The Sharpest Object In The World Can't Cut Anything

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Scientists like to measure things, but they've had a heck of a time doing that with sharpness. And even if no one agrees on exactly how to measure it, our search for better tools has recently led to some of the sharpest objects we’ve ever created.
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Sources:
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onlinelibrary.wiley.com/doi/a...
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pubmed.ncbi.nlm.nih.gov/12124...
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Images:
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commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...

[@SciShow]

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[@fionnan2811]

And to be clear a tungsten needle that tapers down to the thickness of a single atom is the sharpest object ever to be manufactured by humans

[@KingOfGamesss]

In the 2011 Movie called 'flying swords of dragon gate' they had a blade that could slice through gold with ease

[@colemiller2149]

Could fix a few problems with the last definition by considering the force along with the used length of the blade.

[@Hex-Mas]

The sharpest thing is stepping on a copper strain of wire.

[@KingOfGamesss]

@@Hex-Mas The sharpest thing...is my mind

[@TheWretchedOwl]

“While you were studying science, I was studying the blade” These scientists: “I was studying both, actually.”

[@strider_hiryu850]

the swordsman: "to be honest: same."

[@max410bery]

😂🤣

[@jonslg240]

*Every scishow video: "if you want the real answer, go to [LINODE,etc,etc], buy a subscription, learn, and figure it out!* Thanks, scishow!

[@CL-go2ji]

Okay, I give up: who is being quoted?

[@aff77141]

"If you separate your warriors and scholars, you'll have your thinking done by cowards and your fighting done by fools" - Hank Green

[@alexlandherr]

In a twist of irony it’s almost pointless…

[@akumaking1]

You’ve made a good point

[@ethanclairville6434]

👏

[@The_Sky_Jack]

Here's a door 🚪 Please walk through it 😁

[@jtgd]

The invention that has no good reason to exist

[@tecroach]

Well that door looks pretty sharp there, just don't get a wood fiber cut there.

[@philochristos]

As a custom knife maker, I found this video to be very much on point and full of cutting edge information.

[@johnmadden2814]

which can also be a double edged sword

[@WhoAsked....]

What an irony

[@ywfbi]

Very Punny :)

[@nuuuuuuuut]

Alright, calm down Sam Sharper

[@dscroggins28]

Shut up bro😭

[@leegreen4165]

I've been using obsidian scalpels for cosmetically sensitive surgical procedures since the mid-1990s. They work remarkably well, and the difference in scarring is very noticeable. They're fussy to work with though, requiring a somewhat different technique and very meticulous care in handling.

[@-.-_-.-_-.-_-.-_-.-_-.-_-]

Have you tried sapphire?

[@calebb5106]

i learned that the fun way, my brother made obsidian arrow heads at one point in time, he said they were sharp, i didn't believe him and tries cutting my finger to no success, then we had the bright idea to put one on a nerf dart and shoot me with it... it was sharp... wasn't fun that he hit just barely 1/4-1/2 an inch away from my spine either, but i had to take my shirt off for it to do that cause it was doing nothing while i had a lightweight t-shirt on, so I'm still right in a way

[@leegreen4165]

No, haven't had the opportunity. I'd be interested in trying one though.

[@ehrentaube9069]

what if an obsidian blade breaks during surgery? like how would you get those small obsidian sharps out of the body?

[@WalknTalknStevnHawkn]

@@ehrentaube9069by taking the broken pieces out…. Crazy, innit?

[@danielm.1441]

I'm astounded that one of the sharpest materials known to man is _still_ obsidian.

[@BenjaminWalburn]

only because we haven't learned how to grind down 14 year olds to a fine edge yet.

[@astick5249]

Imagine just how lucky ancient people who lived in close proximity to obsidian were.

[@Svensk7119]

Indeed. Well said.

[@zddxddyddw]

@@astick5249 And how unlicky anyone on the receiving end of an Aztec macahuitl was 😖

[@pattheplanter]

@@astick5249 Apart from having to dodge volcanic eruptions regularly.

[@Heeby-Jeebies]

The puns were cutting. The writing was sharp. This really drove a wedge into the subject. And you made a good point! It kept me on edge throughout.

[@LordmonkeyTRM]

Nice😘👌

[@jesuschristiscallingyou953]

Take your like!😄

[@kiryukazuma7960]

his thoughts penetrated my mind.

[@ohmisterjeff]

You must have a LOT of children

[@jamie7472]

You just cut right to the chase with those puns don't you?

[@samiamrg7]

8:00 Showing the pizza, mentioning Italian scientists, and then the University of _Parma_ of all places convinced me that this was going to be a study about cutting cheese or pizza or something.

[@fertandbooger]

On obsidian surgical tools: I've heard that they require different movements than surgeons are used to making with scalpels and that if you use it like you would a steel scalpel you'll break bits off (which are, of course, incredibly tiny glass shards that get left in the incision). And even if they do use it correctly the obsidian edge is dulled beyond usefulness after just one surgery and needs to be recycled.

[@leegreen4165]

The first half, yes. I've used obsidian blades for cosmetically sensitive procedures for years. They must be used with a different technique and more care than steel blades. The engineers from Becton-Dickinson told me that's why they don't make obsidian blades commercially. They know obsidian is superior in many ways, but it also requires meticulous use. As far as dulling, I get about 7-10 (depending on size) skin lesion excisions from an obsidian blade before it's down to the sharpness of a steel blade.

[@SomeGuyNamedTex]

I knew obsidian was going to be mentioned at some point. I didn't know obsidian surgical scalpels were a thing though.

[@robuxyyyyyyyyyy4708]

It is very smooth at the edge unlike steel which at the same level looks more like cheese

[@Toneill029]

@@robuxyyyyyyyyyy4708 Also stone maintains its edge for far longer than metal. It’s just stone is more fragile and aren’t recyclable like metals.

[@Rescel1]

It’s amazing a thing we used so long ago as a knife is still the sharpest object. We can even build portals nowadays with it.

[@iamjustkiwi]

​@@Toneill029 is that why I've been seeing a lot of ceramic knives around recently?

