Wikipedia:Reference desk/Archives/Science/2016 September 20

= September 20 =

Glucose instead of fructose
Isn't glucose better for you than fructose? If so, why don't people just put glucose in their coffee instead of white sugar, which is half and half? Anna Frodesiak (talk) 04:52, 20 September 2016 (UTC)
 * Sucrose (white sugar) is not "half and half" glucose and fructose, it is a different substance formed by the reaction of glucose and fructose with the loss of water (ie. glucose + fructose &rarr; sucrose + water). It is true that sucrose hydrolyses to a 1:1 mixture of glucose and fructose, and that that process is much faster in acidic environments, but sucrose has its own properties (include sweetness separate from those of glucose and fructose).  White sugar is a product of sugar cane which contains easily extractable sucrose but relatively little free glucose.  It does contain glucose polymers (cellulose) as a structural material, but this is not easily converted to free glucose.  By contrast, potatoes have starch as their glucose polymer which is easily converted back to glucose, so sugar cane may not be an ideal source for glucose.  Even if the sucrose from sugar cane was hydrolysed, there would be need to separate the fructose and approaching half of the mass of sucrose extracted would be lost as (waste) fructose, so it is unlikely to be economically attractive.  Further, the fructose would likely not be cost competitive with high fructose corn syrup due to the subsidies.  Fructose is sweeter than glucose but metabolised much faster so it is a desirable additive from a business perspective (less is needed for a given sweetness) but undesirable from a health perspective - because you are correct that glucose is better than fructose from a health perspective.  EdChem (talk) 05:23, 20 September 2016 (UTC)


 * From the "better for you" point of view I would humbly suggest no sugar in your coffee. Richard Avery (talk) 06:50, 20 September 2016 (UTC)


 * Or put some L-Glucose in your coffee. Count Iblis (talk) 07:02, 20 September 2016 (UTC)


 * See also: Glycemic load -- Hans Haase (有问题吗) 09:22, 20 September 2016 (UTC)
 * Hi Richard Avery. Actually, I don't use sugar in coffee and rarely eat anything sweet at all. Anna Frodesiak (talk) 01:56, 21 September 2016 (UTC)
 * Sorry Anna Frodesiak, I did not mean to imply that you did. It was bad wording on my part. If more people in developed countries followed your example there would be more healthy people in the world. Richard Avery (talk) 06:25, 21 September 2016 (UTC)
 * No need to say sorry, my friend. There's nothing wrong with saying "...I would humbly suggest no sugar in your coffee...". :) Anna Frodesiak (talk) 06:58, 21 September 2016 (UTC)
 * I don't deny publications about fructose and diabetes, but it seems absurd to call a major natural sugar "unhealthy". There are unhealthy people who need specialized diets, but fructose is part of the human evolutionary story and the body is reacting to it according to a carefully regulated procedure.  That procedure just doesn't take into account every modern trend.


 * If you're going to use a different sugar, you can use grape sugar, i.e. glucose Gee, I wonder if "powdered raisins" or lyophilized raisins exist as a thing... I'm not seeing it, but it seems like it might be neat for such purposes., or stevia and erythritol, which to me seems like the perfected version of an artificial sweetener at least until somebody's patents expire and some dread side effect is published to get us on to the next thing. Wnt (talk) 12:08, 20 September 2016 (UTC)


 * Grapes were not the main diet during human evolution. Modern grape varieties like the red seedless grape accentually contain more fructose than glucose.  We are also omnivores. It is only in a  blink of the eye (in the time-line of human evolution), that so much convenience food has included such high sugar content, available not just seasonally -but all year round. It is not the natural sugars per sa (as you point out) that  should  considered unhealthy but the vast quantity the are now being consumed to the detriment of our evolutionary omnivorous needs.--Aspro (talk) 20:04, 20 September 2016 (UTC)


 * Inulin used to be added to stevia-based sweeteners, and I found it improved the taste of stevia in my coffee. Inulin's got a number of health benefits (it's a soluble fiber and incrases calcium absorption in young women, and is metabolized only about 35% as much as other carbohydrates) but makes some folks gassy and can aggravate irritable bowel disease and related diseases.  I don't know if that's why no one puts it in their stevia sweetener any more, or just that straight stevia's cheaper to make and sell. I eat a lot of beans anyway, so a little more gas is no issue.  I guess I need to check out local health stores for inulin. loupgarous (talk) 18:48, 20 September 2016 (UTC)


