nm/sqrt(nm)
June 17, 2024 5:38 AM Subscribe
Nearly a year and a half ago, Joseph Newton did an excellent video about Cursed units. Now he's back with Cursed Units 2: Curseder Units! From fuel efficiency in square millimetres to the barrer, the definition of which has cm appear no less than four times, you're sure to encounter some weird (metric) units you'd not heard of. [2LYT]
It's a unit, not a calculation - nanometers per square root nanometer!
posted by Dysk at 6:23 AM on June 17, 2024
posted by Dysk at 6:23 AM on June 17, 2024
Are there smoots? I hope there are smoots.
posted by Ishbadiddle at 6:31 AM on June 17, 2024 [2 favorites]
posted by Ishbadiddle at 6:31 AM on June 17, 2024 [2 favorites]
He explicitly omits "joke units like smoots."
posted by adamrice at 7:33 AM on June 17, 2024 [4 favorites]
posted by adamrice at 7:33 AM on June 17, 2024 [4 favorites]
Ah yes. I have now watched the videos and understand why the smoot was omitted. I don’t wish to derail this thread but the fact that the eponymous Mr Smoot went on to head up the US Bureau of Weights and Measures is still one of my favorite moments in history.
I occasionally get to teach dimension analysis to 9th graders. Maybe I will show them these videos and watch their heads explode.
posted by Ishbadiddle at 7:45 AM on June 17, 2024 [1 favorite]
I occasionally get to teach dimension analysis to 9th graders. Maybe I will show them these videos and watch their heads explode.
posted by Ishbadiddle at 7:45 AM on June 17, 2024 [1 favorite]
I hated dimensional analysis as a ninth grader. I think these are the first time I've ever appreciated how weird it can get.
posted by Hactar at 7:47 AM on June 17, 2024 [1 favorite]
posted by Hactar at 7:47 AM on June 17, 2024 [1 favorite]
Long tangent here.
Radians are hard to teach. In Trig, when I introduce them, I point out that the arc length formula rearranged is theta = s/r. Since both s (arc length) and the radius are measured in the same units, they cancel, so radians are “unit less”. But this is confusing, since the word radians appears in the answers to the previous section’s problems, so it seems to students that sometimes we write “rad” and sometimes we don’t. I try not to dwell on it too much.
But then it gets worse in Calculus II, when we introduce power series for sine and cosine. Because now, we essentially say we are finding sine and cosine of a number - no reference to an angle in degrees or radians necessary. Now, sine and cosine are just these functions of some real number, that no longer need to have any reference to a triangle or unit circle. In fact, you can prove all of the basic trig identities just using the power series (it’s not easy - you have to know how to do double summations, but it can be done).
Radians are definitely a case when I’m teaching where I fear I’m doing “hand waving”, which I try, as much as possible to avoid. I have not solved this dilemma to my satisfaction yet.
posted by wittgenstein at 7:56 AM on June 17, 2024 [7 favorites]
Radians are hard to teach. In Trig, when I introduce them, I point out that the arc length formula rearranged is theta = s/r. Since both s (arc length) and the radius are measured in the same units, they cancel, so radians are “unit less”. But this is confusing, since the word radians appears in the answers to the previous section’s problems, so it seems to students that sometimes we write “rad” and sometimes we don’t. I try not to dwell on it too much.
But then it gets worse in Calculus II, when we introduce power series for sine and cosine. Because now, we essentially say we are finding sine and cosine of a number - no reference to an angle in degrees or radians necessary. Now, sine and cosine are just these functions of some real number, that no longer need to have any reference to a triangle or unit circle. In fact, you can prove all of the basic trig identities just using the power series (it’s not easy - you have to know how to do double summations, but it can be done).
Radians are definitely a case when I’m teaching where I fear I’m doing “hand waving”, which I try, as much as possible to avoid. I have not solved this dilemma to my satisfaction yet.
posted by wittgenstein at 7:56 AM on June 17, 2024 [7 favorites]
Long tangent here.
I see what you did here.
posted by jimfl at 8:00 AM on June 17, 2024 [11 favorites]
I see what you did here.
posted by jimfl at 8:00 AM on June 17, 2024 [11 favorites]
I suspect that every industry has weird units they use for a combination of historical reasons and because using them gives results that are human scaled - units scaled to give normally occurring results that are integers between zero and twenty tend to stick around.
The barrer pushes this to the limit though. It breaks any attempt at dimensional analysis because the cm's are all being used in specific contexts that are not themselves defined by the unit. It is a trash unit and anyone who uses it should go to jail.
posted by thatwhichfalls at 8:10 AM on June 17, 2024
The barrer pushes this to the limit though. It breaks any attempt at dimensional analysis because the cm's are all being used in specific contexts that are not themselves defined by the unit. It is a trash unit and anyone who uses it should go to jail.
posted by thatwhichfalls at 8:10 AM on June 17, 2024
one polarizing thing not mentioned in the second video was actually polarizing: PMD (i found this neat, relative to Vavilov–Cherenkov [2*wiki]) thank you
posted by HearHere at 9:54 AM on June 17, 2024 [1 favorite]
posted by HearHere at 9:54 AM on June 17, 2024 [1 favorite]
Heat rate is defined as BTU / kWh, and I die a little inside every time I see that unit
posted by scruss at 11:37 AM on June 17, 2024 [3 favorites]
posted by scruss at 11:37 AM on June 17, 2024 [3 favorites]
Oh God that's joules per joule in the worst possible way: an imperial unit over a metric one. And neither is actually joules.
posted by Dysk at 12:50 PM on June 17, 2024 [4 favorites]
posted by Dysk at 12:50 PM on June 17, 2024 [4 favorites]
millibarns per steradian
posted by neuron at 1:05 PM on June 17, 2024 [1 favorite]
posted by neuron at 1:05 PM on June 17, 2024 [1 favorite]
→
The BTU is for the gas into the turbine, the kWh is the energy out of the generator. But still, bleeah.
