Showing posts with label chemistry. Show all posts
Showing posts with label chemistry. Show all posts

Sunday, August 30, 2020

Fun with geekage for August 2020

Technical fields aren't like other fields.

But there's a disturbing trend in education (brought in from non-technical fields) and in the reporting of technical fields (done by people with minimal-to-none interest in the technical matters, and yes, that includes those with putative training in the technical fields whose work is now in the infotainment business) of moving away from technical knowledge even in those technical fields:



The answers to the type 2 questions, real technical questions, from the top:

First question: The combustion equation would be

CH$_4$ + 2 O$_2$ $\rightarrow$ CO$_2$ + 2 H$_2$O

but it's unnecessary; since each methane molecule will yield a CO$_2$ molecule we can simply calculate the ratio of the masses: m(CO$_2$)/m(CH$_4$) = (12+2*16)/(12+4) = 44/16 = 2.75, so a metric ton of methane will yield 2.75 metric tons of carbon dioxide.

Second question: The density of air at one standard atmosphere and 19°C is 1.225 kg/m$^3$, so a 25 m$^3$ room contains 30.625 kg of air. A 1000 W heating element releases 3.6 MJ of energy in one hour. The increase in temperature is therefore (3600 kJ)/(30.625 kg x 0.72 kJ/(kg °K)) = 163 °K, for a final temperature of 182°C.

(Assuming no losses to the outside and using a constant value for the isochoric specific heat for air throughout the temperature range 0-200°C to avoid computing an integral, a reasonable approximation given it varies between 0.70 and 0.74 in that range.)

Third question: At resonance frequency  $wL = 1/(wC)$ so $w^2 = 1/(LC)$, $w = 57,735$ radian/s or f = 9189 Hz. At that frequency the capacitor and inductor cancel each other out (impedance is zero and power factor is 1), so peak power is $5^2/100 = 250$ mW and RMS power is $250/\sqrt{2}$ = 177 mW.

These are not "gotcha" questions: I learned to solve the second in 11th grade; I learned electronics and chemistry by myself as a kid, but the material to solve the first was taught in 9th grade and the third in 11th grade, for students taking a chemical or electronics track in high-school (9th-12th grades). All of this was assumed known for incoming EECS students in the early 80s in Portugal.



Tempora mutantur, nos et mutamur in illis



From a video of an event in 2016. Most of the weight loss happened in the last 12 months as the result of intermittent fasting and a focus on high-protein, low-energy foods.



Another growth industry in San Francisco






When authors want to be science-y, but don't want to do the science…



From a mil-fic book that we'll keep unnamed.

At 18 km altitude, the gravity is 99.4% of the gravity at sea level ($6378^2/(6378+18)^2$), so Colonel Z would need super-human perception to be able to separate that $0.006 g$ from the turbulence and change in aircraft acceleration due to atmospheric changes.

(The story itself makes little sense, it's a remake semi-update of Tom Clancy's "Red Storm Rising," but with several errors of logic and biased by the need to make Russians super-hyper-badissimo-evil idiots.)



Chocolate milk, the high Protein-to-Energy version





Geeky linkage


(Because work has gotten into the way of blogging, social media, and other things. Book is 90-95% complete.)


Claustrophobia-inducing video by Smarter Every Day crawling inside a torpedo tube in a submarine while it's under the Arctic Ice Cap.



Nasa makes Einstein-Bose condensates aboard the ISS.



Scott Manley showcases the ideal villain lair, complete with a rocket to take the villain to a secret space base. Or a smart way to use the oceans to position a launch pad precisely where one wants (on the Equator, for example, to minimize the energy necessary to change the inclination of the orbit for a GEO satellite).


Because a real geek needs some sci- fi in their life.

Saturday, October 19, 2019

Fun with numbers for October 19, 2019

(Yes, yet another tweet-recycling post. When I unfroze the blog the reason was that I was tweetstorming blog posts, so now I'm refactoring ideas from twitter, with — one hopes — improvements.)


Negative [effect on carbon capture]


Via Thunderf00t, who manages to find the occasional bad product gem amongst the many non-bad products he "busts!" by not understanding engineering (or pretending not to), we learn of Negative, a captured-carbon bracelet.*


Enter basic math, illusion exits stage left.

