Wikipedia:Reference desk/Archives/Science/2014 September 12

= September 12 =

Better than a human at combined swim/run part of triathlon?
Excluding the Bicycle, (which I'm not sure *any* animal could do better than a human), is there an animal which could complete the combined swimming/running parts of the Olympic Triathlon (1.5km swim followed by a 40km run (approx 1 mile/25 miles)) faster than a human. I know there are a lot of animals (dolphin, etc) that could finish the swim first and some animals, I think could beat a human in in the run (antelope?), but any that would get to the end of the race ahead of us?Naraht (talk) 00:06, 12 September 2014 (UTC)


 * I can't think of any. Before we get too cocky about that, though &mdash; which species made up the rules? --Trovatore (talk) 00:29, 12 September 2014 (UTC)


 * Best comment of the week award goes to Trovatore! SteveBaker (talk) 00:31, 12 September 2014 (UTC)


 * Interesting question. Since the running portion is much longer than the swimming portion, a creature that is a fast runner and an "okay" swimmer might win.  The pronghorn antelope can run at 56 km/h for 6 km (according to our article). This speed is useful to outrun lions and other predators.  There is no mention of its time over a 40 km course.  I think they can swim fairly well.  CBHA (talk) 00:46, 12 September 2014 (UTC)


 * See Man versus Horse Marathon for something akin to a real-life example. It's 22 miles cross-country (not on a level track), with no swimming - the current stats are 32-2 to the horses. Over a shorter distance on the level, the horse would definitely win every time, although I'm not sure about the swimming.  Tevildo (talk) 00:55, 12 September 2014 (UTC)  Irrelevant portion stricken out. Tevildo (talk) 00:58, 12 September 2014 (UTC)


 * The man versus horse marathon is significant here. A man doesn't stand a hope in hell against a horse over 1 mile - but over 22 miles, it's actually possible to win...but as the distance gets longer, it becomes more and more possible for a human to outrun almost anything.  We've evolved to hunt animals like antelopes.  We don't do it by out-sprinting them like a cheetah - but by having more stamina over the long haul.  So I think it would be a relatively close thing between a fit human and almost any land animal.  The issue is how fast land animals can move through the water.  List of successful English Channel swimmers shows that fit humans can manage between 1 and 3mph over 20 miles.  It's hard to find date about how fast land animals can swim - this video  of a horse swimming makes it look like it can swim about as fast as it can walk...which could be around 4mph.  So if the horse could keep up that pace, maybe a horse is in with a chance.  But it's back to the stamina thing.  If humans are just beginning to out-stamina horses after a 40km race - the horse is going to be slowing down a lot for the swimming.  I've seen data on polar bears who have the stamina to swim for days.  They also seem to be managing 3 to 4mph over long distances...but it's not clear how fast they are over long distances over land.  They can probably out-sprint a human, but I doubt they could keep up a winning pace over miles.


 * I think it would be close for a typical human and a typical horse or polar bear - but it's all about stamina, not raw speed. SteveBaker (talk) 02:56, 12 September 2014 (UTC)


 * Note that in the man-versus-horse marathon, the horse has a human riding on it. I think it is nearly certain that a good horse could beat the best humans in a one mile swim followed by a 25 mile run. Looie496 (talk) 17:47, 12 September 2014 (UTC)


 * Perhaps this animal? Count Iblis (talk) 01:11, 12 September 2014 (UTC)


 * Maybe a polar bear ? They are excellent swimmers and fast runners, but that distance might be too long of a run for them. StuRat (talk) 01:58, 12 September 2014 (UTC)


 * Dogs are also very good at doing long distance running, it is a bit far for them but I think they could manage 40km at about the same pace as a human. Kangaroos also are a possibility. I'd have thought elephants would heat up too much but I've heard of them walking long distances without stop at about 10 kilometers an hour. Dmcq (talk) 07:52, 12 September 2014 (UTC)
 * OK - so where is the video of the kangaroo swimming?  I'd really like to see that! SteveBaker (talk) 15:17, 12 September 2014 (UTC)
 * https://www.youtube.com/watch?v=KFWNSeHDN2M Judging from that they'd find 1.5km a bit of a struggle.Dmcq (talk) 15:42, 12 September 2014 (UTC)
 * plus apparently there's a dog out there named norman who knows how to ride a bicycle haha  ~Helicopter  Llama~  11:25, 12 September 2014 (UTC)


