[HN Gopher] Karate physics: How your hand can break concrete wit...
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Karate physics: How your hand can break concrete without breaking
itself (2021)
Author : PaulHoule
Score : 57 points
Date : 2024-05-03 19:25 UTC (3 hours ago)
(HTM) web link (daily.jstor.org)
(TXT) w3m dump (daily.jstor.org)
| hi-v-rocknroll wrote:
| Impulse control. ;)
|
| Also, the videos "demonstrating" breaking multiple bricks or
| boards are fake.
| tiltowait wrote:
| People absolutely can break multiple bricks or boards, without
| fakery[0]. Or are you referring to specific videos?
|
| [0] "Fakery" including scoring the wood. But multiple breaks
| usually takes some setup, such as putting small spacers between
| the pieces of whatever you're breaking. If you consider that
| fakery, then ... I guess?
| hi-v-rocknroll wrote:
| Scoring is absolutely fakery, and sometimes the boards are
| cut 90% of the way through on the hidden side (evidenced by
| clean breaks). So are spacers because "breaking X boards"
| means stacking the boards directly on top of each other, not
| using the leverage of displacement of breaking each one one
| at a time.
| khazhoux wrote:
| > "breaking X boards" means stacking the boards directly on
| top of each other
|
| That's just your interpretation.
|
| If a man breaks /n/ boards which were not pre-cut, then he
| broke /n/ boards.
| hi-v-rocknroll wrote:
| Ethics > lawyering. If they can't break x boards
| unqualified, then they can't do it. If they can break x
| boards specially arranged or modified, sure, but that's
| called "cheating". It's a gimmick.
| anamexis wrote:
| Let it be known that according to hi-v-rocknroll's
| personal code of ethics, it is cheating to break x boards
| if they are arranged in a specific fashion
| margalabargala wrote:
| That doesn't seem right.
|
| Logically, the claim "I can break X boards" evaluates to
| true if there exists some configuration of X boards which
| that person can break. They aren't claiming "I can break
| X boards for all possible configurations of those
| boards".
|
| No one can break even one board unqualified, because the
| board could be 20 inches thick and made of lignum vitae.
| Thus by your definition the phrase "can break a board"
| becomes useless.
| kragen wrote:
| i've definitely seen people breaking multiple boards by hand
| and foot without spacers or scoring the wood, repeatedly, up
| close, over years. i've done single-board break demos myself.
| the one piece of 'fakery' they did use was that they broke
| the wood parallel to its grain, not across the grain, and the
| individual boards were only ever "one inch" thick (which
| means less than one inch in the usa due to reasons), even if
| there was a stack of eight of them
|
| the force required to break a beam is proportional to the
| square of its thickness, so breaking one two-inch board
| requires the same force as a stack of four one-inch boards
| hi-v-rocknroll wrote:
| Videos or it didn't happen.
| tmtvl wrote:
| You want to see people break multiple boards without
| spacers? https://www.youtube.com/watch?v=MoZhFSakOf0
| rabbits77 wrote:
| While I am sure there are faked videos out there somewhere I
| have personally performed multiple non-fake multi-board breaks
| as have many other people. Generally there is one "trick"
| though: pencils or small wooden dowels are used to space the
| boards apart which makes the stack of boards weaker than if
| they were stacked without spacing. I'd argue this is an
| allowable aspect of showmanship in that five separated boards
| is cooler looking than two or three stacked without spacing!
| hi-v-rocknroll wrote:
| "Cooler" is bullshit fakery and cheating. Stack those boards
| without spacers and try it again. Make a video of it showing
| the top and bottom of each board as they are stacked onto
| each other. Also use green grade A solid pine boards no more
| than 2' / 61 cm long, and at least 5.5"/139 mm wide and
| 1.5"/38 mm thick. ;@)
| Cthulhu_ wrote:
| Nobody is claiming they can do that though, so it's not
| cheating.
| zitterbewegung wrote:
| This isn't taught or done as much anymore due to insurance claims
| .
| jackbravo wrote:
| In the US :-p
| MarcScott wrote:
| Breaking in on my Tang Soo Do sylabus at every belt grading. We
| do use plastic break boards rather than natural wood or
| concrete though.