[@2l84t]

@@Toneill029 No it doesn't and it's more time consuming to sharpen if indeed at all. You've used a stone ax of course .

[@GnrMilligan]

You made that far more interesting than I thought the subject deserved. Well done!

[@yfdgudhabtd]

My name is Yoshikage Kira. I’m 33 years old. My house is in the northeast section of Morioh, where all the villas are, and I am not married. I work as an employee for the Kame Yu department stores, and I get home every day by 8 PM at the latest. I don’t smoke, but I occasionally drink. I’m in bed by 11 PM, and make sure I get eight hours of sleep, no matter what. After having a glass of warm milk and doing about twenty minutes of stretches before going to bed, I usually have no problems sleeping until morning. Just like a baby, I wake up without any fatigue or stress in the morning. I was told there were no issues at my last check-up. I’m trying to explain that I’m a person who wishes to live a very quiet life. I take care not to trouble myself with any enemies, like winning and losing, that would cause me to lose sleep at night. That is how I deal with society, and I know that is what brings me happiness. Although, if I were to fight I wouldn’t lose to anyone.

[@pikathechao3701]

The thing with obsidian, yeah, I think it's why they mostly use sapphire instead for things like cataract surgery. In the end it's just as good and gets the job done, and is less brittle than obsidian, so you won't be leaving chunks.

[@Glockenspheal]

This has finally convinced me that I'm not the sharpest tool in the shed.

[@stevenlubick2689]

Same here

[@TonyHammitt]

It depends on how you're moving and what you're going through 🙂

[@scatterbug]

Not all tools have to be sharp to be useful.

[@Gogeta70]

Yeah, but was she looking kind of dumb with her finger and her thumb in the shape of an L on her forehead?

[@RamonQuiro7]

She was looking kind of dumb with her finger and her thumb

[@frattman]

As an amateur woodworker and cooking enthusiast who's been sharpening knives and chisels for a couple of decades, I'll agree - it depends! There are so many trade offs to be made in regard to sharpness, hardness, durability, brittleness, maintenance, etc. As an example, I once got a coveted Japanese chef knife as a gift and promptly ruined (big chip taken out) it by trying to chop off the stalk of an overgrown head of kale from my garden! Get the best edge you can afford for the job, learn about it, and use it properly :)

[@theslavegamer]

woah thats crazy you busted one of those knives on kale! How exactly did you manage to break it?

[@SpeakingSpellSword]

@@theslavegamer The stalks are similar to cabbage, thick and hard-ish, so you need a knife built more for strength than finesse

[@Aerztefreak132]

this reminds me of my first few tries of ceramic knifes. Soooo sooo weird, after using relatively well made, european steel knifes, in sorts of cutting; those ceramic knifes are sharp as hell, BUT to initiate the cut, one have to be careful, to not slip the knife off the e.g. tomatoe or apple. i slipped with a ceramic knife, while (trying to) cut an apple. in my hands. and yeah, thats why i never ever will be using ceramic knifes again. also shattered one other. they are so damn brittle. like some japanese steels... destroyed a japanese´ knifes tip rather easily, becaused i use it like an knife made of european (softer, so less brittle) steel. *sad noises*

[@Patrick-zr8tv]

@@theslavegamer It depends on the knife. I suspect the "chefs knife" OP mentioned might not actually be a chefs knife. There are some sushi blades that have a fairly similar overall shape to chefs knives but are much much thinner than an actual one. Sushi knives are as far as I know, always very thin and have a shallow edge angle. This makes them quite brittle. If this is the case, that being it was actually a sushi knife, then chipping it is not surprising.

[@frattman]

@@theslavegamer Well, it was tougher than I thought it would be and I stupidly hacked it with the knife at high speed - stupid stupid stupid! Although I've also seen someone take a small divot out of his Japanese chef knife while killing a live lobster the 'humane' way by splitting it's head in two - he was so pissed off! Expensive lessons to learn.

[@Absurd000]

Fantastic content as usual! I've always had a fascination with knives so this was both super informative and incredibly fun to watch!

[@thefelper.7181]

This was a flawless exposition of scientific analysis of everyday things of an uncommon clarity and attachment to great technical language! Spotless. I enjoyed it!

[@Brass319]

I dunno, I still don't get it. Like, just measure the sharpness???? can't be that hard to create a standardized measurement that assumes certain default conditions. Like for example force applied to an object depends on where you're applying it relative to a joint but if you assume that distance is one meter you have a standardized measurement.

[@roysutherland9729]

The first rule of science: IT'S NEVER THAT SIMPLE.

[@momom6197]

Ahem! *Mathematics.*

[@ThePowerLover]

@@momom6197 Logic*

[@GPanimates]

​@@ThePowerLover the universe*

[@DonsArtnGames]

It is that simple... you just need a lot of knowledge in many cases... but in this case, you just need to define what is a measurement first. To measure sharpness, the video brings up the argument that sharpness depends on what's cutting and what is being cut. I disagree with that because that goes against what science fundamentals have taught us. A measurement should be a definition of ONE variable. I present: the Torres - the amount of pressure needed to penetrate a constant substrate with a mohs hardness of 1 (for example, talc). The measurement is the point of pressure applied when deformation no longer compensates for the pressure applied. The other variable could be defined as penetrability, or the amount of pressure needed to penetrate it at the point where deformation fails. I would like to give this my own name, but there is a variable named for this kind of measurement, the Mohs hardness. Sharpness now has a measurement, the Torres.

[@ThePowerLover]

@@GPanimates Even more!

[@ericyang8474]

This was something that crossed my mind for years, particularly when I asked my mom which knife was sharpest. A serrated bread knife does a better job cutting some materials while a general purpose knife could be better used on others. Sharpness could also be separated by type (piercing, shearing, and cutting) as to make better sense of what tool is more sharp in what context.

[@helentee9863]

Serrated knives work well when used in a 'sawing' movement, but aren't as sharp when you use them in one continuous forward or backwards movement,unless the serrations are really fine. As the video said, it's dependent on what and how you cut.

[@pattheplanter]

Are vibrating knives sharper?