 * If the race started in the water, I think a tiger would win easily. It would handily swim to the shore and then eat the human, finishing the run at a leisurely pace. Come to think of it, if you start in the water, a tiger shark has a greater chance of making it to the finish line first. Matt Deres (talk) 15:51, 12 September 2014 (UTC)
 * The other way round if pitted against Jaws (James Bond) ;-) Dmcq (talk) 16:40, 12 September 2014 (UTC)


 * Not quite an answer, but this site is sort of cool. Lets you compare animal speeds in land, sea and air, both in real speed and if they were scaled to your height (or whoever's). Not exactly practical info...yet. InedibleHulk (talk) 16:01, 12 September 2014 (UTC)


 * Why would any animal bother doing it? HiLo48 (talk) 16:10, 12 September 2014 (UTC)
 * Glory, I suppose. Maybe food. InedibleHulk (talk) 18:37, 13 September 2014 (UTC)
 * Perhaps a Hippopotamus? "Adult hippos move at speeds up to 8 km/h (5 mph) in water" (Wikipedia article) and "30 km/h (On Land, Running)", which would be times of 11.25 minutes (1.5 km swim) and 20 min (10 km run), assuming they maintain the quoted speed. Compare this with the times for men's triathlon Triathlon at the 2012 Summer Olympics – Men's, where the winner had a 17 minute swim and a 29 minute run. I don't know what the endurance of a hippo is like, though, and if they would be able to maintain those speeds over those distances. -- 160.129.138.186 (talk) 17:45, 12 September 2014 (UTC)
 * Clearly polar bear. Was already mentioned. I am shure many other species, probably not a cow but very likely a horse, are also capable of winning such a race. Most would likely fall back in the swim section but many can run long distances multiple times faster than humans. --Kharon (talk) 21:10, 12 September 2014 (UTC)
 * Actually, not so much on the horse. Horses, over marathon length distances, run only marginally better than humans.  See Man versus Horse Marathon, already mentioned above, so I'm not sure why you missed it.  The horse usually wins.  But not always, and not by enough to say it would be a shoe in.  Indeed, given the swimming advantage of humans, I'm pretty sure top triathletes could take beat the horse often enough.  -- Jayron  32  00:21, 13 September 2014 (UTC)
 * This article claims that humans are "the right honorable kings and queens of the planet when it comes to long-distance running", but I'm not convinced. Maybe in a cold climate the European moose or elk would be the winner: "They have very long legs, which make them appear ungainly while standing but very elegant when trotting. Designed for speed and endurance, they can gallop at up to 60km per hour and are also excellent swimmers. This comes in useful when they need to escape predators such as wolves, lynx and brown bear. (source). Difficult to find hard data on distance... In a hot climate many species would be at a disadvantage, see Persistence hunting.  Ssscienccce  (talk) 21:13, 12 September 2014 (UTC)
 * A lynx's snowshoe-like paws would tune us if we were running in boots. But if we were racing in the north, the swimming part would kill us anyway. InedibleHulk (talk) 18:43, 13 September 2014 (UTC)

Laser energy greater than nuclear explosion
Over here ,Laser it lists some of the most powerful lasers, 700 TW and 1.3 PW. A watt is 1 joule/sec. So these lasers presumably pulse in a fraction of a second, but even so the total energy output of those lasers should exceed some nuclear weapons. But yet, when those lasers are fired, the resulting explosion created isn't comparable to a nuclear explosion. But yet according to those energy levels, they should be. Why the discrepancy? ScienceApe (talk) 06:19, 12 September 2014 (UTC)


 * Isn't the answer given in the section to which you linked? The peak power quoted is many orders of magnitude greater than the average power. Average power output of most powerful lasers is just a few kilowatts (perhaps a bit more for the really big and most deadly lasers).  It is fair to say, though, that if the pulsed power is concentrated in a small area, then the effect is comparable to that at the core of a nuclear explosion, just not so widespread.    D b f i r s   06:44, 12 September 2014 (UTC)

Perhaps someone is failing to distinguish between energy and power. Jim.henderson (talk) 13:19, 12 September 2014 (UTC)


 * Not only do those exceedingly high power lasers fire for only a very small amount of time - they also only strike a very small target.