 * Yes, the problem with eating sugars has more to do with not getting enough fibers as a result and fibers are the food for gut bacteria who convert it to Short-chain fatty acids which we need: "The short-chain fatty acid butyrate is particularly important for colon health because it is the primary energy source for colonic cells and has anti-carcinogenic as well as anti-inflammatory properties[7] that are important for keeping colon cells healthy.[8][9] Butyrate inhibits the growth and proliferation of tumor cell lines in vitro, induces differentiation of tumor cells, producing a phenotype similar to that of the normal mature cell,[10] and induces apoptosis or programmed cell death of human colorectal cancer cells.[11][12] Butyrate inhibits angiogenesis by inactivating Sp1 transcription factor activity and downregulating VEGF gene expression.[13]" Count Iblis (talk) 20:19, 20 September 2016 (UTC)


 * I'm curious as to why you refer to "fibers" rather than "dietary fiber". Is that what it's called on your planet ? :-) StuRat (talk) 20:46, 20 September 2016 (UTC)


 * Yes, adding "dietary" is too much effort for me :) Count Iblis (talk) 02:32, 21 September 2016 (UTC).


 * I'm more curious about the "s" you added at the end. StuRat (talk) 17:17, 21 September 2016 (UTC)


 * Hi User:EdChem. But from what I understand, sucrose is just fructose and glucose and your body just splits it into two easily and then processes each seperately. Is that right? If that is the case, and economics aside, can one not just buy a jar of glucose or use corn syrup (which I think is glucose) and stir that into coffee and not tell the difference and be healthier? Best, Anna Frodesiak (talk) 01:56, 21 September 2016 (UTC)


 * Beware of simple-minded "this is healthier than that" comparisons. I suppose there are some (water is healthier than arsenic, say), but in general they don't tell the whole story.
 * Fructose is fruit sugar. It's the main thing that plants use to bribe animals to carry their fruit around and spread their seeds.  Presumably the animals wouldn't do that if it were a terrible thing per se.
 * Also consider that fructose is sweeter than sucrose, whereas glucose is less sweet than sucrose. See the table at sweetness.  So even assuming, for the sake of argument, you would come out ahead by replacing fructose with glucose gram-for-gram, you might use more grams of glucose if you sweeten to the same taste.
 * That said, I'm not saying you're wrong. Maybe you really would come out ahead.  But I don't think your arguments thus far convince me of that. --Trovatore (talk) 02:23, 21 September 2016 (UTC)


 * I don't think corn syrup tastes as good as cane sugar. When US soda pop companies switched from sugar to corn syrup, the result just didn't taste as good, and sales have started to lag due to this and other reasons. StuRat (talk) 02:25, 21 September 2016 (UTC)


 * Hi Trovatore and StuRat. There's only one way to know. If either of you have a can of corn syrup, why not add the equivalent amount as white sugar to a coffee and let us know. :) I would be very curious to know the answer. I would do it, but I don't like sugar. I find it addictive and it makes me start shrieking in the night, although that could be caused by the monsters. I've been having a problem with monsters lately. Anna Frodesiak (talk) 02:49, 21 September 2016 (UTC)
 * So first of all, corn syrup also has fructose. And other things, which may be what Stu is tasting.  As for me, I take my coffee black, like any self-respecting coffee snob. --Trovatore (talk) 03:18, 21 September 2016 (UTC) Actually that's not entirely true &mdash; I do often put cream in brewed coffee, though not in espresso.  But no sugar in either case. --Trovatore (talk) 03:20, 21 September 2016 (UTC)


 * So what product is just pure glucose? Anna Frodesiak (talk) 04:06, 21 September 2016 (UTC)
 * Well, you can buy actual glucose. I found it easily on Amazon, for example. --Trovatore (talk) 04:08, 21 September 2016 (UTC)
 * No kidding? Come to think of it, we have the Glucose Barn and The Glucossery just round the corner, or if want the five-gallon drum, there's the Bulk Glucose Shopper's Club. Seriously, can't someone there do a taste test and let us know? There must be some product in your cupboard that is just glucose. Anna Frodesiak (talk) 04:19, 21 September 2016 (UTC)
 * There "must"? Why?  As far as I know, the only product that is just glucose is what is sold as "glucose". --Trovatore (talk) 05:59, 21 September 2016 (UTC)


 * Well, Trovatore, I figured there ought to be some product that is just glucose, considering that it's just sugar, and a preferable sugar, health-wise. Heck, if I used sugar in recipes and had a jar of glucose handy, I'd reach for that over sucrose. Wouldn't you? Anna Frodesiak (talk) 06:23, 21 September 2016 (UTC)


