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pH stands for the power of hydrogen. H+ is hydrogen ion in aqueous solution. To calculate pH, you need to take the negative logarithm of the ion concentration. 50.4.236.254 (talk) 02:17, 19 March 2017 (UTC)[reply]
pH explains how it is calculated. 50.4 has given you the wrong answer (well, mostly wrong. There's some negative logarithming going on there, but he doesn't tell you WHAT is being negative logarithm. An ion is not a number, and cannot be logarithmed.) If you want the right answer, read the article on pH. --Jayron3202:22, 19 March 2017 (UTC)[reply]
I live at 40 degrees latitude and -83 degrees longitude. There are a lot of grocery stores here. But some things aren't local. Avocados, for example, come from California or Mexico. Oranges may come from Florida. There are countless corn fields here. And there are many coniferous trees and dandelions and cattails, so I may be able to gather pine nuts. I wonder if I may store them in a safe space for the winter. If I want to eat local, then what should my diet be? What should I do about the winter? 50.4.236.254 (talk) 02:53, 19 March 2017 (UTC)[reply]
Wikipedia has an article titled Local food which explains some of the benefits and pitfalls thereof. Please do not solicit opinions from the ref desks as to what you should do. You can come to those conclusions on your own, and don't need us. We can, however, provide you reading material such as the article Local food. This search contains several links to good locally-sourced foods near your locale. --Jayron3203:04, 19 March 2017 (UTC)[reply]
Not exactly "locally sourced food", per se. But anything in the vicinity, which includes pine nuts. So far, I only know that pine trees, dandelions, and cattails grow here, because I've seen them. I once saw an oak tree too, but I'm not sure if that's common in these parts. I wonder if it's possible to locate specific flora and fauna in the vicinity. 50.4.236.254 (talk) 03:39, 19 March 2017 (UTC)[reply]
Yeah, I know that. I found a website that provides information on how to prepare acorns to make them edible. But I wish to know how various trees - oaks, for example - are dispersed. That may give me some hint to find them. 50.4.236.254 (talk) 04:33, 19 March 2017 (UTC)[reply]
IMHO, a wide variety of food is more important than local sourcing, at least as far as health is concerned. Of course, local sourcing also helps the local economy, at least until everyone else does it and stops buying the food you export. StuRat (talk) 03:46, 19 March 2017 (UTC)[reply]
Eating local is not simply about eating what happens to grow locally - it is about what can be grown locally. If enough people wanted to do it, a lot of those corn fields could easily be used to produce local fruit and vegetables, and to farm animals for meat. If you are the only one wanting to do it, you need to get a bit of land, and grow your own. Wymspen (talk) 12:58, 19 March 2017 (UTC)[reply]
Those coordinates seem to put you at the Ohio State University which certainly has resources to teach you about the local flora, fauna and agricultural practices. Googling "ohio state university" "local food" shows many promising links. Rmhermen (talk) 17:13, 19 March 2017 (UTC)[reply]
Eating local is BS. It is a general postulate of economics that what is cheapest is least detrimental. For example, electric cars "sound" green but they require huge amounts of toxic heavy metals, and the electricity they run on is produced by highly toxic coal-burning electric plants. (That might change with nuclear/fusion and better batteries, but not soon.) The best policy is ALWAYS to buy the cheapest, non-subsidized product. You can pretty-much assume anything from Sacrifornia is the spawn of the Jevil. See "Capitalism" by Reisman. Here's the downloadable PDF http://www.capitalism.net/ (on the left) and the general principle here is division of labor. μηδείς (talk) 17:49, 19 March 2017 (UTC)[reply]
That might be true, but only if the total cost of the entire product life cycle is considered, and if you compare amounts of products that last the same amount of time. Otherwise, plastic forks seem like a better deal than real ones, because each costs less and the disposal costs aren't included. Also, a large part of the reason gasoline cars are cheaper is just economies of scale, so, once electric cars are created on that scale, the price should come down some. (BTW, what is the "J" in Jevil for ?) StuRat (talk) 21:02, 19 March 2017 (UTC)[reply]
Yes, that's why I mentioned "non-subsidized". If transportation is subsidized by taxes, and that is not calculated in, you don't get the actual cost. μηδείς (talk) 01:13, 20 March 2017 (UTC)[reply]
Venezuela#Shortages is an example of what can happen if you don't buy locally. The government there actively discouraged it, instead preferring to export oil and use that money to import food and other goods. Unfortunately, when the price of oil collapsed, this left them without enough cash to import what they need. StuRat (talk) 21:09, 19 March 2017 (UTC)[reply]
