Wikipedia:Reference desk/Archives/Science/2013 August 25

= August 25 =

Fear and adrenaline
I read an article ( http://www.scientificamerican.com/article.cfm?id=scared-to-death-heart-attack) which claimed that fear can cause high levels of adrenaline which can lead to arrhythmia and eventually cardiac arrest, even in healthy people. But surely, this is very rare in people who don't have underlying health conditions. Even intense exercise, a popular activity performed by many, releases adrenaline and raises heart rate, and this is seen as beneficial to overall health. So how can fear be any different? I would argue that fear may also be beneficial, many people enjoy controlled fear such as roller coasters, which have the same effect and claim that this actually reduces stress. Clover345 (talk) 00:36, 25 August 2013 (UTC)


 * It normally only becomes a problem with long-term fear. Brief episodes of fear rarely cause heart attacks, despite it being a TV trope where the murderer scares somebody with a heart condition in order to kill them. StuRat (talk) 01:30, 25 August 2013 (UTC)

What is long term? Even people who have anxiety over an upcoming event whether its an exam or a speech they have to give to a large audience, rarely die from cardiac arrests. People who are uncomfortable with public speaking may for example be anxious and therefore have elevated heart rates for up to weeks before the event. Clover345 (talk) 10:41, 25 August 2013 (UTC)
 * Those roller coasters all have rules prohibiting people with heart problems - who also have to get clearance from their doctors to exercise. Martial54 (talk) 02:59, 25 August 2013 (UTC)
 * Nobody has to get clearance from doctors to exercise. Doctors can give "orders" to their patients, but there is no law requiring the patients to obey those orders. Looie496 (talk) 05:49, 25 August 2013 (UTC)
 * The legal authority of doctors over their patients has nothing to do with the effects of high heart rate on heart attacks which is the question asked. Rmhermen (talk) 13:30, 25 August 2013 (UTC)
 * You can be scared to death, but this isn't something I would be seriously concerned about. The purpose of the study was, probably, less "here's a way you can die" and more "let's see if this trope can actually happen". At any rate, if you're interested in the phenomena, some articles (related) you may have interest in are Parasympathetic rebound, Baskerville effect, and Takotsubo cardiomyopathy; and, less directly related, Fear, Panic attack, Acute stress reaction, Fight-or-flight response. The latter links are related only in so far as they involve stress responses due to fear/anxiety.Phoenixia1177 (talk) 03:53, 25 August 2013 (UTC)
 * For Op: stress increases your risk for heart disease, you may want to consider for the general idea. The links I've given above discuss more acute cases of stress response. It is unlikely that a single given event will cause heart  to happen, thus while the anxiety over public speaking may not cause you to just keel over on the spot, if you have to do it repeatedly and it is a stressor, it can cause you to be more at risk for heart related issues.Phoenixia1177 (talk) 10:54, 25 August 2013 (UTC)
 * But there is also conflicting research which suggests that stress has no direct link to heart disease or high blood pressure and only indirect links. How can this be explained?. Clover345 (talk) 00:03, 27 August 2013 (UTC)
 * I'm not sure what exactly you're asking. Whether stress directly physiologically impacts the heart or causes you to smoke/eat/etc. more, it's still the case that people under more stress are going to have more heart problems. Similarly, people who drink lots of alcohol are, generally, going to have more brain damage than the usual person; it doesnt matter that some of these are the result of driving drunk or falling (instead of just directly chemical), alcohol is still a contributing factor- same idea here.Phoenixia1177 (talk) 01:15, 27 August 2013 (UTC)

Not too bright...
I just bought a floor lamp with 5 light bulb sockets. Each says "To reduce the risk of fire, do not exceed use of a 60 watt incandescent or 13 watt CFL bulb". Now, a 13 watt CFL puts out the same amount of light as a 60 watt incandescent bulb. However, I don't see why I couldn't use 23 watt CFL bulbs, which are equivalent in lumens to 100 watt incandescent bulbs. As I understand it, there are three ways a high wattage bulb could cause a fire:

1) The electricity in the wires leading to the bulb could cause the wire to overheat. This should strictly be proportional to the wattage, shouldn't it ?  That is, a 23 watt bulb should always create less heating of the wires than a 60 watt.  Am I wrong here, and does the power factor play a role in heating ?

2) The bulb itself gets hot, and this is a result of inefficiency in conversion of electricity to light. However, the CFL is far more efficient, so I'd expect a 23 watt CFL to only convert some 5 watts to heat, while an incandescent 60 watt bulb converts something like 45 watts to heat.

3) A CFL does also have a ballast, and heat is produced there, too. Is heat here somehow worse than up in the bulb ?  Maybe it can't dissipate as easily ?

