Wikipedia:Reference desk/Archives/Science/2014 November 10

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 10

Efficiency of body at energy conversion

I want to find out how efficient a person's body is at converting the chemical potential energy of food into mechanical work (eg. lifting a weight). The article food energy says the food energy realised by respiration is converted to muscular output with roughly 20% efficiency. But this leaves out earlier stages in the chain: presumably not all of the potential heat of combustion of food is realised in respiration; and also I think about 10% of the energy from food has to be `ploughed back', so to speak, into the work of digesting food, so there's another 10% energy loss. I think there may be other inefficiencies.

Then there's that whole thing about, if you hold a 100 pound barbell over your head for an hour, that's not `work' according to the physics definition of the term because there's force but no distance; but it certainly is `work' according to the common English sense of the word – rather hard too, in fact.

Finally, how much mechanical work can a reasonably fit person do in a day? (Eg. in joules.) How about a top athlete? -- Communpedia Tribal (talk) 05:24, 10 November 2014 (UTC)

According to Horsepower#History_of_the_unit, a reasonably healthy human can burst at 1.2 horsepower (890 W), an athlete at 2.5 hp (1,900 W). A healthy human can sustain 0.1 hp (75 W) indefinitely, and an athlete 0.3 hp (220 W) for a few hours. Also note, that the body normally has to burn food just to keep you warm (Thermogenesis#Non-shivering_thermogenesis); if you are exercising heavily then the waste heat is more than enough for warmth, so that saves the body from using food for warmth. CS Miller (talk) 10:31, 10 November 2014 (UTC)

• The net thermal efficiency of a healthy human is about 20%. See also, basal metabolic rate. μηδείς (talk) 18:17, 10 November 2014 (UTC)

What makes this difficult to answer is that "efficiency" is defined in terms of useful work done (our article says: "Efficiency generally describes the extent to which time, effort or cost is well used for the intended task or purpose.") - but the definition of "intended" or "useful" is tough to nail down here. For example, when you run...the energy conversion into kinetic energy is one measure of efficiency - but the muscles generate heat, and as warm-blooded creatures, generating heat is "useful" - so do you count the incidental heat generated by the muscles when running as a part of the useful energy or as a part of the waste energy? Clearly it depends on the situation. In a hot climate, that extra heat is a major problem because it has to be removed from the body somehow - but in a cool climate, we might deliberately use our muscles to increase heat production. So when we're shivering, the kinetic energy generated is "waste" and the heat produced is "useful" - which is a complete reversal from the situation when we're running.

So until you can meaningfully partition wasted energy from useful energy, calculating efficiency is difficult.

That gets worse when you think of things like the energy consumption of the brain. Our brains use about 25% of our energy production...but (for example), a lizard gets by with only about 2% of it's energy devoted to brain functions. If we're simply trying to run fast in a straight line, then that 25% consumption is nearly all wasted because it should be possible to run in a straight line using only 2%...but if we're actively navigating to find the shortest route then thinking more equates to running less, so the brain's contribution to getting from A to B is just as "useful" as piling on more kinetic energys - and so it should be counted. But what about if we're using the time to compose poetry or design the next high-tech widget...then how do you account for that brain energy?

So, (as is often the case here) we need to tie down our terms rather more precisely in order to deliver a reasonable answer.

SteveBaker (talk) 19:01, 10 November 2014 (UTC)

The brain using 25% of our energy is a common trope for which you provide no source, SteveBaker. Is our article wrong when it says the brain uses about 20%, while the liver uses about 30, and the heart only 7? μηδείς (talk) 21:25, 11 November 2014 (UTC)

Sources I've looked at are all over the map from 20% to 30% - it probably depends on the individual, and on how much brain activity is going on during the period that they're observed. It's certainly not a precise number. At any rate, the precise answer doesn't affect my answer in any way - so I really don't see the need to quibble over 5%. My point is only that measuring "efficiency" entails asking whether all of the energy consumed by the brain is "useful" or waste...and that clearly depends on the task we're measuring the efficiency of. "How efficient is the body at running marathons?" is not remotely the same question as "How efficient is the body at solving quadratic equations?". It doesn't matter whether the number is 20% or 30% or someplace in between - that's not the question here. SteveBaker (talk) 05:11, 12 November 2014 (UTC)