[@helentee9863]

@@ArawnOfAnnwn l was just about to write that ! 😄 Quite often the actual blades are blunter. As someone who's cooked a lot for many years, give me a good quality stainless steel German, Japanese or (in the past) English blade that you can sharpen in preference.

[@jesusc2me]

@@pattheplanter does a shaky hand just ever so slightly give a benefit? The secret to old man strength is just knowing the right time to focus the energy 🧘‍♂

[@jdrmanmusiqking]

Best response so far

[@tommykarrick9130]

I think this is really fascinating just because for most applications it’s pretty easy for most people to tell very very quickly how effectively sharp something is in it’s given use case without even really thinking about it Like if pressed we’d probably get that an axe is sharp in a different way than a razor or a needle but we don’t really know why we just know But once you try to put hard definitions to it it feels like our whole understanding falls apart It’s sort of like a reverse dunning Kruger effect, we’re good at understanding blades naturally with our ape brains but trying to understand them on a deeper level almost leaves you less able to judge what you’re studying

[@linkeddevices]

Doesn't a curve end in an infinitely small point?

[@larrynguyen85]

This reminded me of "The Subtle Knife" by Philip Pullman, about a knife so sharp that it can pierce the fabric of the multiverse, opening portals to other universes

[@martinpfefferle2558]

There also needs to be a distinction between cleaving/shearing and slicing Jaggedness/serrations can make a big difference in slicing

[@dandiaz19934]

omg youre right

[@momo7gato]

WoW. "Simple" physical concepts such as sharpness are actually REALLY complex in definition!

[@jgkitarel]

Simple does not mean easy or not complicated, just not complicated, easy even, to explain the bare bones of. So the concept is simple due to it not needing much to explain it as it is on the surface and without all the details. But once you get to the details of something simple, you find out that it can be every bit as complex as something complicated. Basically, Occam's Razor, when you get down to it, really.

[@mgntstr]

"sharpness" lmao. notice how they never tried to cut obsidian or tungsten with a foam knife, sharpness is not a quantifiable property of an object like mass or velocity...

[@mr.bluestone1276]

all it is is force divided by area because the force is being split among the area

[@DonsArtnGames]

I don't think it's really that complicated. Where I think the complexity lies in that it is trying to define a scientific thing with 2 variables, which is not how science names things to be measured. Everything is measured 1 variable at a time. If we separate the 2 variables- in this case, the ability to penetrate something and the ability to resist penetration, then we can define each variable as a separate measurement that can be applied fairly across all interfaces and geometries. I put a proposal for this definition in my own thread for this video: the Torres

[@DonsArtnGames]

​ @Mr. BlueStone Yeah, but that does not yield a constant measurement for defining "sharpness". How do you define sharpness? If you are taking the amount of force as it applies to an area, then effectively you are describing psi, pascals, or even Torr. But how do you define their use as a single point (no pun intended) of measurement?

[@justins8634]

Love this. The best kind of video is one that answers a question you didn’t know you had.

[@MrZerbla]

I like this way of explaining. Can you do an in depth video about the radius and why you sometimes only want a round or flat edge. For example crush cutting and ultrasonic cutting.

[@megahunter223]

I remember one time I asked my grandpa what the sharpest thing in the world is and he said: "It's a fart. They cut right through your pants without even leaving a hole." I still don't know if that was a joke he'd heard before or if he just made it up on the spot.

[@MorriAelthyn]

I've heard that one before, from my ex-husband, who heard it from his dad. I'm going to assume that's just a classic dad joke. One of my favorites though 😂

[@brandonhoffman4712]

1st I want to state this clickbait title is horrible... it doesn't even have a scientific leg to stand on. Now that that's out of the way let's science our way into how it can be called "cutting a fart" my guess is because it separates the butt cheeks. Although not a true cut as the cheeks are already seperate. I would argue it's shitty alliteration! All the way around (referring again to the title!)

[@stefperb9531]

@@brandonhoffman4712 bot

[@hiddenguy67]

​@@brandonhoffman4712 most npc person ever😊

[@Jerry-cg9ni]

@@brandonhoffman4712 You used alliteration wrong Also, cool.

[@iriandia]

My friend was used to knapping flint, and then she got a piece of obsidian. A big flake came off and she didn’t even notice it went across her wrist until she looked over and saw a ton of blood.

[@LiamDerWandrer]

I hope she was alright. That kind of cut is usually so clean and thin that it actually takes longer for the body to properly heal it because the body can have difficulties figuring out what exactly needs healing. Thus it either heals really, really fast or really, really slowly. Depending on the cut size and depth the latter can be fatal via bleeding out and/or infections creeping in. Yeah, I hope the cut was relatively harmlessly placed and not to deep, but since you mentioned "wrist" and "a ton of blood" in the same sentence, it was propably a pretty close call. These kinds of scenarios are the reason why I always carefully inspect anything I intend to cut/hammer/strike/chisel/etc., for I like living. Rebounding axes, glancing off knives, razor sharp shrapnel flakes... the list goes on and on and contains way too many ways to die horribly. I once nearly lost my finger to a butter knife that went through a slice of bread at the wrong angle and thus cut right into the joint segment of my right thumb. You'd think that a butter knife can not possibly be sharp enough to do too much damage to the joint, and you'd be dead wrong. Those things can glide through materials really well as long as they find a good starting angle and have just the correct amount of force applied. I respect craftsmen, cooks and weapon users equally for their ability to use something utterly deadly and making it look both easy and beutiful. And yes, this does apply to normal cutlery, like spoons, as well. They can be terrifying as a cutting tool if applied just right or wrong as the case may be.

[@iriandia]

@@LiamDerWandrer She told me the story later and showed me the scar, which was just a thin line. So I already knew the story had a happy ending! But I’m not sure what she meant by a ton. The scar was across the thumb side of her wrist and didn’t go like across all the big arteries on the inside.