So, is there any logic to the 13 watt CFL restriction, given that a 60 watt incandescent is acceptable ? StuRat (talk) 02:17, 25 August 2013 (UTC)


 * According to EnergyStar, you can use any bulb that is 60 watts, incandescent or cfl. These sites come to the same conclusion , ; but, they'r not as authoritative (though, it appears to be a common question.) As far as I can tell, the reason for the recommendation is that it should produce roughly the same amount of light; rather than prevent fire. (Just to point it out, since it is about fire risk, some people online say that there is a risk, but I haven't seen any clear explanation of why, nor have I seen this from any authoritative site.)Phoenixia1177 (talk) 03:10, 25 August 2013 (UTC)


 * Incandescent lamps convert about 5% of the electricity into light - and all the rest has to be waste. So 57 watts of waste.  A CFL is about 5 times more efficient - about 25% of the energy turns into light.  That's why a 13 watt CFL produces roughly the same amount of light as a 60 watt incandescent.  But the CFL generates only about 10 watts of waste.  Naively then, the 13 watt CFL ought to produce about five times less heat than the 60 watt incandescent...and I'd guess that heat is what matters in your floor lamp.
 * My best guess is that the people who printed that label had read that a 13 watt CFL is equivalent to a 60 watt incandescent - and mindlessly reasoned that they know that their appliance overheats with a more-than 60 watt bulb - and therefore it must also overheat with an "equivalent" CFL.
 * I think the label is wildly wrong! You ought to be able to use CFL's up to about 76 watts (which produce six times as much light - but only the same amount of waste heat as a 60 watt incandescent).
 * I suppose it's remotely possible that the inefficiencies in CFL's manifest themselves more dangerously than incandescents (eg producing more UV light or something) - and it's possible that the shape of the CFL blocks airflow and traps heat to a greater extent than an incandescent.
 * But the remarkable coincidence of the numbers they chose strongly suggest that the lamp manufacturers are idiots. SteveBaker (talk) 03:25, 25 August 2013 (UTC)


 * Yes, that was my guess, which explains the dual meaning of the title I chose. I just wanted to check with you guys to see if I was missing something. StuRat (talk) 03:37, 25 August 2013 (UTC)


 * Is the lamp certified by Underwriters Laboratories? μηδείς (talk) 17:31, 25 August 2013 (UTC)


 * Yes, but how is that relevant ? StuRat (talk) 07:57, 27 August 2013 (UTC)


 * Quick point. The risk of fire might come from the quality of the wiring in the fixture, rather than the accumulated heat output. So using a CFL of 76 watts would exceed the 60 watt rating of the wiring (a watt of electricity is a watt of electricity, regardless of if it's being converted to light or heat), even if it didn't exceed the 60-watt lightbulb heat equivalent. -- 205.175.124.72 (talk) 20:23, 25 August 2013 (UTC)


 * The wiring is almost certainly safe up to several hundred watts. It's actually amps that matter, and wiring that can carry less than an amp is rarely used for mains electricity.    D b f i r s   06:49, 26 August 2013 (UTC)


 * If the OP is from a 120 V country, his 5 60 W bulbs will draw a total of 2.5 A. -- 200.7.90.57 (talk) 11:43, 26 August 2013 (UTC)


 * Apologies. Yes, you are correct.  I'd missed the fact that there were five bulbs.  2.5 amps through thin wiring in a very narrow channel could generate significant heat.     D b f i r s   13:40, 26 August 2013 (UTC)


 * Note also the power factor of Compact fluorescent lamp can be poor, so the demands on the wiring will be greater. Obviously they're not so bad as to make the 13W make sense but the point remains even if the wiring could support 5*76W incandescents (or a 380W heater) it doesn't mean it could support 5*76W CFLs. Nil Einne (talk) 15:30, 26 August 2013 (UTC)


 * Yes - but we're really talking about why they'd put a 13 watt limit on the CFL - it makes no sense since even a 60 watt CFL would produce less heat (and need the same wire thicknesses) compared to the 60 watt incandescent. The 76 watt number comes about from heat considerations alone - so technically, you're right and a 60 watt CFL ought to be the highest power you could be 100% sure would be safe.  That said - it's pretty safe to assume that the wiring will have enough of a safety factor to support 76 watts without problems. SteveBaker (talk) 22:26, 25 August 2013 (UTC)


 * Perhaps it's just a bit of an "idiot proof" measure? If someone put in a 100W equivalent CFL bulb, the next person to swap it might assume that 100W is safe for the fixture, since they got used to the high light output. Vespine (talk) 23:16, 25 August 2013 (UTC)


 * I suppose that's possible...but then it takes a special kind of idiot to look closely at the equivalent wattage of the CFL yet completely ignore the warning on the floor lamp itself. The vastly more likely scenario is that some klutz might just think "Huh - this 60 watt (incandescent) bulb is kinda dim - I'll just stick a 100 watt one in there instead."...just ignoring the labeling entirely. SteveBaker (talk) 13:07, 26 August 2013 (UTC)

OK, thanks all. I will now feel safe using 23 watt (100 watt equivalent) CFL bulbs. StuRat (talk) 15:14, 26 August 2013 (UTC)

StuRat (talk) 15:15, 26 August 2013 (UTC)


