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February 24

Crushing

I remember reading about the study of crumpling or crushing paper or another two-dimensional object. But we don't seem to have an article on this. Are there any sources giving information on how well paper crumpled within a cylinder can support a weight above it? Thanks. μηδείς (talk) 02:25, 24 February 2013 (UTC)[reply]

I don't quite understand. The more weight you place on it, the more it will compress, until it reaches a point where it can't compress much more (about the density of wood, I imagine). StuRat (talk) 08:08, 24 February 2013 (UTC)[reply]

The question has relevance and merit if the crumpled paper is used for packing fragile products. There's bound to be someone who has studied it from that angle - what density of object can be protected by crumpled paper packing. What is the optimum crumpling density for use in packing? Of course, whether or not this is what Medeis had in mind - who knows? Wickwack 60.228.244.46 (talk) 10:56, 24 February 2013 (UTC)[reply]

My interest is in the abstract. I remember reading about ten years ago that researchers had found some sort of fractal constant that would predict how much a two-dimensional sheet of material--say paper or aluminum foil of the same thickness--would crumple within a confined space, like a tube, before it would cease compressing under a certain weight. If I remember properly, it turned out the actual material being crumpled didn't matter, the effect was a geometrical one. μηδείς (talk) 16:25, 24 February 2013 (UTC)[reply]

The place to start on the engineering properties of crumpling would be to look up the physics of crumple zones that are the structural safety feature of modern cars. The point is that the crumpling action itself absorbs energy -- if the structure it is already partly crumpled, much of that absorbing potential is lost. So thin supports such as those inside cardboard are in an ordered honeycomb structure instead.

An interesting place to look at the fundamental physics of crumbling is in newer research on mathematical origami. An artist makes the incredibly-complex fold pattern on a computer, prints the pattern and burns the perforations on paper. But instead of assembling fold-by-fold, the artist finds that they can get most of the folding in place immediately by gently crumpling the sheet. SamuelRiv (talk) 16:39, 24 February 2013 (UTC)[reply]

Yes, both crumple zone and mathematical origami are interesting articles, and I have watched a documentary on the latter. But I am looking specifically for some sort of fractal treatment of the random crumpling of paper and other two-dimensional substances. μηδείς (talk) 21:33, 24 February 2013 (UTC)[reply]

I'm not familiar with that research. You said you saw an article on it somewhere - can you try again to find anything on it? I'd be interested, and from there maybe I can lend guidance from there.

For now, if I were to make such a model, I'd start with finding folding arrangements that make all triangles, after which one might find a small set of transformations that collapse each triangle into smaller ones and maybe find a volume limit from there. But see if you can find an article. SamuelRiv (talk) 19:21, 25 February 2013 (UTC)[reply]

The only thing I can say for sure is that it was in Discover or Scientific American or American Scientist or the New York Times Tuesday Science section (about 60/34/5/1%) and that it included the words paper and fractal and something about crush or crumple or fold or bend, and what I have said above. Had I written the hook, it would have been, "Did you know that according to the new science of folding, fractals mean more than packaging?" But I didn't write the hook and my searches haven't worked. μηδείς (talk) 02:59, 28 February 2013 (UTC)[reply]

Quantum mechanical stability of historical timelines

"The Moving Finger writes: and, having writ,

Moves on: nor all thy Piety nor Wit

Shall lure it back to cancel half a Line,

Nor all thy Tears wash out a Word of it."

- Rubaiyat of Omar Khayyam

How well does that stand up against quantum mechanics?

Is the past in any way fixed or is it instead a swirling storm of uncertainties that we don't notice simply because we're just the product of the current history and so can't see the pasts that used to be? Hcobb (talk) 03:53, 24 February 2013 (UTC)[reply]

It's impossible to tell. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 04:28, 24 February 2013 (UTC)[reply]

Further reading I found while looking for this: Transactional interpretation. Hcobb (talk) 04:44, 24 February 2013 (UTC)[reply]

I've got two tests for the thread of history being in a vibrational state.

Dark Matter might be echoes of past states of the past and so its fine scale structure could have certain harmonics.
The Big Bang if connected to the present could have its structure influenced by the current configuration of the universe.

