be:

1) How close to perfectly transparent the lens is. If it really was 100% transparent, then an infinite amount of light could pass through (unless we count photons occasionally spontaneously decaying).

2) How small the lens is. A smaller (and in particular thinner) lens should be able to cool off more quickly.

3) What surrounds the lens. Some materials will carry heat away faster than others.

4) How hot the lens can get before it fails. If glass, melting is one possible failure mode, but uneven heating might also make it crack. A material with a zero coefficient of thermal expansion would resist cracking best, as long as the material to which the lens was mounted also didn't expand or contract.

5) The duration of the light beam. For use in lasers, it can be extremely short, and very little heating will occur in that time.

6) Note that some form of active cooling system, like oil circulated through the center of the lens, might keep it much cooler (although then you would also need to worry about the boiling point of that fluid). StuRat (talk) 04:57, 28 October 2015 (UTC)[reply]

Re 1) At 150,000 to 300,000 photons to the electron mass and Avogadro's number of atomic masses to the gram, the mass-energy of finitely bright light in the 100% transparent lens would exceed the supertanker in a pinhead density of a neutron star and therefore the maximum possible luminosity and the entire light-path will collapse into a black hole. Presumably, far before that you could put supertankers in orbit around the light beam if this was in deep space? Sagittarian Milky Way (talk) 05:26, 28 October 2015 (UTC)[reply]

Transparency of glass to sunlight is the key question. I'm not finding much. Cpergielx (talk) 11:53, 28 October 2015 (UTC)[reply]

The technical term is "Laser Damage Threshold" - see, for example, this datasheet for details on how it's calculated and results for various lenses. Tevildo (talk) 13:22, 28 October 2015 (UTC)[reply]

It depends on what you mean by "glass". I recall someone telling me that the glass used in optical fibers is so transparent that a kilometer of the stuff has the same transparency as a single sheet of window glass. So there is a massive variation possible between the best and the worst and "glass" becomes an impossibly vague term. SteveBaker (talk) 15:33, 28 October 2015 (UTC)[reply]

I'm someone who spends time putting LOTS of light through small lenses every day, (my wife's business involves laser cutting - and I maintain our two Lasersaurs) - our CO2 lasers put out 120 watts of infra-red light in a ~10mm diameter beam and a 25mm diameter gold-coated zinc/selenium lens focuses the beam to an 0.03mm spot. As you might guess from the exotic nature of the materials - getting that much IR light focussed though that much lens is difficult.

As a practical matter, there are three issues:

1. What percentage of the incoming light is reflected away, back towards the source? This is wasted energy (because it didn't end up where you wanted it) - but that reflected energy has to go someplace - and there is a lot of incoming energy, that might be problematic (it certainly is in my case). A lens may scatter the light back out through a wider angle, effectively diluting it to the point where it may not matter - but when the amount of incoming energy is really high - that may not be enough to prevent problems.
2. What percentage of the incoming light is absorbed by the lens? This is also wasted energy - but where the energy goes is almost certainly in heating up the lens. If the lenses I used were (say) 99% transparent - then the lens would heat up and shatter in a matter of seconds because 1% of the incoming energy is still a lot of energy! So I need something like 99.9% to allow the heat to radiate off of the lens as fast as it accumulates. Overheating the lens can cause a variety of problems - the lens might overheat and shatter or melt - the thing holding the lens in place might suffer - any fancy coatings on the lens might boil away or corrode in some fashion - it's certainly not a good thing!
3. What contaminants or other damage is likely to occur on the lens? Any kind of scratch or scuff will wreck the transparency of the lens...(see (2), above) and any kind of contaminant (dust, water condensation, etc) will also absorb the incoming light, get hot, etc, etc. So keeping the lens clean and avoiding it being touched by anything that might scratch it becomes a big deal. Ordinarily, when you care about something being contaminated by the environment, you encase it with something. But in this case, the "something" has to transmit light at least as efficiently as the lens - and then it has to be protected too - so you just get into an infinite regress.