 * Since I actually own a couple of 100 watt lasers - I can add more light onto this subject. :-)


 * On the face of it, my 100 watt lasers don't sound all that impressive...the amount of light energy they produce is more or less the same as a 100 watt light bulb.  The difference is that a 100 watt light bulb spreads that energy out over perhaps 100 square centimeters of surface area.  It gets hot enough to hurt if you touch it - but it's not really going to cause significant destruction.   My lasers are focussed to a spot that's about 1/30th of a millimeter across - so those hundred watts are dumped into an area 9,000,000 times smaller than the lightbulb.  The energy delivered per unit area is about 9 million times greater - which means that whatever you point the laser at pretty much "goes away" - this machine can happily slice through a half inch of wood at a speed that's only a little slower than a table-saw.


 * To wreak destruction, delivering a peta-watt (1015 watts) for a nanosecond (10-9 seconds) has about as much effect as pointing one of my 100 watt lasers (102 watts) at a target for 104 seconds...about 2.5 hours.  My lasers are capable of producing 100 watts continuously - and I routinely cut up bits of plywood (to make little model buildings - as it happens) by running my two lasers for 12 hours - which is 10 times as much light energy as the petawatt/nanosecond device.   So far, there has been no giant smoking crater anywhere near my house!


 * Put another way, the total energy from a peta-watt for a nano-sec is about the same as leaving your bedroom light on overnight - but it's enough to (briefly - and in a very, very tiny space) create the same conditions as are found on the surface of the sun!


 * It's all about how the energy is concentrated - both in time and in space.
 * SteveBaker (talk) 15:11, 12 September 2014 (UTC)


 * But then by extension if you were to make the beam more diffuse (less concentrated), it should produce an explosion comparable to a nuke. ScienceApe (talk) 15:58, 12 September 2014 (UTC)
 * No! That's the opposite of what I'm saying.  Spread out that peta-watt laser both in time (from a nano-second to a few hours) and in space (from a tiny spot to the surface of a light bulb) - and you have something with enough energy to run an easy-bake oven...not flatten a city. SteveBaker (talk) 16:30, 12 September 2014 (UTC)
 * Well then that means the energy released by the laser in that nano-second should equal the energy to run an easy-bake oven, not a nuke. But if it did equal a nuke's energy, then it should produce an explosion comparable to a nuke. ScienceApe (talk) 17:02, 12 September 2014 (UTC)
 * Yes...although whether expending all of that energy would produce an explosion or not depends on what you do with the energy.  If you dumped that much energy into the ground, you'd get an impressive explosion - but if you fired the laser up through the atmosphere and out into space, then the energy would gradually dissipate and there wouldn't be that much disruption.  Also, again, it's dependent on how fast you release the energy.  The distinction between a 'high explosive' and (say) gunpowder is that even when the exact same amount of energy is released, it matters how fast it's released.  So I'd be nervous about comparing the two explosions - even when the raw energy and power numbers could be meaningfully compared.   A single lightning bolt produces about 109Joules - which is about the same as a quarter ton of TNT, but a lighting bolt can be safely dispersed using a simple lightning conductor where a large car-bomb with the same amount of energy could bring down a large building and leave a decent sized crater. SteveBaker (talk) 17:59, 12 September 2014 (UTC)


 * Perhaps someone failed to read what I said. "A watt is 1 joule/sec. So these lasers presumably pulse in a fraction of a second, but even so the total energy output of those lasers should exceed some nuclear weapons." ScienceApe (talk) 15:18, 12 September 2014 (UTC)
 * No, I'm pretty sure we all understood what you said.


 * 1 joule per second, is a rate of energy production - so one joule-per-second running for a nanosecond (which I believe is the typical pulse duration of one of these things) is 0.000000001 joules. A petawatt is 1015 watts which means that over one nanosecond, the total energy it delivers is 1015J/s x 10-9s...which is 106J ...a million joules...which is the exact same amount of energy (Joules) produced by a 100 watt light bulb (102J/s x 104s) in a few hours (104s = 166 minutes).


 * Google says that 1 megatonne TNT is 4.18400 × 1015 joules.  So a one megatonne nuke produces 4x1015 joules of total energy, spread over however long it takes to explode...which is 109 times as much energy as the petawatt laser produces in a nanosecond.   So this laser is a BILLION times less energetic than the bomb.   The amount of power that the bomb is generating depends on how long the explosion takes...which is kinda fuzzy...and really bears no relevance to it's destructive capability.