Say Bay Area Bob commutes from San Francisco to Palo Alto (100 mi roundtrip), 5 days/week (500 mi/week) on a 25 MPG car; that's 20 gallons of gasoline burned per week.

Gasoline is a complicated mixture, but let's simplify by treating it as 100% iso-octane (2-2-4-trimethylpentane), C8H18; let's simplify further by assuming perfect stoichiometric burn, so 1 kg of iso-octane generates 3.1 kg of CO2.

Gasoline has a density of 0.7489 kg/l or 2.835 kg/gal; this generates 8.75 kg(CO2)/gal(gasoline), so a weekly commute creates 175 kg of CO2.

Say that bracelet is 25 g of pure carbon. That corresponds to 1/1910th of the carbon in a single one-week commute for Bob. (175 kg of CO2 contain 47.7 kg of carbon.)

I'm sure every Bay Area Bob will be sporting one of these Negative bracelets.

What about other hydrocarbons? Given the small mass differences between alkanes, alkenes, and alkynes, we can take a look at the CO2 per kg(hydrocarbon) with a simple calculation:


Note that the maximum CO2 per kg is when the fuel is pure carbon, at 3.67 kg (CO2)per kg (C). So the approximation above (for Bob) isn't too bad.

-- -- -- --
*Another annoying habit of TF is to gloss over the math, usually to the point where his approximations accumulate into nonsensical territory and occasionally even significant technical errors.



Much ado about Ruby Rose's petite physique.


One of the criticisms of Batwoman that might have some merit is that a petite person like Ruby Rose is not credible as an action hero; that a punch from her not-very-muscular arms would not knock out a 250-lb henchman. To which I reply: as opposed to not-exactly-Schwarzenegger Ben Affleck or Christian Bale throwing said 250-lb henchman clear across a parking lot with a single arm? Pah!

This scene, where Batwoman gets shot by a pistol led to some comments on how she would have been thrown in the air, backwards. Because "momentum," say the people who love science but can't do math (or actually bother to learn the science they profess to "love").


The batsuit is bulletproof (has been all along); assuming that it completely distributes the pressure of the impact over the 1/4 square meter of her torso front, there's little effect, as can be seen from the delta speed for the system:

Say Batwoman (Ruby Rose + suit) = 50 kg, bullet (looks like a .45 ACP) is 15g at a muzzle velocity of 250 m/s, so conservation of momentum shows the after-impact speed to be (0.015 * 250)/(50.015) = 0.075 m/s or less than 0.3 km/h, a very small change in velocity to Batwoman that can be easily countered by a braced position.

An alternative way to see the limited effect:

Consider that the bullet is stopped by the suit and loses all its velocity while pushing back 5cm. Assuming constant force, it takes t = 2 s/v = 2 (0.05)/250 = 0.0004 s to stop, for an acceleration of a = v/t = 625000 m/s^2 and a force F = 9375 Newton (almost 975 kgf, but just for 400 microseconds), which spread over 1/4 square meter of her torso is a pressure of 0.38 kgf/cm^2, which is the pressure of a light finger poke (again, for 400 microseconds).

And a tip of the hat to old-style scifi machinery (no labels on buttons or indicators):




Flexagons. Not the hexa ones.





A late entry: more battery nonsense.




Via eevblog, we learn of yet another life-changing momentous innovation by a lone inventor squashed by the Big Industry Conformance Bureau:


I didn't read the article, but from the photo we can see that the '1500-mile battery' volume is about 2 liters, so a little bit of arithmetic ensued:
1500 miles w/ better-than-current vehicles (say 200 Wh/mi): 300 kWh (1.08 GJ)
Volume of battery, from article photo let's say 2 l) so energy density = 504 MJ/l
Current Li-Ion battery energy density ~2.5 MJ/l to  5 MJ/l (experimental)
Home inventor creates something something 100 to 200 times more dense than
current technology (and about 15 times more energy-dense than gasoline)?!

Nope, not credible.

(Note: apparently the photo is deceptive, and the actual "1500 mile battery" is larger, only 9 times more energy-dense than current technology. Which is as non-credible, especially the idea that car manufacturers would be able to stop small electronics makers from adopting a technology that would allow for smaller batteries in laptops and longer times between charge in cell phones. Added Oct 21.)

Wednesday, November 16, 2016

Why I write careful posts on nonsensical topics

Basically, because I'm not allowed to write or talk about work-related matters.