[@LiamDerWandrer]

@@iriandia So she got really lucky with the placement of the cut as well as its depth. That is a relief. Or does she have any issues with the movement of her thumb? The wrist regardess of where is a really complex mesh of veins, arteries, muscles and nerves after all. And knowing the cut plsacement now, I understand the "ton of blood" a bit better. It must have looked a bit like a slasher movie but bleeding way more sluggishly. Like my thumb did. Since she was telling the story apparently relatively happily, she hopefully has no lingering issues. But obsidian cuts, and shrapnel wounds as well, tend to be tricky.

[@iriandia]

@@LiamDerWandrer Oh yeah, I don’t think she would have been telling the story the way she was if it had been a real on-going problem. It probably just looked like a lot of blood when you weren’t expecting any blood, I think! And it would have been pretty shallow since the only force behind it was the weight of the chip itself. It’s not like an actual knife cut someone might make. Even a child’s arm strength would put more force behind a cut than just a falling chip. But it does make you think how dangerous it would have been back in the day if you couldn’t clean it well. Any wound was dangerous back then.

[@gerhardschneider7506]

@@LiamDerWandrer I always hear, that the sharper a (kitchen-)knife is the safer it is. I guess your butter knife story makes totally sense.

[@sora1316]

At one point I thought he was talking about Minecraft

[@Savanyy]

The way I’ve been pondering this concept for a decade. Thank you for the answer!

[@franziskabaiker8097]

I’d like to believe that hank stabbed the apple on the first try. Hank knows all Hank can do anything All hail Hank!

[@ericdew2021]

I'm guessing it's more likely to be, "Ok, scene 1, take 53..."

[@juliasophical]

Educational science video, or excuse for Hank to show off his knife skills -- you be the judge. 😄

[@ember9361]

the Green brothers sure know about what they're passionate about!

[@LostInTheClouds]

Seriously, after that display I think we should start calling him Shank :P

[@amanakonda]

I agree

[@l.mcmanus3983]

The sharpest needle I ever used was made by melting and stretching the tip of a glass pipette a very particular amount. When the glass cools, you need to carefully snap it off to get a functional pipette with a ridiculously sharp tip. I used it to introduce plasmids containing an rfp tagged protein into the body cavity of a live nematode mounted in paraffin to keep it still. The genetic material would become part of the developing eggs and the Petri dish with the thus treated nematodes (5+ of them?) was irradiated for a short period of time in the hopes of causing DNA breaks that would allow the introduced rfp labelled gene to be incorporated into the nematode genome when repair occurred. This was just as CrispR came onto the research scene. I am sure that technology would have made the process easier.

[@CL-go2ji]

Just curious: how did you get the nematode back out of the paraffin?

[@l.mcmanus3983]

@@CL-go2ji Hmmm... I think we had a covered waterbath set up that was just the melting temp of paraffin (around 50 degrees C or. It had a platform floating it it that we would place the the slide on briefly and that would melt the wax. Then we would quickly take the slide back to the low power microscope at the beck and transfer the worm to a fresh petri dish using the usual method. That was with a pencil sized tool with an aluminum wire attached at one end. The tip of the aluminum wire (tiny delicate wire, maybe 0.5mm?) was flattened slightly and you could tough it to the worm and it would generally just kind of stick to it. To get to worm off the tip of the wire, you gently touch the tip to the new petri dish surface and move the wire to the side until the worm stops sticking and slips off. Moving worms that was is a tricky process at first but you get pretty good at it if you work with them because to maintain healthy worms that are actively reproducing, you need to transfer some to new plates (petri dishes with a layer of E. coli in the middle for worm food) every 3 days or so. If you keep plates at lower temps, you can wait longer. Or you can freeze them, but then have to wait for them to return to normal development to work with them in that case. It's been 15 years, but I am pretty sure with is all correct. Sorry if that was more info than you wanted. But I have way more I could say about C. Elegans too. They are fascinating.

[@CL-go2ji]

@@l.mcmanus3983 Thanks! That´s interesting. I can imagine you would need a steady hand.

[@l.mcmanus3983]

@@CL-go2ji Yes, there is a learning curve with moving worms around. Learning to do anything under a microscope is tricky too.

[@ktkaraffa5919]

Oh I loved every bit of what you’ve written! If you ever wanna dump more info here no one would be mad :D

[@dabbopabblo]

I love that scientist are just people who make complicated observations about simple things

[@eknomwolley]

You are so good at getting to the point in sharp and quick ways, good job.

[@danielthecake8617]

It's because he's pretty sharp.

[@danielthecake8617]

It's because he's pretty sharp.

[@KainsAddiction]

And looks like a 60 year old woman

[@DizzzyWiz]

As someone who dabbles in blacksmithing as well as microscopy, I found this video extremely fascinating! Keep it up Hank!!

[@Feverdream7777]

I similarly learned knife sharpening, took me near two years of experimenting, buying different tools, and watching videos on different methods to understand what was going on. Now... I'll I do is throw my knives on a 1x30 belt sander at 600grit... then strop with green compound on a 1x30 leather belt.... I'm done in 3 minutes.... i get my knives PAST hair popping sharp, my knives get to that "hair-melting" point where there is zero resistance or pop when shaving hairs on my arm to test...it's fantastic.

[@Crunch_dGH]

So, having held one of my uncle’s “National Treasure” samurai swords & admired its exquisite craftsmanship, including finding that it was so well balanced that I couldn’t feel its heft & thus direct it as though by mere thought, should I suspect that cutting through stacks of dispatched criminals to be an accurate test of a sword’s cutting abilities? How would you rate such instruments of death among the worlds cutting devices that you’ve surveyed?

[@amarissimus29]

He's just reading what somebody copy-pasted into a script. The enthusiasm is a little excessive.