Hcobb (talk) 04:55, 24 February 2013 (UTC)[reply]

You may want to check your ideas against this standard. --Jayron32 05:49, 24 February 2013 (UTC)[reply]

I think this is a deep and important question. We live in an indeterminate universe, and just as one present might be mapped to many futures, it might be mapped to many pasts. It seems like the religion of causality seems to suppose that a Watchmaker God decreed the past in some arbitrary and uninformative way, and the present is random, and the past is set in stone; but it would seem to me that the past is indeterminate, and the present is what we know. Indeed, I suspect you could argue solipsistically that whatever consciousness is - if it relies on some algorithm to somehow provide it with input - that it is impossible to distinguish the nature of the universe beyond what is consistent with the input of the present moment, and all the rest of the physical certainty, even memory, is an illusion, no? Wnt (talk) 07:58, 24 February 2013 (UTC)[reply]

There is no backward causality in quantum mechanics. -- BenRG (talk) 22:44, 24 February 2013 (UTC)[reply]

Would german V-2 rocket left earth orbit?

If a V-2 rocket would have been launced straight vertically with a 100 kg payload. Would it stay in space or fallen down ?, in particular would it left earth gravity for planetary space? Max altitude is specified as 206 km. Electron9 (talk) 05:50, 24 February 2013 (UTC)[reply]

This sounds like homework, but here's a hint: find out what the maximum velocity would be with a 100 kg payload and compare that with the escape velocity at your launch latitude. Zoonoses (talk) 06:59, 24 February 2013 (UTC)[reply]

Data on height vs velocity and escape velocity at specific height is missing.. Electron9 (talk) 07:53, 24 February 2013 (UTC)[reply]

You might like to read our Low Earth orbit article. Alansplodge (talk) 09:23, 24 February 2013 (UTC)[reply]

The article you link states that 206km is the maximum altitude if launched vertically. If it were capable of leaving the Earth's orbit, there would not be a maximum altitude, so it must fall down. Someguy1221 (talk) 09:26, 24 February 2013 (UTC)[reply]

So no secret Nazi base on the Moon? Clarityfiend (talk) 11:23, 24 February 2013 (UTC)[reply]

The first rocket reaching a low orbit with such payload was an R-7 Semyorka (280 tons) with its payload Sputnik 1 (83.6 Kg) in 1957. A V-2 was only 12,5 tons. --Kharon2 (talk) 21:31, 24 February 2013 (UTC)[reply]

Some book I read in high school many years ago said that the Germans in WW2 could theoretically achieved orbit with a V2 as the 1st stage, a cluster of some type of antiaircraft rockets as the 2nd stage and one such antiaircraft rocket as the third stage, implying that one stage to orbit was impossible for the V2. Getting the timing and steering to work is a different problem than thrust or specific impulse. Edison (talk) 22:15, 24 February 2013 (UTC)[reply]

A V-2 rocket couldn't possibly reach orbit -- but the proposed V-10 "Amerika-Rakete" two-stage version just might have. 24.23.196.85 (talk) 00:33, 25 February 2013 (UTC)[reply]

Something to remember is that V-2 is designed for a 1000 kg payload. If this is reduced, other orbits should be possible. Electron9 (talk) 02:37, 25 February 2013 (UTC)[reply]

No, to "reach orbit" means to stay there. Reaching the same height does not suffice. ForLow Earth orbit you need to accelerate into a trajectory with roughly 8 Km per second speed around the planet in addition to the height to stay there for a while. If a V-2 had been capable of that, the first satellite in orbit had been one of United States origin because they where the ones that actually captured all the remaining V-2's and their science- and engineering staff including Wernher von Braun. But as already pointed out the Russians won hat part of the race into space 12 years (1957) after WWII (1945). --Kharon2 (talk) 10:57, 25 February 2013 (UTC)[reply]

Think of it this way. Firing a V2 straight up means it moving up a gravity well as far as 206 km, where it stops going any higher. Now that it has stopped going up there is no kinetic energy left for it to resist the pull of Earth's gravity, which will cause it plummet back to earth. Fired straight up -on say the equator- and it will have a suborbital velocity of about a 1,000 mph, yet, fall back to Earth it will do ... quickly. To stay up, it will either have to have enough orbital velocity or perpendicular velocity or a good thick coating of Cavorite.--Aspro (talk) 19:35, 25 February 2013 (UTC)[reply]