| achow wrote:
| Now it makes sense..
|
| _Human bone is five times stiffer than concrete and fifty times
| harder to break_
| Cthulhu_ wrote:
| Caveat: the bones in the hand are really thin.
| krapp wrote:
| My old kenpo sensei used to say punching someone in the face
| is the last thing you want to do in a fight, since you're
| likely to do more damage to your hand than to your opponent.
| And most people don't know how to make a fist properly
| anyway.
| Terr_ wrote:
| On the subject of "what to strike with", I'm reminded of a
| Terry Pratchett book-quote:
|
| > [The werewolf] gave him a ringing slap and that would
| have ended it, except that it also pulled itself a little
| further up the tree and brought itself within the range of
| the Vimes Elbow.
|
| > It justified the capital letter. It had triumphed in a
| number of street fights. Vimes had learned early on in his
| career that the graveyards were full of people who'd read
| the Marquis of Fantailler. The whole idea of fighting was
| to stop the other bloke hitting you as soon as possible. It
| wasn't to earn marks. Vimes had often fought in
| circumstances where being able to use the hands freely was
| a luxury, but it was amazing how a well-placed elbow could
| make a point, possibly assisted by a knee.
|
| -- _The Fifth Elephant_ by Terry Pratchett
|
| A footnote from an earlier reference explains that:
|
| > * The Marquis of Fantailler got into many fights in his
| youth, most of them as a result of being known as the
| Marquis of Fantailler, and wrote a set of rules for what he
| termed 'the noble art of fisticuffs', which mostly
| consisted of a list of places where people weren't allowed
| to hit him. Many people were impressed with his work and
| later stood with noble chest out-thrust and fists balled in
| a spirit of manly aggression against people who hadn't read
| the Marquis's book but did know how to knock people
| senseless with a chair.
| Delk wrote:
| The classic martial arts trivia (or possibly a teaching) is
| that serious brain injuries became more common in boxing
| after padded gloves started being used. Bare knuckle boxing
| seems more brutal but it's said to have been safer in that
| regard.
|
| Using padded gloves allows for hitting the opponent much
| harder without injury to the hand, so they make it possible
| to hit with a lot more force. Serious brain injury is
| caused by accelerational forces, and those are only
| slightly reduced by the padding, but the padding gives
| significant protection to the thin bones of the hand.
| Without the protection the bones in the hand could break
| when struck against the relatively hardy bones of the
| skull.
|
| Of course if you did happen to nicely hit the jaw, that's
| one of the common target spots for a knockout. A hit on the
| jaw causes a rotational force on the head which can more
| easily lead to a knockout (as well as injury to the brain).
| Terr_ wrote:
| Stuff like that is why I laugh a little at cyberpunk "cyborg
| metal arms" stuff.
|
| Sure, it opens new possibilities for when you really need to
| crush a brick in your hands... but often people don't realize
| how impressively irreplaceable our _natural nanotechnology_ is
| when it comes to delivering on a total package of features, ex:
|
| 1. Supports a very large number of individual movements and
| articulations
|
| 2. Meets certain weight-restrictions (overall system must be
| near-buoyant in water)
|
| 3. Supports a wide variety of automatic self-repair techniques,
| many of which can occur without ceasing operation
|
| 4. Is entirely produced and usually maintained by unskilled
| (unconscious?) labor from common raw materials
|
| 5. Contains a comprehensive suite of sensors
|
| 6. Not too brittle, flexes to store and release mechanical
| energy from certain impacts
|
| 7. Selectively reinforces itself when strain is detected
|
| 8. Has areas for the storage of long-term energy reserves,
| which double as an impact cushion
|
| 9. Houses small fabricators to replenish some of its own
| operating fluids
|
| 10. Subsystems for thermal management (evaporative cooling,
| automatic micro-activation)
| mywittyname wrote:
| I was a karate practitioner and instructor in my youth. Board
| breaking is really, really easy. The key is the boards designed
| for breaking are cut in their weakest orientation. Wood is
| incredibly strong going with the fibers, even a pine board is
| very hard to break long ways using a sledge hammer. However, if
| it's cut on its short axis, it's incredibly easy to break. Most
| people, even children don't need any guidance beyond, "punch
| through the board" to be successful. Breaking boards is more
| mental than physical. If a student is struggling or a novice, the
| person holding the board can hold their hands a little wider to
| make it easier to break.
