Wikipedia:Reference desk/Archives/Science/2017 March 23

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March 23

Two seemingly self-contradictory statements in the chemistry textbook

On the same page:

"We must be careful not to confuse the extent to which an electrolyte dissolves (its solubility) with whether it is strong or weak. For example, CH3COOH is extremely soluble in water but is a weak electrolyte."

"...you need only to remember that water-soluble ionic compounds are strong electrolytes."

Acetic acid is a water-soluble ionic compound, no? 69.22.242.15 (talk) 02:22, 23 March 2017 (UTC)

It is not ionic. It is a molecule which only dissociates in water to a small extent. Pure acetic acid (insofar as it can be isolated, which is tricky as hell) has a melting point of 16-17 degrees C. There is no ionic compound with such a low melting point. --Jayron32 03:07, 23 March 2017 (UTC)

Ethylammonium nitrate is an ionic compound, and its melting point is 12 °C. 1-Butyl-3-methylimidazolium tetrafluoroborate is about –80 °C. See ionic liquid:) DMacks (talk) 03:19, 23 March 2017 (UTC)

Yes, but obviously the OP isn't helped in their understanding of chemistry by bringing up oddities and exotic examples. At the level of misunderstanding they are having, bringing up such things, while true, is likely to confuse them more. Pedagogy involves more than espousing randomly true statements. If learning were that easy, the internet would already suffice and we'd all know everything already. Please don't confuse the OP further. At their level of understanding, they need to know that acetic acid is a molecular compound, and that ionic compounds can generally be expected to be high-melting solids. They can have fun with the oddities later in life. --Jayron32 03:44, 23 March 2017 (UTC)

If you must bring up such things, I would imagine that you should also qualify it with some sort of rationalisation that is understandable at that level, such as "in this case, the cation and anion are very asymmetrical and don't pack well; most cases are not like that". Double sharp (talk) 03:52, 23 March 2017 (UTC)

Is you them or is you me? Or is you someone else? --Jayron32 03:54, 23 March 2017 (UTC)

DMacks. Sorry for the lack of clarity there. Double sharp (talk) 03:59, 23 March 2017 (UTC)

It's certainly important to teach generalities early, but I think it's also important not to teach them as absolute rules. DS is right, in that I usually use words like "generally" and "in most cases" when stating these patterns in this context. It helps minimize the need to lie to children as blatantly about patterns that even at an introductory level become just narrowly scoped parts of larger patterns. Even intro-chem textbooks talk about symmetry and packing to discuss trends of physical properties not strictly boolean, and that ionic vs covalent is a continuum. Otherwise my students have learned a strict fact like "ionic substances are soluble in water" and then a few weeks later it's contradicted by "silver halides are not soluble in water". I'm not sure if they eventually become numbed by a pile of loose facts "for this exam" and then brain-purge for next time or just don't care to integrate their knowlege, but either way, they seem to do better in later classes if at least there was a seed that things are not "either/or" and that there is more going on than we can teach right away. DMacks (talk) 15:04, 23 March 2017 (UTC)

To build on what others have said, acetic acid's solubility in water isn't deriving from a dissociation into ions. In a 0.1M solution of acetic acid, only about 1.3% of the acid molecules will have dissociated into hydronium and acetate ions, the rest will still be CH3COOH. Despite that fact that 98.7% of the molecules didn't dissociate, ~100% of the molecules are dissolved in water in that solution, so there must be some other mechanism for the solubility than just ionic dissociation. What might that be? Well, the carboxylic acid end of the molecule has a great proton donor and proton acceptor for hydrogen bonding, which is great for solubility in water. This is one of the reasons why being strongly soluble may not have anything to do with being a strong electrolyte; there are other solubility mechanisms. --OuroborosCobra (talk) 12:23, 23 March 2017 (UTC)

Torque, Moment of inertia

I'm trying to get the rigid body science. It's even tougher for me than regular classical mechanics - and you could guess how long I had to work on that.

As I understand, in classical mechanics the only things we get "a priori" are velocity and acceleration. Other stuff, force for example, we tend to measure experimentally by using springs etc, and then get mass. That's how we derive ${\vec {F}}=m{\vec {a}}$ .

What I'm trying to find is if similar experiments were done in rigid body science. Angular acceleration I can understand "a priori", but what about the others? Had people measured moment of inertia by connecting a spring to a lever, applying constants forces on it, defining them as torque and measuring the angular accelerations?

