Wikipedia:Reference desk/Archives/Science/2014 May 17

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May 17

University/college life

Could it be argued that university/college life a risk factor for cancer, heart disease etc later in life? For many students, university/college life involves studying for long hours creating stress, drinking a lot in response to stress and also eating unhealthily. Clover345 (talk) 03:14, 17 May 2014 (UTC)

This looks to me like a classic request for opinions, rather than well sourced answers. HiLo48 (talk) 03:28, 17 May 2014 (UTC)

The Op's not looking for a reference. He's already got his premises, and he wants to see if we'll accept his conclusion. μηδείς (talk) 16:43, 17 May 2014 (UTC)

There probably are stats on life expectancy differences between college grads and non-grads, if we can find them. StuRat (talk) 05:48, 17 May 2014 (UTC)

Except that wouldn't do anything to establish a causative link between college lifestyle and the conditions in question. Snow talk 10:04, 17 May 2014 (UTC)

If you can establish a correlation in two events, and that event A happens before event B, and provide a plausible mechanism by which event A might cause event B, then you have a reasonably strong case for A being the cause of B. Of course, no matter how strong the evidence is, one could always argue that everything is just a coincidence, so cause-and-effect can never be 100% proven. StuRat (talk) 15:48, 17 May 2014 (UTC)

It would be interesting to see alcoholism rate relative to education and income level. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:19, 17 May 2014 (UTC)

1, 2, 3, 4: here, hopefully these will give you something less morbid to think about. :) Snow talk 10:43, 17 May 2014 (UTC)

What makes you imagine that spending those years NOT going to college is going to result in less stress, drinking and so forth? If not in college, you're probably going to get a job sooner - and for sure jobs can be stressful. College graduates generally have higher income and better access to healthcare and good nutrition in later life - which is certainly going to have a huge impact on cancer risk...there are a million differences in the long-term prognosis depending on the choices you make - it would be extremely simplistic to take the handful of poorly-correlated-with-college-life factors that you list and ignore all of the other effects. SteveBaker (talk) 03:40, 17 May 2014 (UTC)

The only way to be stress-free is to be dead. The dead have no problems. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:19, 17 May 2014 (UTC)

So bleak Bugs...do you need a hug? ;) Snow talk 10:43, 17 May 2014 (UTC)

"Life is trouble; only death is not. To be alive is to undo your belt and look for trouble." Deor (talk) 12:56, 17 May 2014 (UTC)

Sure. Not bleak at all. Stress is natural. Dealing with it is how we grow and change. As Dennis Miller once said, "The worst moment of being alive is better than the best moment of being dead." ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:07, 18 May 2014 (UTC)

Your premises are wrong. I don't believe most students study for longs hours, expect before examinations, I don't believe they drink more than school drop-outs, nor that they eat less healthy (why would they, if they are on average wealthier). On the top of that, they smoke less, and are more probable of getting a white collar job. Check [| CDC: Higher Income and Education Levels Linked to Better Health ]. Going to college might not be the be all end all, but going to college definitely is related to a life expectancy of 8-9 additional year. The obvious caveat that correlation does not imply causation, that it might be a common cause elsewhere, blahblahblah, apply, but yes, going to college is good for you. OsmanRF34 (talk) 17:34, 17 May 2014 (UTC)

fusion as a resource?

sir my question is why can't we still use the the fusion energy as a sustainable resource? — Preceding unsigned comment added by 14.96.133.124 (talk) 04:27, 17 May 2014 (UTC)

Good sir, this article may be of interest to you, as it details some of the development spearheading research into fusion. Our own fusion power article supplies a lot more of the technical details and the history of research and development, but is not written in the most accessible manner to get at the root of your question. In the broadest possible terms, the issue which prevents fusion from being a viable technology is that, using existing technology, techniques, and materials, we are as yet unable to produce more energy from the process than is put into it. Starting a fusion reaction requires immense amounts of energy and we do not yet have the means to start and maintain such a reaction in a process that allows us to recapture a net balance of energy. Even once this hurdle is overcome, it will be another matter entirely to accomplish the same feat at industrial scale. However, as the first article details, significant funding and resources are still being put into this area of research, so the next couple of decades may bear out to major developments. Snow talk 05:22, 17 May 2014 (UTC)