 * The "preferable health-wise" part is not clear to me. But in any case, as far as I know, if you want to buy just glucose, it's going to say "glucose" on the package.  Or possibly "dextrose".  If you find out otherwise, I'd be curious to hear about it. --Trovatore (talk) 06:47, 21 September 2016 (UTC)


 * Hi Trovatore. Well, everything I've read says that bodies handle glucose better than fructose. Anyhow, if I find glucose, I may buy it and try it. Anything to reduce the night-shrieks. :) Kidding. Cheers, Anna Frodesiak (talk) 06:58, 21 September 2016 (UTC)


 * Hi Anna, the taste of sucrose is different from that of glucose, fructose, or a mix of the two. Even if after hydrolysis in the stomach your body treats sucrose as a 1:1 mix of glucose and fructose, the difference in taste will be notable in the mouth as you consume it and before any significant processing has occurred.  Further, L-glucose, the enantiomer of D-glucose (which is the naturally occurring form) are identical in taste but the L-form is not metabolised as a regular sugar would be, and so has the sweetness but not the calories.  Swapping one compound for another frequently gives unanticipated consequences in a system as complex as a living animal.  Certainly, given the differences in sweetness and glycemic properties, the amount of glucose required to produce identical sweetness (and that doesn't mean taste, necessarily) will not be 1:1 with sucrose or fructose.  To produce identical glycemic load will also be a different amount.  Comments above that the health issue is much more about the large increase in sugar consumption of all types so recently that substantial evolutionary adaptation is only beginning are highly relevant, in my opinion.  EdChem (talk) 08:03, 21 September 2016 (UTC)


 * Yes, the taste of glucose (which I have been given when my blood sugar is low at the doctor's office) is markedly different from sucrose, and not something a kid would like as candy, to be sure. μηδείς (talk) 18:09, 21 September 2016 (UTC)

Thank you everyone. This has been very educational. By the way, regarding the large increase in sugar consumption, 10 years ago here in Haikou, you'd see a fat person once a year, no kidding. Today, it seems like 20% of women are fat-obese, lots of men too, and students are really putting it on. What's changed? Sugary drinks and products everywhere. Sugar cane has always been something they ate, but it never made them fat. Oh, and people are richer, so they can afford more fatty food too. Maybe that's a factor. Anyhow, thanks again to all. Anna Frodesiak (talk) 23:01, 21 September 2016 (UTC)

Scotch and water
Apparently adding water to scotch is a thing. These sites purport that water somehow "opens up the flavors of Scotch" in some way, and one even says "A chemical reaction occurs between the water and the tightly-wound chains of amino acids in the whisky."

But what's really happening here? Is there actually a measurable effect or is this all just the placebo effect?

And is all that stuff a about a chemical reaction possible? I remember from high school that when you have a equation like:

A + H20 = B

And then given enough time to react then it will reach chemical equilibrium with the concentration of A, B, and H20 all reaching some stable point. A bottle of whisky has plenty of A, B, and H20 and it has had more than enough time to react. So I don't see how adding a few drops of water, which is a negligible amount compared to the amount of water already in the scotch, could shift the equilibrium in any noticeable way. Pizza Margherita (talk) 07:16, 20 September 2016 (UTC)


 * An explanation here. Mikenorton (talk) 10:14, 20 September 2016 (UTC)
 * "Did you also know that water warms the whisky? Yep, that’s right. As you add water to the whisky, you are mixing two different liquids, each with different arrangements of molecules that are simultaneously mutually attracted and repulsed. Since the attractions are stronger, the liquid stays together. As you mix whisky and water together, you have to break the attractions and reform a new equilibrium of attractions and repulsions. Mixing water with whisky causes the attractions to be a little stronger, that is to say, that they form stronger intermolecular bonds. Try mixing 10 ml of water and 10 ml of ethanol, you get LESS than 20 ml of liquid because the molecules are grabbing hold of each other more tightly, or bonding. When bonds are formed, molecules move less, giving up their energy, in this case heat. This heat then contributes to a temperature rise, we call this the heat of mixing."
 * What's the heat of mixing for adding 0.5ml water into 50ml of 50% water/50% alcohol solution? I'd like the check whether that actually makes a significant difference or not.Pizza Margherita (talk) 22:46, 20 September 2016 (UTC)
 * This may help, but I've not had time to go through it in detail - see also Ethanol (data page). Mikenorton (talk) 14:46, 21 September 2016 (UTC)


 * And another here. Mikenorton (talk) 10:17, 20 September 2016 (UTC)


