Wikipedia:Reference desk/Archives/Science/2013 March 14

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March 14

Piston bow

Is it possible to make a bow using pistons? ScienceApe (talk) 00:39, 14 March 2013 (UTC)

Meaning using compressed gas to drive the arrow forward ? Sure, it's possible, but I doubt if it would work as well as a normal bow and arrow. StuRat (talk) 00:47, 14 March 2013 (UTC)

• First, how do you define "bow"? If you mean a device that stores potential energy exclusively by bending (i.e. a spring) then releasing that energy to launch a linear fletched projectile (arrow), pistons don't fit in well. If you allow some amount (from 1% to 100%) of the energy to be stored in pistons (e.g. [1]), then we need to modify the definition of "bow", and in the extreme (100%) it stops being recognizable as a "bow", except perhaps cosmetically. -- Scray (talk) 01:44, 14 March 2013 (UTC)

You mean a pneumatic Speargun/harpoon, that uses compressed air to launch an arrow/bolt? CS Miller (talk) 21:06, 14 March 2013 (UTC)

I certainly didn't, nor would I call that a bow. -- Scray (talk) 14:21, 15 March 2013 (UTC)

Galactan and raffinose

Are galactan (a galactose polymer) and raffinose types of galactooligosaccharide (GOS)? Galactan seems like it should qualify, but raffinose contains other saccharides, so I don't know whether it's strictly true that it's a galactooligosaccharide.

(The galactooligosaccharide article needs a section on dietary sources and their impact on gas-formation, health, and the restriction of these under the FODMAP diet, but I think the first step is clarifying the relationship between these three terms. Raffinose is apparently found in beans and broccoli and I think it's the reason beans are the "musical fruit" - just to make it less abstract.)

I asked about this on Talk:Galactooligosaccharide 6 months ago but there's been no response. --Chriswaterguy talk 02:21, 14 March 2013 (UTC)

The most boring question about boiling ever. Again.

This question has been asked 8 billion times and I find nothing but answers from all sides on a Google search. So I'm actually not finding a definitive answer. Let's say I'm at sea level and I put a pot of water on the stove and turn the stove on high... will the water boil faster covered or uncovered? The answers I've found are (paraphrasing) "covered: the pot will boil slower because pressure has now been increased" and "covered: the pot will boil faster because you are retaining heat and not letting it escape".

For the record, I would like an answer for a normal kitchen pot and cover, no airtight hermetically sealed theoretical covered pots. Just your standard kitchen science please. Thanks so much! – Kerαunoςcopia^◁_galaxies 02:56, 14 March 2013 (UTC)

Well, since a normal pot will not hold pressure, it will essentially be the same pressure inside and outside, so it will boil faster due to retained heat. Try the experiment yourself, with two identical pots, one covered and one uncovered. However, note that a pressure cooker is a common kitchen appliance, not "theoretical". StuRat (talk) 03:04, 14 March 2013 (UTC)

Precisely. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:30, 14 March 2013 (UTC)

I started to write an answer, then had lunch, and I see StuRat beat me to it. But here's my answer, saying basically the same thing.

• Boiling point is the temperature where the vapor pressure of the liquid exceeds the ambient pressure. So we're concerned with pressure inside the vessel, not the partial pressure of water vapor. And we can't increase pressure much, unless the lid is sealed (i.e. unless it's a pressure cooker). I'd be surprised if pressure is a factor to any significant degree.
• Retaining heat: The hotter the stove, the quicker it will reach boiling, and the less net heat loss there will be. If it's a small heat, we could expect that heat loss will be major, and not having the lid on would have a very large impact, whereas with a high heat, it should have less impact, relatively.