A slightly more enlightened version of it is GJ / MWh. GJ is always pronounced "jeejay" in the energy industry
posted by scruss at 6:25 PM on June 17, 2024 [2 favorites]
And neither is actually joules
The BTU is for the gas into the turbine, the kWh is the energy out of the generator. But still, bleeah.
A slightly more enlightened version of it is GJ / MWh. GJ is always pronounced "jeejay" in the energy industry
posted by scruss at 6:25 PM on June 17, 2024 [2 favorites]
Watched this video... on the day it debuted I guess...? Wow the algorithm has me pegged on this one.
It got me thinking about cmH2O, a pressure used a lot in Respiratory Therapy... and I guess not many other places. It's absolutely a convenient unit because most of the time you can use integers between 5 and 50. It's also likely not going away as many places still use a column of water to regular airway pressure in CPAP devices, so you literally stick a column to a depth of 6 cm in a water reservoir to give a patient CPAP of 6 cmH2O.
But it often tricks us into direct comparisons of airway pressure (measured in cmH2O) and Central Venous Pressure or Jugular Venous Pressure (measured in mmHg) which are actually surprisingly close, but still different by bout 25-30%. Additionaly if you want to correct some calculations of alveolar oxygen concentrations for elevation, you might be looking up atmospheric pressure in kPa, meaning that assessing cardio-respiratory physiology might use three completely different units of pressure (though local atmospheric pressure is usually easily available somewhere in Torr, which is functionally the same as mmHg, for our level of precision).
Also it's hilarious to me that wikipedia defines cmH20 down to SIX significant digits, with a specified temperature of 4 Celsius, which is not a temperature any ventilator operates at. Sometime's I want to go on a crusade against false precision in medical documentation, other times I just shake my amongst fellow nerds on Metafilter.
posted by midmarch snowman at 10:29 AM on June 18, 2024 [3 favorites]
It got me thinking about cmH2O, a pressure used a lot in Respiratory Therapy... and I guess not many other places. It's absolutely a convenient unit because most of the time you can use integers between 5 and 50. It's also likely not going away as many places still use a column of water to regular airway pressure in CPAP devices, so you literally stick a column to a depth of 6 cm in a water reservoir to give a patient CPAP of 6 cmH2O.
But it often tricks us into direct comparisons of airway pressure (measured in cmH2O) and Central Venous Pressure or Jugular Venous Pressure (measured in mmHg) which are actually surprisingly close, but still different by bout 25-30%. Additionaly if you want to correct some calculations of alveolar oxygen concentrations for elevation, you might be looking up atmospheric pressure in kPa, meaning that assessing cardio-respiratory physiology might use three completely different units of pressure (though local atmospheric pressure is usually easily available somewhere in Torr, which is functionally the same as mmHg, for our level of precision).
Also it's hilarious to me that wikipedia defines cmH20 down to SIX significant digits, with a specified temperature of 4 Celsius, which is not a temperature any ventilator operates at. Sometime's I want to go on a crusade against false precision in medical documentation, other times I just shake my amongst fellow nerds on Metafilter.
posted by midmarch snowman at 10:29 AM on June 18, 2024 [3 favorites]
Can't believe people complained about the music in the first one. I'm working on a spoken word project that was going to be just speech, but the piano playing was so apropos, I raced to see where it had come from. Improvised by the creator! Awesome!
posted by ASCII Costanza head at 11:52 AM on June 19, 2024 [1 favorite]
posted by ASCII Costanza head at 11:52 AM on June 19, 2024 [1 favorite]
There's a funny mathematical coincidence that cyclists take advantage of. If you're measuring your power output, and from that are measuring joules of work performed (by sampling your power every second and adding all those measurements together), you can say calories burned is about equal to joules of work performed.
"But there are 4.184 joules in a calorie!" you say.
"But the human body is only 20–25% efficient at converting energy to useful work, so it nets out," I say.
posted by adamrice at 12:11 PM on June 19, 2024 [3 favorites]
"But there are 4.184 joules in a calorie!" you say.
"But the human body is only 20–25% efficient at converting energy to useful work, so it nets out," I say.
posted by adamrice at 12:11 PM on June 19, 2024 [3 favorites]
Oh, my other favorite Medical pet peeve is when measurements have no units. There's a technology called Near-infrared spectroscopy which is able to give a proxy measurement the venous oxygenation but is also reported everywhere as just a number. I somewhat suspect this because the measurement is fairly low precision in a lot of clinical situations and noisy and so the manufacturer doesn't want you to assume a NIRS of 65 means the Venous Oxygen Saturation is currently 65%, but I find it odd that people will just accept a measurement of "NIRS are 65" without saying... 65 what?
Some devices have settings that have no units, like the Power setting on HFOV mechanical ventilator. I believe it goes from 1.0 to 10.0 but is specifically state in the manual it's not a percentage scale.... so WTF is it then?
posted by midmarch snowman at 4:00 PM on June 19, 2024
Some devices have settings that have no units, like the Power setting on HFOV mechanical ventilator. I believe it goes from 1.0 to 10.0 but is specifically state in the manual it's not a percentage scale.... so WTF is it then?
posted by midmarch snowman at 4:00 PM on June 19, 2024
And why would you ever have a unitless dial not go to 11?
posted by Mitheral at 6:18 PM on June 19, 2024
posted by Mitheral at 6:18 PM on June 19, 2024
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posted by sammyo at 6:08 AM on June 17, 2024 [1 favorite]