 * To be sure though, I'd expect amino acids to be quite rare in whiskey, especially as long polypeptides. Not unless somebody dumped a protein supplement into it. Wnt (talk) 11:58, 20 September 2016 (UTC)


 * Another possible effect is that, by diluting the ethanol, the other flavors become more apparent, as ethanol tends to overpower other flavors in strong concentrations. Note that this effect may vary by the taster, as some are genetically more sensitive to the taste of ethanol.  See TAS2R38.  StuRat (talk) 16:56, 20 September 2016 (UTC)


 * Old saying: The proof of the pudding is in the eating. The OP now needs to experiment. Personally, I am a bit of a heathen during the winter, when I enjoy the odd dram or two in a sort of brandy glass (of this type) to savour the bouquet, but to get the full flavour a little water is required. For  long cool drink however, do not use tap water. Although, tap water is wholesome and safe to drink it is totally unstable for all spirits as it has been chlorinated (producing unpleasant tasting chlorophenols)  and brighteners such as aluminum compounds which have been added to the mains supply. Use either (glass not plastic) bottled 'soft' spring water (i.e. those with little calcium) or use just an ordinary home water filter (I use a Britawhich produces acceptable results) – and if you whant to add ice... make sure that those too has been made from spring or filtered water. P.S. Boil (in a clean glass vessel) in the microwave before freezing and you will get much clearer, transparent ice cubes, as the boiling drives off most of the dissolved gasses so doesn’t produce all those little bubble that cloud the ice. Finally, always choose a good malt. They needn’t be the very expensive ones, just avoid the blended grain whiskeys. They are as bad as the American Bourbons. Then sit back and Enjoy!--Aspro (talk) 18:29, 20 September 2016 (UTC)
 * Oh, this was all going good, until that last unnecessary insult. Bourbon isn't Scotch and shouldn't be evaluated by the same criteria.  It's like saying rum isn't very good Scotch.  Have you tried Maker's Mark? --Trovatore (talk) 18:42, 20 September 2016 (UTC)
 * In fact, I've always said: "Rum isn't a very good Scotch."  General Ization  Talk   18:46, 20 September 2016 (UTC)
 * I've drunk in English pubs (at one point I lived over one for a month) and I think I see the issue. Most pubs in Great Britain have Jack Daniels, and that's all the Bourbon they have.  Maker's Mark is better, but Weller's Special Reserve is the standard by which Bourbon ought to be judged - a single malt sour mash which makes the mouth sing with pleasure.  Judging all Bourbon by Jack Daniels is almost exactly like judging all Scotch by an indifferently-made, mass-marketed blended Scotch whisky (like J&B).  I don't drink any blended whiskies, Scotch or Bourbon, they actually give me indigestion.  On the very rare occasions I drink at all, it's Weller's or the Glenlivet. loupgarous (talk) 18:57, 20 September 2016 (UTC)
 * Judging ANY bourbon by Jack Daniel's is a bad idea because Jack Daniel's isn't bourbon. It's Tennessee sour mash whiskey.  Jim Beam is a bourbon.  If one must have a mass market bourbon, the best is probably Maker's Mark, while Evan Williams makes a single-barrel bourbon which is pretty good.  -- Jayron 32 19:14, 20 September 2016 (UTC)
 * Bourbon and Tennessee whiskey are legally separate categories, but to my no doubt unsophisticated palate, they seem close enough that I'm comfortable comparing them head-to-head. --Trovatore (talk) 19:22, 20 September 2016 (UTC)
 * Note that (safe) tap water is not chlorinated in many parts of the world. It's certainly not where I currently live. --Stephan Schulz (talk) 00:40, 21 September 2016 (UTC)


 * Ah. Here is a link on how to savour a single malt. Enjoy.--Aspro (talk) 21:00, 20 September 2016 (UTC)


 * I was honestly expecting to see a fellow pouring the whiskey over his shoulder while savoring a glass of "sparkling wine". :) Wnt (talk) 02:28, 21 September 2016 (UTC)


 * How about eating one chocolate malted milk ball ? :-) StuRat (talk) 13:22, 21 September 2016 (UTC)


 * I agree with StuRat, but in Russia vodka IS water. μηδείς (talk) 00:05, 21 September 2016 (UTC)


 * A very good point μηδείς, it is indeed. Think I might just take a late summer holiday there and book into a hotel with an en-suite marbled bathroom that has hot & cold running Vodka.--Aspro (talk) 15:46, 23 September 2016 (UTC)

Feynman Lectures. Lecture 24
Explain me please formulas 24.3 and 24.4. Namely how did Feynman get that $$\langle (\tfrac{dx}{dt})^2 \rangle = \tfrac{1}{2} \omega^2x_0^2 $$?