We did this in HS biology just looking at the caloric value of food consumed versus excreta. Maintaining body temperature was not considered waste heat. All I remember is that the body was more efficient than most engines, but still not very efficient. I think it's a read herring to worry about work, since that's a teleological engineering concept, not a physically fundamental one. A toy train running around in circles may be performing no work when no one is watching, but if it produces giggles in a child it is. And I won't quibble, but a difference between 25% and 20% is a 25% difference, not a 5% difference. μηδείς (talk) 17:47, 13 November 2014 (UTC)

The value of the electron in the world of science

Did it true, that since the discovery of the electron world science had not progressed, because the electromagnetic electronic balance of all elementary particles is always been the same (equal) and always been constant?--Alex Sazonov (talk) 09:32, 10 November 2014 (UTC)

No. Science has made plenty of progress. There is a fringe theory around that says that once a physical quantity is measured then it causes other similar measurements to come up with the same value. Some kind of precedent setting. I don't know what this is called and I don't trust it. Graeme Bartlett (talk) 12:17, 10 November 2014 (UTC)

(ec)No, not at all. There is plenty of science that is progressing all the time. E.g. all of computer science, or special relativity, or the decoding and application of DNA. Or, to stay subatomic, the discovery of quarks (with non-integer charges) and the whole standard model.--Stephan Schulz (talk) 12:23, 10 November 2014 (UTC)

Pretty much all of modern geology has progressed a lot, starting with plate tectonics, which is the Sine qua non for geology. Plate tectonics started as a concept some 20 years after the discovery of the electron (though under a different name) and made major leaps forward in the 1950s and 1960s. Nearly all of meaningful discoveries in meteorology, astrophysics, psychology, etc. etc. came about in the 20th century, while the discovery of the electron occurred in 1897. The discovery of the electron was certainly very very important, but it isn't like it was the only thing that happened in science in the past 120 years. --Jayron32 13:01, 10 November 2014 (UTC)

Atomic electric charge of all elementary particles is always been the same, so it turns out, that in the natural nature are always been only once electrons!--Alex Sazonov (talk) 13:36, 10 November 2014 (UTC)

Except quarks. --Jayron32 13:59, 10 November 2014 (UTC)

And, to be pedantic, protons and positrons. --Stephan Schulz (talk) 15:00, 10 November 2014 (UTC)

Atomic structure of all elementary particles is been the same (universe), so we can conclude that in the natural nature are always been only once electrons, as ideal atoms.--Alex Sazonov (talk) 17:28, 10 November 2014 (UTC)

That statement makes no sense whatsoever in English. AndyTheGrump (talk) 17:32, 10 November 2014 (UTC)

It makes even less sense in the 3000+ other languages of the world. --Jayron32 17:33, 10 November 2014 (UTC)

You might be interested in One-electron_universe. SemanticMantis (talk) 17:42, 10 November 2014 (UTC)

Electrical properties in the natural nature had only once electrons!--Alex Sazonov (talk) 17:47, 10 November 2014 (UTC)

No, they didn't. Saying it over and over again doesn't make it so. --Jayron32 17:52, 10 November 2014 (UTC)

Are you thinking of the plum pudding model, a now-discredited model of the atom? It suggested that the atom consisted of electrons floating in a goo, without any other specific components. Meanwhile, Graeme Bartlett, what do you mean? It sounds like you're describing a researcher with a form of confirmation bias, whereby he's prejudiced toward finding results similar to the one he already got. Nyttend (talk) 20:33, 10 November 2014 (UTC)

I heard it on a podcast recently, but I can't remember exactly which one, or who was the proponent. It was more of a theory of reality. It said that various measurement values were indeterminate until they were first measured and thereafter all future measurements would come back the same. Graeme Bartlett (talk) 22:39, 10 November 2014 (UTC)