Is That how we derive ${\vec {\tau }}=I{\vec {\alpha }}$ ? יהודה שמחה ולדמן (talk) 09:29, 23 March 2017 (UTC)

It wasn't really done experimentally for force, and once you have defined F=m.a then T=omega_dot.I can be worked out analytically. Greglocock (talk) 09:52, 23 March 2017 (UTC)

But am I in the right direction? There are scientific things that at first were actually thought experiments, like understanding inertia by minimizing friction - and this was confirmed in physical experiments and also in outer space.

Is the torque—spring experiment above doable? יהודה שמחה ולדמן (talk) 10:14, 23 March 2017 (UTC)

Torsion spring might be of interest to you. Otherwise, your "a priori" vs. "experimentally" distinction (BTW, the technical term, coined by Kant, is the a priori and a posteriori distinction) seems fairly muddled. Position, velocity, etc. are no more pure platonic ideas than force, charge, mass. You need experimental checks to know a speed/acceleration. Tigraan^{Click here to contact me} 12:12, 23 March 2017 (UTC)

• If they had looked at moments of inertia, it would almost certainly be from trying to invent new sorts of escapement for clocks and timepieces. In particular, look at verge. It was understood how to adjust the foliot of these by moving two masses in and out, adjusting the moment of inertia. Andy Dingley (talk) 13:10, 23 March 2017 (UTC)

How did people derive the definition of torque as $\tau =r\cdot F\cdot \sin(\theta )$ ? How did they understand that this product is all they need? Yes, I know about the lever — is this how we know that the force applied on the lever is $F_{\perp }\propto {\frac {1}{r}}$ ? יהודה שמחה ולדמן (talk) 13:36, 23 March 2017 (UTC)

Torque was first understood from the static case, for levers in balance, long before it was considered for continuous rotation. Also the idea of $\sin(\theta )$ only really comes in once you move away from gravity on a horizontal beam.

What's interesting though (and I'd never considered before) is that the moment of inertia of a foliot was being understood enough to be practically used in the 14th century, three hundred years before Newton is considering linear inertia. I guess that the absence of air resistance and its effect as a confusing factor (see impetus) would have helped. Andy Dingley (talk) 13:49, 23 March 2017 (UTC)

Newton's great innovation was not the discovery of kinematics: his contribution was a specific mathematical method (the calculus of derivatives) that accurately modeled elementary kinematics as second-order linear equations. If you study the history of physics, you'll find plenty of examples of earlier great thinkers who were nearly correct. The simplified narrative suggests that everyone used Aristotelian physics until one day the proverbial apple fell... but that's a bit of an abridged version of the history of science! As the first example that comes to my mind - Kepler's equation of planetary motion invokes the inertia of a revolving body quantitatively - it's just less generalized than Newton's models for kinematics and gravity. But if we're holding physicists to the arbitrary standard that their equations need to be even more generalized, Newton's model falls short as well... Nimur (talk) 14:13, 23 March 2017 (UTC)

How could you not quote "standing on the shoulders of giants" when the example involves Newton not discovering mechanics from scratch... Tigraan^{Click here to contact me} 14:39, 23 March 2017 (UTC)

Because Newton was a git. Andy Dingley (talk) 16:22, 23 March 2017 (UTC)

Why wasn't the torque defined as a scalar, like work and energy? If work as a scalar can be positive\negative, so can torque etc. יהודה שמחה ולדמן (talk) 22:37, 23 March 2017 (UTC)

Obviously torque has a direction too. Andy Dingley (talk) 23:14, 23 March 2017 (UTC)

Why? What is the point of using pseudovectors? When we talk about work, we could refer to it being directional by $W=|{\vec {F}}|\cdot |{\vec {x}}|\cdot \cos(\theta )$ . And we still call that a scalar.

Maybe torque can be defined to be a circular vector. יהודה שמחה ולדמן (talk) 23:56, 23 March 2017 (UTC)

Read some of Feynman, such as his explanation of gyroscopic precession. As usual, he's wonderfully clear on it - because he picks the right frame of reference: one that relies on the representation of torque as a vector like this. Andy Dingley (talk) 00:13, 24 March 2017 (UTC)

Sorry, I had my own Eureka! moment about the Gyroscope a few months ago after many years reading the same damn useless "crap" (pardon me) of angular momentum and torque.

At the end, I didn't need to understand any of these — it finally hit me when I understood that the force applied perpendicular to a rotating wheel's plane behaved just like the centripetal force in a circular motion.

But if you could show me pages or videos of Feynman I might learn something more. יהודה שמחה ולדמן (talk) 00:40, 24 March 2017 (UTC)

Web search, there's lots out there. His very short book on a graphical demonstration of Newtonian orbital mechanics, rather than calculus, is very good demonstration of the sort of "other ways of looking at things" approach that he was so good at.