There are certainly theoretical limits to what you can manage - but the practical issues are much more of a problem. Our lenses last only a couple of months before they have to be replaced. SteveBaker (talk) 15:29, 28 October 2015 (UTC)[reply]

What is the typical failure mode for your lenses ? As for keeping dust off them, there's a clean room or an evacuated chamber for the entire apparatus, but, in addition to being prohibitively expensive, if you are using the laser to cut, that will generate lots of gas and/or dust. StuRat (talk) 16:52, 28 October 2015 (UTC)[reply]

Laser cutting wood (which is what we do most of) produces a lot of smoke - which we pull away from the lens with some seriously powerful fans. There is also a small air compressor that blows clean air both over and under the lens in an effort to divert more smoke away from it. However, despite all of those efforts, it does slowly get contaminated - which soon becomes be fatal for the lens because the dirt collects laser energy, heats up and wrecks it. So we have to clean the lens every dozen or so operating hours - but because the surface of the lens is coated with a layer of gold that's just a few atoms thick - and the zinc/selenium stuff is about as hard as candle way - it's terrifyingly easy to scratch or scuff the surface. It winds up being a trade-off between the benefits of cleaning it versus the hazards of cleaning it! So no matter how careful we are, we end up replacing the lens every once in a while. We used to pay $300 for them - but with the popularity of these small laser cutters growing, we now find we can get them for around $60...which is some small fraction of a dollar per hour for a machine that can easily earn $1 to $2 per minute while it's running. SteveBaker (talk) 20:27, 28 October 2015 (UTC)[reply]

Wouldn't enclosing the lens in a glass box solve the problem ? The smoke would accumulate on that, which you could clean without fear. StuRat (talk) 01:52, 29 October 2015 (UTC)[reply]

You've entirely missed the problem though - how does the light get through the glass box (and out of it again)? Glass is much less transparent (and more reflective) to light at this frequency than my lens is - so the glass box would heat up and pretty soon shatter. Also contamination would wind up on the surface of the glass - with much the same result. The point is that the lens is already made of the best material for the job - so all you could do would be to surround it with more of that same material - so you'd be no better off! The best we can do (and what we actually do on the more vulnerable underside of the lens) is to enclose it in an opaque box with holes just large enough to permit entry and exit of the light beam. Then we pump filtered air into the box to create enough positive pressure inside to keep the smoke out. Sadly, that's not 100% effective - there is inevitable turbulence in the air leaving the box, and those swirls are enough to pull small amounts of smoke and other contaminants into the box and onto the lens. There is no easy way out of this - which is why high transparency and low reflectivity of the lens material and the avoidance of contamination impose practical limits on the amount of light you can push through a lens. SteveBaker (talk) 15:41, 29 October 2015 (UTC)[reply]

A "lens" may be more than a convex piece of glass, where the failure mode would be cracking due to uneven heating, or in the extreme literal melting. A multi-element lens may have multiple types of glass in it (if I recall correctly, crown and flint glass) to correct for certain aberrations. It may have groups of such elements to achieve the best image quality, if used as a telescope, binocular or camera lens. Lenses which are ideal for use in a view camera, for instance, may overheat and fail when used in a projector or photo enlarger. A similar focal length of lens made for use in a video projector, slide projector or movie projector would not have cement which would fail when light from a high power lamp passes through it.A camera lens might also have an iris or Waterhouse stop in it to reduce the light transmission and increase the depth of field, and it could overheat and warp r catch fire if made of a flammable substance. The shutter itself could similarly fail form overheating before the actual glass/plastic lens elements failed. A projector system I'm familiar with used a "cold mirror" in front of the lamp which selectively diverted visible wavelengths of light from the longer infrared wavelengths, which contributed to overheating of the film and optical path without contributing to image brightness. Edison (talk) 17:19, 28 October 2015 (UTC)[reply]

Does everyday masturbation increases DHT production thereby increasing hairloss ? — Preceding unsigned comment added by 175.101.24.136 (talk) 09:11, 28 October 2015 (UTC)[reply]

Probably not on your palm. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:32, 28 October 2015 (UTC)[reply]

The general consensus is that there is no such effect. Most studies that have looked at the effect of masturbation on testosterone levels in men have found it to be small and inconsistent. Looie496 (talk) 20:32, 28 October 2015 (UTC)[reply]

"Everyday" meaning daily, or "everyday" meaning non-exotic? Enquiring minds would like to know. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 14:23, 29 October 2015 (UTC)[reply]