So the effect of retaining heat is variable, but the effect of pressure will be insignificant - so keeping the lid on will cause it to boil faster. --Chriswaterguy talk 04:36, 14 March 2013 (UTC)

1. Get a pot.

2. Fill it with water.

3. Boil it

4. The next day, repeat the experiment with a lid

5. Compare results --140.180.249.27 (talk) 05:42, 14 March 2013 (UTC)

To put some numbers on the "pressure" hypothesis, I grabbed a 3-quart pot from my kitchen and measured it. The lid weighs 0.19 kg, and the top of the pot measures 0.18 m in diameter, giving a maximum pressure increase (assuming a perfect fit between pot and lid) of 73 Pa, or about 0.07% of atmospheric pressure at sea level. WolframAlpha tells me that this would raise the boiling point of water by 0.3 degrees C. --Carnildo (talk) 07:39, 14 March 2013 (UTC)

Think about it this way. Any hot surface or object is going to radiate heat in a variety of ways. The pot will be transferring heat to air molecules by convection, and also radiating heat in the infrared. Additionally, each water molecule that turns to vapor sucks up a certain amount of energy, and carries that energy around with it until it finally condenses on some surface. When it condenses, it gives the energy up again. If you don't put a lid on the pot, you're pouring a large amount of energy into vaporizing water molecules, and then those water molecules are traveling outside of your pot (by convection) and depositing their energy on the walls and ceiling of your house. Also, energy that is radiated from the inside of the pan will also escape through the top. Now put a lid on the pan. You're still vaporizing the water, but it now condenses on the bottom surface of the lid and drips back into the pan. The lid heats up, of course, since it's collecting energy from condensing vapor, but it's going to radiate up to half of that extra energy back into the pan, in addition to reflecting heat radiation back into the pan. Also, the convection is minimized because you don't have cool outside air getting into your hot pan to cool things off. ~Adjwilley (talk) 18:08, 16 March 2013 (UTC)

What biological mechanisms regulate a bird's weight ?

(I was inspired to ask this by the "Eat like a bird ?" question over at the Language Desk.)

Excluding chicks and flightless birds, the remainder must keep their weight down to be able to fly. How precisely is this accomplished ? I can think of several possibilities:

1) They stop eating. This then brings up the Q as to what forces them to do so. That is, what satiety mechanism is at work.

2) They stop digesting and/or purge the undigested food, before it packs on permanent weight. In this case, what causes this ?

3) They exercise more, to burn off the weight. Would high blood sugar drive this reaction ?

4) Some combo of those.

It seems to me, if we knew the answer to these Q's, they would have possible application towards regulating human weight. StuRat (talk) 03:46, 14 March 2013 (UTC)

Is there a serious question about whether a bird in the wild is too fat to fly stops eating? How do they get to the food?

As for captive birds, see http://www.petplace.com/birds/is-your-bird-overweight/page1.aspx --Guy Macon (talk) 03:54, 14 March 2013 (UTC)

Say a fish-eating bird comes across a massive fish kill, like when a lake dries up due to drought. If they just gorged themselves as much as possible, they would then be unable to fly away from the dried up pond, and would be easy prey for predators. Presumably this doesn't happen. StuRat (talk) 04:14, 14 March 2013 (UTC)

This source says: "It's very rare for birds to be obese, because they couldn't fly anymore."[2] Also: "Do wild animals get medically obese? Do they overeat or binge eat? I learned that yes, they do."[3] Bus stop (talk) 04:36, 14 March 2013 (UTC)

Thank you Bus stop for the link. I was not aware there is a Catkins diet. --PlanetEditor (talk) 05:10, 14 March 2013 (UTC)

• (edit conflict)As a thought experiment, let's presume this does happen. How would your observations differ (from the situation where it doesn't happen)? The bird carcass would not persist for long. I've seen bird remains near ponds. Birds that tend to gorge themselves would not survive, and to the extent that this behavior is genetically-determined, this trait would be under negative selection. Applicability to humans: make being fat disadvantageous - for example by raising insurance premiums or fees associated with obesity-related problems in general (aligning incentives) - in a manner analogous to the wild, wild world. -- Scray (talk) 04:42, 14 March 2013 (UTC)

• To make it applicable to humans, you'd need to kill or sterilize the obese, then continue for thousands of generations until new biological mechanisms manifest to regulate our weight better. I'd prefer to find whatever hormone, etc., is regulating weight in birds, find a human analogue, and sell that. StuRat (talk) 05:14, 14 March 2013 (UTC)

