In physical therapy school we’d place a single human hair under sheets of paper to practice palpating.. Can’t remember the most sheets someone was able to feel a hair through, but it was several.


We did this in massage school using hair and a phone book (much thinner paper). 8 years into the profession and it's amazing how sensitive my fingertips have gotten.


14 years here, I absolutely believe you! 😊


20 years here! I'm a bit skeptical


Become a carpet installer. You'll lose your fingerprints and most of the sensitivity.


Perfect for committing crimes!


Funny enough I did learn this because I was arrested for speeding and the cop had the hardest time getting my prints to print.




Interesting. I wouldn't have thought so. I'm a machinist who sometimes has to test the surface finish of products before they ship. We just use a little board with a dozen labelled samples on it. "Yeah, it's smoother than this one, but rougher than that one." You can usually just tell visually by the sheen, but we do feel them as well. All of the samples are labelled in various micron ranges, though (a micron being 1/1000 of a millimeter, and 1000 nanometers), so these numbers are in a whole different ballpark of smoothness. [Here's an interesting video of measuring some really flat & smooth items with an atomic force microscope.](https://youtu.be/2cZ0XJWxyH0)


I work in a machine shop too. I call that my *calibrated fingernail*


I work with lots of shops and I still use, 'can you feel it with your fingernail' as a check on tool marks. Tactile is the best, rub a nail on the part, then rub a nail on the roughness checker, now you know if its in spec.


We had this one old journeyman who would just run his hands along the job and he could tell you if it was off by a thou. He'd be right




Skilled human workers who've spent decades doing the same thing are absolutely fascinating. I know one guy who can just visually measure length and cut boards to a hairs breadth of accuracy for framing and carpentry. I know a mechanical engineer who just just know the volume of a space visually. Theyve tested experience clock makers/tuners and found their internal clock is accurate regardless of environmental conditions. The human brain is incredibly plastic, so it takes work to get it to reliably output data, but once you can it's absolutely astounding. Humans can do a lot without electron based computers it just takes training and practice in numerous specific jobs to do so.


Better safe than sorry I guess?




I mean that's completely fair. Imagine having to explain that on your audits...


It's odd when you're pulling a number out of thin air like that. It's not exactly like I'm doing any thinking about the distance when eyeballing something. Eh sure, looks like 2'. Pull out the tape measure, sure enough, it's a hair under 24".




I worked with composites in aerospace, trust me, we had some tight tolerances to hit. And I got very good at this sorta thing. But regardless of how minute the thing I was eyeballing was, I still didn't actively do any processing that I was aware of when pulling a number out like that, and it was usually pretty damn close. I'm usually just waiting until my brain spits a number at me, not me thinking something like "well 12 inches looks like my forearm, and I could fit at least 3 of them in there, so it must be around 36".". Nah, it's more staring at the part pretty blankly, and waiting. My example is larger numbers because it's easier to understand the principal I'm trying to get across. It's wild how much is going on under the hood, so to speak. Edit: happy cake day lmao.




Gotta admit, I've never really encountered that specific scenario with the drilled hole, but I could definitely see it. I spent a lot more time with fiberglass than carbon, and a lot more time with wet layups vs dry layups. Nowadays I'm back at the good ol boat building I started with, and usually we layup the full part before doing any real fab work or hardware installation, and now that I think about it, usually I don't immediately go to hardware after finishing the last layer of glass, it's usually onto gelcoat. Which can be multiple days in itself, so all in all things should be pretty done with the bulk of the initial curing by the time I've usually gotten to the stage of cutting holes and whatnot. When I was in aerospace, I was making Blackhawk components mainly, and it was all graphite carbon and at that, it was all pre preg, which was totally new to me at the time. It was odd heading to the freezer to grab material, lol. But I never saw my parts again once they left layup, unless I fucked up. Which did happen once, nearly had a heart attack as they showed me a single one of my hairs had caused one of the layers to not bind and they had to scrap the part, no repairs allowed. That was a few hundred grand down the drain, lmao. At least, that was what the part cost to purchase. But they were cool about it, everybody gets one or two, they said. Trying to locate a single hair on black carbon ain't easy. Anyway, parts went like this on sorta assembly line layup>autoclave>ultrasound/x-ray the part>cutting>assembly. Each step generally being its own department. I worked in layup the entire time I was there, but that's a different story. I miss working in a temp controlled clean room vs a dusty ass workshop, but can't really beat working for yourself.