 * Now, admittedly, if the laser could be left running, continuously, for four second - then it would hypothetically produce a megatonne of energy and it could level entire cities.  But it can't run for a second - it's only able to produce that number of watts for a billionth of a second...so the total energy is only as much a leaving your bedroom light on all night.


 * As an earlier respondent pointed out - you're getting confused between energy and power. SteveBaker (talk) 16:30, 12 September 2014 (UTC)
 * Well no I wasn't confused about energy and power, I just wasn't aware the total amount of energy the petawatt laser actually produces. I knew it was a fraction of a second, but I didn't know it was only a nanosecond. According to the boom table, 1 million joules however is equal to 239 grams of TNT, so it should still produce an explosion equal to that much TNT detonated at once. ScienceApe (talk) 17:07, 12 September 2014 (UTC)
 * The Petawatt laser at the University of Texas, here in Austin produces a petawatt - but the total energy output is just 190 joules...so it must be firing for considerably less than a nanosecond...more like the femto-second range, probably. SteveBaker (talk) 18:05, 12 September 2014 (UTC)
 * Also these Lasers only work for a tiny fraction of a second at peak so you have to brake it down as "Joule" is "watt * second". The 1.3×10^15 W Laser in Livermore only works 400 femtoseconds aka 400×10^-15 seconds so formaly its only 520 Joule really if i calced it right. --Kharon (talk) 21:33, 12 September 2014 (UTC)


 * The generation time in a fission explosion is about 0.01 microsecond, and 99.9% of total energy is released during the last seven generations. (source) A 100 kiloton explosion releases 0.4184 PJ (see TNT equivalent), so the average power during the last seven generations is 0.4184 * 0.999 / (7*10-8) or 5.97*106 PW. That's 4 million times more power than the most powerful laser mentioned. If my calculations are correct... Ssscienccce  (talk) 21:41, 12 September 2014 (UTC)
 * Something I don't see mentioned in this discussion is that, in fact, the function of the laser at the National Ignition Facility is to ignite very small thermonuclear explosions. They use tests on this system to improve nuclear weapon designs, and also for research on inertial confinement fusion for civilian use.--Srleffler (talk) 01:36, 13 September 2014 (UTC)

pearl index and decrement table
What is the first year failure rate of Mirena IUD according to life table method    not pearl index — Preceding unsigned comment added by 199.119.235.142 (talk) 07:40, 12 September 2014 (UTC)
 * See IUD with progestogen. According to Bayer's datasheet here, the first-year failure rate is 0.21%. Tevildo (talk) 08:04, 12 September 2014 (UTC)
 * NOTE: Our article includes a short video of the device being removed.  I wouldn't call it _erotic_, but it's probably NSFW. Tevildo (talk) 08:10, 12 September 2014 (UTC).

According to life table method not pearl index199.7.159.62 (talk) 09:07, 12 September 2014 (UTC)

Skin lesion and std transmission research
Has there been any research done to suggest that skin lesions and fissures as a result of skin conditions such as psorasis or eczema increases the chances of skin to skin transmission of stds such as syphillis or herpes? 90.192.105.196 (talk) 09:50, 12 September 2014 (UTC)


 * Not sure it makes sense to test every combination of skin condition with every disease that can be transmitted through the skin. Obviously having skin damage makes transmission more likely, but knowing exactly how much more likely is of limited value.  Perhaps testing remediation methods might be of value, like whether bandages prevent infections.  Nurses with skin problems could then act accordingly, and either tend patients when they have bandages on, or avoid working until their skin heals. StuRat (talk) 16:15, 12 September 2014 (UTC)

Energy extraction from would-be tornadoes
I heard that some tornadoes form in the US because hot air becomes trapped below cold air. What about building towers that bridge the gap with turbines in between to harness the energy? This might then also reduce the occurrence and severity of tornadoes in those areas (as well as other wacky changes in weather patterns). --78.148.104.246 (talk) 14:01, 12 September 2014 (UTC)
 * It's a good idea except for having to come and replace said towers every time a tornado tears them out of the ground and scatters them around the landscape. Also, very unreliable, and you have the problem with having LONG lulls of no wind energy, giving you a worthless tall thing, and then a very short burst of very intense energy.  The system doesn't deal well with that, the electric grid works best with a constant flow of reliable energy, not short bursts.  So yeah, basically your idea is just fine, except for all of it.  -- Jayron  32  14:44, 12 September 2014 (UTC)