So I apply my considerable intelligence, broad knowledge, and unbeatable modesty to things like the differences between powerlifting and bodybuilding (and the superiority of the former over the latter), using the standard B-school two-by-two matrix format (click for bigger):



I also take to task people who think that knowledge is superfluous as long as their intentions are good (or at least consistent the the current "virtuous" narrative). For example, I did congratulate TIME for not using a photo of cooling towers for this article (unlike almost everyone else who uses images of cooling towers' steam to write about pollution),


but I do have to point out that most of what's seen coming out of those stacks is also steam. First, the color and the shape of the expansion give that away, but even if they didn't, gaseous $\mathrm{CO}_{2}$ is transparent, as is water vapor. (Steam is liquid water suspended in water vapor.) And soot and other common pollutants have distinctive colors; that white means water.

If you're surprised that combustion would generate water vapor, which condenses when it expands at the top of the stack, remember that hydrocarbon-based fuel combustion is mostly
$ \mathrm{C}_{n}\mathrm{H}_{m}  + (n+ m/4)\,\,\, \mathrm{O}_{2}\rightarrow n\,\,\, \mathrm{CO}_{2}  + m/2 \,\,\, \mathrm{H}_{2}\mathrm{O},$

and most of the rest (nitrous and sulfurous compounds, metals, soot and ash, the souls of the damned) are removed from the smoke before it's allowed to leave through the stacks (because of laws against pollution):



Sometimes I do take the nonsense dial to 11 --- but all the calculations are correct.

About a year ago, when I temporarily changed the name of this blog to Project 2016, the idea was to track non-work related learning, which is one of my hobbies; but time constraints made me choose between actually learning stuff and blogging about it, and I chose the learning.

So, expect some more carefully thought-out nonsense. Careful thinking is another one of my hobbies, so I practice it even on nonsensical topics. I have very strange hobbies: another one is moving heavy objects for no immediate purpose, like this gentleman



Live long and prosper -- JCS

Sunday, February 8, 2015

Science popularization has an identity problem

Some influential science popularizers are doing a disservice to public understanding of science and possibly even to science education.

Yes, it's a strong statement. Alas, it's a demonstrable one.

With the caveats that I enjoy the Mythbusters show, especially the recent series with their back-to-origins style, and that this post is not specifically about them, the recent episode about The A-Team presented an almost-perfect example of the problem.

"Stoichiometry."

Midway through the episode Adam uses this word. It's an expensive way of saying "mass balancing of chemical equations" (not how it was described in the show). And then, well... and then Jamie proceeded to not use stoichiometry.

To be concrete: they were exploding propane. Jamie tried mixing it with pure oxygen and got a big explosion. Then they mention stoichiometry. At this point, what they should have done was to introduce some basic chemistry.

The propane molecule has 3 carbon and 8 hydrogen atoms, $\mathrm{C}_{3} \mathrm{H}_{8}$. It burns with molecular oxygen, $\mathrm{O}_{2}$, yielding carbon dioxide, $\mathrm{C} \mathrm{O}_{2}$, and water vapor, $\mathrm{H}_{2} \mathrm{O}$.

Chemists represent reactions with equations, like this:

$\mathrm{C}_{3} \mathrm{H}_{8} + \mathrm{O}_{2} \rightarrow \mathrm{C} \mathrm{O}_{2} + \mathrm{H}_{2} \mathrm{O}$

This equation is unbalanced: for example, there are three carbons on the left-hand side, but only one on the right-hand side. By changing the proportions of reagents, we can get both sides to match:

$\mathrm{C}_{3} \mathrm{H}_{8} + \mathbf{5} \, \mathrm{O}_{2} \rightarrow \mathbf{3} \, \mathrm{C} \mathrm{O}_{2} + \mathbf{4} \, \mathrm{H}_{2} \mathrm{O}$

Once we have this balance, we can determine that we need 160 grams of oxygen for each 44 grams of propane. For this we need to look up the atomic masses (to compute molar masses) of carbon (12 g/mol), hydrogen (1 g/mol) and oxygen (16 g/mol). (*)

Back on the Mythbusters, after mentioning stoichiometry, Jamie starts trying out different proportions of propane to oxygen. If he had actually used stoichiometry he'd already have the proportions calculated, as I did above, about four times more oxygen than propane by mass; no need to experiment with different proportions.