The OP's rantings remind me more of Prout's hypothesis, which was actually considered a reasonable conjecture until disproven, which held that all elements were composed of aggregations of hydrogen. Prout proposed his hypothesis because all pure isotopes were multiples of the mass of hydrogen-1 (protium), which implied that hydrogen was in some way fundamental. He was wrong, but in interesting ways. Prout's hypothesis provided an important step in the discovery of the proton and neutron, which (to a rough approximation) DO weigh the same as hydrogen does, and explain why Prout's hypothesis works. Still, it has nothing to do with electrons, and the OPs repeated insistence that everything is somehow made of electrons (it isn't), or that electrons have the smallest fundamental charge (they don't) or that all science since the discovery of the electron is somehow directly derivative of it (it isn't). --Jayron32 23:15, 10 November 2014 (UTC)

Are Mark 60 CAPTOR naval mines being phased out?

This site[1] says: "The CAPTORs are gone, and the SLMMs will be phased out in 2012." in reference to the Mark 60 CAPTOR naval mines. Is this true? I can't find any other collaborating sources. I don't usually trust random online sources, but the author, Scott C. Truver, is on the editorial board of Naval War College Review. WinterWall (talk) 11:39, 10 November 2014 (UTC)

I think this is better asked at Humanities, because notions of chivalry, budget, and perhaps international law are involved. How gone is "gone" is another question for them to chew on. The science aspect I see in the source is Suggestions that the Navy acquire modern foreign mines have been met with “not invented here” indifference. Here it might be worth pursuing what technological improvements the "modern" mines have that the U.S. ought to copy. Wnt (talk) 17:01, 10 November 2014 (UTC)

I did a little reading on the topic; and my conclusion was, roughly summarized: I don't know. But I found some good reading material!

Our Department of Defense keeps a pretty tight lip on its capabilities regarding undersea warfare. You can read about the Navy Undersea Warfare Center and the Naval Mine and Anti-Submarine Warfare Command, but ... there's not much information on technologies or capabilities. Compare this to the websites of the Air Force or the Army, where the public websites advertise all kinds of nifty specifications about airplanes and armored vehicles and guns, arguably for the purposes of recruitment. This is consistent with everything I know about submarines: they're pretty much Top Secret, so there's no good reason to make noise about even their mundane factual details.

I went to the website of the Department of Defense to see if there's any public information - budgets or press releases or speeches. There's a 1996 speech: Three Musts for Affordable Naval Mine Warfare, by Paul Kaminski - who would have had a pivotal role in executing the national defense policy for naval mine technology. And if you search the public Defense Department budgets, there are line-items scattered among the results for naval mine warfare technology development and system acquisition. So this is an ongoing effort; but it's not highly publicized. It is probable that the Navy can not justify losing a capability, even if that capability has no immediate application to any existing conflict.

Even still, it seems cheaper and easier to deploy undersea mines from surface ships and aircraft. There are no shortage of news reports on that: for example, the P-3 Orion Practices Aerial Mine Laying in Gulf of Thailand. To deter enemy mine-laying, there are a variety of effective techniques, from aerial surveillance to diplomatic efforts. When possible, the Navy would prefer to keep its submarines out of the spotlight, because their much more critical role - second strike - depends on keeping them out of combat.

Finally, I would direct you to read this statement from the Department of Defense. In 2014, the United States made a critical policy statement, reversing many years of prior policy: "The United States will not produce or otherwise acquire any anti-personnel landmines in the future." On the whole, the Defense Department has decided that antipersonnel land-mines are not a good thing, from a defense standpoint. They bring bad publicity; they are hazards to friendly forces; and mines persist for a long time after the conflict is over. When confronting conventional state-based opponents, it is easier to enforce treaty-compliance through diplomacy, and avoid mine-warfare by "gentleman's agreement;" and when fighting a non-state actor in asymmetric warfare, there is little advantage in deploying the mines ourselves; in fact, our biggest problem in the last few wars has been that the asymmetric opponent had far too easy access to land mines and improvised explosives. The reversal of American policy is huge - landmines are a very big problem throughout the world, even in places where conflicts "ended" many years ago.