Communist governments do encourage people to buy locally, often by having high import duties or just flat out banning many imported products. In fact they have to do so if they want to stay out of the capitalist market. However, shortages are the bane of such countries because of poor planning of production and importation, and dependence on a bureaucracy to manually balance out the market by import/export. I would bet money that Venezuelan people are eating a lot of local food right now, and probably from their very own gardens. 93.138.122.175 (talk) 01:58, 20 March 2017 (UTC)[reply]
I don't think it's true, in general, that communist govs encourage buying locally. For example, they may form huge farm collectives, and grow one item in each province, and expect everyone to buy from that collective. (In addition to the counter-example of Venezuela, we also have China during the "Great Leap Forward", where Mao encouraged farmers to abandon farming and build backyard forges, with disastrous results.) StuRat (talk) 07:26, 21 March 2017 (UTC)[reply]
In the old Iron Curtain countries, plain economics tended to enforce the consumption of home-grown over imported food from outside the bloc, which would have required hard currency, On a visit to Bulgaria in the twilight of the Communist era, the only fresh fruit or vegetables in our tourist hotel were cucumbers and tomatoes, although one day we had some thoroughly bruised apples. Alansplodge (talk) 10:52, 22 March 2017 (UTC)[reply]
That food may well have been black market, as communist governments tended to think everything could be grown more efficiently on a huge scale, in communes. This is at the core of why communism failed, that they didn't recognize that people who gain nothing from growing food (or any other activity) will do a terrible job at it, while those whose livelihood depends on it will do a good job. Towards the end of communist regimes the people in charge often start to realize that communism doesn't work, but they can't say that, so they just stop enforcing laws against local production. Thus it becomes more grey market than black market. StuRat (talk) 19:37, 22 March 2017 (UTC)[reply]
Buying local is encouraged in developed countries by environmentalists to reduce carbon emissions (see food miles), each individual kiwi fruit is said to require its own weight in aviation fuel to get it from NZ to the UK. Apparently, EU rules prevent the UK government from promoting local produce over imports from other member states. [1]Alansplodge (talk) 11:21, 20 March 2017 (UTC)[reply]
In fact as the article Alansplodge linked to itself says, food miles in itself is a much criticised concept due to the concentration on only one factor, when as it also says, much of the carbon emissions tends to come from the production phase. Things don't have to be that exotic, in at least some cases NZ grown dairy and sheep meat can be more energy efficient (which is a somewhat different thing from carbon footprint) than UK grown in the UK, even taking into account transport costs. Apples is another example although it may only be during the off-season (and at least many by local movement due encourage seasonal fruits and vegetables). Nil Einne (talk) 10:21, 22 March 2017 (UTC)[reply]
Aqua streaksDifferent-colored areasLong streak in the distance
I was at Key West, Florida the other day and the ocean there has aqua-colored streaks in it. (Well, that is the closest color I know - they are actually a little more greenish than aqua.) This photo is a sample. What causes that? Bubba73You talkin' to me?04:58, 19 March 2017 (UTC)[reply]
I would guess you are seeing white sand bars close to the surface. There are many other factors which can affect water color, but most are more subtle than this. StuRat (talk) 05:12, 19 March 2017 (UTC)[reply]
Sometimes sunlight getting through the clouds creates patches or streaks of brighter color on the water. Here's how you can tell. If it's the bottom and/or seaweed affecting the water color, the patches don't move much. If it's the clouds and/or wind affecting the water color, the patches move or appear / disappear. In the picture I'd guess it's the sun shining on the water through the breaks in the clouds. Dr Dima (talk) 08:34, 19 March 2017 (UTC)[reply]
It's sunlight, as suggested by Dr Dima above. The ship in the middle pic is in shadow surrounded by darker sea. The third pic shows "aqua" sea and sunny beaches on the left; darker sea with beaches in shadow on the right. Bazza (talk) 16:22, 19 March 2017 (UTC)[reply]
It can't be from sand bars but it did look a lot like the top photo at the algal bloom article and like the second photo at Florida Keys ("...tan sediments and microscopic marine organisms (like phytoplankton and algae) discolor the water...") . Bubba73You talkin' to me?00:35, 20 March 2017 (UTC)[reply]