Had a new foreman who needed it explained to him that putting the dye out IN THE SUN FOR 12 HOURS can mess with the measurements when we need to work on it again last minute because "this super rush job that we totally forgot about while we had you sweep for two hours came in".


Woodworker here, I trust my fingers way way more than my eyes.


And that bamdsaw just sitting there like *I like fingers too*


It's OK, luckily I was born with 10 of em!


You mean you don’t use ur eyecrometer?


My eyecrometer failed calibration years ago


You heat but there's actually a 'fingernail' test in aerospace. It's used to define if there's 2 much off a ridge between 2 adjacent paint jobs I think. If you can feel it with your finger nail, it goes back to the paint shop!


My boss calls them finger micrometer


I'm a calibration guy and I giggled at this lol.


How often do the samples need to be replaced? Wouldn't they wear out pretty quickly or become similar to each other by the constant rubbing?




Wouldn’t particles of fingernail and oils build up, filling in the pattern?




I always wondered about this, too. "Constant" would be an exageration, though. It was a rarity to have to do that check. I would imagine cleaning it with alcohol would take care of oil & dead skin.


My dad used to work in radio communications and I can remember him telling me about the inside of a large antenna or something that had to be a certain smoothness, and they would check it by feel against a calibrated sample.


I think the title suggests a repeating pattern, not a singular defect


That was a cool video, splitting mica like that _by hand_


Generally they mean that the nerves can sense it. Having the brain be able to perceive the difference is a whole different matter! The classic one is for the ocular system. We can technically 'see' a small number of photons (~100 for a favoured chance) but essentially no one can actually tell the difference between pitch black and the occasional 100 photon pulse with any accuracy. Yeah, the ocular nerve did send off a signal to the brain but the brain gets a lot of signals.


Yet I still can't I find the end of packing tape when I forget to fold a corner...


But can’t tell the difference between wet and cold


Interesting. I guess we assume its wet of its a few degrees cooler than we expected


The wetness (let’s assume water) wouldn’t necessarily be cooler. Having body-temp water touching us would still be felt, but only because of the removal of heat by evaporation. If there was no evaporation, by being in a closed and humid system at the same temp, we would likely not feel it. Things feel [cooler] or [hotter] because of our skin’s relationship with heat transfer. A cooler thing *removes* heat from us, and a hotter thing *adds* heat to us.


I once put my finger in a small bowl with water that was standing for hours at room temp and i remember it felt like my hand wasn't even in water


It must have been warm that day..


Yup! This is how sensory deprivation tanks work.


Lol…I have a spot on my forearm that started getting confused a couple years ago. Anytime a cold wind hits that spot, it reports back to me that it’s wet. It took me a couple times of it happening to figure out what was going on. At first I was like “it’s not raining, where the fuck did that drop of water come from‽‽”


Hate to break it to you but the problem is in your brain and it could be a tumor.


Lol….I did some googling when it started happening and it’s pretty common. I think I’m fine.


Or why kids like the taste of Cinnamon Toast Crunch


Kids? I’m 43 and can’t keep Cinnamon Toast Crunch in the house because I’ll eat it all on day one.


doesn't help that we can't really sense temperature itself but rather the in or outflow of heat... conductive things feel colder than they are when cooler than us and hotter than they are when hotter than us, and the opposite with thermally insulative materials... to a point, they'll feel warm even when cooler than us, especially after a few seconds because they reduce the outflow of heat, and when hotter than us they don't feel that hot if they can't conduct heat into us efficiently. wet just changes how efficiently they conduct heat into us... so anything wet that's above our body temp wouldn't feel cold... it'd probably feel hotter than it actually is


The problem with this is your own body heat creating condensation on the cold surface so now it's wet and cold.