What is the element with least amount of weight that follow all those rules?
1-Its not ultra rare
2-Can be used safely, its not radioactive, not burn easily......
3-Is found on solid state on normal temperature.
201.79.56.139 (talk) 16:36, 28 October 2015 (UTC)[reply]

Carbon ? Note that "burns easily" and "can be used safely" are somewhat at odds. Carbon has both radioactive and nonradioactive isotopes, as do most elements (there are three naturally occurring isotopes, with ¹²C and ¹³C being stable, while ¹⁴C is radioactive, decaying with a half-life of about 5730 years). "Light weight" is somewhat subjective, as different molecules will have different weights. Diamonds are a fairly heavy form of carbon, while carbon nanotubes and buckyballs are fairly light. StuRat (talk) 16:39, 28 October 2015 (UTC)[reply]

I read item #2 as "not burn easily", in keeping with the "can be used safely" theme. While carbon can be ignited and then it burns easily (at least in some forms), it's pretty easy to simply not ignite it (unlike pyrophoric materials). DMacks (talk) 16:50, 28 October 2015 (UTC)[reply]

Yes, we need a clarification from the OP on whether it should burn easily or NOT burn easily. As for how simple it is to avoid igniting it, that rather depends on the use they had in mind. If it's going to be used for the walls of a kiln, that's not so easy (although still possible, say by coating it with something fireproof). StuRat (talk) 16:57, 28 October 2015 (UTC)[reply]

Also, he needs to clarify "least amount of weight". Are we talking density or are we talking molar mass? By molar mass, the lightest "shelf stable", non-radioactive, non-flammable, common solid element is probably aluminum. It is the Third most abundant element on earth, while it is nominally very chemically reactive, any sample of aluminum exposed to air produces an impenetrable coating of protective aluminum oxide, which is why aluminum is stable enough for use in cans, food wrapping, cooking dishes, etc. It doesn't burn, it isn't overly radioactive, etc. In terms of density, however, the element that matches the OP's requirements is likely [silicon]. Every element less dense than silicon is either a gas, or highly chemically reactive, or flammable. Silicon is fairly inert stuff. The reason why silicon is less dense, even though its atoms weigh more than aluminum is because the crystal structure of silicon means that its atoms are more spread out, making the bulk material "lighter" than aluminum. I hope that helps the OP get what they are looking for. --Jayron32 17:05, 28 October 2015 (UTC)[reply]

Aluminium does burn, aggressively and hotly. Powdered aluminium is used in pyrotechnics. Solid aluminium is hard to ignite, but once it burns, it burns. --Stephan Schulz (talk) 19:42, 28 October 2015 (UTC)[reply]

Almost every element burns. Iron burns. Aluminum, in any form the OP is going to work with it, is not dangerously inflammable. You can safely use aluminum cookware on your stovetop, and stand no chance of it bursting into flame. --Jayron32 20:10, 28 October 2015 (UTC)[reply]

If the OP's "burn easily" is meant literally, calcium is probably the best candidate (1.55 g/cm³, lighter than graphite at 2.27) - lithium and beryllium are lighter, but probably fail the "used safely" test. Tevildo (talk) 17:12, 28 October 2015 (UTC)[reply]

And yet, graphite is used to line kilns and crucibles, as lubricants even at very high temperatures, and as electrodes in furnaces. DMacks (talk) 17:15, 28 October 2015 (UTC)[reply]

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.--Aspro (talk) 19:29, 28 October 2015 (UTC)[reply]

In what sort of school is "not ultra rare" considered an appropriate way of specifying a homework question in science? (Never mind, don't answer that.) --70.49.170.168 (talk) 04:51, 29 October 2015 (UTC)[reply]

I'm not sure why people haven't considered boron here. Yeah, it's expensive - $5 a gram, or about 1/8 the cost of gold (though also 9x less dense) - in its crystalline state. But you can buy a bottle for a couple of bucks in oxidized form as a roach killer, so the cost is basically purification, and of course if you purify anything enough it costs ... question said rare, not cost. Rare in the cosmos, not so much in certain dried-up lakes. Wnt (talk) 21:42, 28 October 2015 (UTC)[reply]

It's too heavy - 2.34 g/cm³, as against silicon at 2.33. Tevildo (talk) 21:57, 28 October 2015 (UTC)[reply]

