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Wikipedia:Reference desk/Archives/Science/2015 November 25

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November 25

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Induction cooking, and induction charging

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Is the physics behind induction heating a pan and induction charging a smartphone (aka wireless charging) basically the same? Except for the fact that the devices (pan or phone) are different. One is designed to resist and get hot, the other to let the current flow through a coil and get charged? I don't get though why you can place the smartphone in any orientation on the charging pad, and why its components don't get hot.--Scicurious (talk) 02:19, 25 November 2015 (UTC)[reply]

The saucepan needs a fairly big chunk of metal to set up a big eddy current. Small pieces will net get much voltage across them, and less current with heating much much smaller. Graeme Bartlett (talk) 09:36, 25 November 2015 (UTC)[reply]
We have pretty good articles on induction cooking, induction heating, inductive charging, and see also conductive wireless charging. SemanticMantis (talk) 15:18, 25 November 2015 (UTC)[reply]
I took a look at those, but still... It's quite a mystery for me that you can orient the smartphone in any direction. Shouldn't the coils be parallel? Does the charger or phone adapt internally? --Scicurious (talk) 16:00, 25 November 2015 (UTC)[reply]
Some of the simpler inductive chargers do demand a specific orientation, like the Nokia one mentioned here [1]. This patent [2] explains a bit about the proper orientations are achieved, and this blurb [3] talks about some methods to allow for multiple orientations or devices. Qi_(inductive_power_standard)#System_overview has some info and refs about how orientation-independent charging can be handled. SemanticMantis (talk) 17:31, 25 November 2015 (UTC)[reply]

Gaining/losing weight too fast

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Any associated health risks with either one? If any? What's the maximum rate for someone's height? Theskinnytypist (talk) 04:50, 25 November 2015 (UTC)[reply]

Yes, there can be major health risks for either. But the factors that come into play are too complex for me to try to summarize. Looie496 (talk) 15:53, 25 November 2015 (UTC)[reply]
I doubt the rate can be calculated precisely.
A crash weight-loss diet can imply loss of water, loss of muscle mass (including heart), lack of nutrients, saggy skin, among others. A crash weight-gain diet could imply too much fat is built up. Or, if you are trying to build muscle, fatigue and injuries.
Any one of both are long-term goals.--Scicurious (talk) 16:05, 25 November 2015 (UTC)[reply]

Orientation of solar system ecliptics to galactic ecliptic

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Without going into specifics - is there any relationship between the orientation of the ecliptic planes of individual solar systems, and that of the parent galaxy? Or is there no reason to assume such, and solar ecliptics are likely to be oriented every which way relative to the galactic plane? Gut feeling says that since ecliptic planes at both scales are the result of similar mechanics, there might well be some correlation, but I haven't been able to find a statement either way.-- Elmidae 12:43, 25 November 2015 (UTC)[reply]

As far as I know, there is no significant correlation. Methods of detecting exoplanets and Kepler_(spacecraft)#Objectives_and_methods seem to assume random orientation. And, anecdotally, the Galactic plane is inclined by about 60 degrees to the ecliptic (the plane of Earth's orbit), according to Milky Way. --Stephan Schulz (talk) 16:05, 25 November 2015 (UTC)[reply]
Too bad. If alignment were commonplace, Kepler (spacecraft) would work better. Jim.henderson (talk) 17:46, 25 November 2015 (UTC)[reply]
Or worse, depending on where you point it. In particular, Kepler "points to a field in the northern constellations of Cygnus, Lyra and Draco, which is well out of the ecliptic plane, so that sunlight never enters the photometer as the spacecraft orbits". If all orbits were aligned, Kepler would need point along the ecliptic, too, and that would be very bad for the 1/30s of its orbit where the sun would be directly in its field of view, and probably quite bad at other times when it points closely to the sun. --Stephan Schulz (talk) 18:46, 25 November 2015 (UTC)[reply]