As the ship moved through these waters, the patches seemed to be more-or-less fixed. It was very windy that day - the cold front that resulted in the winter storm in the northeast had come through, so the clouds should have been moving at a pretty good pace. And a few miles out to sea they were gone. For what it is worth, here are two more photos taken about that time: File:Sunset Key Island, Key West, FL, US.jpg
I don't know how to describe this, but I think it's related to overthinking. I have a habit of overthinking and checking things again and again, and oftentimes, this leads to more inaccuracy. When I rely on my "gut response", I get it right most of the time. I remember the time when I was in 9th grade geometry class and how I initially was a B or C student and then jumped to A student. I finished each test or quiz very quickly and accurately, because I stopped overthinking. I answered all the questions correctly, including the bonus questions, so I always got more than 100%. Later, I've heard that my instructors would caution students about overthinking. So, this phenomenon may not just apply to me. I am wondering if there is a neurological basis for "overthinking". 50.4.236.254 (talk) 05:28, 19 March 2017 (UTC)[reply]
That's not quite the same, since that refers to cases where the overthinking is done first, and a conclusion is never reached, versus this example, of having a conclusion, then rejecting it later, due to overthinking. StuRat (talk) 19:46, 22 March 2017 (UTC)[reply]
It is very useful to be able to think of two different ways to analyse a complex problem and then compare the two solutions. As an example one method might be your gut reaction, and the other a carefully weighted evaluation of the alternatives with score for each attribute. If the two disagree then it can be productive to see why the careful analysis came up with the 'wrong' answer. This can be useful in real life such as choosing where to live, not just engineering and so on.Greglocock (talk) 07:33, 19 March 2017 (UTC)[reply]
I removed someone's ridiculous "hat" that they put on this claiming that this was "psychiatric advice". Their racket is big enough already without letting them take over teaching too - you'd have to give your kids a little bar of gold apiece to cover the day's tuition fees. Wnt (talk) 13:26, 21 March 2017 (UTC)[reply]
Some thoughts:
1) Double-checking your work is a good idea, in the real world. However, tests often have time limits, or you just might get fatigued from double checking everything, and either run out of time or start to make mistakes near the end. So, I would only go back and double-check my work after all Qs were answered.
2) As Greglocock mentioned above, it's better to have two different ways to find an answer, so that if one method is in error, you don't repeat the same mistake. For a simple example, if asked for the answer of 8x9, you might recall that it's 72, or you could do some math: 8×9 = 8×(10-1) = (8×10) - (8×1) = 80 - 8 = 72. If you got different answers both times, you might try another method: 8×9 = (10-2)×9 = (10×9) - (2×9) = 90 - 18 = 72. Hopefully 2 of the 3 answers will match.
3) Also, after the test has been handed in and graded, then it's time for a post-analysis. That is, determine what went wrong, and what you could do differently next time. In the simple example above, maybe you need to memorize your times tables. But don't start this analysis during the test, as it will just distract you then. StuRat (talk) 19:53, 22 March 2017 (UTC)[reply]
Is it feasible to have a space station orbiting both Earth and Mars such that, periodic arrival takes place during shortest distance between both planets?--Almuhammedi (talk) 07:57, 19 March 2017 (UTC)[reply]
Yes according to Buzz Aldrin who promotes plans for a Mars cycler, a continuously orbiting ferry around Earth and Mars. It would sail endlessly in a complex interplanetary orbit, picking up passengers or sending them off in space taxis when it nears a space station near our Moon or one of the moons of Mars. See The Martian Metro by Frank Braun and Owen Davies, OMNI magazine November 1987. — Preceding unsigned comment added by Blooteuth (talk • contribs) 13:38, 19 March 2017 (UTC)[reply]
Hohmann transfer orbit (and its 'See also' section) may be helpful. Read literally, the OP's question is difficult to follow, but it's not easy to formulate purely verbal descriptions of such dynamic situations without using diagrams. {The poster formerly known as 87.81.230.195} 2.123.26.158 (talk) 18:54, 19 March 2017 (UTC)[reply]
Is there anything in physics that theoretically allows an infinite power source? Alan Guth refers to the universe as "the ultimate free lunch", so I'm thinking cosmic inflation or some other phenomenon of GR / cosmology.
I have already searched through the refdesk archives to no avail.