 * (ec)
 * We get quite a lot of ideas like this - capturing the energy from lightning strikes, to pick another example. The root problem with all of these ideas is that building a gigantic, expensive machine to capture this energy is likely to leave you with a multi-million dollar investment that sits there for decades doing nothing until it *FINALLY* gets struck by lightning or hit by a tornado - or whatever it's designed to use.  Then it generates a reasonable amount of energy - and then it's sitting there waiting for more decades.


 * Just think about that. How often does a tornado strike the exact same place twice?    Sure, it happens - but it's always an astounding coincidence - and nobody can predict where that place is.   But for your machine to earn money (or even to generate any energy at all before it rusts into oblivion) - it has to be exceedingly lucky.


 * You might (I suppose) be able to capture energy from temperature inversions in the atmosphere and other high energy weather events that happen a little more predictably.  The conditions for tornado formation probably happen a dozen times a year in some parts of "tornado alley" here in the USA.   I've been living in that region for the last 20 years - and I've only once been within 10 miles of a tornado touch-down...but probably had at least a couple of "tornado watch" alerts over my house each year.   So if you had built your machine where my house is and given it a 20 year operational life - it would never have generated an erg of energy from an actual tornado - and it would only have generated a few bursts of energy per year if it operated under "tornadic conditions".


 * What you're REALLY talking about is windmill farms. Those operate in any windy conditions - and windy conditions happen during temperature inversions and such.  So those machines (which exist in LARGE numbers around my area) do exactly what you want - but they are also capable of capturing energy from mere light breezes as well as from more violent storms.   That's a more practical kind of machine for the job...and because of that, people have built them.


 * But even so, one of the biggest criticisms of wind farms is that they don't produce energy reliably.  When it's dead calm - the energy to run nearby cities has to come from someplace else.   A hypothetical tornado-energy-machine would have that problem about a million times worse!


 * So, no - sadly, this idea is a non-starter.


 * SteveBaker (talk) 14:48, 12 September 2014 (UTC)




 * Well, if we forget about generating power, the idea that large structures could decrease incidence of tornadoes is basically sound, see e.g. here . (btw Steve, I don't think Austin is firmly in the tornado alley, see also here . As a recent immigrant to Austin, I'm just glad we get any storms at all, even if they are far less common and violent than the other areas I've lived :) SemanticMantis (talk) 15:38, 12 September 2014 (UTC)
 * Yes, but I'm relatively new to Austin - for most of the last 20 years, I've lived in Cedar Hill (near) Dallas - which (I believe) is solidly inside the orange bits of Tornado Alley - at least according to our map at right. The only tornado I got close to touched down to the west of me on Joe Pool Lake - it was heading east across the length of the lake while I was driving south across the width of it - along the two mile-long bridges with a very open stretch of road between them.  When I heard on my car radio that the tornado had touched down - I was on the then-deserted section of land between the two bridges and faced with the "go-on/go-back/sit-still" decision.  Since the car I was driving was possibly the worst imaginable for riding out a tornado in (a race-tuned MINI Cooper'S convertible!) - but had a pretty good turn of speed, I made the decision to go on - and basically floored it.   As it turns out, I was basically racing the tornado, to the far end of the bridge - and I was hitting 130mph as I got out of the way.   There was inch-sized hail pounding the car - and although I was concerned about the toughness of the cloth on the roof - having a convertible turned out to be a good thing because I only took hail dings on the hood of the car.  As I arrived home (on the south shore of the lake) - I had to slalom between tree limbs to get down the 300' driveway into my garage.   Quite an exciting ride home! SteveBaker (talk) 16:02, 12 September 2014 (UTC)
 * Ah, my mistake. Sounds like a fun adventure! SemanticMantis (talk) 16:07, 12 September 2014 (UTC)


 * Talk about Dark Satanic mills. μηδείς (talk) 16:06, 12 September 2014 (UTC)