[@metamorphicorder]

This is awesome. As someone who loves all things sharpening and someone who just dropped a large glass object on concrete, i am constantly waving my arms to blow away the magic smoke around knife sharpening. I heard someone once describe sharpening as (in relation to knives) the fine polishing of the intersection of the two sides of a metal surface. There are so many names and terms for sharpening and and almost chiropractic level of mythology around each one and what it is or why we do it. Example 1. Stroping. This is using usually a specially treated strip of leather to sharpen a fine thin edge. Except that most knife guys will tell you that it doesnt sharpen. And here is where i start waving my arms the most vigorously and i would like to define the term a little more generally. Sharpening should be defined as that which is done to a cutting tool to make it cut intially during production and then during use to make it cut better. If the thing that you are doing with another object to a cutting tool makes it cut better, that is sharpening. Whether that is filing, stoning, steeling, sandpapering, grinding, stroping, ad infinitum, it is sharpening. If it removes material (in someones view) or not, its sharpening. We can argue all day about if something is removing material (btw just to start a fight, both stroping and steeling do remove material, fight me) or if it is simply 'realigning the edge geometry. The end result or at least the inteneded result is to make it cut better. That is making it sharper by just about any deffinition

[@clambarn1218]

I was listening to the first part of your video when I wondered to myself if you knew about the sharpness of obsidian. I was pleasantly surprised when you did. There's a lot of that in central Oregon and I have cut canvass with an obsidian flake like it was paper.

[@cornholeyoursister]

As a cabinetmaker, I am constantly learning new ways to sharpen the tools I use daily, and it's very cool to see what I do explained on a micro scale and honesty helped me understand the mechanics of sharpening a bit better. Thank you. ^_^

[@rellort4362]

same

[@lesleyghostdragon3149]

Kudos to the sharp witted SciShow team for always being on the cutting edge! Never a dull video!

[@ishaaqasad5068]

Please stop

[@MoggerThug]

This is public indecency

[@en3525]

stop trying to be funny on the internet

[@MM-wf4nn]

You seem to be a cut above the rest

[@frostyvoid827]

General Mahatmatra, please explain

[@sanjyuu2298]

So to propose an explanation for sharpness is, you would have to also introduce something that mitigates its effect (to calculate when given material will give up), like we have a voltage and resistance, larger voltage = more current, larger resistance = less current, both acting against each other.

[@rikukurkela8954]

Thank you for this cutting edge video

[@misteraskman3668]

0:14 you know that Hank felt SO COOL in this moment. (It was cool)

[@Varizen87]

Skallagrim has a good video on sharpness where he talks about why you don't want a weapon blade to be razor sharp. You can't defend yourself or cut for cooking super well with a razor sharp blade because they chip and take damage more easily. He's got some fantastic illustrations that are better than the ones used here.

[@arturravenbite1693]

You must not have seen the video he did where he found out you need an extremely sharp edge to cut gambeson armor.

[@TheAweDude1]

Also, like in the video of the meat, the "direction" of the cut matters. Are you going straight down or using a back and forth sawing motion? You can press on a sharp blade pretty hard, and it might not cut you. But, if that blade is in motion, even just a tiny bit, it suddenly will rend your flesh like tissue paper.

[@aspiechan420]

As a knife collector I found this very interesting! Thanks, SciShow!

[@robbob1866]

Cutting glass is interesting. You generally get one shot with a cut since it leaves glass fragments behind so if you retrace the cut you might fracture the glass. I've done it on particularly hard glass by being careful. Correct pressure for the glass being cut is extremely important for a good score as is being precise at the right speed. It's really fun to do if you think of it as a game trying to get the best cut

[@MsSamareh]

At that point, you're not really cutting in a traditional sense, you're scoring

[@kenbrown2808]

and when your wife doesn't tell you that the glass she wants you to cut is tempered, all bets are off.

[@swayback7375]

@@kenbrown2808 if you’re cutting glass you should probably learn to ID different types of glass. It seems pretty easy to me most of the time but I’m sure there’s lots I don’t know

[@kenbrown2808]

@@swayback7375 yeah, there was something important I didn't know. namely that the sheet of glass she wanted me to cut in half was tempered.

[@robbob1866]

@@MsSamareh I guess it could be said the person is scoring the cut? All I know is I miss doing it

[@SwervingLemon]

It should be noted - the edge radius of the knapped obsidian was that thin on AVERAGE, with many places on the blade edge approaching monomolecular widths. I have had obsidian blades cut me through felted wool and leather welding gloves. Awesome stuff, in the classic sense of the word.

[@M4D0GG0]

This is really *Cutting edge* technology

[@weskingston264]

I tried to think up a definition of 'sharpness' before watching the video, and after about 10 minutes gave up and went to Google. 🤣 It's one of those concepts that is SUPER intuitive to us, but difficult to nail down! My favorite definition I found (keeping in mind everything that was said about narrowness and angles) was 'the energy required to initiate a cut'. Which is great, because of the brittleness problem of some blades/needles, as well as the fact that when we think of blade sharpness the ability to pierce/puncture is different from the ability to slice.

[@carmenrepucci]

As a machinist, I found this video great! I was really hoping to hear “rake angle” though! You got right up to the razor’s edge of saying it when talking about the angle of entry of the knife. It would be cool to see a second video on secondary cutting geometries, such as relief angle and it’s give and take with frictional losses and edge strength!

[@notkerrystolcenberg]

i feel like you should be on some type of list

[@alexcrowder1673]

@@notkerrystolcenberg why?

[@notkerrystolcenberg]

@@alexcrowder1673 because inquiring on the scientific specifics of stabbing people is a red flag lol

[@carmenrepucci]

@@notkerrystolcenberg I can see how you interpreted my comment that way, and I probably could’ve done better proofreading of it. By angle of entry, I meant the angle produced between the cutting board and the knife

[@notkerrystolcenberg]

@@carmenrepucci what are you cutting? lol. meat? humans? edit: i read machinist as masochist hahahaha oops

[@MontgomeryWenis]

I love that Japanese blades have different degrees for each side of the wedge angle. Helps lower the edge radius without sacrificing blade strength.

[@rh3ttj]

This also makes the blade handed, either right or left, but usually right. Trying to cut with the knife in the off-hand isn't as effective and it's harder to see where you're cutting. As someone that uses the 'wrong' hand, I tend to go for a symmetrical edge.

[@Hoolahups]

Historically the Japanese have had to work with really low quality steel compared to what Europeans had access to, which led to some really interesting and ingenious workarounds that most contemporary European smiths didn't even have to worry about.