quantum fluctuation might also be relevant, as it refers to changes in energy, and it was quantum fluctuations that were amplified in the inflationary epoch that gave rise to the structure of the universe. Or maybe something completely different. Any ideas for an infinite power source? PeterPresent (talk) 09:07, 19 March 2017 (UTC)[reply]
Let's say you have a small region of space with high energy density. If you could trigger inflation in that region, it will expand so you have much more total energy. If you could repeat the process, why couldn't you create arbitrarily much energy? Is it because the energy gradients remain the same (so all you do is magnify unusable heat)? PeterPresent (talk) 10:15, 19 March 2017 (UTC)[reply]
It's not actually known if energy is conserved in General Relativity. See Conservation_of_energy#Relativity. In brief, the Stress–energy tensor of General Relativity does not predict conservation of energy, but also does not include all possible forms of energy (such as gravitational waves). Tensors that do incorporate such things do not behave well. Someguy1221 (talk) 22:57, 20 March 2017 (UTC)[reply]
Even if we had one, it may not be such a good idea. "Free energy" has often turned into profligate use of that energy, with resulting pollution or simply heat pollution. Waste energy ends up as heat, so a society with free energy on offer is likely to become very hot, then using more free energy to run air conditioning and make its surroundings even hotter (air con moves the heat 'outside', but it doesn't make it vanish). Andy Dingley (talk) 10:32, 19 March 2017 (UTC)[reply]
Not if the energy density remains the same. Inflation doesn't change energy density; it changes total energy by amplifying the energy over a much larger volume. PeterPresent (talk) 10:38, 19 March 2017 (UTC)[reply]
Could we not (theoretically) just create a new universe of low entropy (using whatever process created our universe, including cosmic inflation), and migrate? PeterPresent (talk) 10:42, 19 March 2017 (UTC)[reply]
I'm amazed how few people are trying to solve this problem. Once we defeat aging, we will need to find a way to overcome the heat death of the universe if we want to live forever (the SENS approach of repairing the body will require thermodynamic free energy). PeterPresent (talk) 01:53, 20 March 2017 (UTC)[reply]
A thank-you treat for anyone answering this question! :)
Hi all - apologies if this is the wrong branch of RD - it seems closest of the alternatives.
If you by a tub of nice creamy ice cream, and keep it frozen in between servings, it says nice and creamy. If, on the other hand, you let it thaw and then re-freeze it, it gains a solid, ice-like crust. Does the thawing process somehow separate out a coating of water from the ice cream, which then rises to the surface and freezes, or is there something else going on here?
Not really. As Ice cream#Physical properties mentions, ice cream is a colloid. As Ice cream#Production, this is generally achieved by churning the ice cream as it freezes. Our article perhaps isn't the best at explaining this but [2] has what looks to be decent info on the structure of ice cream. If you refreeze it after it's thawed, the structure is lost unless you refreeze it in the same way (which doesn't seem to be recommended for food safety reasons anyway). If you let the ice cream partially thaw you have the same problem but perhaps only on the surface (although even if the ice cream hasn't completely thawed, from my experience it is often still affected mostly throughout if you let it thaw too much). This is an interesting source [3] which talks about the complexities of ice cream melting. Nil Einne (talk) 09:57, 19 March 2017 (UTC)[reply]
There are two processes.
One is simply the growth of larger ice crystals within the mix, crystals grown from the original mix and with the same taste (but not texture). Your ice cream converts to an ice lolly. If you're making ice lollies deliberately, it's usual to use a mix that is physically softer when frozen, to improve its texture - i.e. it freezes to small crystals but won't form single big ones. An ice lolly / popsicle is just a sorbet / ice cream mix that's frozen in one piece, without the churning action that's used for ice cream. They can both benefit from being frozen extra-quickly in manufacture, as that gives less time for large and coherent ice crystals to form.
Another effect is formation of a layer of clear water ice on top of the ice cream. This is atmospheric moisture condensing out and freezing. Don't just keep the ice cream cold, keep the tub sealed airtight too. Andy Dingley (talk) 10:29, 19 March 2017 (UTC)[reply]
Diagram of how metal can recrystallize at nucleation points and then exhibit crystal growth. If you consider the fresh ice cream to be roughly like c), then a few warm ups and re-freezes will leave you with something like d), with a noticeably different texture.We do have three articles on recrystallization (I think they should be merged, but that's an issue for another day). The Recrystallization_(metallurgy) has the best pictures, and may help OP visualize some of the possible changes. SemanticMantis (talk) 16:03, 19 March 2017 (UTC)[reply]
When my ice cream starts to melt, I immediately eat the melted part so it won't refreeze like this, which leads to me "accidentally" leaving it out quite often. :-) StuRat (talk) 13:09, 20 March 2017 (UTC)[reply]
My reaction is that, as we say at the top of the page, we don't answer homework questions, even if you copy them out accurately (which you haven't done here – A uniform 1m long what? Supported where? Suspended 10cm from where?).
However, if you show us your working so far and tell us where you're stuck, someone may give you hints on how to proceed. (The poster formerly known as 87.81.230.195} 2.123.26.158 (talk) 19:06, 19 March 2017 (UTC)[reply]
Have you tried drawing a diagram showing forces on the unnamed object (possibly a rod?), then taking moments about certain points? Let us know how you get on. Dbfirs20:57, 19 March 2017 (UTC)[reply]