Actually, I just realized that the very orientation of the Milky Way in the night sky at the equator (incl. range of seasonal precession) shows a significant departure from the solar ecliptic. Heh. - Seems the far-fetched SF plot device I was trying to falsify is Go *rubs hands* Cheers, people! -- Elmidae 19:41, 25 November 2015 (UTC)[reply]

One could also say "And, anecdotally, the Galactic plane is inclined by about 60 degrees to the ecliptic (the plane of Earth's orbit)" ;-). --Stephan Schulz (talk) 20:07, 25 November 2015 (UTC)[reply]
I suspect that there IS a relationship, but it's at such a large scale that it's only revealed on the galactic level, i.e. that if you add up ALL the solar systems' orientations, they "add up" to the orientation of the galaxy. However on an "individual level" the solar systems would form up every which way. Vespine (talk) 23:32, 25 November 2015 (UTC)[reply]
I take back the above. Reading articles such as these it is possibly just random, up to chaos theory. Vespine (talk) 06:01, 26 November 2015 (UTC)[reply]
That does sound pretty definite, thanks!-- Elmidae 07:41, 26 November 2015 (UTC)[reply]

Little Boy and Fat Man detonation timings

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According to Little_Boy#Fuse_system, the detonation was supposed to occur at the most destructive altitude, similarly to Fat Man. Why it was decided not to detonate both bombs upon ground impact or at very lower altitudes (via different timer and altimeter settings) where damage would be the greatest? 93.174.25.12 (talk) 21:37, 25 November 2015 (UTC)[reply]

Note: I have changed the heading to Little_Boy#Fuze system. A fuse is typically just a piece of some sort of cord that burns; a complicated detonator is a fuze. So the original poster's link will no longer take you to the right section; use the one I posted instead. --Trovatore (talk) 21:47, 25 November 2015 (UTC) [reply]
One factor may well have been that they didn't know what altitude would produce the most damage, so wanted to try various altitudes. StuRat (talk) 21:45, 25 November 2015 (UTC)[reply]
Against non-hardened targets like an ordinary city, damage is the greatest when the weapon detonates above the ground as an air burst (as the bombs used on Japan were). Think about the physics of an explosion. An explosion expands roughly spherically. A ground burst directs much of the weapon's energy (the bottom part of the sphere) into the ground. In an air burst, the explosion is free to expand over a wider area. Sometimes a ground burst is desirable, like when the target is underground, or you want to maximize fallout. --71.119.131.184 (talk) 21:56, 25 November 2015 (UTC)[reply]
Definitely the premise that a ground detonation or very low altitude detonation is the "most destructive" is mistaken. The topic is discussed here Effects of nuclear explosions. Vespine (talk) 23:24, 25 November 2015 (UTC)[reply]
Yes, anything in a city pretty much directly under an air burst is going to be wiped out anyway. An air burst will spread the destruction over a wider area. Bubba73 You talkin' to me? 02:41, 26 November 2015 (UTC)[reply]
Funny you say that because one of the buildings most directly under the blast at Hiroshima was not "wiped out" but remains standing to this day, precisely because it was directly under the blast. Obviously it was still "destroyed" to a large degree and everyone was killed, but most of the actual structure withstood the mostly "downward" force of the blast. I don't mean anything Bubba said is not correct, I just think it's a fascinating bit of trivia. Vespine (talk) 21:29, 26 November 2015 (UTC)[reply]
More details at Now It Can Be Told: The Story Of The Manhattan Project by Leslie R. Groves and The Making of the Atomic Bomb: 25th Anniversary Edition by Richard Rhodes. Alansplodge (talk) 16:37, 27 November 2015 (UTC)[reply]
Surely the reason for not detonating these on impact, especially for a weapon like Fat Man, was to ensure that the carefully constructed device would not be damaged before it had a chance to work properly.122.109.117.69 (talk) 02:45, 29 November 2015 (UTC)[reply]
I believe they had a fail-safe that would destroy it on ground impact. Detonation altitude would be determined by lethal/destructive blast radius. They can measure the pressure wave and determine the most destructive altitude. Japanese cities cities were prone to fire especially in residential areas and the goal was to destroy as much of the target city area as possible. One of the differences was terrain. The hilly area around Hiroshima, I believe, reflected and amplified damage. --DHeyward (talk) 03:48, 29 November 2015 (UTC)[reply]