Someone said "Fusion power is always 50 years away." Bubba73 ^{You talkin' to me?} 05:30, 17 May 2014 (UTC)

Or as I remember the saying, "Nuclear fusion is the energy source of the future... and it always will be." 24.5.122.13 (talk) 06:32, 17 May 2014 (UTC)

Yup, but indeed that's why I stressed the point; the scale of investment has followed a steady ramping up, and for the first time procedures are near or beyond the break-even point, on a small enough scale. That's not nothing. Snow talk 08:20, 17 May 2014 (UTC)

The OP can be assured that all the energy we use came originally from the local fusion generator 84.209.89.214 (talk) 12:58, 17 May 2014 (UTC)

What about energy from fission reactors? Bubba73 ^{You talkin' to me?} 17:13, 17 May 2014 (UTC)

Well, that originally came from remote fusion generators. 24.5.122.13 (talk) 20:07, 17 May 2014 (UTC)

But that's not our local fusion generator. :-) Bubba73 ^{You talkin' to me?} 21:15, 17 May 2014 (UTC)

Then there's tidal energy, and the portion of geothermal energy caused by tidal heating. Since the tides are caused by stealing a bit of the Earth and Moon's orbital energy, and that in turn is caused by massive objects being blown away from each other, we could say that ultimately those energy sources derive from the Big Bang and dark energy. StuRat (talk) 23:24, 17 May 2014 (UTC)

I think we will eventually get there, but I don't know if it will be in my lifetime. Bubba73 ^{You talkin' to me?} 17:12, 17 May 2014 (UTC)

It's pretty clear that fusion power is a feasible thing - it will eventually work and become amazingly important. There are test reactors that already run and produce small amounts of energy - but not enough to be useful - and not enough to cover the amount of energy it takes to run them. The limitation isn't the energy that's available in fusion reactions (the Sun, the starts and hydrogen bombs amply demonstrate that there is plenty!) - it's that containing and harvesting that energy so it doesn't melt the reactor is kinda tricky. One hope for getting fusion working economically is to use Helium-3 as a fuel - but the snag is that the most likely source for the stuff is on the moon - which presents significant problems of it's own! The science is well-understood here - the problems are not so much of a scientific nature as in the raw engineering and control techniques. But, as has been pointed out, progress has been horribly slow - and every ten years there is a new pronouncement about when it'll be ready to use - which always seems to have slipped another ten years into the future.

Humanity can't wait for fusion to come along before we switch away from fossil fuels - and that's a problem. If it's not the immediate solution, then governments and industry can't pump enough money into R&D to solve the problems - so we slip the schedule another ten years every ten years. Those slippages cause disillusion with the entire process - which further dampens down enthusiasm for funding the research. What's needed is a massive, concerted push, but it's not happening.

My hope is that the expanding field of commercial spaceflight will result in more interest in robotic helium-3 mining on the moon. The dollar value of helium-3 would easily support the cost of doing it, but it's going to need a commercial company to do the work, and they are still a little short of the technology it would require. A company with the right tech, funded by a handful of the billionaire tech geeks out there (who well understand the potential gains), could make this happen.

SteveBaker (talk) 13:21, 17 May 2014 (UTC)

I would love to see nuclear fusion as a primary energy source. We know that fusion can release massive quantities of energy, because humans have built hydrogen bombs and astrophysicists have thoroughly described the inner workings of our sun. We know that there are massive quantities of energy to be harnessed! But as an engineering problem, extracting that energy from nuclear fusion - for civil power use - in a safe way - is intractable today, and will probably remain so for the next several decades.