 * One point I did not see above: a plain old incandescent bulb can function well when it gets extremely hot (hot enough to bake little cakes in an Eazybake Oven, or while turned on in a kitchen oven. The glass envelope temperature of an incandescent bulb can be 200C to 400C, while a halogen bulb may be up to 1200C. . Nothing in it is affected much by high temperature, within reason (eventually the glass will melt, or the solder will melt, or the adhesive holding the glass to the metal base will fail But a plain old inefficient light bulb has a very high permissible operating temperature, and the weak link might be paper insulation in the socket, the glass cover of the fixture, or the copper wire's insulation. A CFL, on the other hand, has all sorts of electronic devices in its base which are likely to fail at a far lower temperature. Some sources say to keep CFL's below 50C ambient. In a test I found online, a 10 watt CFL in a 3 liter container not really airtight, exceeded 58C inside 10 minutes. A somewhat sealed enclosure with the same amount of waste heat dissipated by each type of bulb, should allow more waste heat from an incandescent bulb than from a CFL up to the point of thermal failure of the bulb.  Heat shortens the life of CFLs.  A hot CFL also produces less light and lower efficiency. .  (The latter ref says keep the ambient below 40C for CFLs. Edison (talk) 20:15, 26 August 2013 (UTC)


 * That is a good call, Edison. But in general, fittings for ordinary incandescent bulbs will have been designed so that the bulb is in free air, and the heat will drive convection air flow over it.  The thermal resistance to ambient of a moderately hot object in free air can be roughly estimated by Pressman's formula:-
 * Rta =  7400 A-07
 * where Rta is thermal resistance to ambient, K/W; A is surface area in mm2.
 * So, the thermal resistance is roughly a constant for constant area, so we can estimate the surface temperature rise of a CFL by proportion. If a 60W incndescent dissipates approx 60 W and has a surface temperature of 200 C, or 175 K above room temperature, an equivalent CFL dissipating approx 13 W should have a surface temperature of 175 x 13/60 ie 38 K above room temperature, or a surface temperature around 63 C.
 * Pressman's formula is only a rough empirical guide, but this does confirm you are right - a light fitting designed for 60 W incandescents should be restricted to the equivalent CFL, and no attempt made to use the greater efficiency of CFL's to get more light. In practice, convection becomes somewhat non-linear as temperature increases, so the temperature rise of a CFL might be underestimated.  But CFL's have a greater surface area, cancelling this out. 120.145.62.173 (talk) 01:02, 27 August 2013 (UTC)


 * Interesting. This particular lamp has 5 separate "goose necks" each with a bulb in a cone at the end, open to the air.  I suppose I could remove the cones, but then I'd see the blinding bulbs.  Maybe they needed to make fluorescent bulbs bigger, not smaller, so you could leave them uncovered and still not be blinded by them.  (I've often thought this for cars, especially, where two blindingly bright lights is a bad idea, unless you think blinding the guy coming the other way as you drive over a hill is a good idea.)  StuRat (talk) 07:54, 27 August 2013 (UTC)


 * I would not remove the cones. Apart from providing mechanical safety (they prevent broken glass should you knock the floor lamp over), removing them may not change the degree of air flow much.  There are a variety of empirical formulae used by electronic and electrical engineers for estimating convection driven air flow, such as the following formula for the air flow rate through two apertures in an enclosure containing a hot object:-
 * V =  Cd A [ 2 g Hd {(T1 - T2)2/(T1 + T2)} ]0.5
 * where V is air flow rate; Cd is aperture discharge coefficient; A area of one aperture, g is accel due gravity; Hd is aperture vertical separation, T1 is temperature outside enclosure; T2 is tempertaure inside; all in standard SI units. This formula is known under the name of the Greek boffin who worked it out, but I can't recall his name right now.  So, you can look these formulae up if you wish.  I wouldn't bother though, as they give only rough estimates.  With 5 bulbs you should have plenty of light.  I agree with you about cars only to a certain extent.  Headlights at full beam are designed to direct almost all light forward down the road a kilometer or so.  That means a degree of focussing that may blind other drivers no matter how broad the source.  Also, it is important that oncomming drivers can immediately tell whether there is one headlight or two, so they know whether they are passing a motor cycle or car on a narrow road. 124.178.180.228 (talk) 11:18, 27 August 2013 (UTC)


 * I'd think a wide "light bar" would be easier to distinguish from a motorcycle, where you'd still have a single headlight. Also, two headlights can sometimes mean a pair of motorcycles, causing a great deal of panic when they pass on either side of you. :-) StuRat (talk) 12:16, 28 August 2013 (UTC)


 * Crikey, Stu! Don't know about your country, but in mine, unless on a well lit 6-lane freeway, motorcyclists doing that would rightly attract a charge of Dangerous Driving (a very serious charge), and should an accident occur and the offending motor cyclist survive, possibly a charge of Dangerous Driving Causing Death, with a possible jail sentence - should any police patrol be in the vicinity, or the car driver reports it.  In any case, such a motocyclist would certainly have a death wish. Not forgetting that motor cyclists are taught to ride near the centre line of their lane (for max visiblity to car drivers), and avoid riding abreast.  58.169.233.56 (talk) 16:24, 28 August 2013 (UTC)