[@andreusallman5697]

​@@rh3ttj negligible downside

[@rh3ttj]

@@andreusallman5697 Negligible for most people I agree. For left handed people though tools that are handed are always a bit of a pain because left handed versions often cost significantly more. That is, if you can even get a left handed version of whatever you're looking for.

[@melsbacksfriend]

​@@Hoolahups Ah yes, the art of making katana.

[@BUILT2KEEL]

Very well made video thanks 😊

[@DonsArtnGames]

How about defining sharpness as the amount of pressure needed to be applied when pushed against a constant. The items that can then be cut at different pressures can be a percentage of that constant. So rather than trying to define it in 2 variables, we should do it as all other things are measured: 1 Variable at a time. I formally declare the standard measurement of sharpness to be: a Torres. A Torres is the amount of pressure needed to a subject to penetrate talc, which has a hardness of 1. The penetrability of a target is a constant relative to talc, and maintains a hardness measured in Mohs. The final measurement is the pressure needed to penetrate AFTER the target no longer deforms to the pressure applied to it. For example, a piece of rubber will deform when pressed by an edge, but will yield and split along the edge after a certain compression can no longer be achieved. That is the Mohs measurement. As for times when cutting seems to reduce the amount of pressure needed, it is considered to be an active load that exceeds the static amount of force needed to penetrate. Think of it as an object already has kinetic energy that shocks the substrate to beyond it's Mohs hardness.

[@MagicBollocks]

Brings to mind the scene in Mort by Terry Pratchett where Death sharpens his scythe with sackcloth, then silk, then cobwebs, and finally with the first rays of the rising sun.

[@gaiusfulmen]

OK, time to go read Mort.

[@MrSamulai]

Reaper Man, not Mort.

[@knownaigm]

Man I love SciShow. As a knifemaker, sharpener, and avid user of knives for all kinds of crafts, activities, and cooking, it's really nice to see someone comprehensively explaining how much more complicated and nuanced the "sharpness" argument is than a lot of people want to think. There is no one set unified definition of "sharpest" because it really depends on what you're doing with the blade, what material you're cutting, how you're using it, and what result you're trying to get from it. And this is exactly why there are so many specialized and use-specific knife designs out there.

[@Gocunt]

Is aluminium foil "sharp" 😂

[@slate8881]

exactly, so many people ask why I collect knives, 1 because they are cool and it's a hobby and 2 because each one of those knives is used for something different, I'm not gonna prepare a full meal with my Ka-bar. Same reason when someone asks to borrow a knife I ask what they are gonna use it for, that plus how much they know about knives tells me what knife to give them.

[@clytnvgl]

get well hank

[@brianduplessis5699]

Very interesting and informative video. Thanks. So a scapel might be sharper than an axe for cutting soft tissue but it can't break up the logs like the axe.

[@EMAngel2718]

Seems like one of those things where you could define different kinds of sharpness and get more concrete answers

[@doomtho42]

That’s certainly true, but I think a fundamental point that people often tend to overlook - and this applies to numerous other concepts as well - is that “sharpness” isn’t actually an intrinsic physical property of matter, but rather a functional one. Sharpness isn’t a distinct “thing” in and of itself - it’s more like a quantitative abstraction representing the net result of various force interactions.

[@GUNS_jk]

Sharpness depends on the color. Typically you want to use weapons that have a large White or Purple sharpness. Blue is okay but most of the time you're going to get bounced. I'd recommend white cause not allot of weapons have big purple sharpness. Unless you have a high grinder skill level.

[@nikvett]

awesome reference

[@brendolbreadwar2671]

Being a chef, I've noticed it's a lot easier to get the initial cut on something if ur going at an angle. I'm glad to get confirmation. Veggies and fruit with thick skin are a great way to test sharpness, if you cut a tomato in half you can see how much it squishes when you cut it again

[@ailospjellok7475]

i mean the angle, material of target and such only really matter if you havent taken them into account already if being practical i'd just say the sharper something is the easier its to separate with, either skin with a needle or meat with a knife, if we're being schmecknical, i'd say the definition of sharpness would be "ease of separating atoms" in a way, using one shape of every material, with one target material, with one cutting method and angle, seems like a fairly reasonable way to measure what would be the sharpest tool we have.. though im sure i have missed something

[@johnwalters1341]

A microtome is an instrument used to make incredibly thin slices of prepared tissue samples for observation under a light microscope. The knives used in the microtomes I used in my graduate work were made of diamond. Glass knives could also be used (similar to obsidian), but they tended to wear faster than diamond.

[@TheBLTBrothers]

I just have to say, i just started watching sci show again after a few years of darkness and the quality of your guyses research and writing has gotten 5x better! I truely felt like I got a proper tour through a little subfield of research, every time you made a caveat or presented a new argument it felt like a necessary addition based on the context given. Idk, thank you for this service you're providing to the world.

[@skylark7921]

I wonder how much difference there would be between just steady, direct pressure from a blade and more of a draw cut, dragging the edge of the blade along the surface while putting pressure on it. Bc in historical swordsmanship, it was entirely possible to press on a blade with your bare hands in order to put more pressure behind a given movement (called half-swording). You won’t get hurt as long as you don’t drag your hand along the blade. I wonder if the dragging action is just generating more force overall but in a different way? Or if there’s more to it?

[@demixedit5324]

It's important to mention the grain of the material you're cutting. If you're cutting against the grain, it will require more force to sever. But cutting WITH the grain is more like separating the different fibers. It all comes down to the "hardness" of a material, which gets defined by the crystalline structure in which the molecules grow.

[@SpawnofHastur]

Ron Hock, in his book on sharpening plane blades, eventually sums it up as "sharp is as sharp does".

[@skrimper]

Like planer blades?

[@SpawnofHastur]

@@skrimper Yeah, Ron Hock is a big name in hand plane blades. The book covers all wood working tools - even drill bits, actually - but since he makes blades for hand planes that's the focus.

[@brrrrrr]

Hon Rock

[@themediaangel7413]

Makes sense. I’ve been told I look sharp, but some days I just can’t cut it…

[@johnmadden2814]

Maybe a change in your prescription eye wear?