You can scour the web pages of reliable sources like the United States Department of Energy's Office of Nuclear Energy. You can read the Annual Report for the International Nuclear Energy Research Initiative, sponsored by the DOE. If anyone anywhere was making active progress towards harnessing energy from nuclear fusion, there'd be some mention of that work in these types of report. ...But there isn't. Experts who have studied the problem already know that with the technology we have today, we aren't making forward progress towards using nuclear fusion as a safe and reliable energy source.

Decades from now, when new science and technology are known, the story might be different.

On the other hand, there is a job opening for Director for the Office of Inertial Confinement Fusion at the National Nuclear Security Administration... fusion research is alive and kicking for "certain specific applications." Nimur (talk) 18:46, 17 May 2014 (UTC)

I asked something similar at https://wiki.riteme.site/wiki/Wikipedia:Reference_desk/Archives/Science/2014_January_5#Can_fusion_ever_be_a_real.2C_competitive_power_source.3F Wnt (talk) 19:29, 17 May 2014 (UTC)

Did a kreagenny sleep been real

Did a kreagenny sleep been real if a man been update by genо-modification?--Alex Sazonov (talk) 09:44, 17 May 2014 (UTC)

Can you explain what a kreagenny sleep is? I can find no reference to it, but I do rather like the idea of genetic modification as a kind of "update" ;) ... so maybe there's a patch for my baldness gene that I've been stuck with since Humans '98. Note that mean this nicely - it's a great metaphor. IBE (talk) 11:41, 17 May 2014 (UTC)

Be careful with that kind of update – before you know it, you come acrossone of the irreversible updates, like Girlfriend 3.11 to Wife 95. And don't get me started about the child processes which keep eating up all my resources. - ¡Ouch! (^{hurt me} / _{more pain}) 06:21, 19 May 2014 (UTC)

Probably the OP means cryogenic sleep i.e. Cryonics although I suspect they knew that. Nil Einne (talk) 12:11, 17 May 2014 (UTC)

Assuming that's what he meant:

1) We have been able to freeze and revive small animals, but not humans, as larger organisms have the problem that they freeze too slowly, resulting in ice crystal formation that damages the cells.

2) You couldn't genetically modify an organism while frozen, as that requires gaining access to the cells by a virus carrying the new genes, etc. StuRat (talk) 12:54, 17 May 2014 (UTC)

Now for the distant future: If you've seen transporters, as in Star Trek and SG-1, they would have to work by scanning the body, destroying it, and reassembling it molecule by molecule at the other end. Such a technology would also allow you to genetically modify the copy, and you could keep the original version, as is, too, if you wanted. StuRat (talk) 12:54, 17 May 2014 (UTC)

The supposedly survivable cryosleep state promises to be an ideal staging of a patient for surgical procedures including complex Neurosurgery and Reconstructive surgery because it eliminates the usual constraints of Anesthesia, hemorrhaging or Surgical stress and allows unlimited time for analysing samples, consulting other specialists and for obtaining or cultivating replacement organs. 84.209.89.214 (talk) 13:20, 17 May 2014 (UTC)

We seem to lack an article on cryosleep. Is that just where they lower the body temperature, but not below freezing, so they can do longer surgery, etc., without causing brain damage due to lack of oxygen ? StuRat (talk) 15:44, 17 May 2014 (UTC)

I originally linked the OPs question with our cryonics article above suggesting it was the same thing but after more reading and consideration I think this is wrong. I have no idea what 84/CA3 means by cryosleep and even less idea what the OP meant (I suspect they didn't really think about it and so probably couldn't say whether they were speaking their native language be that Russian or more likely Spanish or may be even English).

But from what I can tell cryosleep or cryogenic sleep generally refers to something related to but not generally the same thing as what's covered in our cryonics article. Our cryonics article primarily discusses the mostly real world practice of people being preserved after death at low temperatures with the hope they can one day be revived, when there is both the technology to heal them and to revive them successfully. Alternatively perhaps some sort of mind transfer may be used.