 * It's probably illegal here too (unless some lobbyist for a company wanting to sell more underpants managed to legalize it), but motorcycle riders aren't known for being sticklers for the law. StuRat (talk) 05:14, 29 August 2013 (UTC)


 * The responses above miss an important issue: a large fraction of the energy wasted by an incandescent bulb is emitted as infrared radiation, which in most cases leaves the bulb and the fixture/lamp. CFLs emit almost no infrared; their waste heat load is much smaller, but it is nearly all generated inside the bulb and must be carried away by conduction through the base. The safe operating power for any given fixture will certainly be lower with a CFL installed than an incandescent bulb, particularly for enclosed fixtures. Using a 50 W CFL in an enclosed fixture designed for a 60 W incandescent bulb will most likely result in premature failure of the bulb, and possibly also damage to the fixture. The manufacturer has obviously taken the easy way out and not done engineering tests with CFLs to determine the safe limit, but rather just picked 13 W (60 W-equivalent) as a conservative safe value. --Srleffler (talk) 17:30, 27 August 2013 (UTC)


 * I question your assertion that incandescents loose a large fraction of their heat through radiation. The lamp stand "cones will reflect a lot of it back to the globe anyway.  But let's assume it's true.  That would mean that their surface temperature is lower than would be expected by Pressman's formula, as there is not the full 60W to drive up surface temperature.  So my simple proportion estimate of CFL surface temperature above underestimates it.  That makes it even more likely the lamp stand manufacturer was right to limit CFLs to 13 W.  58.169.233.56 (talk) 09:34, 28 August 2013 (UTC)


 * Pressman's formula is improperly applied in the discussion above. An incandescent light bulb is not a "moderately hot" object dissipating heat by convection into free air. The filament is intensely hot (thousands of degrees), and is in an enclosed space (the bulb). The filament is primarily cooled by radiation, not convection. From Luminous efficacy and this paper, a typical incandescent bulb's spectrum is roughly that of a 2800 K blackbody radiator. The emitted light itself has a luminous efficacy of radiation (LER) of about 15 lm/W. This indicates how much visible light there is, as a fraction of the total amount of radiation present. A typical 60 W incandescent bulb emits about 870 lm of light. At 15 lm/W LER the emitted radiant power is about 58 W. The bulb is about 96% efficient at converting electricity into radiation, but most of the radiation emitted is infrared. The remaining 4% (about 2.4 W) goes into heating the envelope of the bulb and its base.


 * I don't know offhand what the LER is for a CFL, so let's consider a hypothetical "ideal" daylight CFL that mimicks a 5800 K blackbody in the visible spectrum, but has no infrared or ultraviolet. The LER for that would be 251 lm/W (from the same paper referenced above). Assume the 13 W CFL emits 870 lm just like the 60 W incandescent bulb does. The radiant power is about 3.4 W. The remaining 9.5 W of power consumed by the CFL is waste heat that must be carried away from the bulb by convection or conduction through the base. In this worst-case comparison, the CFL dumps about four times more heat into the fixture than the equivalent incandescent bulb would.


 * In practice, not all of the infrared radiation makes it out of the fixture, so the incandescent bulb will dump more heat in the fixture than the above analysis suggests. Also, a real CFL probably has a lower LER than the best-case estimate above, and so emits more radiant power to produce the same luminous flux. The real CFL would dump less heat into the fixture than the above analysis indicates.


 * My point is that the lamp manufacturer is right to limit CFLs to a lower electrical power than the limit for incandescent bulbs. I doubt that they have put in the effort to determine the exact safe limit for CFLs. Rather, they would at best have done an experiment where they run 60 W-equivalent (13 W) CFLs in fixtures designed for 60 W incandescents, and verified that the fixtures do not burst into flames. They may well have also tried using a 25 W CFL and found that the fixture became too hot.--Srleffler (talk) 04:01, 29 August 2013 (UTC)