Liquid nitrogen and frostbite

The image on the right shows liquid nitrogen is boiling and a person put his hand in the gas. Since the boiling point of liquid nitrogen is −196 °C, I am wondering why the person is not getting frostbite in his hand? The temperature of the newly formed gas is supposed to be −196 °C. --PlanetEditor (talk) 06:44, 24 February 2013 (UTC)[reply]

They might, eventually. However, being a gas, it has a low density and doesn't have much heat capacity. If he submerged his hands in the liquid, he'd get frostbite quickly. Try putting your hands in the refrigerator at 40 degrees F, then submerging them in water stored in the same refrigerator (which has reached 40°F), and you will notice how much quicker your hands get cold in the liquid. That said, having bare hands that close to liquid nitrogen is foolhardy. He should wear thick leather gloves. One slip and he could be seriously injured. StuRat (talk) 07:46, 24 February 2013 (UTC)[reply]

(ec) There are two important things about liquid nitrogen that make this less likely. First, low heat capacity - it doesn't store as much "cold" as it would seem - I'm getting "1.341j/g/K (gas), 2.042j/g/K (liquid), enthalpy of vaporization: 198.8j/g" from [1]. Our article properties of water says water has heat capacity 4.2 J/g/K around the freezing point, so you heat up the boiled nitrogen gas 3.1x faster than water, plus it absorbs the equivalent of 152 degrees when boiling, so it's sort of like "3.5 times colder than ice water" in terms of the energy it absorbs from your hand, in terms of hypothetical heat absorption.

But second, the liquid nitrogen surrounds itself in gas which rapidly pushes away from the skin, making it very hard to bring that full cooling to bear on it; there's poor heat conduction in a gas. It's a bit like a firewalk in that regard. I've held little drops of liquid nitrogen in my hand, but as the skin cools, they start to bite a little. If some prankster loaded a container of ethanol into the vessel holding the liquid nitrogen so that the demonstrator dipped his hands into that, I think there would be immediate injury. Wnt (talk) 07:52, 24 February 2013 (UTC)[reply]

The ethanol would freeze, of course. It melts at 159 K, whereas nitrogen boils at 77 K. Maybe you mean it would get cold enough to cause immediate injury before it froze? I suppose that's possible. But the violently boiling nitrogen around the container should be a clue. --Trovatore (talk) 08:00, 24 February 2013 (UTC)[reply]

You have a good point there. I suppose I was thinking that ethanol that has been sitting on dry ice is already quite cold enough! Wnt (talk) 08:44, 24 February 2013 (UTC)[reply]

Well their hand isn't really in the liquid nitrogen, probably just in the boiled off nitrogen and water vapour from the air. Making icecream with LN2 is very safe providing you know what you are doing. Your hand can get a bit cold when making ice cream like this over the minutes but unlikely to be so cold so as to cause any damage. When dipping your bare hand into liquid nitrogen you are protected by the Leidenfrost effect for several seconds so it feels cold but little heat transfer takes place. Damage is much more likely if the nitrogen gets stuck next to your skin for a longer period such as if it gets accidently poured in your glove or shoe and these can't be removed quickly. JMiall ₰ 10:23, 24 February 2013 (UTC)[reply]

Thanks everyone. --PlanetEditor (talk) 13:26, 24 February 2013 (UTC)[reply]

One more interesting and important concept: the Leidenfrost effect. It's how people can stick their hand into boiling lead, for example. SamuelRiv (talk) 16:20, 24 February 2013 (UTC)[reply]

T-90 tank shtora system

Can Shtora system disable javelin missile ? 87.236.232.97 (talk) 08:19, 24 February 2013 (UTC)[reply]

It seems not, because Shtora "disrupts semiautomatic command to line of sight (SACLOS) antitank guided missiles, Laser rangefinders and target designators." The FGM-148 Javelin uses "an imaging infrared seeker". According to the China Defense Blog, "the Shtora is less effective against the more advanced third generation of ATGM such as the US Javelin or the German PARS 3 which relies on laser or electro-optical imager for guidance". Alansplodge (talk) 09:20, 24 February 2013 (UTC)[reply]

String or Higgs boson

Which fundamental particle give mass to all other particle? Is it string or Higgs boson? 106.215.104.44 (talk) 10:04, 24 February 2013 (UTC)[reply]