We have: $$\langle x^2 \rangle = \tfrac{1}{2}x_0^2; $$ $$x= \hat{x}e^{i\omega t};$$ $$ dx/dt = i\omega\hat{x}e^{i\omega t} = i\omega x.$$

But $$\langle (i\omega x)^2 \rangle = \langle -\omega ^2 x^2 \rangle = -\omega ^2 \langle x^2 \rangle = -\omega ^2(\tfrac{1}{2}x_0^2).$$

So we get minus Feynman's result. Where is a mistake? — Preceding unsigned comment added by Username160611000000 (talk • contribs) 10:37, 20 September 2016 (UTC)


 * In this case, the velocity and the magnitude of the velocity are being used interchangeably, because, um... isn't it obvious? This is a little bit of sloppy physicist-math.  Thinking like a physicist means making conceptual leaps - why do you care about the average velocity?  (Hint: think back to your thermodynamics class).  And if you can answer that, you'll probably see that the direction of the average velocity doesn't matter - so you can drop the minus-sign.
 * Last week, I wrote extensively on the topic of why Feyman's lectures are not really great for new students of physics - you have to already know all the material - plus you have to also know boatloads of other physics - if you intend to appreciate any of Feynman's insights and see his connections.
 * If you want a mechanics text that pulls no punches, but is written with a little more sensitivity to proper pedagogical methods, I can't recommend highly enough Classical Dynamics, by Marion & Thornton. It is written at a level that will appeal to an intermediate or advanced-novice student of physics who has not yet been introduced to every single mathematical method or physical application of theoretical physics.  You will probably find no serious mathematical issues in that book - not even sloppy physicist math.  If you're a true pedant, this is the book for you - casually flipping through my copy, I randomly landed on three independent pages in three independent chapters, for which the foot-note by Jerry Marion analyzes some ancient calculation of Josiah Willard Gibbs using some new mathematical method to derive more decimal-places of precision.  This book is a real nail-biter, in terms of physics-textbook excitement and suspense.
 * If you'd rather read the Feynman lectures, just know this: the lectures are bad. We all know they're bad.  Other professors at Caltech know they're bad.  We can critique Feynman's work without dishonoring his legacy: he wasn't writing those course-notes for your audience.  From the introductory editorial, including a discussion of nearly a thousand points of errata in his lectures, is this commentary: "Feynman was too slick... he knew tricks and what approximations could be made, and had intuition based on experience and genius that a beginning student does not possess."
 * My point is this: we can hand-hold you as you stumble through every equation, each week, from now until forever... but at some point you must admit to yourself that you're just reading the wrong book - for you, at this point in your education-level - and you will benefit by switching to a better book. For now, at least.
 * Nimur (talk) 13:12, 20 September 2016 (UTC)
 * Feynman lectures are not so hard, and I like them. I have already finished physics course for technical profession (but I want to get in-depth study, besides other traditional university textbooks on physics are much worse). So I'll continue to read the Lectures and if I find some trouble I'll write in this topic. So your answer is that formulas are correct, but we can just omit the minus sign, isn't it? — Preceding unsigned comment added by Username160611000000 (talk • contribs) 15:41, 20 September 2016 (UTC)
 * It seems we must take real part of $$i\omega\hat{x}e^{i\omega t}$$ which must be equal:
 * $$i\omega (ix_0\sin(\omega t + \Delta)) = - \omega x_0 \sin(\omega t + \Delta)$$
 * So $$(\tfrac{dx}{dt})^2 = (- \omega x_0 \sin(\omega t + \Delta))^2$$. Now it's positive. Am I correct? — Preceding unsigned comment added by Username160611000000 (talk • contribs) 19:24, 20 September 2016 (UTC)
 * As the mathematicians say, the second-power exponentiation projected onto the complex plane is a twofold cover such that each nonzero number has exactly two roots.
 * As the physicists say: we're always gonna square it, so the sign doesn't matter.
 * Right?
 * Nimur (talk) 22:52, 20 September 2016 (UTC)
 * Right? -- No. Feynman warned against taking square of complex number:
 * if, for some reason, we want to use the square of $A$, it is not right to square the complex number and then take the real part, because the real part of the square of a complex number is not just the square of the real part
 * But it's just little weird for $$\tfrac{d}{dt}$$. — Preceding unsigned comment added by Username160611000000 (talk • contribs) 06:56, 21 September 2016 (UTC)