Important to note, though, that anti-vehicle landmines and naval mines were not mentioned in the policy statement. Evidently, the Defense Department had no comment on those topics.

Nimur (talk) 16:46, 11 November 2014 (UTC)

Thanks, guys. WinterWall (talk) 14:08, 13 November 2014 (UTC)

Resolved

High humidity in refrigerator

If the relative humidity inside a refrigerator is high (in the high 80s range), what could be the cause? --173.49.12.187 (talk) 13:02, 10 November 2014 (UTC)

Here are some possible answers to your question. --Jayron32 13:12, 10 November 2014 (UTC)

I have that problem in my fridge, too, in the summer, when the house air is humid. In fact, water drips from the divider between the top freezer and bottom fridge. I simply put a bowl under where it drips and dump it regularly. I think of it as a fridge plus dehumidifier. The fact that it's dependent on house humidity implies that keeping the humidity in the house low will solve the problem, too. StuRat (talk) 16:36, 10 November 2014 (UTC)

My parents' fridge has a little heating element which when turned on evaporates the condensation that otherwise drips from the freezer to the fridge. She gets upset if it is activated, and then accuse people of spilling water on the refrigerator door! My OR would be to leave a jar of baking soda in the fridge as a desiccant and stir it occasionally until it cakes up. This is actually a recommended use by the manufacturer (see the box) to keep the fridge "fresh". μηδείς (talk) 18:09, 10 November 2014 (UTC)

Baking soda is most probably the most cost effected method normally, as it is cheap. Yet, if one has very high humidity then maybe Blue Indicating Silica Gel might be better Blue Indicating Silica Gel. One rejuvenates it in the oven. If on the other-hand, (say for augments sake) one's daughter's boyfriend always raids your fridge every time you go out (in the hope that by by leaving them together – alone- without Mom and Dad's eyes following and analyzing their every interaction; in the faint, faint hope that they ignore everything the have seen on TV and might discover the same magic- Oh that's for another time). Then leave a diaper in the fridge. That has silica gel in it too and will bring down the humidity. Should the boy- fiend see this diaper, then come to terms with the fact that he is probably dating a member of the Adams family, then you're almost home and dry. Suggest however, one uses, unused diapers in the fridge.--Aspro (talk) 23:36, 10 November 2014 (UTC)

The ambient humidity is not the problem. The refrigerator was recently serviced for a different problem. There is another refrigerator in the same area. The relative humidity inside the latter is the 40s. --173.49.12.187 (talk) 02:18, 11 November 2014 (UTC)

You misunderstood me. I'm not saying that a properly operating refrigerator should drip water when it's humid in the room. I'm saying a malfunctioning fridge may only drip when the ambient humidity is high.

Some models of fridge have a drip pan under the fridge to catch drips, so they admit that this is a possibility. But my question is just what is supposed to happen to your ambient moisture ? It enters the fridge each time the door opens, and is likely to condense at the lower temperatures, and it has to go somewhere. A heater to evaporate condensed water and blow it outside the fridge is one way to handle it. Personally I think pouring the waste water down the drain is a better option, rather than using energy to evaporate it and put it right back into an already humid room, where it will again enter the fridge the next time the door is opened. StuRat (talk) 04:52, 11 November 2014 (UTC)

The drip pan is normally mounted on top of the motor/compressor unit, and uses waste heat from it to evaporate the condensate. CS Miller (talk) 12:36, 11 November 2014 (UTC)

That's not where I've seen it. It was maybe an inch off the floor. StuRat (talk) 16:59, 13 November 2014 (UTC)