See higgs boson, higgs mechanism. "String" is not a particle, but a hypothetical model for all known particles. See string (physics). The higgs boson could hypothetically be a string. Someguy1221 (talk) 10:15, 24 February 2013 (UTC)[reply]

I guess you mean gives mass to other fundamental particles rather than all other particles i.e. not composite particles like a proton for the most part (see Proton#Quarks_and_the_mass_of_the_proton). Sean.hoyland - talk 10:33, 24 February 2013 (UTC)[reply]

Name of all 11 dimensions of space

I read in M-theory article that there are 11 dimensions of space. What is the name of all 11 dimensions? One is time and other 10 are ........ I read further in an another article that elementary particles are zero-dimensional. Then, what is the number of dimensions of an atom? 106.209.220.49 (talk) 11:58, 24 February 2013 (UTC)[reply]

To answer the first part of the question, space is four dimensional with the three spatial dimensions we are familiar with — you can call them length, width, and height or X, Y and Z — and time being the fourth dimension — see: Dimension (mathematics and physics)#Additional dimensions. It is not known whether any others exist, different theories posit 10, 11 and 26, so they haven't been named yet. Richerman (talk) 15:07, 24 February 2013 (UTC)[reply]

Also, it's useless to try to assign them names when we don't still know what they "look like". For example, they could be circular, so that walking along the "Q-axis" (a dummy name: t,x,y,z,q,l, etc) will quickly bring you right back where you started. For anything larger than the tiniest particles (e.g. gravitons), this "Q" is virtually non-existent. Or it could be like a sphere with "L" and "M" corresponding to latitude and longitude, again only fat enough for tiny particles to experience. One thing an extra dimension almost certainly is not, however, is like normal spatial length-width-height. If it were, we'd have seen it by now. SamuelRiv (talk) 16:18, 24 February 2013 (UTC)[reply]

This "names" thing is fairly silly in my view.

For spacetime (@Richerman: only spacetime is four-dimensional; space is still three-dimensional), you have one distinguished dimension which may be called "time". More precisely, there are "timelike" and "spacelike" intervals, and all observers will agree on which is which.

The remaining three, however, have no fixed "names". The names all correspond to a choice of (possibly local) coordinate system. For example, on the surface of the Earth, you'll probably use up/down for one axis, but whether you use left/right forward/backwards, or port/starboard fore/aft, or north/south east/west, depends entirely on your immediate purpose.

For what it's worth, and it isn't worth much, a writer by the name of Charles Howard Hinton proposed the names ana and kata for opposing directions in a fourth spatial dimension. How, or even whether, he proposed to distinguish between them, I am unaware. --Trovatore (talk) 00:05, 25 February 2013 (UTC)[reply]

In computer graphics, we use 'w' for the fourth dimension - hence x,y,z,w - but we rarely use more than 4 spatial dimensions. Isn't it the case with some varients of M-theory that there might be multiple time dimensions? That hurts my head! SteveBaker (talk) 21:02, 25 February 2013 (UTC)[reply]

Food energy

The standard food energy values, as given in our article and appears in most publications, are as follows:

carbohydrate: 4 kcal/g
protein: 4 kcal/g
fat: 9 kcal/g

On the other hand, as given here and mentioned this journal article, energy value of fat is 9.3, and that of protein is 4.2 for meat protein and 4.3 for vegetable protein.

Now, this article published by the USDA says (p.4) energy value of protein is 5-6 kcal/g. This also describes the energy value of protein is 5.6 kcal/g. Why so many variations? I cannot understand the reason for the differences. --PlanetEditor (talk) 13:13, 24 February 2013 (UTC)[reply]

I found this book which says "in vivo, the oxidation of protein is only party complete .... calorific value of protein, in vivo, is less, i.e. 4.1 Kcal/gm". The the book does not cite any reference. Definitely the USDA article is the most reliable. --PlanetEditor (talk) 13:20, 24 February 2013 (UTC)[reply]

The main point here, is there any way to know whether the energy value of a food, as determined by bomb calorimeter, is different from energy value of the same food in human body? --PlanetEditor (talk) 13:36, 24 February 2013 (UTC)[reply]