 * Hmpf. Feynman lectures are not so hard, and I like them. - well, the question you ask proves that if anything that particular one was too hard for you.
 * I have not looked at the lecture itself, but those equations have harmonic oscillator written all over them. The error stems from the fact that the formulas $$\langle x^2 \rangle = \tfrac{1}{2}x_0^2$$ and $$x= \hat{x}e^{i\omega t}$$ do not refer to the same x. The first one applies when x is the real, physical position (i.e. $$x= x_0 cos(\omega t)$$), the second one applies when x is the complex number "position" that is used as a trick to solve the differential equations (because it is easier to deal with exponentials than sines and cosines) (i.e. $$x= x_0 exp(i \omega t)$$). The first one is the real part of the second. As a consequence, your fourth line is incorrect, because $$\langle x^2 \rangle = 0$$ for the second definition.
 * If you want to take the RMS of Y in complex notation, it is not $$\langle Y^2 \rangle$$ but $$\langle Y^*Y\rangle$$, for no other reason than the complex notation is a calculation trick and $$Y^*Y = |Y|^2$$. Tigraan Click here to contact me 09:42, 21 September 2016 (UTC)
 * I don't know if this is justifiable to say or not, you tell me, but my feeling is that, in general, the worse the university, the better the teaching. This is because a poor university hires someone to focus on teaching, who can deal with poor students, while a world-class university hires someone to do research and indulge the students at odd moments; also because (as a separate rule) you are always worse off with a professor who writes his own textbook, since you have nothing to fall back on.  At the best campus you may end up being taught by a graduate student, which is great for his career but perhaps not as much for yours.  There are exceptions of course, most notably, quacks and lazy profs who sometimes exert peculiar power at a poor university, but they are not that common. Wnt (talk) 17:27, 21 September 2016 (UTC)
 * Strange, but in the next chapter "24–2Damped oscillations" Feynman says that we should not take an imaginary part to eliminate $$i$$. We should do that only when we have 2 solutions. — Preceding unsigned comment added by Username160611000000 (talk • contribs) 12:53, 22 September 2016 (UTC)
 * Here is a book that will explain how to use elementary complex analysis for damped harmonic oscillator: Alciatore and Histand's Mechatronics. How frequently do you need to be reminded that Feynman's lectures are not easily-understood by most new students - they were not well-understood even by students who held the highest academic qualifications, the highest test scores, and were immersed in an incredibly supportive, cooperative, collaborative peer-group?  This author's style is not suited for new learners.  His descriptions skip over important conceptual explanations because his unspoken expectation is that his readers have already completed many years of prior formal instruction.  His mathematical terminology is sloppy, his teaching-style baffled the most academically-gifted students in the United States, and his lecture notes are not used by most modern physics instructors at the university level, because they aren't a great introduction to the formal study of mathematical physics.  Modern instructors do not even follow the broad or general layout of his course!
 * You're really committed to keep struggling through these lectures, nitpicking at minutia in class-notes that have been stale for over a decade (after over a thousand points of error were corrected by other professors). What you are reading is a sort of abridged and cut-up version that has the glossy veneer of Feynman on its front cover, but the text and equations come from Kip Thorne, Rudolf Pfeiffer, and dozens of other authors who worked in a not particularly coherent or cooperative fashion to edit this monstrosity.  Wikipedia articles are written with better editorial control.
 * And guess what book those guys actually use when they run a class? (Kip Thorne runs the whole department, so you can be darned certain he has a stake in selecting the textbooks!)  Hmm... not the Feynman lectures... Hand and Finch, Analytical Mechanics, because Caltech students are quantitatively, literally geniuses - and if that book is too difficult for you to read, they recommend Marion and Thornton - just like I suggested earlier!
 * Here's a hint: you aren't learning the material properly because you're barely understanding Feynman's notes, and even if you finally succeed, it ain't gonna impress anybody. Non-physicists are not going to care which boring math books you read; and physicists are just going to ask why you didn't read a better book.  Want to impress a real physicist?  Run the homeworks in Jackson's textbook.
 * The fact that you repeatedly struggle against this workload is simply demonstrating that you are so completely unprepared for the study of advanced physics that you can't even orient yourself enough to locate the proper study-material. Get a better book.
 * Nimur (talk) 15:21, 22 September 2016 (UTC)