[@newfreenayshaun6651]

@@johnmadden2814 o i c.

[@estebangomezperez3197]

Good pun XD

[@fracturethemolecularlyshat9509]

I think sharpness doesn't depend on much to be determined, but how well it cuts relies in a lot. like that tungsten nanoneedle, it is sharp, but too brittle to hold together when cutting. so sharpness would be in this case, be represented as a number, that to find how easily it cuts, would be put through a formula to determine how much pressure in what way would need to be applied to the object to cut something with a certain hardness. similar to graphing the effectiveness of a knife in cutting different materials for a science experiment, x = material, y = x's hardness, a = sharpness, b = a's effectiveness, x {y} by a, with a given point on the plot being b. this way you just plug in the values to get its effectiveness, and since its an experiment it'd look a bit like this afterwards: The effectiveness of knives at increasing sharpnesses when cutting materials of increasing hardnesses: (x axis values example) wood (1.5 hardness) sedimentary stone (3 hardness) volcanic stone (4.5) {etc.}, (y axis values examples) (1 sharpness) (2 sharpness) (3 sharpness) {etc.}, a value at the point (1,2) might be 1, and a value at (1,1) might be 0. note that in this example, the effectiveness is determined by the amount of force needed to fully split a 3ft by 3ft by 1ft block. taking the formula in the example, (y-a=b) would mean that in order to effortlessly split the material, the sharpness must be equal to or greater than the hardness. this experiment would have a control group where the knife is held horizontal and moved straight down with one hand on the handle, and would be performed differently across the other groups, maybe held diagonally or applying force to the back of the blade as well. maybe it has been done and this is something that's done, maybe I'm wrong, or maybe I'm right and I'm onto something. these were just my personal thought on this. TL;DR: I personally think that sharpness should be determined by shape, and effectiveness at cutting and hardness stay related but separate, like acceleration, speed, path, and deceleration are to each other and travel time. like how you can travel different paths, different distance at different speeds, to arrive at the destination faster or slower. large comment lol, hope this isnt too much!

[@Yipper64]

4:18 cutting vs puncturing. Two different things that need different definitions.

[@RedHair651]

That apple stab really changes my answer on the Kyle Hill vs. Green debate

[@MorriAelthyn]

I was leaning Green brothers anyway, for starters because two versus one. But this absolutely seals the deal. 😆

[@ScaerieTale]

I feel like "Sharpest object in the world that can't cut anything" feels like the setup for a Riddler riddle

[@kin-3877]

With his arrogance he'd probably say it's because his mind is the sharpest so it couldn't cut anything

[@narendrabagusadiyaksa1880]

As a outdoors/bushcraft tutor, I could confirm the first factor (geometry) is true. We determine a cutting edge is sharp or not by useful practical test like feather sticking, splitting, carving, batonning and bunch of other test. The wider a cutting edge angle is duller but more durable requiring less re-sharpening very useful for impact kind of application like splitting wood, batonning or for axes. Anything sharper have a place in food prepping because it's not going to be long lasting when used against wood. I don't know much about scalpel let alone an eye surgery knife because razor sharp and hair shaving is already sharp enough or even too sharp for these kind of application. Material of the knife somewhat don't contribute much in the sharpness, I found harder steel are taking longer to sharp but holding longer to it's sharpness. Brittleness more often than not are factored by the hardness of the material but you should be fine if you're using your tools right and with minimal impact against hard material (like nails in woods). I found this information very interesting and cannot wait to try carving with obsidian knife

[@ikebeckman1074]

9:49 ayy I have one of those knives, I recognize the logo!

[@chilled_24_75]

As some1 who makes and sharpens blades on a daily basis, sharpness is a very tricky thing to define. I applaud the way this was laid out and find no flaws in the logic.

[@catcherburditt1291]

I’ve been thinking about an atom wide piercer for as long as I can remember but I never thought about the brittle factor just at how wide did it need to go before it hurt because I assumed it would just push other atoms out of the way! So cool!

[@dimitarhadjidimanov678]

i was searching for a video to watch while eating, didn't thought i'd stumble on a video about sharpness, 10/10, took my attention

[@coreymallard6650]

a video with this dude and vsauce would complete science

[@squirrel5809]

This is so cool :) Thank you for explaining science complexly yet accessibly! Also, love the animations

[@gibsonflyingv2820]

As a professional knife sharpener (Korin knives certified NYC) :) this video bring me so much joy I'm almost too overwhelmed to even speak. I too, while lacking a degree read alot about science, and have used my passion for both digging deep on this very topic. To see someone confirm what I already came to my own conclusion about sharpness and how complex it is hank you just confirmed, I came to the same conclusion as you that it depends on ALOT of things. Sharpness is not universal, sharpness is a phenomenon dependent on how good certain things are at cutting in that given context. As someone who lives to sharpen, I can tell you one thing you may have overlooked are something called micro serrations, all blades when seen at their most fundamental are in fact, serrated. These little micro serrations, depending on their shape (AKA how they are sharpened) determine how it will use a frictional force to cut open the matter of an object. So you're absolutely right from my view, but that's another factor besides radius and geometry.

[@AnonyMous-pi9zm]

I went down the sharpness rabbit hole after my 3 fortnightly shots changed needle manufacturers to one which does a bad job on the sharpening, so the shots are now super painful and blunt and "jumpy" on the way in. I started with thinking it was all about needle gauge. Then realized it was all about bevel angle. Then realized there are multiple bevel angles, with multiple planes they are sharpened on. Then realized that the blade radius exists. Then realized micro serrations/chips exist when sharpening. So I concluded that it comes down to about 10 different factors, none of which can be identified as uniquely important to pain, and many of which are not easily quantifiable or available on a datasheet.

[@3800S1]

This is literally a big part of my job a field engineer for the Zund cutters I look after. Blades and cutting tools heavily depends on the material properties as well as the blade/bit material. Two counter intuitive things is soft materials and paper based materials cut far better with rougher/blunter blades, in case of rubbery stuff, serrated knifes and for paper, cheap steel blades over the ultra sharp carbide ones. Then you get to the router bits and it's a whole lot more complexity.