It obviously is not. A bomb calorimeter can burn sawdust. A human body can not. The ash that a bomb calorimeter leaves behind cannot be ignited and burned. Dried dung can. The question is what the calorimeter operators do to compensate for these sources of error. See [ http://www.fishersci.com/ecomm/servlet/cmstatic?href=Scientific/researchAnalytical/ProductsServices/Food_Diagnostics/food_beverage_newsletter_bombcal.jsp&store=Scientific&storeId=10652 ]. --Guy Macon (talk) 19:49, 24 February 2013 (UTC)[reply]

Very interesting question; my first instinct would be that the caloric values given are for proteins/carbs/etc. which have already been digested and are being oxidized in the mitochondria, but I can't find a reference for that; note that the efficiency of digestion, for lack of a better phrase, varies between species and foodstuffs; cats don't extract as much from their food as goats, for instance. Gzuckier (talk) 06:26, 25 February 2013 (UTC)[reply]

I believe the caloric values are reference for calories available to humans. --DHeyward (talk) 05:27, 28 February 2013 (UTC)[reply]

Our mirror image is chiral or achiral

What is the nature (chiral or achiral) of our image formed in a mirror? 106.209.220.49 (talk) 13:25, 24 February 2013 (UTC)[reply]

This question indicates that you don't understand the meaning of the words "chiral" and "achiral". A chiral object is an object whose mirror image can't be superimposed on the original. An achiral object, in contrast, has a mirror image that matches the original. Looie496 (talk) 16:13, 24 February 2013 (UTC)[reply]

Then, what about our image formed on mirror? I want to know whether this image is able superimpose our body (achiral) or it isn't (chiral). 106.209.220.49 (talk) 16:56, 24 February 2013 (UTC)[reply]

If you are chiral, then your mirror-image is chiral. If you are achiral, then your mirror-image is achiral. --catslash (talk) 17:34, 24 February 2013 (UTC)[reply]

You may be interested in Julian Wolkenstein's Symmetrical Portraits series and his echoism.org site. Sean.hoyland - talk 17:46, 24 February 2013 (UTC)[reply]

If you part your hair on the right, the person in the mirror parts his hair on his left. If you take a picture of yourself and take a picture of yourself in the mirror, when you try to superimpose the pictures on each other the parts of the hair will be on opposite sides. So you are chiral. Even if you part your hair in the middle, you are still asymmetric and therefore chiral. Duoduoduo (talk) 18:14, 24 February 2013 (UTC)[reply]

Vegetarian Experience

Last summer I decided to be a vegetarian, and since then, something weird happened to me, I began to have dreams of me eating meat, and after a while I began to feel guilty about it in the dream, and in the last dream I had I actually spitted out the meat. I was just curious is it common/normal? Is it a way for my body to tell me I need meat? (Probably like sexual dreams?) I'm interested to know what's happening in my brain... Thanks!--Irrational number (talk) 15:15, 24 February 2013 (UTC)[reply]

I have taken the liberty of removing the first two copies of this question. It looks like something got screwed up with the post. Falconus^{p t c} 15:17, 24 February 2013 (UTC)[reply]

Thank you, I clicked on the "save page" button more than once, very slow connection here this is embarrassing... I feel like a cave man... — Preceding unsigned comment added by Irrational number (talk • contribs) 15:22, 24 February 2013 (UTC)[reply]

This falls into the category of "wish fulfillment" dreams -- a major type. (Freud thought that all dreams are of that type.) It simply indicates that you had a strong desire to eat meat. Looie496 (talk) 16:15, 24 February 2013 (UTC)[reply]

To continue using Freud, the desire to eat the meat comes from your id, while the desire to avoid it comes from your superego (which aims for perfection), and these are mediated by the ego. This conflict is being fought out in your dreams. StuRat (talk) 16:48, 24 February 2013 (UTC)[reply]

I think it might have been more normal if you had spat out the meat, rather than sticking it on spits. Food cravings are usually conscious. If your dreams are bothering you you need to see a medical professional. We can't do oneiromancy here. μηδείς (talk) 16:17, 24 February 2013 (UTC)[reply]

There's nothing in the question that would indicate that this is a wish fulfillment dream, or that Irrational number has a strong desire to eat meat. The only emotional reaction to eating meat that was expressed in the question is guilt, and the dream behavior of spitting out the meat would be consistent with disgust. Red Act (talk) 18:12, 24 February 2013 (UTC)[reply]