''You misread my suggestion. I wasn't suggesting you hardness tornadoes. I was suggesting you hardness the power of what would otherwise become a tornado.'' — Preceding unsigned comment added by 78.148.104.246 (talk) 16:39, 12 September 2014 (UTC)
 * It doesn't matter. Either way, if you design it to harness the most extreme conditions, then your equipment will be idle for far too large a percentage of the time.  You need to make it harness less energetic - but more frequent events - and that's precisely what a wind farm does. SteveBaker (talk) 17:44, 12 September 2014 (UTC)
 * So you mean this layering of air only occurs some of the time? I thought it was constant. 78.148.104.246 (talk) 18:16, 12 September 2014 (UTC)


 * I think what he means is that this tower would extract energy that would otherwise go into generating a tornado in the first place so the tornado, in theory, is never produced at all. Presumably, the towers would allow hot air trapped under the cold air cap to travel up through the tower, spin turbines and generate power. Thus preventing tornadoes and producing electricity. The tornadoes never have to be formed in order to produce power, the power is produced from trapped hot air. I have no idea if this is possible or not, but that's what I got out of his posts thus far. ScienceApe (talk) 19:53, 12 September 2014 (UTC)


 * Sounds like a Vortex engine --Digrpat (talk) 20:29, 12 September 2014 (UTC)
 * You would need a aproximately 5,000 ft high tower that builds a very huge tube. It would cost probably 20-30 Billion to build given the highest Building Burj Khalifa at 2,722 ft is just a short needle compared that already cost 1.5 Billion to build. But it has to withstand storms tho its not a needle but a wall. I doubt such a structure could be build with current technology and expertise. --Kharon (talk) 22:00, 12 September 2014 (UTC)


 * The energy that drives a tornado comes ultimately from convection: when moist air is lifted to a higher altitude, the drop in pressure causes some of the moisture to condense, which releases energy.  Tornadoes typically occur when the convective available potential energy is very high.  However, there are lots of situations where the potential energy is high but no tornado occurs.  In principle that energy could be tapped, but at a technical level it seems very difficult.  The basic problem, as Steve has been saying, is that the energy is hard to get to, and even though there is a lot of it, its density is not very great. Looie496 (talk) 14:06, 13 September 2014 (UTC)
 * Yep, exactly. The diagram at right shows the total number of tornadoes per 2400 square miles between 1950 and 2006.  The peak numbers are around 15.  So that's one tornado every 3.5 years in 2,400 square miles.  If you built some kind of a machine that would pull energy from a tornado within (say) a square mile around the machine - then the odds of it producing any energy is something like 1 in 8400 every year.  If you built 8400 of these contraptions across the countryside - then every year, ONE of them would produce energy for an hour or two - then nothing.  Windmills, placed in moderately windy places, can produce electricity at a cost of about $40 per megawatt-hour. A 2 MegaWatt windmill costs around $2,000,000.  You can't come remotely close to that payback with a machine that's operating so rarely. SteveBaker (talk) 22:17, 13 September 2014 (UTC)
 * To be exact, the diagram at right shows the number of F3-F5 tornadoes over that period. I've witnessed about a dozen, or their effects, from teh 70's til present, (.e.g., one blew my shed about 1000ft into the bay), but they were the much more common F0 to F1. μηδείς (talk) 17:28, 14 September 2014 (UTC)
 * Well, convective energy -- the energy that drives tornadoes -- is present during any thunderstorm, or even whenever you see cumulus clouds. In principle it could be tapped simply by creating a horizontal windmill.  The problem is that the altitude at which strong convective winds occur is highly variable, and usually thousands of feet above the ground.  The comparison isn't quite as extreme as the passage above makes it look, but still wouldn't come close to the overall efficiency of an ordinary windmill in a windy spot. Looie496 (talk) 14:11, 14 September 2014 (UTC)

The evaporation of water (which in turn happens due to solar energy) accounts for a large part of the energy here, despite the fact that it actually costs energy to evaporate water. The energy itself is irrelevant, what matters is how much useful work you can generate from the process in the given environment. Processes that require energy to run can yield useful work if more than the required energy can be extracted free of charge from the environment, this is the case for evaporating water. So, the relevant question here is to ask how much work could you in theory extract from your 1 litre bottle of water on your desk using only local processes (so the machine that is going to do this is assumed to only work onder the local ambient conditions, otherwise the sky would be the limit). The maximum amount of work is less than or equal to the drop in the Gibbs free energy when the water is changed to water vapor and dumped in the environment. Because the water can exist in equilibrium with saturated water vapor at the ambient temperature, the Gibbs free energy of the water is equal to that of saturated water vapor. So, we only need to calculate the drop in the Gibbs free energy for saturated water vapor and the water vapor at the partial pressure the ambient vater vapor is at. If we treat water vapor as an ideal gas, then it's an easy computation to obtain the result