Degreasing steel
I have already asked this question a few days ago, but it hasn't been answered: Which solvents (of the ones currently available) work best for degreasing stainless steel after machining? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 11:13, 20 September 2016 (UTC)
 * "Best" is a really unqualified adjective - are you concerned with environmental or health side-effects? If not, a really strong acid wash will take everything off!  We have an article on pickling, which can be used to clean and to chemically treat the surface.  Nimur (talk) 13:32, 20 September 2016 (UTC)
 * As the part in question is stainless, then pickling is also going to involve passivating it afterwards. Which you can do easily with some citric acid, just from a homebrew shop. Andy Dingley (talk) 13:45, 20 September 2016 (UTC)
 * As you didn't like the earlier answers, I suspect your question paraphrases as "What can I buy cheaply on the high street?". In which case an aerosol of disc brake cleaner  (and not carburettor cleaner).  This is a spray-on solvent mix, chosen for its ability to drain off with the oils and then the residue to evaporate cleanly afterwards.  Other similar sprays in a car shop will leave some oily residues of their own, which you don't want. Andy Dingley (talk) 13:45, 20 September 2016 (UTC)


 * Xylene can also be used. Count Iblis (talk) 16:49, 20 September 2016 (UTC)


 * We used to use Toluene and a sonicator for removing fingerprints from the small metal lenses we used in mass spectrometers after removing them to clean the soot off of them. But xylenes are roughly the same.  -- Jayron 32 16:54, 20 September 2016 (UTC)


 * The best solvent for degreasing stainless steel after machining is a n-propyl bromide based solvent in a vapor degreasing machine. I recommend the SharperTEK US-WC, available at ultrasonics direct starting at USD $14,200.00. Check the tank size to see if your part fits, and I would strongly recommend the subzero secondary and filtration options. And no, you will not be happy if you just try the n-propyl bromide without the vapor degreasing machine. --Guy Macon (talk) 17:00, 20 September 2016 (UTC)


 * The answer really depends on what processes the stainless steel item is going to be subjected to next and how long it is going to be in storage before the next process. If it is a simple, effective degrease, there are many (one that hasn’t been mentioned but we used a lot is Trichloroethylene) but if it is going to   be bonded (with say) an epoxy resin then a acid pickle is called for. Even, domestic washing-up detergent works for many things.  We really need to know the context.--Aspro (talk) 18:57, 20 September 2016 (UTC)
 * What's wrong with plain old acetone or methylated spirits ? Vespine (talk) 22:37, 20 September 2016 (UTC)
 * Are they as effective as TCE? Because I have to degrease the part thoroughly -- I can't have cutting fluids or other organic impurities in my reaction mixture! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 09:10, 21 September 2016 (UTC)
 * Methylated spirit is bright purple and stinks of pyridine. It leaves both behind as a residue. Andy Dingley (talk) 12:40, 21 September 2016 (UTC)
 * Then methylated spirit (did you mean denatured alcohol?) is not an option for me. As for acetone, is it as effective as TCE?  For that matter, is toluene/xylene as effective as TCE in degreasing? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 22:01, 21 September 2016 (UTC)
 * Acetone is variable. It's somewhat hard to get (bomb precursor controls - as is isopropanol, for drug precursor controls). It can be quite awkward to get a clean grade of it - if it's in plastic gallon cans, then it won't be that clean.
 * Acetone is my go-to workshop degreaser, because I don't like working with trike outside of fume extraction. It would probably do you. But then so would most things, provided they evaporate cleanly, and you can get hold of them. Andy Dingley (talk) 12:48, 22 September 2016 (UTC)
 * [un-indent] The item will be used as part of a chemical reactor (hence cleanliness is very important), and it will not be bonded with any adhesive or coating. So all I'm looking for is an effective degreasing.  Thank you for all your answers -- I think I'll go with TCE (unless someone suggests an even better option), or if I can't get it, then my second choice will be brake cleaner. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 00:34, 21 September 2016 (UTC)
 * Trichlorethane ultrasonically agitated.--86.187.166.72 (talk) 01:46, 21 September 2016 (UTC)
 * Sorry I meant trichlorethylene--86.187.166.72 (talk) 01:49, 21 September 2016 (UTC)