No, it's just that we don't have the ability to sense "wet" other than estimating it from heat and pressure.


Also if you submerge a part of your body, you can feel the surface tension as well because it has a different pressure, and it moves your body hair.


How would your body feel wetness though? That's like saying you can feel dryness.


Idk. Idk shit about biology but for amazing as our bodies are it kinda blew my mind when i learned this


Several animals have electrosensory organs and receptors. I suppose if we had some sort of receptors in our fingertips that detected voltage, we could discern wetness based on changes in conductivity.


We do not have receptors that are able to feel wetness. It’s mostly just temperature difference caused by evaporative cooling once your hand is moistened by the wet thing you touched, but texture and traction between the item your skin also play a pretty big part in it.


Stupid useless fingers.


Except the fretting hands of guitar players




Sometimes I touch my face with my left hand and it feels like someone else is touching my face


Sorry, I'll stop.


"I can't feel the left side of my face...I mean I know it's there...I just can't feel it."


"But I like it... But I like it.... I can't feel the left side of my face when I'm with you"


Didn't Ringo shout that?


He did, and the wood clanging noise was his drumsticks that he threw across the room


Wiki says yes. EDIT: Which is probably your point considering he's a drummer not a bassist




I’ve read that if the Earth were a pool cue ball, a human fingertip could hypothetically feel a row of cars lined up on the surface (assuming the rest was completely smooth).


I was bored so I figured I’d run the numbers, please see my findings below. ​ **Statement:** "If the Earth were a pool cue ball, a human fingertip could hypothetically feel a row of cars lined up on the surface" ​ **Math:** `Average Earth Diameter = 12'735km | 12'725'000'000mm` `American Pool/Billiard Ball Diameter = 2.25" | 57.15mm` `Average car height = 6' - 7' | 1.8288m - 2.1336m` `Minimum Finger Detection Value (MFDV) = 13nm` `nm = nanometer = 0.000001mm` ​ Size difference between the Earth and a pool ball = 12'735'000'000 ÷ 57.15 = 222'834'645.67 MFDV Upscaled = 222'834'645.67 × 0.000013 = 2'896.85mm = 2.90m ​ **Conclusion:** An object on earth would be almost 23 million times smaller if the earth was reduced to the size of a pool ball (2.25"). Ergo for an object to meet the 13nm requirement and still be detected by a finger once shrunk, it must be at least 2.90 meters in size normally. The average car measures 1.83 to 2.13 metres in height from ground to roof. As even the larger average here (2.13m) is less than the minimum required value of 2.90m this statement is false. If the vehicle in question had a height equal to or greater than 2.90m then the statement would be true. Thanks for coming to my Ted Talk! ​ **References:** [https://www.discovermagazine.com/the-sciences/ten-things-you-dont-know-about-the-earth](https://www.discovermagazine.com/the-sciences/ten-things-you-dont-know-about-the-earth) [https://getjerry.com/questions/how-tall-is-the-average-car](https://getjerry.com/questions/how-tall-is-the-average-car)


I think this does an excellent job of demonstrating that while the comparison isnt quite accurate, it's very close. While we might not detect a car itself, we could pick up other things that are roughly car sized, like construction equipment or small buildings.


I was actually hoping someone would try to do the math. Thanks! So a row of semi-trucks, then? 🤓


Average car height 6 to 7 feet? Wtf? How?


US <> The World Stupid petrol-guzzling trucks are the 'norm' there


Found the SQL programmer


Hi! What is this symbol <>, is it an expression of “does not equal?” I’ve seen it as =/= in writing but would like to know the accepted notation.


It is another way to write that yes


Yes, it's standard mathematical notation when using a computer, also standard in some programming languages too


What languages? Feel like != is much more standard


SQL is the only one I can think of. Although for most flavours != also works.