Sorry, I should've made it clearer that I was shifting gears from the specific question of genetic plausibility to the more general - how birds not getting fat might be relevant to humans. If it's not genetically determined, but rather related to day-to-day negative consequences of being fat, then aligning incentives might work. It would be far safer for people to reduce calories and exercise more, than take a medication for many years without knowing the long-term effects. Obesity is a result of modern culture, so cultural adjustment should be feasible and safe. -- Scray (talk) 07:00, 14 March 2013 (UTC)

Yes, but obviously that approach isn't working for everyone. I'm talking about alternatives to weight-loss surgery. StuRat (talk) 14:39, 14 March 2013 (UTC)

So far as I know poverty is still associated with a higher birthrate everywhere, and a higher rate of obesity wherever there isn't outright famine. Your proposal therefore would have the inverse effect even before the selective effect of the revolution is taken into consideration. Wnt (talk) 15:09, 15 March 2013 (UTC)

anatomy

how do bones make muscles more efficient? — Preceding unsigned comment added by 67.58.138.196 (talk) 06:29, 14 March 2013 (UTC)

See Bone#Functions and Human_skeleton#Function. --PlanetEditor (talk) 06:34, 14 March 2013 (UTC)

Most muscles are attached to bones. They gives them something solid to pull against. Without that, whatever they pull on would give way. There are a few small muscles like that, in the face, for changing our facial expressions. StuRat (talk) 06:36, 14 March 2013 (UTC)

Leverage. A muscle is only as "strong" as its connection to the bone. (in conjunction with the bone strength).165.212.189.187 (talk) 14:25, 14 March 2013 (UTC)

I you have ever tried to move an octopus from one tank to another when he didn't want to go, you might have a different opinion about how strong something with no bones can be. Oddly enough, he never bit (I guess that isn't considered polite on octopus society) but he sure would arm wrestle!

Our solution was to put a nice tasty crab in the other tank and put the two tanks together. He would go up and over the side into the other tank with no assistance. I love summer intern jobs! Ask me about being a Turkey hanger sometime... --Guy Macon (talk) 19:04, 14 March 2013 (UTC)

No doubt he was secured to the tank (bone substitute) in some way. Would you find a contradiction for everything? You get my point, I was specifically speaking about muscles in humans. 165.212.189.187 (talk) 14:01, 15 March 2013 (UTC)

Turkeys can commit capital offences!!?? Richard Avery (talk) 07:49, 15 March 2013 (UTC)

Based on the percentage which end up being beheaded, they must all commit rather serious crimes. StuRat (talk) 12:57, 15 March 2013 (UTC)

165 is correct about leverage. To just elaborate briefly, most muscles are attached to bones very near the actual joint - look for example at where the bicep attaches to the forearm. The bicep uses the upper arm/ frame as a solid base, and moves the forearm. If it attached to the bone further down, it would have more strength, but would not be able to move the bone as fast, or as far. I couldn't find this observation in any of the links, so I thought I'd add it. IBE (talk) 01:36, 16 March 2013 (UTC)

electro chemical cell

what is abnormal transport number? please discuss in brief101.210.150.63 (talk) 08:41, 14 March 2013 (UTC)

Will we lose marks if we discuss it extensively? HiLo48 (talk) 10:35, 14 March 2013 (UTC)

In brief: it's a transport number that's not normal. Does that help? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:03, 14 March 2013 (UTC)

I don't think I understand the question. ~Adjwilley (talk) 21:38, 16 March 2013 (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. StuRat (talk) 16:04, 14 March 2013 (UTC)

Ozone Silver Tarnish

What does it look like? Silver sulfide may look brown and can be reversed using aluminium, sodium bicarbonate and water. How can it be reversed? Is there a picture of silver oxide tarnish on silver?Curb Chain (talk) 15:10, 14 March 2013 (UTC)

Same way you reverse sulfide tarnish -- just polish the silver with an acidic polish (EXCEPT hydrochloric acid -- it will form insoluble silver chloride, or nitric acid -- it could damage the metal itself), and the tarnish should dissolve. Generally, any acid that removes silver sulfide should also dissolve silver oxide. 24.23.196.85 (talk) 01:28, 15 March 2013 (UTC)

