Wikipedia:Reference desk/Archives/Science/2010 April 1

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April 1

TEMPERATURE TIME GRAPH

i got this question in my exams . may you answer and explain

Four students set up the experiment on plotting the temperature time graph of hot body as it cools to room temperature. They all perform the experiment using identical apparatus, under identical conditions and plot their graphs on similar graph papers using similar scales. The teacher asks them to observe their graphs carefully and list down the(approximate) values of the angles, made with time axis, by the tangents to their graphs, at the beginning and towards the end of their observations. The values, noted by them, were as follows:

i dont know how to put the image.Well TEMP is on y axis and TIME is on x axis

Student A : 60^o; 30^o Student B : 65^o; 22^o Student C : 75^o; 14^o Student D : 85^o; 5^o

The best noting is likely to be that of student:

(1) A

(2) B

(3) C

(4) D

..........THANX--Myownid420 (talk) 03:51, 1 April 2010 (UTC)

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. ~ Amory (u • t • c) 06:26, 1 April 2010 (UTC)

Let me answer your question with another question. What temperature is room temperature? Googlemeister (talk) 13:08, 1 April 2010 (UTC)

Another relevant article is Newton's law of cooling. Heat transfer in these sorts of problems describes an exponential decay of the temperature. I'm not sure what to make of the measurement of the angles, because it depends on the temperatures, time scales, and the amount to which steady-state has been achieved. All we can say is that the measurements are all plausible. It's possible that you have graphs as well as angle measurements; if so, try to see which graphs look like an exponential temperature decay toward room temperature. For comparison, here's the omnipresent Science Reference Desk Reference Coffee/Milk Cooling Curve Simulator - the red curve shows a standard cooling curve, which should look like your hypothetical measurements. I'm going to go out on a limb and say that every one of those angle-measurements could be valid, given a particular decay time-constant. If we had enough information to calculate the decay constant, we could narrow down some more. As an engineer, I'm going out on a limb to say "steady state for decay is approximately 5 time constants"; and then, "14° is approximately 1/5 of 75°", and then, "x ≈ tan x", so let's go with C; but to be honest, unless you can personally justify any of those approximations in your specific case, I'd recommend asking your teacher for clarification. Nimur (talk) 14:03, 1 April 2010 (UTC)

Myownid420 says that he has images, but doesn't know how to put it up here. If that's the case, then the question is to basically estimate a couple of angles on a picture. We don't have the picture, so we can't possibly estimate the angles. Buddy431 (talk) 14:53, 1 April 2010 (UTC)

Nimur, all those are not plausible temperatures. If you warm up some water on your kitchen stove to 85C and then set it on the counter, it will never cool to 5C unless you keep your kitchen inside a refrigerator. Googlemeister (talk) 15:31, 1 April 2010 (UTC)

Those are not temperatures, they are angles of the tangent line of the temperature-vs.-time curve. It's slightly confusing because both angle and temperature are measured in degrees ° - but they are different things entirely. I suspect this might have been an intentional trick question. Nimur (talk) 15:45, 1 April 2010 (UTC)

Note that you can't calculate this angle, not even in principle, unless you have the graph paper. Temperature and time have different units, and only if you kow the scale from the graph paper can you convert both time and temperature into distance, after which you can calculate the angle. Might the questioner want you to use a heuristic such as "the value closest to the average of all values is most likely to be correct"? 83.134.157.144 (talk) 16:43, 1 April 2010 (UTC)

Right, but we can calculate the ratio between initial- and final- values, if we make suitable assumptions as I outlined above. We can do this because exponential functions have special properties - the tangent line is defined by the derivative, which is linearly proportional to the function value. Nimur (talk) 19:49, 1 April 2010 (UTC)