BASIC and Excel formulas as well.


Well, the obvious is SQL, but any non-microsoft^1 I think It works in almost every scripting and compiled language I've ever used since ~1980 ^1 e.g. it works in javascript but not jscript


Thank you, Im self taught and would use this operant instead of workarounds if I’d known how to express it before. Appreciate the detail :)


Maybe if you’re taking median as the average? If you split the difference between the largest monster truck ever and something like an MG Midget or a kit car, you might come out somewhere around 6-7 feet. This is definitely way off if you’re going by mean or mode averages, however.


Excellent DD !! If your not already a programmer, I encourage you to look into it.. Gotta say tho, for a rough analogy that involves the diameter of the earth, being a foot off is pretty acceptable. Maybe we should say "humans could detect a row of telcom vans" instead? Feels a little clunky tho..


Agreed. An analogy of this type is made in order to get the average person to comprehend the scale, and it's just darned fun. It's like those "McDonald's has sold enough fries to circle the globe [over 18k times](https://mcdonaldsblog.in/2015/09/food-for-thought/)" analogies. Being off by a foot or so doesn't change the effectiveness of the analogy in *this particular case*. That said, seeing how it could be worked out with the maths was also fun.


That fry number seems low.. Like I feel like one McDonald's open for fifty plus years would be reaching the circumference in fries, 44 odd thousand kilometres, by now. My feelings come in to it a lot more than facts, obviously


>your Stop it.


Then there’s the other analogy that if the earth with all its valleys and mountains were the size of a pool ball it would be smoother than any pool ball ever machined. Neil deGrasse Tyson on JRE: https://youtube.com/shorts/0ub7Yt9WZJs Someone tell me if these statements are contradictory or not. Feels like they are


You're 100% right. Idk what everyone else is talking about. You would not feel a row of cars on earth at that size lmao.


I don't have time to watch that short rn but that doesn't feel right


I've seen numbers saying that if it were the size of a bowling ball it would be within regulation specifications on smoothness and roundness. I'm guessing the same would be true of a pool ball but we surely have smoother and rounder examples of both.


There might be a margin of error on the 13nm figure, a car would be closer to 9nm in this analogy so could still work maybe?


Yeah that's why the statement is supposed to be "houses"


By definition, a truck *is* a car. So if you line up a line of trucks, we could feel them. So *technically* we could feel a line of cars :D


How are you this smart but your username is Iggy Azalea. Calculate that one for me. 😂


Ok, but you have to Beg For It


Quite cool you made the math. But you made one mistake. He did say a row, not a single car.




Okay but how are you gonna park a row of cars on the cue ball?


Veeery carefully.


The ridges on this cue ball are too damn high.


Just a slight difference I remembered about that fact was that with those other conditions, the human finger could *distinguish between houses and cars.*


I wonder if this metric is worse for people without fingerprints?


I work in quality control with furniture, and while we do not use specific measurements where I'm at right now, feeling with your hands is one of the best ways to find minor issues. Not only does it let you pick up something your eyes might miss, there's a good chance your going to find out if that smudge is actually in the finish or if it will just wipe off. I also use the fingernail test a lot of people were mentioning earlier in comments.


“Woman!!! I told you not to tell everyone about my dick”


Your dick can be confused for a 13 nm deep pattern?


Lol ☝️


I was once a subject in this student psych homework experiment, with my consent of course, and my task was to feel with my fingertips which sand paper is more rough. On my right index finger is the control, and on the left they switch different grits sandpaper. I got a perfect score and they were stunned as if what I did was an amazing feat. Well apparently other students they tested didn’t get it perfectly but I feel like those students just didn’t really focus enough… prolly just wanted it to be over and done with cos it was boring haha.


Except if you play violin, bass or any other string instrument


Most of you just touched a nearby surface 🤭


You are now breathing manually


Remember to blink and swallow saliva.