Isn't it true, though:

2 Ag⁺ + S^2- -> Ag₂S_s

the silver sulfide resulting in a reaction of sulfur particulates reacting with silver

And:

3 Ag₂S + 2 Al³⁺ -> 6 Ag_s + Al₂S₃?

How is ozone the same?Curb Chain (talk) 07:40, 16 March 2013 (UTC)

I was talking only about how to remove the tarnish, not about its composition or properties. 24.23.196.85 (talk) 04:20, 17 March 2013 (UTC)

Yes, in the above reactions, the silver mass of the jewllery stays the same. I am inquiring about ozone.Curb Chain (talk) 09:15, 17 March 2013 (UTC)

Can't tarnished silverware be baked in a standard household oven to thermally decompose the tarnish? Plasmic Physics (talk) 08:18, 17 March 2013 (UTC)

This could work for oxide tarnish (which decomposes at 280 C), but not the sulfide (that one is stable at all temperatures). Also, remember to use a conventional oven, NOT a microwave oven -- unless you want to cause an explosion and a nasty electrical fire! 24.23.196.85 (talk) 00:25, 18 March 2013 (UTC)

How does the reaction work? How do you know if it is sulfide or oxide?Curb Chain (talk) 03:33, 18 March 2013 (UTC)

Silver oxide is has a low activation barrier towards thermal decoposition into the elements. The oxide tarnish converts to silver and elemental oxygen, with no loss of silver.

Metal in a microwave does not produce an explosion, what it does do, is create plasma, sparks, damage to the magnetron, and lots of heat. You can actualy melt gold in a microwave oven, there are kits available online for just this purpose. Plasmic Physics (talk) 09:17, 18 March 2013 (UTC)

Can the sulfide tarnish be chemically oxidised to silver oxide, with something like mild base piranha solution (NH₄OH, H₂O₂)_aq? Plasmic Physics (talk) 09:17, 18 March 2013 (UTC)

Sodium percarbonate (uncoated)

I wish to constitute a solution of pure, uncoated sodium peroxide in water such that the resultant solution contains 3% Hydrogen peroxide. Please advice on what measures of the solid sodium percarbonate in what measure of water using the METRIC SYSTEM of measurement that I require to do so. I reside in Nigeria, West Africa. Thank you. JJUU March 14, 2013 — Preceding unsigned comment added by 41.138.168.162 (talk) 16:00, 14 March 2013 (UTC)

3% hydrogen peroxide solutions are available in any store here, quite cheaply. Presumably they are available there, too, so you could just buy them. Or are you a manufacturer interested in selling this product yourself ? StuRat (talk) 16:07, 14 March 2013 (UTC)

I like the metric system too, but yelling at people is not the way to go. Learn how to use a calculator to convert units. --Guy Macon (talk) 19:08, 14 March 2013 (UTC)

The information you need to know is in the Sodium percarbonate molar weight is 157.01 g/mol, but from this you 1.5 mol of H2O2 with molecular weight about 34, so your fraction of peroxide is 1.5*34/157. And a 20-volume concentration of hydrogen peroxide is equivalent to 1.761 mol/dm3, from this you can work out your 3 volume, mols required, then your mass required to achieve this. Graeme Bartlett (talk) 22:25, 15 March 2013 (UTC)

Gas giant, brown dwarf, red dwarf size versus mass plot

It would be a fun resource if we had a plot of the exact relationship between mass and size for objects ranging from the size of Saturn to the smaller red dwarfs. As I understand, they're all roughly the size of Jupiter, but I assume some are at least a bit bigger, whereas M0 red dwarfs according to the article are only 8% rather than 10% the size of the Sun. Since there are so many of these objects, it would be fun for eclipses - red dwarfs hiding behind gas giants, that kind of thing. Does anyone have this? Or is it still too tentative to draw, or too affected by some other factor like composition or age that I'm not taking into account? Wnt (talk) 18:57, 14 March 2013 (UTC)

Composition (known as metallicity) is a factor, See Metallicity. Hertz-Sprung Russell diagrams aren't what you are looking for, but they might poke you in an interesting direction, IRWolfie- (talk) 02:51, 16 March 2013 (UTC)