On the basis of his second reading, you'd suppose that 'D' was most likely to be correct. The temperature should be asymptoting down to room temperature - and therefore the shallower the angle for that second number, the better. But that's guessing - we know that they all stopped the experiment before the liquid reached room temperature because (strictly) it takes an infinite amount of time to do that. If they stopped it sooner then maybe 'C' got the measurements most accurately. But if some of them are sloppy experimenters (which they evidently are) then maybe the most average value is the best to take - but that's 'C' if you take the best average of the first number and 'B' if you take the best for the second. If they used 'log' graph paper then you'd expect the two angles to be the same - so now 'A' got it closest to being right. So I can make the case for any of the four experimenters to have been "the best". This is a REALLY bogus question. SteveBaker (talk) 20:01, 1 April 2010 (UTC)

Not bogus, just missing the accompagning graph I think. Without which it is a waste of time. --BozMo talk 20:10, 1 April 2010 (UTC)

I suppose so. If we could see that the graph was plotted on log graphpaper - then the answer is very different than if it's on linear graphpaper. Perhaps that's what the original questioner was trying to suggest. If it's log graph paper then I think we know that 'A' is the best answer because the slope of the graph is predicted by Newton's law of cooling and it's the same at the start and end of the experiment. Hence whichever person had first and last numbers sufficiently close together has the most accurate data. SteveBaker (talk) 20:34, 1 April 2010 (UTC)

well my question is not home work. i am a tenth standard student and my exams are over this question was in my last exam ie of practical science skills, sorry i still cant upload the photo.

let me tell you how to make it

1. make x axis and y axis of definite length
2. mar a point O(x,y) such that x=y
3. from point O draw an arc of radius less than x (slightly)
4. let this arc touch the line (0,y) and (x,o)

this was the graph that was given. i think the correct answer is D 5^o is near to 0 and 85^o is near to 90 —Preceding unsigned comment added by Myownid420 (talk • contribs) 05:01, 2 April 2010 (UTC)

Is your diagram like this sketch?

 y
  8
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  8
  8
  8
  88                                   ¤
  88
  88
  8 8
  8 8
  8 ¤o
  8  8
  8   8
  8    8
  8     8
  8      ¤o
  8        8
  8         ¤o
  8           ¤o
  8             ¤¤o
  8                ¤oo
  8                   ¤¤oo
  8                       ¤¤¤ooooo
  8ooooooooooooooooooooooooooooooo888888oooooooooooo
0                                                   x

 ::Cuddlyable3 (talk) 01:55, 3 April 2010 (UTC)

Synchronizing clocks.

If, in a reference frame O, two clocks seperated by a distance L are synchronized, then the two clocks may not be synchronized in another reference frame moving at a relative speed v. What, then, is the difference in timing between the two clocks as observed in the moving reference frame? Using length contraction and such (as per http://galileo.phys.virginia.edu/classes/252/synchronizing.html), I get Δt = vL/c^2. However, using Lorentz transformations gives me a different result: t' = γ(t - vx/c^2), t'₂ - t'₁ = γ(t₂ - vx₂/c^2) - γ(t₁ - vx₁/c^2) = γ(t₂ - t₁ +v/c^2(x₁ - x₂) = γvL/c^2. Why the discrepancy? 173.179.59.66 (talk) 05:49, 1 April 2010 (UTC)

Nevermind, I figured it out. 173.179.59.66 (talk) 05:55, 1 April 2010 (UTC)

Wine drinkware

Does the material the drinkware is made of (metal, glass, paper, plastic) really have any effect on the quality and taste of wine? Or is it just snobery? (im looking for science based answers) —Preceding unsigned comment added by 71.98.64.15 (talk) 06:21, 1 April 2010 (UTC)