 * $$W = -N k_B T \log(r)$$

where W is the maximum amount of work that can be obtained, N is the number of molecules, and r is the relative humidity. The maximum amount of work that can be extracted from my 1 litre water bottle here where the temperature is 20 C and the relative humidity is 60% is thus approximately 69100 Joules. Count Iblis (talk) 02:14, 14 September 2014 (UTC)

Will putting toilet unclogger make it worse?
Toilet paper is blocking my toilet. I put at least 3/4ths of a half gallon bottle of drain cleaner in (the rest to speed up a slow sink), turns out it's just water, soap and "grease cutting oil". Which I guess might be their term for "third hot press oil that hasn't had enough hexane removed to meet Chinese FDA standards" (to cut the soap with). This brand worked before (maybe cause paper wasn't blocking that one and only the huge dump, maybe it still had some alkali then (the bottle was smaller). If I put in a bottle of actual toilet unblocker — one with lye, will it turn the ton of oil into soap and block it more? At best the oil will just use up some of the reactant. My small bathroom lacks a fan, vent or window, how much should I put to ensure that I only have to open that door once? Sagittarian Milky Way (talk) 15:32, 12 September 2014 (UTC)


 * I would avoid using chemicals entirely. They are expensive, toxic, can damage the pipes, and, in my experience, rarely work.  Plumbers want nothing to do with them.


 * Use a toilet plunger instead. Note that a toilet plunger is distinct from a sink plunger, in that it's larger and has an extra bit of rubber at the bottom that goes into the hole in the bottom of the toilet bowl (see pic at link).  Make sure that part isn't stuck up inside.  If you only have a sink plunger, you can try that, but they are less effective on toilets.  Push the plunger up and down slowly, at first, to get the air out.  This will prevent splashing.  Then, once it's full of water, give it some good thrusts and pulls to unclog the toilet.  Then flush a couple times to clear any residual paper.  Plungers cost about $5, so you can afford to have one by every toilet.  The lack of a plunger can cause severe damage if the toilet overflows because you can't plunge it out in time.


 * If a toilet plunger doesn't work, a plumber's snake is the next thing to try, but those tend to make a lot of mess and require more skill to use and are more expensive, so you might consider calling a plumber. StuRat (talk) 16:03, 12 September 2014 (UTC)


 * Straighten a wire coathanger, bend a small (1cm) hook shape at the bottom, and use that instead of a snake. Most home plumbing sites I've seen say it's more sanitary and quicker to use that and rinse after than to use a plunger. SamuelRiv (talk) 17:56, 12 September 2014 (UTC)


 * That's how Hulk rolls, but only after one try with the plunger. InedibleHulk (talk) 18:48, 13 September 2014 (UTC)


 * Agree. Those chemicals don't work. I've used them before and never even once have they worked for me. How bad is the clog? Does the water slowly go down, or does it not move at all? If the water goes down slowly, and you REALLY don't want to use a plunger and if you can afford to wait a few days, then: Even every time the water is all the way down flush it once (remove the tank lid and be ready to put the flapper back down if it looks like it's about to overflow). Over time and many many flushes, you will dissolve the paper and solids and it will eventually clear. Otherwise, just plunge it. If it happens a lot you should consider a new toilet, you can get a good one for $200 (not including installation). Ariel. (talk) 18:06, 12 September 2014 (UTC)


 * A new toilet is more likely to be a low-flow toilet, and hence clog more easily. StuRat (talk) 22:41, 12 September 2014 (UTC)


 * That is a common myth and completely incorrect. A low flow toilet has a larger tube at the bottom, and a more intelligent design. Most common is a siphon which can suck the entire contents of the toilet out with very little water. I personally can attest that I went from weekly clogs with an old 4 gallon flush to 1 clog in a year with a 1.8 gallon flush. The old toilet was simply poorly designed. Ariel. (talk) 03:17, 14 September 2014 (UTC)