Iodine and hydrogen peroxide as antiseptics

I've noticed that when used as antiseptics on small cuts, iodine causes minor stinging pain, but hydrogen peroxide does not. Why? —SeekingAnswers (reply) 19:57, 14 March 2013 (UTC)

This is just a educated guess of the top of my head. Hydrogen peroxide just becomes water on contact with body fluids. Iodine preparations however, will fool with the nerves osmotic balance (they are reactive halogen salts). The nerves will start firing. Medically, there is also something called 'iodine burns' which I think is a chronic product of this effect.--Aspro (talk) 21:36, 14 March 2013 (UTC)

The reason is that tincture of iodine is made by dissolving the iodine in a mixture of alcohol and water, and the alcohol can sting. Hydrogen peroxide solutions are just hydrogen peroxide and water, with no alcohol. --Jayron32 21:46, 14 March 2013 (UTC)

The OP doesn’t say what iodine preparation s/he used. Tincture of iodine is only the strength of vodka and that does not sting; Lugol's iodine contains no alcohol at all. So it can't be the alcohol.--Aspro (talk) 22:18, 14 March 2013 (UTC)

I've found this: The stinging probably relates to the osmotic loads delivered by higher concentrations of iodine in some preparations. [4] Nerve cells (and other cells) maintain an osmotic balance and thus a electrical potential of err... hum err... which Iodine will mess up … Oh, just read this Membrane potential.--Aspro (talk) 22:28, 14 March 2013 (UTC)

To be honest, I always assumed the stinging sensation of iodine was the sensation of iodine destroying a few human tissue cells while destroying microorganisms, and had (solely intuitive, rather than based on any actual data/information/reading) doubts about the efficacy of hydrogen peroxide as an antiseptic due to the lack of pain. —SeekingAnswers (reply) 22:32, 14 March 2013 (UTC)

Body cells die all the time. It is the nerve cells alone that register pain, heat, touch, etc. If the nerve cells monitored the health -or otherwise- of their surrounding cells, you would suffer from information overload for no survival benefit.--Aspro (talk) 23:13, 14 March 2013 (UTC)

I know that. I meant that I assumed that it was nerve cells sensing damage much the same way they sense damage in the case of, for example, burns. —SeekingAnswers (reply) 23:45, 14 March 2013 (UTC)

Health food science.

I am interested in eating more healthily but as soon as I do a Google search on health foods I get a load of quack sites.

Does anyone know of some websites or youtube videos where I can get reasoned scientific advice on this issue?

Ap-uk (talk) 21:26, 14 March 2013 (UTC)

You might be better off seeing a doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:10, 14 March 2013 (UTC)

Alternatively, here is a UK NHS site: "Tips for healthy eating" and some corrections of common errors from a UK Government site: "Food myths". These are not medical advice, just common sense, but if you are really worried about your health then you should seek advice from a doctor as advised above. Dbfirs 22:39, 14 March 2013 (UTC)

A doctor would not be the best choice of a person to ask for nutrition advice. Most graduating med students rate their nutrition education as inadequate. Only about 30% of med schools in the U.S. require taking a class specifically on nutrition, and some med schools don't even offer any nutrition education at all.[5] A much better choice would be a registered dietitian with a master's degree in nutrition. The right letters to look for after a qualified person's name are MS, RD. Red Act (talk) 22:45, 14 March 2013 (UTC)

I almost agree with Bugs as we don't give medical advice here, but from the psychical state of many doctors I see, I don't think they have any idea either. If your starting off from scratch, it might be better to become familiar with the food triangle (rather than search out organic berries harvested from the mountain slopes of outer -Mongolia). This guy may be selling health food products but he appears to stick to the science, much of which I have independently already come across.[6] Mankind, has been eating processed food from the time when we learnt to live in climates that required us to process and store food in the months of plenty for use the colder months, where we would have other wise starved. However, in modern times we can and often do, take this too far. Especially, if you live in the US with their epidemic of morbidly obese etc. --Aspro (talk) 23:02, 14 March 2013 (UTC)

why would you judge from their physical appearance? Would you also judge a sports coach or manager by their physical appearance rather than their expertise? IRWolfie- (talk) 02:58, 16 March 2013 (UTC)