Some clarifications, nope its not a homework, burn easily is a typo the real thing is not burn easily, with weight I mean the density201.79.56.139 (talk) 15:24, 29 October 2015 (UTC)[reply]

In that case, the best answer is probably carbon, in the form of graphite - density about 2.2 g/cm³ (lighter than silicon), and "difficult to ignite" (according to our article). Tevildo (talk) 22:52, 29 October 2015 (UTC)[reply]

Hi all, with the recent developments in space (the blood moon and other eclipses, water on Mars, the photographs of Pluto's surfaces, etc.) I would like to be able to share them with a group of kids (~6 to 8 years old). I'm not confident enough to adapt a source that's aimed at adults on the fly, and the NASA Kids Club doesn't seem to be a news service. Could you please help me find a reputable news service for kids which covers outer space topics? If not a service, just some recent kid-focused articles with pictures that I can use to help explain what's new in outer space. Thank you. --211.30.17.74 (talk) 21:43, 28 October 2015 (UTC)[reply]

A good space-related news site for kids may be http://www.timeforkids.com/minisite/space, though some of the articles are quite technical, and better suited for older children. http://www.planetsforkids.org/news/ seems nice but outdated, and http://www.funkidslive.com/?s=nasa&x=0&y=0 may also be interesting. - Lindert (talk) 22:52, 28 October 2015 (UTC)[reply]

The European Space Agency runs a space news website, ESA Space for Kids, but it also looks a bit outdated, the newest item is from September. --Jayron32 23:32, 28 October 2015 (UTC)[reply]

Found a kids news website called "Kids Ahead" which has a space news section: [6] It seems to be more of a news-and-press-release aggregator however, and doesn't seem to have its own content geared towards children. --Jayron32 23:36, 28 October 2015 (UTC)[reply]

How do both compare in terms of efficiency? Is what is happening inside the phone charger the same physical phenomenon (inductive power transmission) as in the case of the wireless charger? Could wireless charging be made almost like conventional charging (using a cable)?--Scicurious (talk) 00:08, 29 October 2015 (UTC)[reply]

See Battery charger which is Wikipedia's overview article. There are many different designs of chargers. You can read about them at your leisure. --Jayron32 01:00, 29 October 2015 (UTC)[reply]

There is a short description there about how an inductive charger works, but little as to how much energy is lost to heat when you don't have a direct connection. --Scicurious (talk) 15:50, 29 October 2015 (UTC)[reply]

As an anecdote (this is not data)... I have both a hard-wired mini-usb charger and an induction wireless charger. My phone goes from around 30% (which is what it has when I get to work in the morning on average) to 100% in about 20 minutes. Neither one works faster. The time is just about the same. I stopped using the wireless charger. It isn't because it is slower. It is just as fast and much more convenient. I stopped using it because it is impossible to turn off the very loud "HEY EVERYBODY!!! I'M CHARGING!!!" tone in Android without completely muting the phone. So, once my phone is charged on the wireless charger, it stops charging. A few seconds later, it realizes it is still on the charger and screams out the "I'M CHARGING!" noise. Then, it realizes it is fully charged and stops charging. Then, it realizes it is still on the charger and screams out the "I'M CHARGING!" noise again - over and over and over. It is OK if I'm at my desk. But, if I'm not, it goes off over and over and over, annoying everyone within earshot. So, I stick with the USB charger which doesn't have that design fault.

I wonder if that's a phone model issue: My phone (Galaxy 5s with a special backing plate) only makes the obnoxious noise on the initial placement of the phone, not after the charge fills. Mingmingla (talk) 01:20, 30 October 2015 (UTC)[reply]

209.149.114.132 (talk) 17:17, 29 October 2015 (UTC) @Scicurious:problem:insufficient research dataMahfuzur rahman shourov (talk) 17:20, 29 October 2015 (UTC)[reply]

Why would the Manhattan Project's Metallurgical Laboratory need a radiobiologist? To track the effects of radiation on the other workers? Obviously she performed useful postwar research on radiobiology, but most of her work seems completely irrelevant to the process of creating a nuclear weapon. Nyttend (talk) 12:01, 29 October 2015 (UTC)[reply]