 * That's a bit like denying that larger cars are inherently safer. Yes, you can poorly design a large car in such a way as to make it more dangerous than a small car, and you can poorly design a regular toilet so it will clog often, but given competent designers, the large car should be safer and the regular flow toilet should flush better. StuRat (talk) 16:08, 14 September 2014 (UTC)


 * No, that's not true. Once the toilet is well designed adding extra water does not help it. Either it will go down or it won't. More water doesn't do anything except overflow and spill everywhere. If more water helped then flushing a second time should do something when there is a clog, but flushing again does nothing. On top of that, the available regular flow toilets are all poorly designed. So your statement "and hence clog more easily" is factually incorrect for the actual toilets in use and is therefor bad advice. Ariel. (talk) 16:50, 14 September 2014 (UTC)


 * I agree with the suggestion above to use a plunger. I can't imagine why anyone would try clearing a plugged toilet with chemicals. Be careful though, about plunging a toilet that is full of caustic chemicals. You may splash them.--Srleffler (talk) 01:50, 13 September 2014 (UTC)

See also here. Count Iblis (talk) 19:42, 12 September 2014 (UTC)


 * I find caustic soda is effective, and cheap. Make a bucketful and pour it in. Leave it to work. DuncanHill (talk) 22:45, 12 September 2014 (UTC)

If you don't have a toilet plunger a twine mop usually works well as a plunger. Richerman   (talk) 14:17, 13 September 2014 (UTC)

I used something with water,bleach and NaOH that worked, with a hiccup. That's a 2-0 record for the Drano-type products and a tens-2 record for the plunger with one cancelled contest. Plunging are filthy, can take many minutes of hard pushing to work, if not more (see the 2 failures), this was some especially stinky feces and this toilet splashes even more than my previous one so I did not try the plunger. (My habit of flushing until either it works or there's no other option contributes, by stuffing the clog deeper and compacting it) Sagittarian Milky Way (talk) 18:32, 13 September 2014 (UTC)

Using conventional explosives to initiate nuclear fusion
This is somewhat related to the previous question I had about lasers and nuclear explosions. It appears the lasers used to initiate inertial confinement fusion only release energy around 1 million joules. That's actually not that much, it's actually only a little more powerful than a hand grenade. I was wondering why is it impossible to initiate inertial confinement fusion with shaped conventional explosives? Obviously I understand that shaped explosives are not as precise as lasers are, but intuition would say that a large enough conventional explosion should do it at a certain point correct? ScienceApe (talk) 21:39, 12 September 2014 (UTC)
 * Thermonuclear fusion needs some billion Kelvin hot Plasma to start. The main problem is not to initiate it. This has been done in 1952 with the first hydrogen bomb. The main problem is to contain a some billion Kelvin hot Plasma which can under laws of physics only be done with help of a "vacuum wall" or in fusion reactor terms a "vacuum vessel" for the plasma. You can not build or cause that thermodynamic isolated cage with conventional explosives. --Kharon (talk) 22:24, 12 September 2014 (UTC)
 * To get efficient fusion you need high temperature, and a high product of density and time. (Details: see Lawson criterion). Magnetic confinement fusion uses lower density for long times. Inertial confinement fusion such as laser fusion uses higher densities for very short times. In the latter approach, containment is not really a problem. The reaction is over long before the plasma reaches the walls of its container.--Srleffler (talk) 02:10, 13 September 2014 (UTC)
 * The initiation problem really does require the focus of a laser. Even a shaped charge explosive can't concentrate the available energy sufficiently.  A typical shaped-charge cut makes a 10mm wide cut in thick steel.  A 1000 watt laser makes a slot that's a fraction of a millimeter wide using a fraction of the energy of a shaped charge. SteveBaker (talk) 00:37, 13 September 2014 (UTC)
 * Precision matters. If you're trying to ignite a fusion reaction by compression, the compression has to happen over an extremely short time, and has to be extremely uniform. If the compression isn't uniform, the plasma doesn't reach the required densities. Note, however, that General Fusion is working on a fusion reactor where the reaction is created by using giant pistons, so your idea is not completely impossible.--Srleffler (talk) 02:10, 13 September 2014 (UTC)