The 'Lectures' are here: http://www.feynmanlectures.caltech.edu/

Andy Dingley (talk) 01:42, 24 March 2017 (UTC)

Torque only became a focus after Strength of materials became important. Today its mainly used in the field of construction and design. Its main essence is not well described as kinematics/motion but much better as Elasticity (physics). --Kharon (talk) 02:47, 25 March 2017 (UTC)

How accurate is this table? (March 17)

Re this exchange:

Even more awesome is the Zoroastrian calendar:

365, 365, 365, 365.

Repeat forever.

Repeats four times sooner than the Julian, 400 times sooner than the Gregorian and 900 times sooner than the Revised Julian. 86.128.233.163 (talk) 22:55, 19 March 2017 (UTC)

And eventually you get to "June in January". ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:02, 20 March 2017 (UTC)

But we already have the opposite seasons in the Southern Hemisphere, so avoiding our seasons slowly drifting isn't necessarily worth all the trouble of leap years (although admittedly they aren't as much trouble as Daylight Savings Time, requiring 2 clock adjustments per year). StuRat (talk) 16:12, 23 March 2017 (UTC)

Nobody has mentioned the Revised Gregorian calendar, which is guaranteed to be 100% accurate forever. See Talk:Tropical year/Archive 3#Source updated and read the seven paragraphs above the section header. This really shouldn't be a redlink - there's more than enough information there to start an article. 86.128.233.163 (talk) 23:24, 20 March 2017 (UTC)

I've created an article at Draft:Revised Gregorian calendar. If someone can review it and transfer it to mainspace that would be appreciated. 86.128.233.163 (talk) 12:12, 21 March 2017 (UTC)

There are some more fictional calendars not mentioned by Sagittarian Milky Way, described at [1] and [2]. Are there any others in books/games/TV series etc.? 86.170.156.155 (talk) 15:41, 23 March 2017 (UTC)

I really don't see the point of the so-called Revised Gregorian calendar since there are so many variables that cannot be predicted this far in advance. The existing Gregorian calendar will suffice for the next thousand years, by which time we might be able to make more accurate predictions of future day (and year) lengths. We already have Sir John Herschel's suggested revision in the article Gregorian calendar so we could mention any other well-referenced suggested improvements there. Dbfirs 17:51, 23 March 2017 (UTC)

Then you probably don't see the point of the 4-4-5 calendar, Armelin's calendar, Discordian calendar, Dreamspell, Hanke-Henry Permanent Calendar, International Fixed Calendar, Invariable calendar, Middle-earth calendar, Pax calendar, Positivist calendar, Stardate, Symmetry454, Tranquility calendar and the World calendar, all of which have articles.

I agree the Gregorian calendar article needs updating, but the problem is it's protected. The needed corrections would appear to be as follows:

• Second paragraph: replace the second sentence with

The motivation for the reform was to stop the drift of the calendar with respect to the equinoxes and solstices. The Church became involved because Easter was traditionally observed in the third week of the lunar month next after the spring equinox but the tables in use were causing it to drift away from both the equinox and the period between full moon and last quarter.

• "Gregorian reform" section: replace "Because the spring equinox was tied to the date of Easter" with "Because Easter was tied to the date of the spring equinox."

• In the "Accuracy" section delete the second paragraph. At the end of the third paragraph add:

Historical proposals for improving the Gregorian calendar have not taken account of this fact. Following the successful introduction of the leap second regime a modification has been proposed which will ensure it remains 100 per cent accurate forever.[Link to article]

carbohydrates

When it comes to dieting carbohydrates are the devil.

If a person only eats 800 calories of potatoes that are mostly carbohydrates, will they lose weight? Will it be slower than eating 800 calories of non-carbohydrates? — Preceding unsigned comment added by 168.10.85.15 (talk) 19:22, 23 March 2017 (UTC)

Before we get into this, define what you mean by dieting. Do you mean it in the true sense of 'diet' or the self-imposed restriction of food? --Aspro (talk) 19:34, 23 March 2017 (UTC)

Carbohydrates can also be good - see Why are Carbohydrates Important for Athletes?. Alansplodge (talk) 19:42, 23 March 2017 (UTC)

If you eat any kind of macronutrient more than what your body can metabolize, then you will gain weight in fat. See this image for details. I would just eat a hearty meal before some kind of vigorous physical activity. 140.254.70.33 (talk) 19:46, 23 March 2017 (UTC)

Whole grain carbs are good, the human body has evolved to use such carbs for almost all of its energy needs. Fat intake should be limited to less than about 15% of the total energy intake, the bulk of this should come from fats that are present in whole foods, like walnuts, chia seeds etc., not from cooking oil, even olive oil will damage the cardiovascular system (studies that show that extra virgin olive oil is healthy are flawed because they compare using this healthier oil to saturated fats, that's like comparing smoking cigars to light cigarettes with a filter and concluding that smoking such cigarettes is good for lung health) it also causes type 2 diabetes. If you get most of your energy from carbs, you'll find it a lot easier to exercise hard, you may then be able to lose weight while retaining your fitness level.