 * Srleffler, your amplification of your earlier post stating that most of the heat is lost via radiation is noted. But as I said before, the error thereby in starting with Pressman's Formula is such that the surface temperature of a CFL was underestimated.  It is the bulb surface temperature (actually the bulb base temperature) that determines the thermal stress on the lamp fitting and wiring. The radiant heat from an incandescent bulb is shielded from the lamp socket by the bulb metal base. Quite a bit of the radiated heat would impinge on the cones, which are often enamelled mild steel or anodised aluminium and the like.  A lot of this heat is reflected back to the bulb, raising the bulb glass temperature, reducing the error in starting with Pressman's Formula.  The cone temperature is however, very much lower in temperature than the bulb glass, partly because of its much greater surface area and partly because of the air space between it and the bulb.
 * Incidentally, electronic engineers routinely calculate the surface temperature of metal parts ("heatsinks") on which hot transistors and other parts are bolted or clamped(using Pressman's F or some other method). I can tell you from much experience that 2.4 W (your estimate of dissipation in the bulb glass and base, and coincidentally of the same order as the power dissipated by transistors in a typical cheap stereo) would not raise the bulb surface temperature anywhere near the 200 C quoted, even if conduction out of the base was not possible.  The diameter of a 60 W incandescent is about 55 mm.  Area (4 pi r2) is thus 9500 mm2 assuming it is a simple sphere, which of course will lead to significantly under estimating the surface area.  Applying Pressman's Formula, the thermal resiatnce to atmosphere is then 12 K per watt.  So, for 2.4 W dissipation, the temperature rise should be 29 K.  You only need to touch the glass of a running 60 W globe to know that's way too low, so the dissipation must be very much greater than your 2.4 W figure.
 * The bulb base "intercepts" about 15 to 17% of the sphere surface. So 15 to 17% of the heat radiated by the filament is intercepted by the base and dissipated in it - about 9.8 W added to the 2.4 W.  That indicates a surface temperature rise above ambient of 140 K, but that is an over-estimate as some heat will be lost via conduction into the lamp fitting.  Still too low.
 * 120.145.29.159 (talk) 04:46, 29 August 2013 (UTC)
 * A 60 W bulb in free space doesn't get as hot as 200­°C. A quick look online suggests ~120°C as a better guess. I wouldn't have guessed quite that hot. I agree that 2.4 W doesn't seem like enough to reach this temperature. Interception of radiation by the base of the bulb is probably sufficient to explain it, however. This does raise the heat load of the 60 W incandescent a little bit above that of the 13 W CFL (12.2 W vs. about 9.5 W). Some of the CFL's radiation will also be absorbed in the lamp, of course. I don't think reflection of radiation back to the bulb is a big factor. The glass envelope of the bulb is transparent, so it does not efficiently absorb infrared. --Srleffler (talk) 18:02, 29 August 2013 (UTC)
 * This is a good discussion - because we both, and the OP, have all learnt something. However you you have not cited any reference to back up your claim that a 60 W incandescent only gets to ~120 C.  I took the 200 C figure from Edison's post.  He got his >200 C figure from a reference he cited which looks pretty authorative to me.  The Wikipedia article on Incandescent lamps quotes the same figure, based on a 1964 GE pamplet on incandescents.  I did a quick google and found a few websites giving >200 C and none giving ~120 C.  Can you cite a reference?
 * The transparency of the glass envelope is not anywhere near as important as you may think. If it was truely transparent to infrared as well as visible and other wavelengths, a bulb in open free air would run at room temperature due to conduction to the surrounding air.  It clearly does not run at room temperature, so there is some absorption.  For a bulb in a typical cone fitting, the metal cone typically surrounds the bulb to about 80% or so.  This largely means that any radiation fed back by the inside of the cone has nowhere to go expect back through the glass a few times, heating it a little bit more each time.  It's a bit like a cavity radiator, where the radiation emitted through the cavity orifice appears as though the cavity is a near perfect black body surface even when it is far from being such a surface.  Any small object suspended within a cavity radiator "sees" radiation corresponding to black body radiation.
 * 120.145.29.159 (talk) 00:16, 30 August 2013 (UTC)
 * I agree it's a good discussion. I did a google search and saw two pages that gave values around 120°C for a 60 W bulb. One was this one. The other I didn't manage to find again. Neither was as authoritative-looking as Edison's reference. I do find it hard to believe that a typical 60 W bulb gets that hot in free air, though. While they are hot to the touch, the level of pain does not seem consistent with such a high temperature.
 * The amount of reflected radiation absorbed by the envelope will be smaller than you suggest. The envelope is heated by convection from the hot filament. (Modern bulbs have a gas fill, not vacuum.) The black body spectrum for a 2800 K radiator peaks at around 1 µm. Absorption for a thin soda lime glass envelope in this wavelength range should be on the order of a few percent at most.. Yes, the light passes through the glass a few times but most of it will eventually exit the fixture. If this weren't the case, the fixture would not be efficient at emitting visible light either. The optical properties of glass in the near infrared are much the same as in the visible range.--Srleffler (talk) 04:04, 30 August 2013 (UTC)
 * Your cited reference for 120 C is a typical public question and answer website and has no credibility. The reference cited by respondent "Chai" is just another typical public question and answer site. Not worth a sniffle in the rain.
 * You are correct about the internal convection though - and it does mean my explanation of some absorbance by the glass is a lot of crock. However, only a few percent absorption, and even less, is all that is required for some cavity radiator - like effect. Of course it doesn't really matter how the glass gets hot, absorbing radiation or by internal convection.  The mere fact that it is hot means so much heat lost by the bulb by conduction to the surrounding air, and thus so much less left to be lost by radiation.
 * Are you familiar with cavity radiators? 124.178.41.65 (talk) 04:43, 30 August 2013 (UTC)