As mentioned people are usually legally dead before this happens as most jurisdictions wouldn't allow it otherwise although our article also mentions scifi cases where someone is accidentally frozen to death. There's also the question of whether it might be possible to intentionally preserve someone in such a way with their consent start before death, in countries with sufficiently liberal euthanasia laws where the person meets the criteria but it appears this hasn't been tested [1].

Cryogenic sleep on the other hand is entirely in the realms of science fiction and generally seems to refer to the preservation/hibernation/stasis of usually healthy individuals for various reasons such as for long distance interstellar travel, or even if the person just wants to wait for some moment in the future. In other words, in this case it would usually be happening when there's already some method of revival of the should be healthy body. (If it ever does happen, there may be a testing period but this is somewhat distinct from cryonics since those currently preserved mostly aren't intended to be 'tests' but more 'hopeful'.) There's obviously other differences, for example cryonics is referring more to the process/preservation aspect while cryosleep is referring more to the hibernation aspect.

Also since cryogenic sleep is highly speculative (and perhaps because some authors don't seem to care if their terms are very accurate), in some scifi examples, I'm not sure if low temperatures are actually part preservation. It's some sort of magic, but it may still be called cryosleep etc. Although there are other terms used e.g. stasis or suspended animation or even hibernation although AFAIK the later isn't used much probably because it isn't seen as 'sexy'.

And clearly there's some overlap, for example if someone gets very bored or frustrated with life and somehow is able to convince someone to cryopreserve them with the hope of waking up to a better future, even though it's still highly speculative whether this will ever happen. And clearly these usages aren't universal, some sources use one term for both etc.

And 84/CA3 is probably correct that if cryogenic sleep ever becomes a reality, even if you need far lower temperatures for any sort of long term preservation/hibernation, higher and non freezing temperatures may be useful for some operations etc. (Although considering the advances we'll probably need before then if it ever becomes a reality, it may never be useful for that purpose.)

P.S. I'm not particularly sure the relevance of GM while a person is cryogenically preserved. I'm fairly sure the OP meant the GM will happen before the cryosleep process, if they actually thought far again before they got distracted with serial killers or whatever.

Nil Einne (talk) 15:38, 20 May 2014 (UTC)

So what do they call it when they lower a patient's body temperature for surgery, so as to prevent brain damage while they are deprived of oxygen during the surgery ? StuRat (talk) 15:46, 20 May 2014 (UTC)

Probably Therapeutic hypothermia (which is linked from our suspended animation article). Note however that reducing brain damage is important but probably not the only function. And since it also currently apparently only has one case of definite advantage (hypothermia therapy for neonatal encephalopathy as its use in cardiac arrest seems more doubtful based on recent evidence) and only involved slightly lower temperatures, it may depend on whether you are referring to the real world practices or the speculative scifi ones.. Nil Einne (talk) 16:03, 20 May 2014 (UTC)

I can imagine future detailed brain surgeries taking many hours, where the body temperature is kept just above freezing, to prevent brain damage during the surgery (because any type of blood flow would interfere with the surgery). StuRat (talk) 17:36, 20 May 2014 (UTC)

Thanks more for all! Did Yours think that a geno-modification is been a private case to solve the problem of Cryonica?--Alex Sazonov (talk) 14:16, 17 May 2014 (UTC)

Oh Yes! Richard Avery (talk) 07:13, 18 May 2014 (UTC)

Is "swimming is far more efficient than walking" like StuRat says above?