Lets break this down into tiny steps: The two fringes may be working at different temperatures. The lower temperature fridge (one would think) has the lower humidity. Second. Humidity meters are notoriously hard to calibrated (unless one has a laboratory grade instrument). Are the same instruments (thermometer, hygrometer) being used to measure both interiors? The average hygrometer bought at the local store are mostly not worth the money. So it one has two they may well not agree with each other.--Aspro (talk) 22:14, 11 November 2014 (UTC)

The two refrigerators may not be at exact the same temperature, but they are not far apart. The humidity measurements were taken using the same digital combination thermometer-hygrometer. Measurements from the same refrigerator were consistent over time. --173.49.12.187 (talk) 04:48, 12 November 2014 (UTC)

Nearest-planet-to-Earth graph

Is there somewhere a graph plotting the Earth–Mercury distance, the Earth–Venus distance and the Earth–Mars distance all against time (for at least a few years around now)? Or is there free data somewhere from which I could build this graph myself? 85.226.205.208 (talk) 18:04, 10 November 2014 (UTC)

This website has utilities that will let you do exactly that, for every planet in the solar system. --Jayron32 18:21, 10 November 2014 (UTC)

FYI, Venus will always be the closest at least once a year, since its orbit is closest to ours, and with its quicker period it laps us at least once every calendar year. μηδείς (talk) 21:57, 10 November 2014 (UTC)

To lap us every calendar year, its angular speed would have to be at least twice ours, i.e. its period must be no longer than six months. —Tamfang (talk) 09:30, 14 November 2014 (UTC)

You might find http://www.fourmilab.ch/solar/solar.html to be helpful.

—Wavelength (talk) 22:05, 10 November 2014 (UTC)

Thanks for all the suggestions! I was a little confused as to how to gather data series from those pages, so I ended up writing a little Python script to send repeated requests to the Fourmilab page, and output the distances to a CSV file. I hope they'll forgive me for flooding the server. It made for a very interesting graph indeed! 85.226.205.208 (talk) 12:52, 11 November 2014 (UTC)

Cool, care to share your graph(s)? It would probably be well placed on our Commons, and could be used in a variety of related articles. SemanticMantis (talk) 14:59, 11 November 2014 (UTC)

Certainly! Here is the graph. The font size should probably be larger if it is to be used as an article illustration, but I guess that is easily fixed. I also uploaded the Python code to the image's talk page on Commons, in case someone needs other date spans. If you're more used to Commons categories than I am, feel free to add some. Cheers, 85.226.205.208 (talk) 08:42, 12 November 2014 (UTC)

Thanks! SemanticMantis (talk) 16:20, 12 November 2014 (UTC)

What's your sample rate? I'm surprised at the "lumpiness" of the curves. —Tamfang (talk) 09:37, 14 November 2014 (UTC)

The sample rate is 24 hours, so 90-ish data points per grid section. I'm sure the "lumpiness" can be explained by orbital mechanics, but I'm very rusty. Seeing that the Mars curve is most "lumpy", the fact that the orbit of Mars is especially eccentric probably contributes. Astrophysicists, please jump in! 85.226.205.208 (talk) 11:57, 14 November 2014 (UTC)

And perhaps a good follow-up image would be an animated image, animating Earth's and Mars's orbits while drawing the Earth–Mars distance graph by their side! 85.226.205.208 (talk) 12:04, 14 November 2014 (UTC)

Two questions here:

1. Is it possible for Jupiter to be closest, or is the closest distance to Jupiter greater than the distance to Mercury when it is completly on the other side of the sun?
2. At least during this time period, when Mars is at its closest, Venus and Mercury are far enough away that Mars is *the* closest to earth. Is this just chance for this time period or is there some sort of Resonance here?Naraht (talk) 17:09, 15 November 2014 (UTC)

Jupiter is far away; even Mars is always significantly closer. The main illustration at Asteroid belt is enlightening. For the other question, there aren't any perfect orbital resonances between the inner planets, but some are quite close (which may be more than a coincidence), so you could probably make out some near-periodicity from that. 85.226.205.208 (talk) 21:35, 16 November 2014 (UTC)