The Linear thermal expansion of technetium

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Where can I find data for the linear thermal expansion of technetium at temperatures from room temperature up to the melting point? — Preceding unsigned comment added by 77.247.29.84 (talk) 22:40, 25 November 2015 (UTC)[reply]

Our article Technetium gives a figure of 7.1 μm/m⋅K, cited to this paper. This is only for the range 0 - 100°C, though. Tevildo (talk) 23:12, 25 November 2015 (UTC)[reply]

Why do humans live so long?

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Why does it take 20 years for a human being to reach sexual maturation and even longer for cognitive maturation? Why do other animal species have shorter life cycles? With the push to delay marriage at later ages, is it ever possible to delay puberty as well and prolong childhood, so that childhood is from 0-20 years, adolescence is from 21-29 years, and adulthood is from 30-death? 71.79.234.132 (talk) 22:44, 25 November 2015 (UTC)[reply]

Sexual maturity occurs far earlier than 20 in most people, although near starvation can delay it substantially. The reason for long human life spans seems to be related to our intelligence, in that it takes decades to learn everything we need to know for optimal survival chances. And prolonging childhood seems to be important for learning, as the more maleable child brain learns more easily, but also isn't sufficient for survival without assistance. As for delaying puberty, yes, there are drugs to do that. I think you have a good idea there, and venereal diseases, teen pregnancies, and teen violence could all be reduced by delaying puberty until people are mature enough to handle it. StuRat (talk) 22:51, 25 November 2015 (UTC)[reply]


(EC) Lots to address here. Let's start with the last: puberty in humans is occurring earlier now than in the past, Puberty#Historical_shift. For animals' life spans, see Life_history_theory#Reproductive_value_and_costs_of_reproduction and r/K selection. For our relatively slow maturation times, see altricial, Neoteny#Neotenic_traits_in_humans, and Observational_learning. For our longer lifespans, see Grandmother hypothesis. Somewhere in there the Obstetrical dilemma comes in. Parental_investment is also relevant. SemanticMantis (talk) 22:55, 25 November 2015 (UTC)[reply]
Also, we live long compared to some other common "small" animals, but we're not even in the top 10 longest lived animals. Vespine (talk) 00:44, 26 November 2015 (UTC)[reply]
No terrestrial warmblooded animal, perhaps. See Bowhead_whale#Lifespan. --NorwegianBlue talk 15:41, 26 November 2015 (UTC)[reply]
I said no warmblooded animal our size.... That's an essential qualification of the argument. μηδείς (talk) 18:32, 26 November 2015 (UTC)[reply]
At the other end naked mole-rats are only the size of mice but can live 30 years. Dmcq (talk) 22:59, 26 November 2015 (UTC)[reply]
Again, they aren't normal terrestrial warm blooded mammals: "The naked mole-rat does not regulate its body temperature in typical mammalian fashion. They are thermoconformers rather than thermoregulators in that, unlike other mammals, body temperature tracks ambient temperatures." μηδείς (talk) 18:28, 27 November 2015 (UTC)[reply]
While the various species of elephant do not live quite as long as humans, they have nearly the lifespan of humans. Elephants are warmblooded and are much larger than humans. Their large size may be a factor in their lifespan. Robert McClenon (talk) 18:34, 27 November 2015 (UTC)[reply]
To clarify my point, I think SM brought up the relevant ecological theories, r/K selection and the grandmother hypothesis, which I repeated in lay terms. But the facts that need explanation is that on graphs longevity in mammals, humans are quite an astonishing outlier for our body size; we should be dying of old age around 30, not 80. This page gives some good graphs based on lifespan versus heart rate (heart rate being negatively correlated with mass). Here are a multitude of graphs with many different pages of interest. μηδείς (talk) 02:14, 28 November 2015 (UTC)[reply]
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