I believe it's normal. My own experience tells me that - I once gave up meat for Lent, and by Good Friday I was getting phantom roast chicken smells. Also my vegetarian friends tell me they still get cravings for meat, most commonly bacon. As to why this happens, I don't think there's any research into it that will tell you. So don't worry about it. --TammyMoet (talk) 16:37, 24 February 2013 (UTC)[reply]

There's no mystery about the attractiveness of the smell of roast chicken or bacon. See Maillard reaction. Bacon is a superstimulus, it's basically the essence of meat all in one high-fat crunchy protein package:again, Maillard reaction as well as Monosodium glutamate, etc. μηδείς (talk) 18:23, 24 February 2013 (UTC)[reply]

I would take the desire to eat meat as a sign that you're not getting enough protein (or possibly some other nutrient, like iron or Vitamin B12). If you want to remain a vegetarian, I suggest beans and nuts. (You might want to get some Beano, if you plan on getting your protein from beans without offending everybody you know.) If your version of vegetarianism permits eggs and/or dairy products, those are other options. My (extremely lax) version also permits fish. If iron or B₁₂ is the deficiency, there are other nutritional sources of those, too. StuRat (talk) 16:58, 24 February 2013 (UTC)[reply]

Re: "We can't do oneiromancy here", sure we can. We aren't allowed to give medical or legal advice, but oneiromancy, like other forms of divination, is certainly allowed, despite the control issues some folks here have concerning what other people post. And who better to interpret your dreams than some random stranger on the Internet? I agree with StuRat that cravings for meat and/or dreaming about meat may very well be a sign of an inadequate diet. It is a well-known fact that, while a vegetarian or even vegan diet can be healthy and balanced, you have to work at it. Wikipedia has some excellent info on this issue at Vegetarian nutrition#Potential nutrient deficiencies and Vegan nutrition#Nutrition. --Guy Macon (talk) 18:01, 24 February 2013 (UTC)[reply]

However, if the OP starts growing towards the light, he should see a doctor. Or maybe a gardener. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:17, 24 February 2013 (UTC)[reply]

I quit smoking at the start of the year and I've had a few dreams of me just chain smoking. Vespine (talk) 21:46, 24 February 2013 (UTC)[reply]

Actually, the OP is asking for medical advice, which is not allowed. However, any kind of change can lead to what I can "anxiety dreams". But if you're really concerned that there might be something wrong with you, see your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:17, 25 February 2013 (UTC)[reply]

Correct me if I'm wrong but I think the definition of medical advice in the reference desk is getting wider. I didn't ask what I should do, I was just curious about how common this is and what is happening in my brain and why. Is any question about human body a request for medical advice? I think a request for advice must at least have a part in which the OP asks what they should do, which I didn't.--Irrational number (talk) 10:40, 25 February 2013 (UTC)[reply]

I agree. You wouldn't go to a doctor to ask him to explain your dreams, so it's not medical advice. (Of course, there are some things you might ask a doctor that don't require a doctor to answer, like "How can I reduce my sodium intake". They would likely refer you to a nutritionist.) StuRat (talk) 15:47, 25 February 2013 (UTC)[reply]

"What's happening in my brain?" is a question only a doctor can answer, through diagnosis of the OP. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:44, 26 February 2013 (UTC)[reply]

Since all learning happens in the brain, then all academic questions, according to your criterion, should be referred to a doctor. StuRat (talk) 17:20, 26 February 2013 (UTC)[reply]

Why stop at academic questions? Let's make it about all questions, period. Here's an idea: We don't allow anyone to ask a question on the Ref Desk, until they produce a certificate from a doctor or a lawyer saying they've attended and asked their question but were advised to seek external help from the Wikipedia Reference Desk. Yes, that ought to fix it. -- Jack of Oz ^[Talk] 22:51, 26 February 2013 (UTC)[reply]

stereoscopic images

How much did it cost to make them in the 1800s' — Preceding unsigned comment added by 172.218.36.253 (talk) 20:45, 24 February 2013 (UTC)[reply]

About twice as much as it took to make a normal photograph. Back then the one-time equipment costs were much higher (new technology) and the per-image costs comparatively lower (they re-used plates instead of buying more film). --Guy Macon (talk) 21:42, 24 February 2013 (UTC)[reply]