If you're asking about Miriam Posner Finkel, this says she "worked on establishing the basic toxicity levels of radionuclides". -- Finlay McWalterᚠTalk 12:15, 29 October 2015 (UTC)[reply]

Yeah, I didn't click your link -- Finlay McWalterᚠTalk 12:24, 29 October 2015 (UTC) [reply]

Their day in the sun: Women of the Manhattan Project (Howes & Hezenberg, p 118) says the biology division was tasked to examine "the metabolism of radioactive materials" and their health effects. MPF et al. did animal studies on the health effects of radionuclides, including plutonium and strontium, other transuranics, and fission products. Given that most of these radioisotopes were novel, and their new (comparative) abundance unprecedented, it's easy to see why this knowledge would be valuable both for the research and production process (and the consequence of its effluent) and the short and long term effects of the weapon. -- Finlay McWalterᚠTalk 12:35, 29 October 2015 (UTC)[reply]

Your question seems to be a teleological one: "Why did those in charge of the Manhattan Project decide to hire a radiobiologist?" There were a lot of employees involved in the Manhattan Project, including the many employees at sites like Hanford and Oak Ridge. Given this, it's not surprising the Project was interested in the biological effects of radionuclides. If your workers are getting sick or dropping dead, that's a problem. The Manhattan Project was inventing entire fields of nuclear physics and engineering from scratch; many of the things it was doing had never been done before. This was uncharted territory. --71.119.131.184 (talk) 22:31, 29 October 2015 (UTC)[reply]

Hey, do you have any good refs for Oak Ridge and the Manhattan Project? I've briefly looked in the past and came up lacking. I'd like to see a nice well-referenced historical account of what went on there ~1935-2000 :) SemanticMantis (talk) 01:40, 30 October 2015 (UTC)[reply]

[Somehow I made my way to the Szilárd petition while investigating for this question. Don't know how many rabbit trails I followed...]

Last year, I added this picture to the Fermanagh Township, Juniata County, Pennsylvania article. I've just revised the caption, but I thought I'd better check: is my new caption an accurate description of the scene? Nyttend (talk) 12:13, 29 October 2015 (UTC)[reply]

Looks good to me. --Jayron32 12:23, 29 October 2015 (UTC)[reply]

I would add in the age of the rocks involved - in this case Silurian (from a map that I downloaded from here - you want the East sheet, but it is in a big (>80Mb) zipped file). I would also reword it - "with visible anticline in Silurian rock strata". Mikenorton (talk) 12:57, 29 October 2015 (UTC)[reply]

...and add that useful reference to back up the text. Bazza (talk) 14:12, 29 October 2015 (UTC)[reply]

OP curiousMahfuzur rahman shourov (talk) 16:41, 29 October 2015 (UTC)[reply]

Impossible to calculate from the information given. For starters, it will depends significantly on battery type, since the typical charging profile varies from battery to battery. The actual charging profile will depend on the device using to charge the battery, which will probably also affect the definition of maximum charge. On a related note, the output of the maximum rate output of the power cord (which is likely to be what is printed on it so I assume is what you mean by "powerchord of given A/mA") doesn't tell you what current is used to charge the battery. Nil Einne (talk) 17:43, 29 October 2015 (UTC)[reply]

@Nil Einne:battery take power same ampere as cord, how long take for given Ah or mAh or MAhMahfuzur rahman shourov (talk) 17:47, 29 October 2015 (UTC)[reply]

Mahfuzur, It will be easier to discuss things here if you follow WP:INDENT, see also WP:THREAD, thanks :) SemanticMantis (talk) 17:50, 29 October 2015 (UTC)[reply]

What battery are you using that can know what the maximum of the power cord happens to be and that uses a constant current charging profile until full? In any case, it's a fairly simply division, the units should make it obvious. (If you make sure you cancel out the outs, this should hopefully also avoid mistakes if one is in A and on is in mA so it's a useful test anyway.) Nil Einne (talk) 18:41, 29 October 2015 (UTC)[reply]