I wonder how is this supposed to work, the lower density of air should make walking more efficient. OsmanRF34 (talk) 17:51, 17 May 2014 (UTC)

What is efficient? Are we talking amount of energy "spent" per unit traveled? Humans evolved with bipedal locomotion as their primary means of conveyance, so it is unlikely that our bodies are more efficient at swimming than walking/running. I mentally compare how far, and for how long I could walk/run or swim before exhaustion, and surely swimming is less efficient. Swimming does however put less stress on the joints because water supports the weight of the body more than being outside of water. Sometimes physiotherapy is done in water for this reason. 92.40.92.10 (talk) 19:15, 17 May 2014 (UTC)

It's certainly an awful lot slower. The world record for swimming 100 metres is 46.91 seconds, but on foot it's 9.58 seconds. If you've ever tried swim as fast as somebody strolling along the side of the pool, you'll know who was most out of breath at the far end. Alansplodge (talk) 19:29, 17 May 2014 (UTC)

A sphere attached to a cable, would need more energy to go forward in water or on a surface? I wonder what StuRat meant. I hope he comes along to explain it. OsmanRF34 (talk) 20:07, 17 May 2014 (UTC)

The main sense I'd think of swimming as "more efficient" is that if you design a quality machine to move across smooth level ground, it should be able to do so using an almost arbitrarily small amount of energy, hindered only by air resistance; but natural walking consumes some significant amount of power in muscle contractions that you'd think could be designed out of the system. By comparison, if you try to automate the process of swimming, no matter what kind of boat and screw you come up with, it's still going to take a certain amount of energy to part the water. That said, nonetheless, the resistance of water really isn't all that much compared to most practical means of land transport; you really have to be to the point of building maglev rails before the hypothetical benefit of escaping water resistance becomes real. Of course in theory, when there is no change in potential energy from elevation, all travel is infinitely inefficient; it is not reversible in any such case and the energy is always lost. Wnt (talk) 21:01, 17 May 2014 (UTC)

I mean an animal evolved for the water moves using less oxygen per unit of distance than one designed for land. This is because the up and down motion of legs is wasteful. Specifically, the energy used to raise a leg is not recouped when you lower the leg back down. Wheels are a lot more efficient on level ground, but unfortunately they didn't evolve for land animals (or for marine animals, either, for that matter). StuRat (talk) 21:19, 17 May 2014 (UTC)

(citation needed) SemanticMantis (talk) 22:02, 17 May 2014 (UTC)

On what exactly ? That wheels are more efficient than legs ? StuRat (talk) 15:17, 20 May 2014 (UTC)

if you want to get from Dover to Calais, then swimming is far more efficient than walking {{no citation neeed}} DuncanHill (talk) 23:06, 17 May 2014 (UTC)

Also, most land is not level, so climbing over hills needs to be figured into the equation. Once again, we don't get back the energy used to climb the hill, when we descend. StuRat (talk) 23:10, 17 May 2014 (UTC)

You don't get back the energy used to overcome drag, whether moving through air or water. The drag is a hell of a lot greater moving through water though... AndyTheGrump (talk) 23:14, 17 May 2014 (UTC)

That all depends on your speed and how aerodynamic/hydrodynamic your shape is. For whales moving slowly, there's very little drag. StuRat (talk) 00:26, 18 May 2014 (UTC)

Citation needed... AndyTheGrump (talk) 00:29, 18 May 2014 (UTC)

On what exactly ? That aerodynamic/hydrodynamic shapes create less drag ? That whales have a hydrodynamic shape ? That drag is less for slower moving objects ? StuRat (talk) 00:57, 18 May 2014 (UTC)

• What's all this beating around the bush? The statement is totally wrong. Swimming is far less efficient than walking or running, because it requires displacing water. The most efficient way to swim is on the surface, with as little of the body underwater as possible. Looie496 (talk) 14:03, 18 May 2014 (UTC)

• If that was the case, why are whales able to hold their breaths for long periods of time during dives, so apparently using it a low rate, while land animals, like elephants, can not ? StuRat (talk) 16:01, 18 May 2014 (UTC)

• I wouldn't be so sure about that claim Looie. Our Backstroke article says "Due to increased resistance at the surface, experienced swimmers usually swim faster underwater than at the surface. Therefore, most experienced swimmers in backstroke competitions stay under water up to the limit set by FINA (15 meters after the start and after every turn)."