(Yes, there'a a lot of experimentation in engineering, but no engineer ignores the basic scientific foundations of her field. Chemical engineers don't figure out mass balances by trial and error; they use trial and error after exhausting the established science.)

This illustrates a major problem in the way science is being popularized: to a segment of the educated and interested audience, science is an identity product. Like a Prada bag or a sports franchise logo on a t-shirt, they see science as something that can signal membership in a desired group and exclusion from undesirable groups.

Hence the word "stoichiometry" inserted in a show that doesn't actually use stoichiometry.

"Stoichiometry" here is, like the sports franchise logo, purely a symbol. The audience learns the word, in the sense that they can repeat it, but not the concept, let alone the principles and the tools of stoichiometry. The audience gains a way to signal that they "like" science, but no actual knowledge. Like a sedentary person who wears "team colors" to watch televised games.

Some successful science popularizers pander to this "like, not learn, science" audience, instead of trying to use that audience's interest in science to educate them.

So what, most people will ask. It's the market working: you give the audience what they want. And there's no question that selling science as identity is good business. Shows like House MD, Bones, The Big Bang Theory, all take advantage of this trend. Gift shops at science museums cater to the identity much more than the education: a look at their sales typically finds much more logo-ed merchandize than chemistry sets or microscopes.

(Personal anecdote: despite having three science museums nearby, I had to use the web to get a real periodic table poster. A printable simple table from Los Alamos National Lab.)

"Liking" science without learning it is bad for society:

1. Crowds out opportunities for education. People have limited time (and money) for their hobbies and activities. If they spend their "science budget" on identity, they won't have any left for actual science learning. Many more people read Feynman's two autobiographies than his Lectures On Physics or his popular physics books.

2. Devalues the work of scientists and engineers, by presenting a view of science that excludes the hard work of learning and the value of the knowledge base (trial-and-error in lieu of mass balance calculations, for example). Some people end up thinking that science is just another type of institution credential (or celebrity worship) instead of being validated by physical reality.

3. Weakens science education. Some people who go into science expect it to be easy and entertaining (in the purely ludic sense), instead of hard but rewarding (deriving satisfaction from really understanding something), as that's what the popularization depicts. They then want schools to match those expectations. While colleges may not want to simplify science and engineering classes, they put pressure on faculty for more "engaging" teaching: less technical, more show. (**)

4. As science becomes more of an identity product to some people, and increasingly perceived as identity-only by others, it becomes more vulnerable to non-scientific identity threats, such as derailing a major scientific and technical achievement in space exploration by talking about sartorial choices and sociological forces in academia.


So, what can we do?

First, we should recognize that an interest in science, even if currently trending towards identity, can be channeled into support for science and science education. As societal trends go, a generalized liking for science is better than most alternatives.

Second, there are plenty of sources of information and education that can be used to learn science. There's a broad variety of online resources for science education at different levels of knowledge, free and accessible to anyone with an internet connection (or indeed a library card; books were the original MOOCs).

Third, current "science as identity" popularizers may be open to educating their audiences. Contacting them, offering feedback, and using social media to otherwise proselytize for science (as in scientific knowledge and thinking like a scientist) might induce them to change their approach.

The most important thing anyone can do, though, is to try to get people who "like" science to understand that they should really learn some.

(Final note on the A-Team episode: Adam should have played Murdock, not Hannibal.)

- - - -
(*) I learned to do this on my own as a kid, but the material was covered in ninth grade chemistry. (A long time ago in a country far away, in ninth grade you chose a technical or artistic area in school; mine was 'chemical technology' because my school didn't have electronics.) A side-effect of my early interest in chemistry is that I have quasi-Brezhnevian eyebrows: you burn them off five or six hundred times, they grow back with a vengeance.

(**) Some schools protect their main reputation-building degrees by creating non-technical versions of the technical courses and bundling them into subsidiary degrees. So, for example, they have information technology courses, which sound like computer science courses but are in fact nothing like them.
          Another approach is the encroachment of humanities, arts, and social sciences "breadth" requirements into science and engineering degrees. When I studied EECS in Europe, we had five years of math, physics, chemistry, and engineering courses. A similar degree in the US has four years and usually a minimum of one-year-equivalent of those "breadth" requirements, though some people can have more than two-year-equivalent by choosing "soft engineering" courses like "social impact of computers."