Lots of materials can react with the wine to put off-tastes into it. Plastics, for example, can attract hydrophobic compounds (basically fats) which don't really ever wash off completely (if you have ever microwaved tomato sauce in a plastic dish, you know what I mean). This could redissolve in small amounts into the wine. Metals can be reactive to acids in the wine, while the wine could also dissolve flavors out of paper. Glass is the only truly non-reactive material out of which to drink. The shape of the glass also matters; remember that most of what you associate with taste is actually smell, and depending on the type of drink, the shape of the glass can be used to direct smells either to your nose or away from it. Different shaped glasses also allow differing surface area on the liquid, affecting how the wine will "breathe" (i.e. oxidize in air) which explains the shape of different stemware. Of course, for most people this will make little difference. For people that care about wine, these are big things. --Jayron32 06:31, 1 April 2010 (UTC)

For most people this make little difference only because they are not paying attention. The difference is noticible. Same thing applies to beer too BTW. Dauto (talk) 06:52, 1 April 2010 (UTC)

How noticeable are these differences? And how long does it take the wine to react to the materials? Is the wine even in the drink ware long enough to make any noticeable difference? —Preceding unsigned comment added by 71.98.64.15 (talk) 08:23, 1 April 2010 (UTC)

For comparison, pewter tankards are traditional drinking vessels in the UK, and some people keep their own tankard behind the bar at their local pub (another tradition, not of course restricted to pewterware) and/or take one along to beer festivals. However, although there is no problem with beer, which is not markedly acidic, it is now illegal for bar staff to serve cider, which is more acidic (and in the UK always what USAians call "hard", i.e. alcoholic) into pewter mugs made before 1974 when a new low-lead standard was set for the alloy, because the acidity of the cider can leach significant levels of lead from the vessel. Obviously one such drink will likely be harmless in itself, but with habitual use the effect will be cumulative. I'm not sure of the relative acidities of beer, wine and cider, but this demonstrates that the potential for reaction with wine is there.

Speaking as a regular beer, occasional cider and rare wine bibber, I myself notice a marked difference to tastes and other sensory perceptions (e.g. smell, lip feel, etc.) made by various vessel materials, and will by choice only drink from glass or porcelain vessels. 87.81.230.195 (talk) 11:24, 1 April 2010 (UTC)

FWIW, I avoid lead crystal glassware due to leeching. Imagine Reason (talk) 15:30, 1 April 2010 (UTC)

Thermal conductivity of the vessel will also have an effect, both on how quickly the liquid warms/cools to room temperature, and on the mouth feel (e.g. a cold glass may distract attention from the contents). --Normansmithy (talk) 15:46, 1 April 2010 (UTC)

Have there been any double blind studies on rather the taste difference exists or is even different enough for the human tongue to distinguish? I understand the some materials such as pewter can react with certain liquids but im look more for the taste factor. So far the answers (pertaining to taste) are based on anecdotal evidence. —Preceding unsigned comment added by 71.98.64.15 (talk) 17:03, 1 April 2010 (UTC)

You seem to be ignoring the smell answer. You can smell plastic, paper, and metal (but not glass) even with no wine in it. You can try that yourself, with your eyes closed. StuRat (talk) 17:13, 1 April 2010 (UTC)

The shape of the container is also very important as is the use of correct technique for pooring the liquid if you're talking about beer. Dauto (talk) 17:28, 1 April 2010 (UTC)

Some would assert that wine can be pretty good right out of the bottle, although proper glassware can allow better development of the olfactory aspects. Edison (talk) 04:21, 2 April 2010 (UTC)

Indeed, see for example [1] Nil Einne (talk) 04:29, 2 April 2010 (UTC)

Minimum protein etc. in a healthy diet

A healthy diet must have at least a certain amount of protein,carbonhidrat and fat. For the concreteness let we assume 2000 kcal diet. He must have at least ?? kcal come from protein,?? kcal come from carbonhidrat,?? kcal come from fat. Is these amounts known? Murat Umut. —Preceding unsigned comment added by 85.102.198.65 (talk) 08:09, 1 April 2010 (UTC)

I am getting the sense in this question that every day one will eat the same thing. You know, one day you could eat a lot of protein, and the next hardly any, and that would be perfectly fine for your health. Vranak (talk) 14:12, 1 April 2010 (UTC)