You can test some of this by going to the beach, getting knee deep in water, then trying to walk or run. Also, compare speeds of man-made sea surface and submarine vehicles vs. airborne and land vehicles. Viscosity is a b*tch. 88.112.50.121 (talk) 19:36, 18 May 2014 (UTC)

Looie496, displacement of water during locomotion, in itself, does not cost energy, and most certainly is not an argument w.r.t. efficiency, unlike arguments using dynamic and static drag, for example. StuRat, the claim of energy not being recouped is similarly not a valid argument; in walking there are several mechanisms that can move energy around between parts of the body, including conversion between kinetic, gravitation and elastic potential energy, also from one part of a limb to another (e.g. via coupled bands of muscle and connective tissue and momentum transfer). The kangaroo is a prime example that uses up and down motion to improve efficiency of locomotion. Yet, nothing has been said here that effectively counters your claim by showing that that swimming is necessarily less energy-efficient than overland locomotion. —Quondum 21:51, 18 May 2014 (UTC)

Changing energy between different types is also inefficient, resulting in much of it ending up as heat. Ever notice how hot you get from running ? That's wasted energy. StuRat (talk)

There is are biophysical aspects here that are not being taken into account in the discussion of the inertial mechanics that has taken place so far. Human beings, like all known complex organisms capable of locomotion, have evolved highly specialized means of movement that, in our case, overwhelmingly prioritizes bipedal movement; the distribution of muscles, the types of muscular tissue employed, the structures for leveraging the force generated by the muscles with relation to one-another, bone, and the environment, and coordination of all of these elements, have all been adapted to suite this primary locomotive function. In this regard, Stu's assertion the idea that humans are more efficient swimmers and humans is absolutely rubbish completely unfounded, as the net cost of transport (the caloric requirement to move a given distance) is significantly higher for human swimming than it is for running (owing to the above factors as well as drag forces), and, at the same time, the amount of distance than can be covered in a given period of time is several times higher for running than it is for swimming (123). This is despite the fact that, evaluating species over-all and in the niches of their typical movement, swimming is a much more efficient means of transport as a whole (4567). Note that the most efficient swimming athletes tend to have body proportions that are markedly outliers in several areas; Michael Phelps, for example, has been said to have something approaching an idealized (relative to human variation) swimmer's physique, owing to his height and arm span and other more minute proportions. But even the world's best swimmer (let's assume for the sake of argument that is Phelps) could still run a greater distance than he could swim in a given time and, even though his body is immensely conditioned to the activity of swimming, he'd still burn less calories in the run. So no matter how you parse the term "efficiency" (time to cover a given distance, caloric cost of transport to cover a given distance, or metabolic cost to specialized tissues to generate the basic underlying mechanical force as determined by the tissue type utilized), I don't see any way in which the statement that, in humans, swimming is more efficient than bipedal locomotion can be considered anything but nonsense and another example of the type of statement that contributors need to be careful about making without adequate expertise to be making that off-the-cuff judgment and, more importantly, without sources to back it up. Snow talk 22:35, 20 May 2014 (UTC)

Please actually read what I say before calling it rubbish. What I said was "an animal evolved for the water moves using less oxygen per unit of distance than one designed for land." Perhaps I should add in the seemingly obvious, just in case: "an animal evolved for the water moves IN WATER using less oxygen per unit of distance than one designed for land DOES WHEN MOVING ON LAND." I said absolutely nothing about humans being more efficient at swimming than walking, and I wish people would stop claiming that I said anything so stupid as that. StuRat (talk) 22:45, 20 May 2014 (UTC)

In that event, I apologize sincerely and profusely, Stu. I took my cues from comments in this thread without exercising due diligence in analyzing the comment and its context in the previous thread; it was sloppy contribution on my part, and I've struck the relevant sections of my post as best I could without turning it into complete gibberish or hiding the elements which you (rightly) took exception to. I hope you'll accept my apology and assurances that I won't make an evaluative claim like that again without taking the time to read the initial comments in full. For what it's worth to others reading this posting, the second group of references in my above comments strongly support Stu's assertion that movements of organisms through a water substrate tends to consume much less energy than does terrestrial locomotion. Snow talk 23:23, 20 May 2014 (UTC)

Thank you. StuRat (talk) 17:00, 21 May 2014 (UTC)

Is this a reference desk, or a forum?

