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I remember in a solid state chemistry MOOC I took, from a professor who was a lithium battery researcher, the professor did mention in passing that we actually
by tzs 3y ago
I remember in a solid state chemistry MOOC I took, from a professor who was a lithium battery researcher, the professor did mention in passing that we actually don't have a really good understanding of lithium batteries.
Of course he was talking about a much lower level than you need to understand when it comes to actually using them.
There are actually a lot of things we know how to deal with when it comes to engineering but have a poor grasp of the low level details. There was a great example in the Feynman Lectures where he says this about friction (Volume 1, section 12-2):
> It is quite difficult to do accurate quantitative experiments in friction, and the laws of friction are still not analyzed very well, in spite of the enormous engineering value of an accurate analysis. Although the law F=μN is fairly accurate once the surfaces are standardized, the reason for this form of the law is not really understood. To show that the coefficient μ is nearly independent of velocity requires some delicate experimentation, because the apparent friction is much reduced if the lower surface vibrates very fast. When the experiment is done at very high speed, care must be taken that the objects do not vibrate relative to one another, since apparent decreases of the friction at high speed are often due to vibrations. At any rate, this friction law is another of those semiempirical laws that are not thoroughly understood, and in view of all the work that has been done it is surprising that more understanding of this phenomenon has not come about. At the present time, in fact, it is impossible even to estimate the coefficient of friction between two substances.
That was written around 60 years ago. Anyone here happen to know if it still holds?
- user_7832 3y ago> That was written around 60 years ago. Anyone here happen to know if it still holds? Not really the same question but I attended a talk by some top tribologists at my uni and I asked them if friction really was independent of contact area (as F=μN would suggest), their reply was that it roughly was, but not really if you were very precise or varying parameters. It would appear that the equation is a good approximation, like classical Newtonian physics.
- _a_a_a_ 3y agoApparently even solubility of compounds in various solvents is empirically derived because there's no reliable theoretical model of this in chemistry/physics. (AIUI anyway)
- catchnear4321 3y agonot to get too leaky, and this is a bit dated, but… the math produces results that are understood but not, because the math is calculating with some implicit inclusions, and things get weird when you start explicitly including. the answers make sense, but not quite for the questions being asked. (but the answers are valid for a question, and more importantly, immediately useful for making dollars.) unfortunately the vagueness of this will likely irritate a doctor. it certainly did years ago.
- photochemsyn 3y agoAt some point, scale-wise, friction problems become electrochemical rate problems, I suppose. See this recently published research article on lithium iron phosphate batteries, opening: > "Reaction rates at spatially heterogeneous, unstable interfaces are notoriously difficult to quantify, yet are essential in engineering many chemical systems, such as batteries and electrocatalysts..." https://www.nature.com/articles/s41586-023-06393-x https://www.nature.com/articles/s41586-023-06393-x It's a much harder problem than working with pure crystals or gas-phase molecules or similar, which makes sense, as a half-discharged battery is a very messy system at the molecular-atomic level. See also news story on the above article: > “We discovered at the nano scale that variation of the carbon coating thickness directly controls the rate, which is something you could never figure out if you didn't have all of this modeling and image analysis,” Bazant says. https://news.mit.edu/2023/pixel-analysis-yields-insights-lithium-ion-batteries-0913 https://news.mit.edu/2023/pixel-analysis-yields-insights-lit... So, the field seems to be progressing steadily - and more funding for fundamental solid-state materials science research makes sense, too.
- KolenCh 3y agoIt depends on what kind of friction you’re talking about too. Eg it is well known that for some fluid (air for example), the friction can be proportional to the speed instead, to a certain extend of course, and can be proved in an idealized situation.