This 1,357 page book from the United States Department of Agriculture has an entire chapter on protein intake recommendations, carbohydrates, fats. The recommendations are nuanced by details. So, there is more information in there than can be contained in any reasonable response; and of course, if you have special medical or dietary needs, you should consult a physician. You can get specific numbers for an average, healthy adult American male or female; for example, the USDA recommends 0.80 grams of protein per kilogram of body weight every day[2]. There is additional breakdown of recommendations in this book for other macronutrients. You will probably be interested in the Summary Tables, which specify recommendations for the nutrients you asked about; you can locate whichever age/demographic group is a close match to you, and see what is recommended. Keep in mind that your dietary needs may differ from these general guidelines. Nimur (talk) 14:43, 1 April 2010 (UTC)

A significantly less technical book is also available from the same source, for free: Dietary Guidelines for Americans, 2005. This has nice summary tables as well as description of nutrients in language that might be more accessible to a non-scientist. "Table 2" in this book breaks down recommended values for all the nutrients you asked about, with amounts specified for two recommended dietary plans. Nimur (talk) 14:49, 1 April 2010 (UTC)

Side question, for anybody knowledgeable: How corrupted are these USDA guidelines by the US food industry? Did the US food industry basically write them? Comet Tuttle (talk) 17:34, 1 April 2010 (UTC)

No, these recommendations were not written by the food industry, they were written by employees of the Federal Government: specifically, scientists, medical doctors, and nutritionists at the United States Department of Agriculture. There is a huge quantity of research that was conducted independently by federal agencies, including the USDA and the FDA; and there was independent review by scholars in academia and industry. The book I linked above has literally thousands of citations to internal studies, external publications, international and third-party research, including dissenting-opinions. It also has an entire chapter outlining motivations of the research. It's not productive to promote an unfounded stereotype about conflict of interest. It is probably true that the food industry applies pressure to shape public perception about nutrition; but the Federal Government is a pretty large organization, and to suggest that its research is invalid, or is easily pushed around by outside interests, without specifying a reason or citing any specific grievance, doesn't accomplish anything productive. Considering the relative scale of the involved parties, it is probably equally valid to insinuate that the American food industry gets pushed around on account of the recommendations of the Federal Government. Nimur (talk) 19:44, 1 April 2010 (UTC)

I haven't investigated the books or their references yet, so can't say anything to that; but I don't think you can just blow off the concern that the dietary guidelines were influenced by the food industries in the US; here's a NY Times story about the pyramid graphic being delayed a year because (allegedly) of pressure from the meat and dairy industries. The Center for Science in the Public Interest slammed the food pyramid back in 1999, and continued to complain in 2005 that the USDA has a mission of promoting US food industries that is incompatible with the mission of promoting healthy food consumption. Again, this may be giving undue weight to a couple of critics, but I think it's not something to summarily brush off. Comet Tuttle (talk) 21:22, 1 April 2010 (UTC)

The legal problems suffered by Creekstone Farms Premium Beef are a perfect example of the USDA being run by the food industry --Digrpat (talk) 00:55, 2 April 2010 (UTC)

While I have no idea what, if any influence the food industry has on the USA, I disagree that there's any evidence there that the USDA is 'run' or even unduly influenced by the food industry. The article states:

The USDA's stated position was that allowing any meatpacking company to test every cow would undermine the agency's official position that random testing was scientifically adequate to assure safety. The USDA also claims that testing does not ensure food safety because the disease is difficult to detect in younger animals

If a government agency (or whatever) is concerned the actions of some organisation is going to undermine their position or the consumers trust in them, cause undue worry to consumers or worse, mislead consumers it is understandable they may wish to prevent such actions. I'm not saying I agree with the USDA position (I'm unconvinced, but it's irrelevant anyway since this is the RD) or that their stated position is definitely the reason why they are doing what they are doing, but simply that it's entirely plausible it is their reason therefore that case doesn't in itself show that the USDA is unduly influenced by the food industry.