 * It's possible that a clear incandescent 60W only heats up to 120°C, while a frosted incandescent bulb heats to 200°C. As for the pain felt while touching either, I assume you don't touch it while it's actually on, and once you turn it off, the temp rapidly drops. StuRat (talk) 05:39, 30 August 2013 (UTC)
 * The reference cited above by Edison does not distinguish between frosted or clear. However there is not likely to be any difference, as there is insignificant difference in light output between the two.  In any case, if Srleffler is correct in saying that most of the heat in the glass comes via internal convenction in the fill gas, and I think he is largely right in that, then there won't be any difference.
 * You are right, the glass does cool down within minutes of the light being turned off. That is because the glass is very thin and has little heat storage capacity.  After all this, I trust you are wary of putting bigger CFL's in your lmap stand, I can touch 60 W globes while they are on, but only for a small faction of a second.  Far too short to usefully assess their temperature.
 * I use high efficiency halogens myself. Our power company gave us free samples of CFL's but they all failed within months. Halogens last longer than both CFL's and standard globes, 42W is regarded as equivalent to standard 60 W globes.  The light quality is much better than standard and CFL.  If you want more light, Stu, you can safely put a 60 W halogen in place of a 60 W standard incandescent and get about 50% more light. This is for 240 V globes.  With your 115 V house current, the improvement may be different.  They are pricey though.
 * 124.178.41.65 (talk) 06:40, 30 August 2013 (UTC)


 * I'm not seeing how a 42W halogen is better than a 13W CFL. There's the higher cost of the halogen bulb itself, the higher cost of the electricity, and, in summer, the higher cost of A/C to fight that additional heat.  I do, however, use halogens in winter.  I think of them as a light bulb with a space heater built in.  I use 300W halogens in two rooms in winter, and can turn down the heat when they are running, because those rooms become nice and toasty.  One downside, though, is when a bug gets too close and fills the house with a burning smell (I imagine the bug finds this to be a negative, too).  The CFLs seem to kill bugs, too, but they don't smoke like that. StuRat (talk) 02:56, 31 August 2013 (UTC)
 * This response is based on what StuRat said, not what any banned sockpuppets have said. I would avoid halogens personally, from my experience they don't last nearly as long as CFLs and they also have totally crap yellowish light similar to incandescent. Nil Einne (talk) 08:25, 31 August 2013 (UTC)

engineering
Good time, I am a ICSE student and i am interested in science. I wanted to know the fields in engineering. As in what what subjects are there, what types of engineering are there, if I like any 1 field in engineering then what to do for it. please help me in this matter. you would be very much thankful. 115.242.18.161 (talk) 03:34, 25 August 2013 (UTC)₵


 * See list of engineering branches, to start. StuRat (talk) 03:39, 25 August 2013 (UTC)


 * See also Engineering education. Duoduoduo (talk) 20:42, 27 August 2013 (UTC)

physics
what would happen to a seed if we planted them in a rotating wheel and provided them with all its needs. The question is how will that plant grow as we know that the roots grow towards the gravity and the shoot part of the plant grows towards the light in what manner will it grow in the rotating wheel??? — Preceding unsigned comment added by 115.242.66.252 (talk) 06:23, 25 August 2013 (UTC)
 * Excellent question. The spirit of science is all about inquiry. Try it and find out. Let us know your results. Dolphin  ( t ) 07:15, 25 August 2013 (UTC)
 * Gravitropism is studied using clinostats as you suggest, and in space stations. In addition to gravity, plants use light (phototropism), water (hydrotropism), and touch (thigmotropism) to orient themselves.
 * In the absence of gravity, plant roots tend to seek out water and nutrients, and shy away from light. Leaves grow to maximize light collection.  Many plants will grow just fine and look like they normally would. I don't know what something like a tree would do though. 88.112.41.6 (talk) 07:39, 25 August 2013 (UTC)


 * What size wheel and how fast? ←Baseball Bugs What's up, Doc? carrots→ 02:12, 26 August 2013 (UTC)


 * There was a Scientific American article about this in the 1970. In essence, you can simulate zero-G by a wheel that rotates fast enough (as I recall, on the order of minutes). There was a way to simulate the entire G range, from zero to arbitrarily high, depending on the design of your wheel and rotation rate. Edit: The article was in the "Amateur Scientist section of the June 1970 issue, page 141. Tdjewell (talk) 11:51, 26 August 2013 (UTC)


 * I don't see how you can simulate zero g with a rotating wheel on Earth. In a horizontal wheel that should always increase the g's, since now you have the vector sum of gravity and the apparent outward force.  If it was spinning at 1 g, that would give you 1.44 g aimed outward and down.  With a vertical wheel spinning at 1 g, you should get 0 g at the top, yes, but 2 g at the bottom.  The only way I can see to get zero g constantly is if the wheel is a great circle around the Earth, and rotates at 1 g. StuRat (talk) 05:23, 29 August 2013 (UTC)

Stanford Torus / Elysium orbital habitat
Hullo. Having just seen the movie Elysium, I've been looking at some details of the Stanford Torus. The movie features an orbital habitat similar to a Stanford Torus, but it didn't appear to be rotating very fast, and had an open "top" on the actual habitat section!! Could someone please answer a couple of questions for me?
 * Your "Stanford Torus" article says that to get about 1G in the habitat ring, a structure 1.8km diameter needs to rotate at 1 rpm.