I ask, because as yet there hasn't been a single source cited for anything. And without sources, the only answer we should be giving the original question is "we don't know." AndyTheGrump (talk) 16:55, 18 May 2014 (UTC)

I'd say that User:Alansplodge nailed it in the second post - with references. The difficulty here is that the original claim uses the word "efficiency" rather than speed - which opens things up quite a bit. If you just float in the water and let the wind/tides carry you, then you'll obviously use less energy than walking. On the other hand when you look at how few people have managed to swim the English Channel - it's clear that relatively few people can do it - and it's hard. On the other hand, most people who are even moderately fit can walk that distance, and many Marathon runners have run it in times under three hours. So what exactly is meant by "efficiency" here? SteveBaker (talk) 17:06, 18 May 2014 (UTC)

A bit grumpy there Andy! Both Alansplodge and I linked to other Wikipedia articles with relevant facts. Presumably they are well sourced. HiLo48 (talk) 21:03, 18 May 2014 (UTC)

I agree with AndyTheGrump that this thread is not actually treating the reference desk as it is ostensibly intended. Simply throwing in a few links does not make up for unreferenced speculations when they do not substantiate said speculation. —Quondum 21:51, 18 May 2014 (UTC)

Not our best day. The fact is it's a poorly phrased question based off of a poorly phrased claim. Of course whales are more efficient at swimming, and kangaroos are more efficient at hopping. If OP is interested in some specific science, he should try over with a more specific claim and scenario, and recall that Stu often just says whatever makes sense to him at the moment. SemanticMantis (talk) 00:15, 19 May 2014 (UTC)

Here's a source (my PC won't display it past the first page, but it seems relevant): [2]. Seasonal migration distances should be a good indicator of efficiency. Humpback whale#Range and habitat says they migrate 16,000 miles (25,000 km), while land animals generally migrate over much smaller distances, if at all. Some of this is due to blockages created by man on land, but even before man, I don't believe seasonal land migrations were on the same order. StuRat (talk) 16:07, 19 May 2014 (UTC)

The problem is still a matter of the definition of "efficiency" - if it's total energy expenditure to get from A to B then everything depends on the speed at which you need to get there. The drag caused by water dominates the cost of swimming - the energy expenditure is proportional to the CUBE of the speed! For walking or running, the air resistance is much, much less significant and the energy is mostly consumed in the bouncing stride (which is why wheels are such good idea) - the energy cost in running versus walking over some specific distance is fairly similar. Walking 25 miles versus running it in a third of the time in a marathon are both pretty exhausting - but you don't need 27 times as much food that day if you were running rather than walking. Calorie charts for human exercise suggest that the energy cost is almost exactly proportional to your speed...so calories per distance on land is pretty much a constant no matter how fast you go. So, we know that at high speeds, swimming is disasterously energy-draining compared to walking/running. But at very slow speeds, the bouyancy of the water means that you're not lifting your entire body mass up and down with every stride - so swimming wins.

Without a precise definition for "efficiency" - we can't say what the answer is. If "efficiency" is expressed in energy-per-distance-travelled, then maybe swimming very slowly wins - but if it's energy-divided-by-speed, then it's not likely that swimming will ever win. For animals, there are other "costs"...being set up with a body plan for efficient swimming really screws up your ability to climb trees - so an efficient organism might be more like a human where the body design permits slow swimming and faster running as a trade for being more flexible over the kinds of terrain you can cover.

That's why this thread has gone off the rails. We're arguing about the meaning of the terms of the question - because it's vague.