 * Ah, now we know the context we know that this means laboratory standard ultra-clean. Which is a lot higher than most industrial engineering standards. However, industries that fabricate integrated circuits for instance  require extreme degreasing because even pico-grams of contaminants will lower production yields of viable IC's. A thing I learnt in tribologyis that such machined surfaces have a very thin solid–liquid interface. It is a sort of macromolecule emulsion of metal and oil. It is only in the order of about half a micron thick but can be seen clearly under an electron microscope. Not even TCE can remove this. So it depends on the  surface to volume ratio of you apparatus as to whether is this level of possible contamination is acceptable. So, to save you coming back here again – do what I would have done when I worked in R&D. Find out from the machinist the exact grade of SS and the supplier. Telephone their technical dept and explain your exacting requirement. Try to speak to a human rather than email. They may not know but may be able to suggest an metallurgical institution or some-such that can provide more reliable guidance than we can't reasonable be expected to do here without us (me) asking for a consultancy fee and you haven't even fully explained what your reactor is. Good luck with what must be some ultra secret experiment.--Aspro (talk) 16:42, 21 September 2016 (UTC)
 * Well, a half-micron layer solid-liquid interface probably won't hurt anything, so I'm sure such a high standard won't be necessary. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 22:05, 21 September 2016 (UTC)


 * Yes, my gut reaction is that you can probable get a way with just a thorough degrease but wanted to warn you about the worst case scenario - ending up with possibly bum results and wasted time. As you are probably working on a small budget then consider this. If your using a balloon type reactor, the advantage of SS is that if you scour it with just soapy water and get down to base metal, the SS forms a thin, transparent, and impervious oxide layer – problem solved. To understand more about what I mentioned about the 'contamination' layer that one just can't remove with TCE or most other degreasing solvents see out article section  Parts cleaning. Note: In this article is give a value of > 1 µm  for the 'deformed boundary layer' for the macromolecule emulsion of metal and oil but it is in the same order of magnitude for freshly machined parts, which may well not matter in your application. Use your own judgment here. Sometimes, simple solutions work just fine. A plastic kitchen scouring pad and 'washing soda' may be all you need – also very cheap, non carcinogenic and very often efficacious. P.S. Just out of curiosity: What are you synthesizing? --Aspro (talk) 17:39, 23 September 2016 (UTC)


 * Actually, I'm using a packed-bed tubular reactor, not a balloon one -- and this is the part which is supposed to hold the catalyst in place. As for what I'm synthesizing, it's artificial turquoise.  So, 2 more questions before you can mark it resolved: Out of the degreasers mentioned so far (toluene, xylenes, acetone, TCE, brake cleaner, bromopropane), which is the most effective?  And after degreasing with that solvent, would an acid pickle significantly improve the results?  (BTW, if pickling is desirable, I've decided to use phosphoric acid for that -- I'll be using it as a reagent anyway!) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 06:30, 24 September 2016 (UTC)


 * It is several decades ago since I personally did any degreasing (lab wise) and back then we normally used TCE because the vapour was non-explosive. However, frequently used acetone for getting rid of very tenacious grease, fats (like tallow lubricants) and oils on small components where good ventilation removed the explosive risk. So given the choice I would give 3 acetone flushes to degreases the reactor. You don't need to use much. Just on the 3rd flush pour a little on a watch glass or glass plate and let it evaporate. If you have any residue – it is not clean. Also do a control test on the fresh solvent  on a watch-glass (which has been cleaned) to gauge what is 'residue'. If you do see a stain left on the  watch glass and feel unsure. Add a few drops of concentrated sulphuric acid on the glass dribbling down the edge of the stain. One evaporated, observe under microscope. The sulphuric will have carbonised any oil which can be compared to the untreated stain. As for pickling, that (to be pedantic) depends a bit on the grade of SS being used, Whilst I should be able to guess, what grade you are probably using for this application, I can't remember what grades I used. However, my gut reaction is that you can probably forgo pickling. It is also not a one step process and as you confirmed,  pico-gram contamination should not be a problem here. Also, as you mention you are going to use phosphoric acid as the reagent. So, think pickling is probably going to be a waist of time. P.S. Is this an aniline dye? My local Pub was next to the site where the discoverer William Henry Perkin had his factory.--Aspro (talk) 20:27, 24 September 2016 (UTC)
 * Thanks! So acetone is even better than TCE for degreasing?  Then that's what I'll use.  And no, I didn't mean turquoise dye -- when I said "turquoise", I meant the stone. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 23:48, 24 September 2016 (UTC)


 * Unlike many of the people here, I know nothing of this topic. Still, I have the vague sense that nasty stuff like TCE is supposed to be phased out and replaced by cleaner solutions like supercritical CO2, and I'll give this source  in support of the idea, though I don't know what it means in real-life terms.  I'm thinking if people have to use expensive equipment and design something finicky, might as well challenge them to go green... Wnt (talk) 03:04, 22 September 2016 (UTC)