I'm not calling the OP's question a request for medical advice. I'm just implying that if someone is giving nutrition advice, often it's the case, by an amazing coincidence, that they have something to sell you. A standard doctor may not be an expert on nutrition, but they can probably recommend someone that is. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:25, 14 March 2013 (UTC)

I use an online tool (but this is not in English) where you have to fill in everything that you eat and drink. They then calculate your average intake of calories, saturated and unsaturated fat, vitamins and minerals. This has been very useful for me, e.g. I had no idea that I was eating way too much salt. I learned that the only way I can stay below the danger limit is by not adding any salt to my food. Also, I learned that my calory intake is about 4000 Kcal/day which is not too much because my weight is stable at 59 kg. Because I eat a lot, I get more than enough of of all the essential vitamins and minerals. And I eat a lot because I work out a lot every day, so perhaps that's the key to eating a healthy diet. Count Iblis (talk) 00:04, 15 March 2013 (UTC)

There is a substantial contingent (including me) who think that the guidelines on salt are bullshit. Bullshit or not, the fact is that virtually nobody follows them. You might find this article by Gary Taubes interesting. Looie496 (talk) 02:51, 15 March 2013 (UTC)

People in my family get sick if we eat restaurant meals packed with salt, so those guidelines do seem to apply to us. StuRat (talk) 03:20, 15 March 2013 (UTC)

I recommend nutritiondata.com:[7], they have a great deal of high quality nutrition info. Be sure to use the search box at the top to look up specific foods, as that's where the bulk of the data is. They have data on many fast food restaurant chain foods and name brand grocery store foods, too. StuRat (talk) 03:20, 15 March 2013 (UTC)

My view is that the medical establishment itself spread junk science. One of the greatest myths of our times is that carbohydrates are essential nutrients and that they should constitute a significant part in a balanced diet. 12,000 years ago, before the advent of agriculture, before the so-called Neolithic Revolution, humans did not eat processed carbohydrates (sugar, wheat, rice etc), they did not have today's problems such as obesity, cardiovascular diseases, diabetes etc. Why We Get Fat: And What to Do About It by Gary Taubes has a chapter about healthy nutrition. For online sources, here are what I personally like:

• Website of Gary Taubes
• http://www.guardian.co.uk/business/2012/jun/11/why-our-food-is-making-us-fat
• Any defence of sugar is pure confection.
• Carbs + Fats = Obesity
• Carbohydrate intake and obesity
• What Really Makes Us Fat --PlanetEditor (talk) 04:30, 16 March 2013 (UTC)

Disclaimer: The above post was not meant to be a dietary advice. Before deciding any diet, consult a registered dietician. --PlanetEditor (talk) 04:20, 16 March 2013 (UTC)

• The Nutrition Source, maintained by Harvard School of Public Health, is an excellent source of information about nutrition. --PlanetEditor (talk) 04:48, 16 March 2013 (UTC)

• Here's my 2 cents, though like others who have responded here, I should note that this is free advice, not medical advice.

  Basically, grains, vegetables, and fruits are good. Refined sugars (candy, soft drinks, dessert foods) bad. Try to eat whole grains (brown rice, whole wheat, quinoa, as opposed to white bread, white pasta, cake, etc. Legumes are good too.); go easy on the meats, and don't worry too much about the dairy. Basically try to use moderation.

  Don't buy into fad diets and people who say that the biggest problem is __fat/sugar/carbohydrates/cholesterol/lack of vitamins/lack of fiber/processed foods/salt/trans fat/saturated fat/fill in the blank__. All these things may be problems, but there's not one fix-all solution. Again, just eat in moderation.

  Learn to listen to your body. If you're craving something, eat it. Eat when you're hungry, and stop when you're satisfied. (Don't stuff yourself.) Drink water.

  Anyway, that's my personal advice for eating healthy. Hope it helps. ~Adjwilley (talk) 22:26, 16 March 2013 (UTC)