Also you're nose is right there on the edge of your vision


Your toes are always touching each other


Fuck everyone in this thread. You all just lost The Game


I sure hope your tongue is resting comfortably in your mouth


The glass on a high end phone is very very smooth. I think.


Train cars would make the math work, right? And they’re classically found stretched out in long lines all over the world!


If it's raised, it can be even smaller but not reliably


I wonder if autistic people who have that thing about disliking/liking texture of objects have an even more sensitive touch.


Human hands are understated in how amazing they are. Intelligence as a defining trait is often discussed, but the tactileness and flexibility of our hands really is incredible. The tools we are able to make have driven our progress.


So when you feel a lump, make your doctor get an additional opinion


I heard if Earth was the size of a marble we could feel individual houses


And the ridges on your fingerprints are *50,000 nm tall*.




>most men still can't find the clitoris I never understood how this could be taken as a legit dig. It's like saying "not one person understands my humor" aka, "I'm an unfunny douche." What is meant as a criticism of men, becomes an indictment of one's own shitty taste in casual, selfish sex.


We can, we just reserve the real fun for women We actualy love and respect.


Your mom?


You love yours , right......or you don't have one?😁


For when you checkin’ her booty for pimples, yah?


Reason 4,365 those random chin hairs are annoying AF.


13 nautical miles? Wow!


How does one measure nautical miles in depth for a fingertip sensitivity test! /s


Yet we still can’t “feel” wetness


Til, my fingertips arent human!


This is how I know when a sunflower seed I blindly picked from the bowl is whether peeled or not


I miss having all my fingertips :(


Finally we have some kind of superpower


The human anus can feel the difference between solid, liquid, gas, and plasma.


I remember coming across this video called "Could you feel the texture of the Earth if you held it in your hand?" Or something to that effect. I was expecting the video to say "You'd think so, but no. The rough globes we use every day are highly exaggerated, the Earth is actually very smooth." But I was mistaken. The human hand is actually sensitive enough to texture that, even on a topologically accurate scaled Earth, you could still feel the mountains, trees, and oceans.


How do you think OP masterbates


Yes, but can the fingertip distinguish such a pattern if it is 13km deep? What is the applicable range of smooth detection for this marvel of biology?


I assume it’s connected to why they have so many tiny blood vessels in them and bleed like a motherfucker when they get cut.


Ex automotive painter here, that’s why painters run their hands over sanded surfaces, you can definitely feel the differences in surface to know when it’s ready to be painted over.


Looked up some facts to try to wrap my head around the scale. A human hair is 80,000-100,000nm. A bacterium is about 1000nm.


Unless you’re a contractor. Then you’re fingertips are just basically callouses


The human body is amazing


3mm if you’re a mechanic


Also the tip of the finger is equivalent to 16000 grit sandpaper


To add to that: "On a dark night, you could even see a candle flame flickering up to 30 miles (48 km) away." https://www.livescience.com/33895-human-eye.html


Why can't we feel things like viruses, they can be anywhere from 20-400nm ?


Makes me wonder how deep is the grooving in your fingerprint is


Only impressive when you put the “just 13 nm deep” in there… for all I know, this isn’t anything that should be considered noteworthy.


Every once in a while I read about how sensitive, say, a dog's nose is, and how it puts our sense of smell to shame, or an eagle's distance vision, or a cat's or owl's dark vision, or whatever, and I get a little jealous that humans don't excel at anything in particular. (Other than, you know, having actual intelligence.) But we do have outstanding color vision, AFAIK better than just about any other animal's other than, for some reason, the Harris hawk. We have fantastic dexterity, though an octopus may rival our abilities in that area. And now this. We're just plain world champs at this. Okay, proud to be a human again. That and the whole technology thing is enough at least for now.


What a shame ..my girlfriend couldn't feel my six inches.. Nah..not enough for her


Wow 🥲




no i don't


just the tip`?


I've had some heavy chemo and now my feeling in my fingers is gone. So things fall out of my hand often. Can't even feel it when I'm holding a pen