Nil Einne (talk) 11:57, 2 April 2010 (UTC)

I find that case troubling, too. A regulatory agency trying to limit safety testing at a private company is bizarre behavior. It's difficult to see how limiting testing will improve food safety, which is supposedly the goal of the regulatory agency. On the other hand, limiting testing can lower prices, but that's not supposed to be the goal of regulatory agencies. Note that there are many other decisions by the FDA which also imply a tilt towards industry and against consumers. Just in the food area, we also have the decision not to require labels on genetically modified foods, the ban (until recently) on selling natural stevia as a sweetener while simultaneously allowing the sale of much more dodgy artificial sweeteners pushed by chemical companies, failure to require nutrition labels on fast food items, failure to ban added trans-fats, and having their inspectors only perform visual checks on meat. There are too many instances to list in the drugs area. While any individual instance could be debated, the total makes a strong case for a regulatory agency that was, indeed, controlled by the industry they were supposed to regulate. StuRat (talk) 13:36, 2 April 2010 (UTC)

Thank you Nimur, this is what I was looking to find. I hope that it will help me convincing my friend that his diet is unhealthy. Murat Umut.85.102.198.65 (talk) 15:29, 2 April 2010 (UTC)

Phosphate

Unlike other polyatomic ions, such as carbonate and sulfate, the phosphate ion can form two partial ions, H₂PO₄^- and HPO₄^2-. What are their names? Are they called biphosphate and triphosphate, or something else entirely? --Natrium-23 (talk) 15:37, 1 April 2010 (UTC)

HPO₄^2- could be called "biphosphate" but the "bi" there doesn't mean two, it means hydrogen. Compare with bicarbonate and bisulfate. More formally, the IUPAC recommends explicitly using "hydrogen", so HPO₄^2- would be "hydrogen phosphate", and H₂PO₄^- would be "dihydrogen phosphate". If you read the phosphate article carefully, you'll notice that these are the terms used. -- 174.31.194.126 (talk) 16:21, 1 April 2010 (UTC)

You will frequently see them called "Monobasic" and "dibasic" on the label of the dry chemical, for example, NaH₂PO₄ = "sodium phosphate, monobasic".[3] This is obviously not the IUPAC nomenclature. -- Flyguy649 ^talk 16:30, 1 April 2010 (UTC)

Actually, the "bi" in "bicarbonate" and "bisulfate" DOES mean 2, and not hydrogen. It is the monovalent form of a divalent ion, so, for example, sodium bicarbonate contains twice as many anions as does sodium carbonate. The name was devised before the structure was fully understood, so when named people noticed that it would take twice as much bicarbonate to precipitate the same amount of a cation as an equivalent amount of carbonate, hence the name "bicarbonate". As far as the phosphate series goes, generally the names are "Dihydrogen phosphate" and "hydrogen phosphate" OR "phosphate, monobasic" and "phosphate, dibasic", as already noted. --Jayron32 21:02, 1 April 2010 (UTC)

Who was the guy who did the first CO₂ readings?

There was a guy, an American scientist, who took carbon dioxide readings starting in the 1930s or 40s and did these readings every day until his death in the 1990s, which were then taken over by his son. Ronald Reagan employed a group of scientists to dispute this scientist's findings, but the scientist group found the same thing that carbon dioxide atmospheric levels were indeed rising. The question is, who is this scientist guy and do we have an article about him? I just got told a story about this by someone.--I have winnie the poo tatoo and im 8 (talk) 19:15, 1 April 2010 (UTC)

I believe you are thinking of Charles Keeling who began his nearly daily Keeling curve in 1958. There are some direct measurements of atmospheric CO2 before that, but they are discontinuous and tend to have much greater uncertainties due to less accurate techniques. Most CO2 records of periods before 1958 are based on studying gas bubbles trapped in ice cores. Dragons flight (talk) 19:21, 1 April 2010 (UTC)