Refs for stripping the emulsion off plates and re-using them? I thought plates were mostly one-time use. Edison (talk) 03:54, 25 February 2013 (UTC)[reply]

There really isn't any reason why they shouldn't be exactly the same price as two normal photographs - that's really all they were. They'd either use a special camera with two lenses that could expose two images at the same time...or for things like landscapes that don't move much, they'd take two consecutive photos - moving the camera sideways by some amount between. They'd develop the two images separately and either print them onto one piece of paper or make two slides - depending on how the viewer worked. But throughout the process - it's nothing more than taking two pictures...it ought to be cheap. Of course they may have charged extra to do it just because that's what the market would stand...but I don't see any particular reason why it should cost more to make them. SteveBaker (talk) 20:59, 25 February 2013 (UTC)[reply]

Rate of exothermic reaction

Let's assume one wishes to measure the rate of reaction for an exothermic reaction in aqueous solution. Would measuring temperature of the reaction and graphing the temperature at given intervals be an accurate way to measure this? Is there a given point where the reaction would be able to be determined "finished"? And if this is a viable method, what type of container would be most useful? Must one use a calorimeter, or just any beaker or flask? 66.41.216.19 (talk) 22:36, 24 February 2013 (UTC)[reply]

Well, the temperature will be cumulative, ignoring cooling to the environment, so you might want to graph the change in temp versus time, rather than the temperature itself. An insulated container would be best, to minimize the effect of cooling to the environment. However, beware that some reactions might get out of hand, leading to an explosion, in such a situation, as the insulated container may increase the temperature, and thus the reaction rate. The reaction is finished when the temperature change is zero (smaller time increments provide better data). StuRat (talk) 22:57, 24 February 2013 (UTC)[reply]

So you're saying I should record the change in temperature over each, say, 5 second period until the temperature ceases to change? I was only planning on reacting zinc with 3.0 M HCl, so an explosion risk is low. However, I am not sure if a calorimeter would affect the rate of reaction as you just said. If so, how so? Would I have to know the calorimeter constant? Or would I be better off with a beaker? I'm just trying to find a way one could measure rate of reaction between these particular compounds. 66.41.216.19 (talk) 23:06, 24 February 2013 (UTC)[reply]

Well, most reactions are sped up by higher temps, but there may be a few exceptions (say if the higher temperatures cause one of the reactants to change into a gas, and leave the reaction vessel). Now, why exactly do you want to know the speed of the reaction ? If there was a Q you were trying to answer, like "does the color change take place during the reaction or after it has completed", then speeding it up wouldn't matter. If, on the other hand, your question is "how long does the reaction take to complete at STP", then you not only need to avoid an insulated container, but you might want to cool it to standard temperature during the reaction, depending on how you interpret the Q.

Also note that in any sealed reaction vessel, you may also need to account for the effect of a change in pressure, as that can change the reaction rate, too.

Is every 5 seconds the fastest you can measure temps ? If you are doing it manually, that's about right, but automated temperature probes/recorders ought to do far better than that. StuRat (talk) 23:38, 24 February 2013 (UTC)[reply]

Maybe once per second with the technology I have available. I want to find out the rate of the reaction to investigate the effect of surface area of Zn(s) on rate. I would use solid lumps of zinc, zinc filings, and zinc powder in a constant amount (molarity) of HCl. Rate is my dependent variable, and form of zinc is my independent variable. The rate of reaction, I thought, might be the initial number of moles of Zinc (constant for each trial set) divided by the amount of time before the temperature ceases to change. Is there an easier way? 66.41.216.19 (talk) 23:46, 24 February 2013 (UTC)[reply]

About how long does this reaction take, in the slowest case ? The only problem with the open reaction vessel is that, when the reaction is trailing off, the small amount of heat produced may equal that lost to the environment, so it will appear that the reaction ended earlier than it did. You might want to try it both in the bomb calorimeter and in the open vessel, to see if the ratio is different between the fastest and slowest reactions. If not, just stick with the open vessel. StuRat (talk) 23:52, 24 February 2013 (UTC)[reply]