First identify the battery type in List of battery types as a Rechargeable battery because the particular battery technology will define what charging process it tolerates. See Rechargeable battery#Charging and discharging. There can be a wide range of charging regimes; these range from A) a simple slow charger that typically takes 14 hours or more to reach a full charge, which finishes in a small trickle charge current that just compensates a cell's self-discharge rate, to B) fast chargers that detect when a cell reaches full charge (change in terminal voltage, temperature, etc.) to stop charging before harmful overcharging or overheating occurs. Common examples for a Lead–acid battery are 1) charge by a constant-voltage 2.23V (13.4) by type A charger (the value is brackets is the Float voltage for a 6-cell automobile battery), or 2) the more complex type B IUoU battery charging regime. For a lead-acid battery rated at 40 Ah the maximum current during the initial phase can be 4 A; this will bring the battery to around 95% of its capacity and may take anywhere between 2 to 8 hours depending on the initial state of discharge. Other battery technologies have stricter charging requirements, and can be damaged by overcharge, so it is essential to follow the manufacturer's recommendations. Lithium-ion batteries now used in electric tools and some electric cars can be dangerous under some conditions and pose a safety hazard since they contain, unlike other rechargeable batteries, a flammable electrolyte and are kept pressurized. Bestfaith (talk) 18:44, 29 October 2015 (UTC)[reply]

That's what I said in my first post, but then the OP insisted that their hypothetical (I'm pretty sure it's hypothetical since the OP only asked for an equation & said nothing to indicate they were actually charging a battery) battery uses a constant current charging profile, that just so happens to be magically the same as the maximum of the power cord. If the OP wants to calculate the charging time for this magical battery, I guess that's up to them, but given how simple it is, they probably should try and do it themselves. 18:51, 29 October 2015 (UTC)

Does science have any axioms that are not actually mathematics or philosophy? --Scicurious (talk) 22:55, 29 October 2015 (UTC)[reply]

The concept of an axiom (something that is assumed to be true without any proof) is somewhat counter to the purposes of science, which is (roughly) to investigate the world and determine how it really works. There are certainly statements that are generally regarded as true and are taken to be the base of a large body of subsequent work (for example, that the speed of light is a constant), but for the most part scientists only make use of them because they're backed up by experimental evidence. Statements about how the world work do not 'commends themselves as evident', at least in an absolute sense. That said, part of the scientific process is making hypotheses about how the world might work, and working out the logical conclusions from there. For example, a group of scientists might say "What if subatomic particles were made of little vibrating strings, instead of being dimensionless points?" and work out how the world would look if that statement were true. But that's not really an axiom of "science", construed broadly. It's just an axiom for that particular hypothesis/theory. If the scientists working with that assumption can't back it up with evidence, then they are (frequently) criticized for it. - If there was anything that came close to an "axiom" in science, in the same sense it was used in mathematics,it wouldn't be with any sort of scientific facts about the world. Instead, the "axioms" of science would probably revolve around the scientific method itself. For example, the assumptions that events are repeatable (e.g. if you set up the experiment the same way twice, you'll get equivalent results), that reality is objective (e.g. two people doing the same thing can get the same results), that the rules of logic apply to reality (e.g. if you reach a contradiction, one of your assumptions is flawed ), etc. But even then, most of these are backed up by experience (evidence), so might not quite be counted as "axioms", depending on how broadly you define what an "axiom" is. -- 160.129.138.186 (talk) 23:33, 29 October 2015 (UTC)[reply]

All good stuff, I'll add the links to the concepts of repeatability and falsifiability. Philosophy of science, Epistemology, and Scientific law are relevant broad articles. WP:OR Most contemporary practicing scientists I know are implicitly Popperian, and if we construe "axiom" broadly enough, then everything is an axiom. If we construe "broadly enough" broadly enough, then everything is a piece of broccoli :) SemanticMantis (talk) 00:20, 30 October 2015 (UTC)[reply]

The other article to read is solipsism, which is where you get when you think about these things broadly enough. Solipsism is the Reductio ad absurdum that we get when we try to require that all knowledge must extend from observation only, and that we can never take any belief on faith. Solipsism is the philosophy without axioms. --Jayron32 01:21, 30 October 2015 (UTC)[reply]

I would suggest that methodological naturalism is generally assumed in science (and for good reason). --Stephan Schulz (talk) 01:34, 30 October 2015 (UTC)[reply]

OP curiousMahfuzur rahman shourov (talk) 03:42, 30 October 2015 (UTC)[reply]