7:28 sad you didnt touch on meteorology. Pretty much everything simplifies down to J/kg. Convective Available Potential Energy: J/kg. Convective Inhibition: J/kg. Storm Relative Helicity: m²/s² (equal to J/kg). Bulk Richardson Number (BRN) shear: m²/s². The stuff that simplifies to J/kg comes from taking an integration of a temperature (usually a ΔT) with respect to the log of pressure, while the m²/s² simplifications are a result of area on a hodograph, which is a polar plot where both axes are velocity, thus meaning area is kt², or (m/s)². Its literally velocity area which is so weird to think of at first.
Speaking of Imperial units I have had to for my job convert units of thermal conductivity between imperial and metric. Specifically converting (BTU.hr)/(Ft²-F) to W/(m²-K)
My friend and I had a discussion on why temperature and energy have different units. We eventually came to the conclusion that temperature and energy have different units because of a similar reason to why radians have their own units. Because you can't add internal energy with the kinetic energy of particles it is helpful to separate the two by assigning different units.
This unit jiggerypokery is exactly how I passed my phyisics exam: you were allowed to have a book of forumals, so I turned everyting into stuffing values into formulas I had possibly never seen before, and then calculating the unknown variable
Saying “we’re building a sensible unit for sensible people” while you still haven’t resolved the question of what’s going to happen to the moles is just cruel.
Electronic engineer here, i had a good dose of cursed units when i was learning why Inductances and Capacitances behave like resistances in complex variable
I love these videos and I hope there's a part III. I randomly watched the first one again literally last night so it was awesome to see this tonight. Also the music is awesome and adds so much, it melts into the background during the long stretches and then metaphorically barges in during big reveals. It's great.
Ok I have one I used professionally, grains per pound, or more specifically, grains of water per pound of dry air. I have seen weight per weight before, but outside of firearms I have never seen grains used officially in any modern standard.
As a learning electrician, I wanna say that everything including Volts, Amps and seconds is cursed. We have As/V, Vs/A, different things when you take V times A depending on what kind of power you're looking at, Watts are just confusing in general... It's all pretty weird to me.
Messages from a different dimension. If you have a shot at imperial units do mention that the so called imperial pound is almost certainly based upon the Sumerian pound which is almost certainly a standardized grain-food ration for a day (c. 500g). Measured in Troy wheat grains it is 7,680 x 7/8 x 100/96 = 7,000 grains It was imposed upon England by Florentine bankers after Edward III went bankrupt, and would have notionally reduced retail food measurement by about 10%, very probably contributing to the (so called) peasant's revolt. Its also worth mentioning how modern archaeology has been simplifying units. During a recent complete reclassification of the world’s largest collection of Ancient Egyptian weights at the Petrie museum, archaeologists decided it was a good idea not to record what they actually weighed…… When vandals invaded the US capital in 2021 it was called an outrage. When archaeologists took control of UK premier museums it was called progress. Who paid the piper?
If I ever have a child, I'll make them go through all of their piano lessons, no matter how much they want to spend their time reading math textbooks instead
I just came from part one, and I can't believe people complaining about the music. To me, it adds a story and makes these complicated concepts feel more intuitive
Due to watching your previous video, I became curious about “What is the minimum number of units necessary to do all physical measurements?”. As a result, I discovered CGS and Planck units, both mentioned in this video. I find it fascinating that after thousands of years of physics, all units can be broken down into 3 “fundamental” units. My current preferred system of units is a combination of CGS and Planck units (Planck units without temperature essentially since temperature can be measured in units of energy), since these units seem less anthropocentric and any additional units would be redundant. While absolutely not practical, I find it mathematically elegant. Couldn’t mol•cm/cm^2 just be thought of as the average number of particles per unit distance of material? Lastly, I always choose tau = 2•pi as my preferred circle constant since the number tau essentially represents 1 revolution, which I think lets radians keep their dimensionless property. n•tau means n revolutions. Thanks for the videos. While maybe not practical, learning that everything in modern physics can be broken down to mass, length, and time has changed the way I look at the world, as well as the fact that there are potentially fundamental versions of these 3 units (Planck units) which are important to physics.
Another thing that makes miles per gallon (or km/L) slightly cursed is that it not linear -- the difference between 30 and 31 mpg is smaller than to 25 and 26, but in L/100km, 7.5 and 8.0 is the same as 8.0 and 8.5. For mpg you have to multiply the cost by the ratio (hard), but, if the difference is 1 L/100km, then the cost difference is just how much 1L of gas costs. "Reciprocal" units (where it's usefullness/expensiveness) are a bit cursed in general, especially over a wide range of values. See also, frames-per-second (what does 300 fps mean? how much margin in frame time is there over the magic 60 fps?) and R-value (upgrading from RSI-20 to RSI-21 is not worth it, but upgrading from 5 to 6 is). I suspect some of these happened for marketing reasons ("higher is better")... which is the worst kind of reason. It also might come from the lack of prefixes in these traditional unit systems. I've heard someone say "X thing was so slow, instead of using x per second, they used seconds per x", and honestly, that's an anti-pattern: just add a 'milli-' to the top or 'kilo-' to the bottom, and we don't loose the ability to compare things linearly. Bonus thought: the choice of 100km in L/100km is actually really great for intuition, since 100 km is a decent trip (1h highway driving; 62 miles), and then you just know how many liters of gas you need for that kind of trip.
I used to be a Calculus II tutor at university and I had a similar "trick" to test all possible line paths that didn't need to check the case x=0 separately. All I did was x=at and y=bt and took the limit with t going to zero. This method could also be generalised to allow limits that go towards any generic point (x0,y0) by having x=at+x0 and y=bt+y0 with t going to zero. Most limits would end up depending on a or b, meaning they give different results for different paths, and this, do not exist.
You should probably have noted that the SI used to define the Ampare using the electromagnetic definition, and now defines a specific charge as we can measure charges more exactly.
In aviation we used to measure air pressure in millibars (mb). Then it was decided that we ought to use SI units so now we measure pressure in hectopascals (hPa). You've guessed it, 1 hPa = 1mb. In the USA you still encounter inches of mercury (inHg).
3:40 The radian is still dimensionless. An equation only involving quantities and not units (think PV=nRT) should remain true regardless of the units. The equation defining angle is s=r theta where s is the signed arc length, r is the radius of the circle, and theta is the angle. 1) theta has to be dimensionless as changing from radians to cycles makes the equation wrong 2) theta has to be dimensionless as mentioned in the video: m/m=1
Chemistry has wacky units, but I do remember some even weirder from Biology (usually botany to be exact). Usual caveat - those units made sense in what they did. They were just beautiful windows into how human mind can work though ;)
My favorite cursed unit is the snail (also called a slinch), which is a lbf s^2 / in, a unit of mass in American engineering units that's pretty common in structural analysis. Another great one from aerodynamics is air density, measured in slugs/ft^3 = lbf s^2 / ft^4
I always thought SI fixed everything and that you couldn't make it too bad. Looks like I was terribly wrong. Now I am scared to even think about units of measurement. Dimensional analysis feels like witchcraft, bizarre and senseless.
Seeing a sequel to one of my favorite videos pop up made my day. As a fan of obscure units, the last one was wonderful for me, and I’m glad to see more, thanks for enlightening the world to the horrors of *units*. Also, do keep the music, I still laugh at the stings when I rewatch the original video, and this one had some great musical moments too!