I actually lost weight while increasing my energy intake to close to 4000 Kcal per day several years ago (I used to weight about 63 kg, I now weight about 55 kg). This is because I eat a very low fat diet and I exercise hard every day (one hour of fast running, this burns more than 1000 Kcal). So, a low fat diet allows you to eat as much as you like, it enables your own body to regulate the metabolic rate to get to its ideal weight. Count Iblis (talk) 20:08, 23 March 2017 (UTC)

Since this is the Reference Desk, can you provide references for any of your claims? --47.138.161.183 (talk) 00:29, 24 March 2017 (UTC)

I posted a more detail reply with more refs here. Count Iblis (talk) 02:06, 24 March 2017 (UTC)

Eating 800 food calories a day without medical supervision is a good way to kill yourself, doubly so if it's just one food, which will inevitably lead to micronutrient deficiencies. Such dramatically low-calorie diets are sometimes used, but only under supervision. Besides that, there appears not to be scientific consensus on whether a low-carbohydrate diet or high-carbohydrate diet is best for weight loss. It's quite possible the answer varies among people. "Carbohydrates are the devil" does not seem to be a widely-held belief in the scientific community. --47.138.161.183 (talk) 00:29, 24 March 2017 (UTC)

OP, your question is not clear. The first question only has one dependent clause, and the main clause is a question. Such a question is impossible to answer, because not enough details are given. Are the 800 kcal of potatoes the only food the person is eating, or are the 800 kcal of potatoes part of a wholesome diet? What kind of potatoes are they? Obviously, potatoes must be cooked, or they will poison the human consumer! What is the person's activity level? How much energy does that person need to consume to stay alive? Your second question is equally unclear. What do you mean by "slow"? Are you referring to the rate at which each macronutrient is consumed in isolation? How would we know? 50.4.236.254 (talk) 01:46, 24 March 2017 (UTC)

Glycemic index may be of interest. PaleoNeonate (talk) 02:49, 24 March 2017 (UTC)

Let's have a look at the actual science. The fact is that, regardless of what people believe, a high-carbohydrate diet is incompatible with our Paleolithic genome. It causes epidemics of obesity, hypertension, diabetes, and atherosclerotic cardiovascular disease. Out diet should be consistent with our hunter-gatherer genetic legacy. [3] --IEditEncyclopedia (talk) 05:38, 25 March 2017 (UTC)

The Case Against Sugar is a book which gives a detained outline of the misguided dietary beliefs. --IEditEncyclopedia (talk) 05:38, 25 March 2017 (UTC)

Sugar industry paid scientists to blame fat [4][5] --IEditEncyclopedia (talk) 11:18, 25 March 2017 (UTC)

One more reference [6]. --IEditEncyclopedia (talk) 11:26, 25 March 2017 (UTC)

"Carbohydrate" and "sugar" are not equivalent. The first review you linked says people should eat lots of fruits and vegetables, which are mostly carbohydrates. I doubt you will find any authority that disagrees that you should minimize added sugar intake. This is not the same thing as "don't eat carbohydrates". --47.138.161.183 (talk) 23:23, 25 March 2017 (UTC)

Running like Forrest Gump

If a person begins running to the next-door neighbor on the first day, stops, turns back, runs to the end of the street on the second day, stops, turns back, then will this person get stronger and faster at running by the end of the year? What kind of animal will the person be able to outrun? Will the person be able to outrun a horse? If one cannot outrun the horse by speed, then can one outrun the horse by endurance or passing of time? 140.254.70.33 (talk) 20:21, 23 March 2017 (UTC)

Persistence hunting is a thing - people in very good aerobic condition can outrun a horse, in the long run. Now as to whether this movie Forrest Gump can be interpreted as a conceivable method of endurance training, that's another question. Wnt (talk) 20:30, 23 March 2017 (UTC)

The article endurance training has a little section about the negative effects of long-term, excessive endurance training. I wonder how long that may be. 140.254.70.33 (talk) 20:40, 23 March 2017 (UTC)