According to the article Locomotion: Energy Cost of Swimming, Flying, and Running Knut Schmidt-Nielsenish that StuRat provided above, fish generally expend less energy swimming than we do walking, and we are more efficient at walking than swimming. --Modocc (talk) 21:59, 19 May 2014 (UTC)

You're still missing the point. "expend less energy than" is utterly meaningless without context. Are these fish/marine-mammals expending less energy to swim the same distance as the human is walking/running? Are they expending less energy to swim at the same speed as the human is walking/running? It *really* matters. If it's the latter, at what speed are we measuring this? Because drag totally dominates the energy expenditure when swimming, yet is almost negligible when walking - the energy cost per unit of time is proportional to the cube of the speed when swimming and (roughly) directly proportional to the speed when walking or running. But the energy cost per unit of distance travelled is roughly constant with respect to speed when walking/running - and when swimming the cost per unit of distance is dramatically influenced by the time it takes to get there, ranging from almost zero to any large number you care to specify. So saying things like "a dolphin can swim 100 miles using half the energy it would take a human to walk the same distance (and therefore swimming is more efficient)" is utterly meaningless because it's entirely dependent on the speeds involved. SteveBaker (talk) 19:07, 20 May 2014 (UTC)

Is sweating (in mammals) secretion or excretion?

The wikipedia articles seem to suggest that the skin carries out excretion, however neither secretion or excretion article specifically states what sweating is. While sweat has left the body, some sources on internet saying that sweat serves to cool body temperature, and therefore sweat is not purely waste and has useful function. Therefore things like feces and urine are waste with no function and therefore are excretions, but sweat is secretion. Much obliged if anyone can sort this. 92.40.92.10 (talk) 18:54, 17 May 2014 (UTC)

The article on sebum says that in hot weather it serves to prevent loss of drops of sweat from the skin. Sebum is undoubtedly a secretion. It seems peculiar to think of sweat as an excretion when it is done only for specific reasons, and when water is scarce is done even at substantial risk to the organism because of its benefits. Wnt (talk) 20:51, 17 May 2014 (UTC)

One could also argue that urine serves a secondary function of cooling or warming the body. When hot, you are likely to drink cold liquids. When cold, you are likely to drink hot liquids. Either inevitably results in urinated warm liquid. It's the temperature difference between the input and output liquid which changes your body temperature. We normally only think about the input side, but the output is equally important to the equation. StuRat (talk) 21:24, 17 May 2014 (UTC)

OK agree. Also just saw that the article sudoriferous gland states that sweat is a secretion. TY. 92.40.92.10 (talk) 22:05, 17 May 2014 (UTC)

@StuRat, I can't agree with your assertion that "It's the temperature difference between the input and output liquid which changes your body temperature", The most significant control of body temperature under normal circumstances is sweating and the subsequent lowering of skin temperature by the evaporation of said sweat. Here in the UK, and elsewhere, people in winter do not heat their beer to keep warm, neither do the vast majority of people drink cold tea or coffee in the summer to keep cool. Some people do these things but not usually for temperature control purposes. (Yes, I have seen the word 'likely' as a cop out) And how the heck does the excretion of urine warm the body? Do you let it run down your leg? Don't do that! it will lose you friends and evaporate, further cooling you. Richard Avery (talk) 07:07, 18 May 2014 (UTC)

If you drink hot fluids and urinate them back out as warm liquid, then the temperature difference between the two warms your body. I was only talking about urine. In the case of sweat, it is designed to lower body temperature by evaporative cooling, which would greatly outpace the cooling process for urine, unless it's a humid day. If you meant to point out that in summer, cool drinks come out both as urine and sweat, that's true, but both come out warm, so the cooling effect is still there, it's just less than the cooling effect of sweat evaporation. And drinking fluids that are not at the ideal temperature for the season certainly happens, yes. Provided that you have sufficient temperature controls by other methods, you need not use this method, too. StuRat (talk) 15:57, 18 May 2014 (UTC)

Why must it be "or?" --Jayron32 23:02, 18 May 2014 (UTC)