 * 1. If the diameter was bigger would it need to rotate faster or slower to get the same G force?
 * 2. If you are in a habitat that has 1 g at your feet level, but zero G at 900 meters above your head, how would the gravity gradient on your body affect you?
 * 3. Would it actually be possible to have an open top on the habitat ring the way the movie does?
 * Thanks in advance 122.108.189.192 (talk) 07:55, 25 August 2013 (UTC)


 * You can read more about artificial gravity created by spinning here, or do the math yourself over here. Spoiler; larger diameters means you'll have to spin slower to maintain gravity. WegianWarrior (talk) 08:45, 25 August 2013 (UTC)


 * A difference of two parts in 900 in gravity from head to foot would not really be noticeable. An open top means that air will constantly be lost, but the rate of loss might not be a serious problem if there is a constant renewal (as on Earth).  According to Atmosphere of Earth, the tropopause is about 12 kilometres up, and there are gases beyond that, so a mere 900m seems inadequate to retain a proper atmosphere.  Perhaps someone can calculate the loss rate?    D b f i r s   16:45, 25 August 2013 (UTC)


 * The Stanford torus is a mile in diameter, which is less than the scale height of gasses in the Earth's atmosphere (as Denver residents will attest). Therefore, it could not exist uncovered.  I don't know if the movie uses a true Ringworld (or at least one around the Earth); if it does, and if it uses very, very high walls, it might work.  Or maybe they have force fields?  Actually just architectural invisibility might suffice, unless you see ships going through the 'empty' space at will - it shouldn't be that hard to make a metamaterial which is transparent with no refractive effect on light, when present as a nearly perfectly flat architectural element. Wnt (talk) 08:13, 26 August 2013 (UTC)


 * Actually, ships can apparently fly into the "interior" of the structure at will. (I haven't seen the film.) The science fiction writer Gary Westfahl has some remarks on this in the second half of the third paragraph in his review here. Deor (talk) 16:27, 26 August 2013 (UTC)


 * You have to spin faster if the ring is larger. Because we fall about 5m (16ft) in the first second on Earth, that 5m has to come from curvature if you want 1g from spin. you can draw a tangent to a ring 5m smaller in radius than the actual floor level; the ring has to spin fast enough to move from the tangent point to one of the intersections with the "floor level" in one second. That would grow with size, but less so than the size itself. (Stupid engineer's trick, does not work if the radius is not substantially larger than 5m) - ¡Ouch! (hurt me / more pain) 06:30, 28 August 2013 (UTC)


 * It can be this way or that way, if you are looking at meters per second, bigger is faster. If you compare rpm, smaller is faster. - ¡Ouch! (hurt me / more pain) 08:24, 28 August 2013 (UTC)


 * 2) While that gradient isn't enough to notice, a larger gradient (from a smaller ring with higher RPMs) causes dizziness, disorientation, and nausea, particularly when standing up (you are literally "lightheaded"). If everyone was lying down (as in a sleeper ship) this would be less of an issue. StuRat (talk) 05:30, 29 August 2013 (UTC)

the heart realy in the size of the fist?
I saw in once forums someone that ask a doctor (cardiologist) if the heart in the size of the fist, and he answered that it's not exactly and it's not scientific to say such. So, my question is how is 'scientific' size of the heart? 176.13.1.78 (talk) 12:34, 25 August 2013 (UTC)
 * Our own article on heart also suggests that it is roughly fist-sized, but that is just a comparison to give lay people a rough idea of how large it is; there's no reason to think it's a particularly accurate measurement. You could very easily have an enlarged heart, but small hands, or vice versa. If an internal organ needs to be measured for size, you'd have to do some kind of medical imaging, such as a CT scan. Matt Deres (talk) 13:01, 25 August 2013 (UTC)
 * I looked briefly before and found that normal hearts were about 300 g, hypertensive hearts over 400.  The actual proportion with body mass wasn't given in that source.  The density shouldn't be much more than 1 so that should be 300-400 ml.  But I got bored and didn't look up the volume of a fist - if one of us happens to have a beaker handy we should push our hand in and see how much water is displaced. Wnt (talk) 08:16, 26 August 2013 (UTC)
 * This paper looks like it may have the data we need on the volume of a typical human hand - but it's behind a paywall. If anyone has JSTOR access, they might maybe take a peek at it for us. SteveBaker (talk) 13:02, 26 August 2013 (UTC)


 * From Table 1 of that paper: Men/Women, dominant hand volume(cm^3) is 431+/-53, 285+/-35, respectively. For non-dominant hand, we get 417+/-51, and 273+/-35. Largest hands were in men 40-49 years old, n=55 men, 45 women. I'll leave interpretation of this up to the others. SemanticMantis (talk) 14:47, 26 August 2013 (UTC)
 * Cool! So now we know!  Hearts are around 300 to 400g - which, if their density is similar to water (like most of our bodies), would suggest a total (collapsed) volume of 300 to 400cc's - which is indeed pretty similar to the volume of a human hand at 280 to 430 cc's.  Obviously, the beating heart will be larger because of all of the cavities - but then a fist encloses more volume than the hand itself...so probably this comparison is in the right ballpark.  Of course the cardiologist is correct in saying that it's an inexact thing - but then how could it not be?  Hearts and hands vary in size between people - and hearts and fists enclose different volumes depending on what state they are in - and just how far up your wrist is "hand" and when does it become "forearm"?  But roughly - it's a pretty good analogy. SteveBaker (talk) 18:50, 26 August 2013 (UTC)