• My father once told me that you could always catch a rabbit if you kept chasing it in the open until it gave up. I was in an oak wood on hills with an understory of mountain laurel, and saw a rabbit. It kept dodging from shrub to shrub, but could not escape my sight. After about 5 minutes it stopped running and I caught it by the nape of the neck. I brought it home, wrapped in my jacket to calm it, and showed my dad, then let it go free. (At the time that wood abutted our back yard.) μηδείς (talk) 22:59, 23 March 2017 (UTC)

Sounds to me like the story of Milo of Croton who got strong by lifting up a calf every day while it grew to be a bull. Dmcq (talk) 23:26, 23 March 2017 (UTC)

There's a famous story about Louis Leakey outrunning game animals like antelopes, think I read about it in an ancient National Geographic. A quick google finds Carl Sagan commenting that he liked to do it naked and this book co-edited by Leakey's son. Should probably be in his or the persistence hunting article.John Z (talk) 01:06, 24 March 2017 (UTC)

The annual Man versus Horse Marathon is generally won by a horse, but occasionally by a person. MChesterMC (talk) 09:03, 24 March 2017 (UTC)

Genghis Khan's troops moved 200 miles a day. Let's see a man do that. The 24 hour treadmill record is 260 kilometers. If the terrain's just the right amount of damp then I can see how the horse might lose occasionally (enough to make horseshoes sink but not sneakers) Sagittarian Milky Way (talk) 18:22, 26 March 2017 (UTC)

Subsistence farming

If a subsistence farmer grows food in a temperate, coniferous region, and the season is marked by extreme weathers (long winters and dry, scorching summers), then can one depend on the pine nuts of the conifers for survival, until nature slowly consumes the person's life due to nutritional deficiencies? Can plants live off of indoor lighting? Does the lightbulb type matter? Do plants have an ideal comfy temperature? Will talking to plants and singing to plants bring more yield? 50.4.236.254 (talk) 22:29, 23 March 2017 (UTC)

Do you mean vampiric pine nuts, or zombiacal pine nuts? μηδείς (talk) 23:01, 23 March 2017 (UTC)

A diet of pure pine nuts would be fairly rich, but missing vitamin A and be very low in vitamin C, so your hypothetical person would likely be facing scurvy, blindness, and a weakened immune system. This would greatly increase his chance of dying from illness or injury, but probably won't kill directly. For indoor plant growth, you might want to read grow light. Your typical house lighting is not very bright compared to the sun, so specialized lights are used instead. And yes, plants do have ideal temperature ranges, outside of which they don't grow as well, and far outside of which they don't grow at all. For your final question, I have no idea where you got that idea. Someguy1221 (talk) 23:05, 23 March 2017 (UTC)

If that's true, the cure for one problem is not far away: pine needle tea has famously been used as a cure for scurvy (Jacques Cartier being an example). [7] I see our article also says it's a source of vitamin A (which I hadn't been expecting). ERmm -- an issue I see with the not very confidence inspiring source I saw the claim in is that the Cartier article says Aneda wasn't pine needles, but a different evergreen tree. Wnt (talk) 00:21, 24 March 2017 (UTC)

Adding dandelion greens to the diet can prevent vitamin A deficiency. With a diet of pine nuts, pine needles, and dandelion greens, one nutrient that will be lacking is vitamin B12, but that can last a long time. I wonder if you can get vitamin B12 from the occasional mealworm. 50.4.236.254 (talk) 00:33, 24 March 2017 (UTC)

The gents at Mythbusters examined the singing to plants item and concluded that it was plausible, as the plants not spoken to did the most poorly among the test subjects. More interesting bits here at the BBC. Matt Deres (talk) 01:30, 24 March 2017 (UTC)

Plants you sing to might be getting more of your CO2 and thus doing better than the ones that don't. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:47, 24 March 2017 (UTC)

Well, maybe. But there seems to be evidence (See mythbusters link above, and many many others) that recordings of voice or music seem to aid plant growth through some unknown mechanism. ApLundell (talk) 14:26, 24 March 2017 (UTC)

Then the question becomes, what kind of music? Like if you played Florence Jenkins, would it cause cell membranes to rupture? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:41, 24 March 2017 (UTC)

That's not farming, that's gathering.
Sleigh (talk) 05:42, 24 March 2017 (UTC)

Maybe unless you planted them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:41, 24 March 2017 (UTC)

You might be surprised at how fast you run out of easy food. The per-person land requirements for hunter-gatherers are surprisingly large[8] even in good conditions, which presumably you're not in if you're thinking about exclusively eating pine nuts.

There's a reason most hunter-gatherers were nomadic. They had to keep moving to fresh land. ApLundell (talk) 14:33, 24 March 2017 (UTC)