I have a styrofoam calorimeter with a small hole in the lid to permit gases to escape, therefore keeping temperature loss at a minimum while keeping pressure constant. Is this OK? (thnx for ur patience) 66.41.216.19 (talk) 23:54, 24 February 2013 (UTC)[reply]

Sounds reasonable to me (provided that nothing will react with the Styrofoam). Of course, keep in mind that any experiment is only a model of "the real world case". So, for example, if you want to know which is faster for designing an industrial reaction process, then you'd want to set up your experiment as closely to the industrial process as possible. StuRat (talk) 00:03, 25 February 2013 (UTC)[reply]

Better quality safety glasses

I noticed when I buy clear safety glasses they don't have very good clarity to them and seem to stop light transmission to some degree. They also get a lot of glare on them. I don't wear prescription glasses but I have friends that do I have looked through their glasses and the plastic they are made from has very good light transmission and is extremely clear. They also seem to get almost no glare. I'm wondering if you can buy safety glasses with the same quality lenses that they make prescription glasses from. --Tommythehook (talk) 23:47, 24 February 2013 (UTC)[reply]

Well, plastic will get tiny scratches over time, which will make them look foggy. Glass won't do that. Of course, glass could be quite dangerous, if it shatters. So, there are special types of glass which are less likely to shatter, which would be suitable for safety glasses. StuRat (talk) 23:57, 24 February 2013 (UTC)[reply]

Most prescription glasses are not made from glass. Also my safety glasses have problems brand new, its not due to scratches.--Tommythehook (talk) 00:11, 25 February 2013 (UTC)[reply]

There are 2 reasons why presciption specs are better: 1) anti-reflection coatings, and 2) frames for prescription use have the lenses closer to the eye - thus making surface imperfections further out of focus and so less noticeable. This question has come up before, for a possible solution - see http://wiki.riteme.site/wiki/Wikipedia:Reference_desk/Archives/Science/2012_June_15 Ratbone 124.178.54.230 (talk) 01:12, 25 February 2013 (UTC)[reply]

I'm pretty sure it's the same banned sockpuppet so I guess the previous answers didn't help. Nil Einne (talk) 05:11, 25 February 2013 (UTC)[reply]

is it possible that prescription glasses are simply made from a higher quality polycarbonate?--Tommythehook (talk) 16:05, 25 February 2013 (UTC)[reply]

Depends on what country you live in. In Europe one can buy safety glasses that meet standards suitably matched for your intended use. [2]. All you need to do is google standards,safety glasses and local retail out lets, etc.--Aspro (talk) 20:13, 25 February 2013 (UTC)[reply]

We also have to be super-careful about what kind of safety glasses we're talking about. My most-often-worn safety glasses are to protect my eyes from infrared light from a CO2 laser. They are made from high-quality polycarbonate - cost close to $100 and they are very different beasts from the $10 ones I use when operating a table saw to prevent wood chips from hitting my eyes. The $100 pair are indeed very clear and I don't get problems with glare with them - I'm fairly sure that they'd stop a fast-flying wood-chip - but that's not what they are designed to do. SteveBaker (talk) 20:49, 25 February 2013 (UTC)[reply]

One might say from the above post that: you get what you pay for. Just a thought: if the OP belongs to a trade union or similar organization he may be able to get good eye protection where he can offset the cost against his income tax. This is common in Europe were you can get eye protection for nothing if it is in connection with your employment. Being a safety concern, one only has to provide the slightest reason why you qualify. Are you ever (even once in 12 months) in an area where your company’s delivery vehicles are are maintained? Right, you might be passing by when a mechanic is toping up the battery with dangerous sulphuric acid – you need eye protection. Your company/government may pay for this. Self employed? Do you ever have to (in connection with your trade) go near any dangerous chemicals – Strong vinegar is a nasty substance if it gets in your eyes. After reading the official safety warnings, why they allow supermarkets to sell it -I don't know. You need googles – even if your an accountant and never come across anything stronger than a letter form IRS. Mind you, when I look at my accountant's bills, I feel like I could do with some super eye protection.--Aspro (talk) 23:29, 25 February 2013 (UTC)[reply]

The thing is I have looked at some expensive safety glasses like $100 Oakley safety glasses and they don't look very clear to me. What brand are your laser safety glasses? --Tommythehook (talk) 15:21, 26 February 2013 (UTC)[reply]