Hairs and nails
Why do our hairs and nails keep on growing even when they consist of dead cells? Concepts of Physics (talk) 14:24, 25 August 2013 (UTC)


 * Because the root isn't dead. See Human hair growth and Nail (anatomy). AndyTheGrump (talk) 14:27, 25 August 2013 (UTC)


 * 1) Because a multi-cellular organism can be dead without all of it's cells being dead. Those cells with a low metabolic rate, like hair follicles and nail bed cells, can survive for a long time just feeding off the blood, tissue, and air around them.


 * 2) Much of the apparent growth after death is really due to the dehydrated body shrinking back more than the hair and nails. StuRat (talk) 15:01, 26 August 2013 (UTC)


 * That's not quite what the OP was asking, but it's a good point. ←Baseball Bugs What's up, Doc? carrots→ 16:00, 26 August 2013 (UTC)
 * ...But a big [citation needed] on the 'low metabolic rate' claim&mdash;cells in the hair follicles are among the fastest-dividing in the human body. (Which is one of the reasons why cytotoxic chemotherapy makes patients' hair fall out.)  For that matter, the fact that follicular cells may remain viable a long time after death doesn't necessarily mean that they are cranking out hair the whole time.  Absent a supply of circulating, oxygenated blood – along with sufficient glucose – those cells aren't going to be secreting much keratin. TenOfAllTrades(talk) 01:46, 28 August 2013 (UTC)


 * Erm, StuRat, you're trying to justify a fable. Or sort of a fable.  Hair and nails "grow" after death because the body dehydrates (I think also there is a loss of smooth muscle tone that contributes a little, but I didn't find it in  and I'm not sure I remember correctly)  Also note hair is a very fast growing tissue with a pretty high metabolism. Wnt (talk) 04:23, 31 August 2013 (UTC)


 * Hmm, is it possible it has a highly variable metabolic rate, and slows way down due to a starvation response ? It would seem to endanger an animal's survival if hair and nails continued to grow at full speed during periods of starvation (moreso with animals fully covered in thick fur), when there's a lack of protein available, so you'd expect them to slow down their metabolic rates, and resume full speed again when protein becomes available.  And, after death, the same starvation response may occur, resulting in slow, but long-term, hair growth.  StuRat (talk) 10:17, 31 August 2013 (UTC)

Underwater train
Are there any trains/monorails that go underwater? ScienceApe (talk) 16:12, 25 August 2013 (UTC)


 * Do you mean without a tunnel?    D b f i r s   16:20, 25 August 2013 (UTC)


 * Yes, without a tunnel. ScienceApe (talk) 18:00, 25 August 2013 (UTC)


 * The Brighton and Rottingdean Seashore Electric Railway had underwater tracks, with the cars supported on suitably ornate ironwork. I don't think there were any railways where the cars themsevles ran underwater - there would be insufficient force (due to the buoyancy of the air in the cars) to keep them on the track.  Tevildo (talk) 16:29, 25 August 2013 (UTC)


 * Only if you filled the things with air. — Preceding unsigned comment added by 109.144.132.49 (talk) 19:27, 25 August 2013 (UTC)


 * True, of course, but the only sensible use for such a train would be for entertainment (as in the Brighton example), so it would need to carry passengers who could see out of it. It wouldn't be commercially viable to move goods by underwater railway rather than by boat. Tevildo (talk) 19:34, 25 August 2013 (UTC)


 * Fair point. The only thing I can suggest then is the rails that ships are dragged in and out of the water on at some shipyards. — Preceding unsigned comment added by 109.144.146.36 (talk) 19:40, 25 August 2013 (UTC)


 * There used to be a ride at Disney World based on 20,000 Leagues Under the Sea, where a mockup of the Nautilus ran around a submerged route on rails. Rojomoke (talk) 23:22, 25 August 2013 (UTC)


 * We have an article - 20,000 Leagues Under the Sea: Submarine Voyage. Not really an underwater train though: "The attraction vehicles were not actual submarines, but instead boats in which the guests sat below water level". 23:45, 25 August 2013 (UTC)


 * I remember going on that actually when I was a kid. Brings back memories. ScienceApe (talk) 04:33, 26 August 2013 (UTC)


 * Conceptually they could be useful for mining manganese nodules and methane clathrate and such, but in practice, the ready mobility and relocatability of shipping must vastly outweigh any leverage that could be obtained taking cars of ore up obliquely to the beach. Wnt (talk) 08:20, 26 August 2013 (UTC)


 * Another option, in the case of a underwater sightseeing train, would be a tunnel, but made of clear plastic. This would allow the passengers to view the sea life. StuRat (talk) 15:06, 26 August 2013 (UTC)