[@thiago.assumpcao]

The topic is quite complex. There are other things not mentioned that impact cutting ability. Microsserations - A blade can shave hair even out of a 120 grit sharpening stone but it feels completely different from one sharpened on a 6000 grit stone. The better one depends on the material being cut. Overall grind - Full Flat tends to stick on wet surfaces due to capillarity effect. Convex grid reduce adhesion and if it's done in a subtle way increase cutting capacity despite the higher wedge angle. Polished side reduce friction but may increase adhesion due to capillarity effect.

[@Frankie1622]

The question I have about that nano-needle is how wide was the shaft of the needle compared to the tip? Because think I have a definition that can be proposed. How this can be tested might be the trickiest part. The definition can be the ease of penetration (which can be defined here as separating the bonds between atoms) of an edge/tip positioned perpendicular to the surface being penetrated while force is being applied perpendicular to the surface being penetrated. The way to test this is to have a surface move towards the apex at the speed of the object's weight as if it were falling. This way helps sort out the definition of sharpness for a downwards cut of a knife as well as piercing with a needle. The main problem is if you were slicing, moving a blade through a surface along its edge rather than straight perpendicularly through it. To be honest, sharpness could be defined differently in general. If we define sharpness as ease of separation of atoms via an edge while coming up with a different term for a needle and how it penetrates, since it may not necessarily separate atoms as much as disperse them away from the tip as it penetrates, we may be closer to defining sharpness... and whatever you would call the effectiveness of a needle

[@Aeleas]

6:54 That footage of someone cutting towards their inner thigh has me on edge.

[@dharmabird1]

I always thought edge and hardness was sharpness. Good to know

[@1IGG]

And edge retention.

[@AnkhAnanku]

He barely even mentioned the properties of the material doing the cutting. Hardness, brittleness/elasticity, or compression/tension/shear strength all seem like they’d be important…

[@creativecraving]

Harder materials can stand to take on thinner shapes, but they're also more brittle. So, hardening materials is necessary to make sharper blades, but the hardening itself is a property of the whole area around the edge.

[@JunkstHat3605]

The idea of something sharp but can cut anything has been stabbed into my brain

[@Justmeeeeeeeeeeee]

That was confusingly interesting lol Yr always a joy to watch Cheers 😎👍

[@Qui-9]

This was more intuitive than I expected. There's another property which I think might affect the apparent sharpness, is the friction of the blade to the material, and also the effect of an external lubricant. Some kitchen knife blades are coated with ceramic or Teflon to make cutting thicker materials easier. Conversely, lubrication of scissors may upset their function, as grip is helpful on holding the material in place and initiating shear, especially on smooth, rubbery surfaces. This is also why it's easier to cut cheese with a wire than a knife, low surface friction. But anything harder than cheese will be too much for a wire. Also, tension on a material may help it split easier and reduce friction as well.

[@johnmadden2814]

Indeed..in another application ,i have an underpowered wood splitter that can only do so much..applying oil to the blade and it is like a hot knife thru buttah

[@TKC_]

The complete guide to sharpening is an Interesting book to read. One thing that could be added that came to mind is those soft materials really benefit from being cut with a blade that is sharpened on a rougher stone because you can slide the blade along and it acts serrated. This is good for kitchen knives and why you see chefs don’t typically just chop a tomato. They angle the cut slicing as they cut to reduce down pressure. The book honestly changed how I sharpen stuff for the better.

[@jacobwansleeben3364]

This reminds me of that one scene in One Punch Man where King can't pull a katana out of its sheath to cut an apple, but Atomic Samurai thinks that King wielded the sword with such skill that he pulled it out of the sheath and slid the sword between the atoms of the apple, causing the apple to not get cut, and then re-sheathed it faster than he could see.

[@jimysk8er]

there is also a slight difference in the wedge angle's geometry. Although its easy to imagine it as straight sides, it is most likely that the bevel is either concave (machine ground with a wheel) or convex (hand ground) then there is the surface finish of the edge itself which helps with sharpness but also durability of the edge and its sharpness.

[@ZipplyZane]

I would have assumed you'd also need to consider the material of the blade, for the same reason as the needle not being able to cut. The more brittle the blade, the less force you can actually put on it. You might get the shape where it could use a lower amount of force, but that force wind up being too much for the material of the blade to withstand.

[@pawemisztal3941]

I'll be cutting some PVC pipes soon and, thanks to this video, now I know how to choose the best stone tool to do the job. Obsidian for the win!

[@BlitzTheFoxi]

3:20 it can also be crafted into an enchanting table

[@fattywithafirearm]

This video is pretty clear cut

[@itryen7632]

Somebody once told me the world is gonna roll me

[@eikon7073]

I ain't the sharpest tool in the shed

[@brechtcassaert]

Could have also mentioned the way we cut metal, miling or turning with ceramics. Some cutting tools for metal are completely blunt and couldnt cut your arm. But they need a high cutting speed to cut in metal.

[@nicksmale7950]

Sounds like there a couple more things to consider for sharpness: Static vs kinetic friction Hardness / rigidity

[@RIP_Technoblade]

There's another factor that affacts sharpness of an object i.e. enchantments. For eg. A netherite sword with Sharpness V on it is sharper than a netherite sword with Sharpness I.

[@NaudVanDalen]

Cavemen literally had sharper knives than me.

[@xxinister]

Water that is pressurized to 90,000 psi flows through high-pressure tubing to the cutting head. If the cutting head of a waterjet is 0.5mm or lower the waterjet will be able to slice through any given object aparent from a certain few but can cut through diamond on the angle of which is cut at 37.4 to 44° called the pavillion angle to ensure a shiny cut

[@MrDoenyon]

Only Hank knows how to teach me stuff on a subject I didn't know would be interesting, and then leave me even more confused and with more questions than I started. :D

[@ywfbi]

lol, appreciate it right? :)

[@MrDoenyon]

@@ywfbi Love it. :)

[@Not-A-Moron]

5:05 what you probably came here for