|
| Concrete is more difficult, but there's still a trick to it. The
| blocks you use for breaking have a bit of flex to them, but are
| also extremely brittle. So just getting it to flex just a small
| amount will cause them to break in half. That's also why you
| place spacers between stacks of bricks or wood. You're leveraging
| the flex of the material to break it, and stacking them without
| spacers makes too rigid to break.
|
| In short, this stuff is 90% magic trick.
| Etheryte wrote:
| What's funny is that the illustration at the start of the
| article shows exactly the kind of plank you would not be able
| to break this way.
| MarcScott wrote:
| Your board holders also have a significant input on your
| success. If they hold the board, but let their arms flex, then
| they absorb too much of the energy of the strike. They can make
| it easier for you as well, by flexing the board inwards towards
| them.
|
| I've gone through boards with a one inch punch with barely any
| effort, and also failed several times, and it has always been
| down to the person or persons holding the board for me.
| entropicdrifter wrote:
| The only board breaks that are really impressive to me are
| speed breaks, where the board is either held one-handed
| (either by the person doing the break or an assistant) or is
| mid-air when struck.
|
| That at least takes a measure of skill.
| sheepscreek wrote:
| It sounds like 90% grit and 10% magic trick, but you were an
| instructor so I'll take your word for it.
|
| I still wish to believe that the creme de la creme, or the top
| 0.1% of the karate world, can muster enough force to break
| concrete regardless of any tricks.
| mywittyname wrote:
| I didn't magic trick in a pejorative sense. Just pointing out
| that there's a specific technique to being successful at it.
| commakozzi wrote:
| Thank you! I saw that article and i was like "wait, what?? are
| they not aware that this is mostly a parlor trick???" I thought
| everyone was aware... No science needed, it's a trick.
| ijustwanttovote wrote:
| Your hand might not break, but it still really painful.
| Breaking a stack of 6 with a knife hand, my wrist would usually
| be sore and bruised up the next day. It would take a week or so
| for full mobility.
|
| I still think most people in the world wouldn't be able to
| break 2 pavers with no spacers. :)
| Simon_ORourke wrote:
| > The key is the boards designed for breaking are cut in their
| weakest orientation.
|
| So you're saying it's all for show, like some 10 kilo barbell
| weights being ridiculously oversized just to soothe the ego?
| black6 wrote:
| The oversized weights are bumper plates for deadlifting and
| snatching so that the bar is at a proper height when sitting
| on the floor.
|
| Ego develops at higher mass.
| krapp wrote:
| It is called "martial arts" for a reason. A lot of it is
| essentially dance and performance.
| crtified wrote:
| What's the trick behind the practitioners who break large
| blocks of ice?
| aidenn0 wrote:
| Ice is very similar to concrete pavers; it's both rigid (i.e.
| requires a lot of force to deflect), but brittle (i.e. takes
| very little deflection to break).
| crtified wrote:
| Understandable.
|
| Still, nothing will detract from the visceral wonder that I
| could never forget after seeing, in person, an extremely
| high ranked karateka (i.e. second in the world, in his
| style) chop a seemingly solid block of ice over a foot
| thick.
|
| I suspect that, while there might be "a trick" behind these
| things, extreme achievements in that field are still rare
| and accomplished acts, as they are in any. The wonderment
| need not be fully extinguished.
| aidenn0 wrote:
| Oh, it's absolutely hard, but like many things the
| apparent difficulty and actual difficulty are only
| loosely related, and good showmanship (perhaps a more
| polite term for "trick") will involve maximizing the
| apparent difficulty while keeping the actual difficulty
| manageable.
|
| You see similar things with e.g. juggling where
| entertainers will do a lot of things that make it _look_
| harder. This doesn 't mean that it's not difficult to
| juggle 7 objects.
| aidenn0 wrote:
| Breaking a board with some techniques is easier than others.
| The front-leg hook (also known as "whip" kick) I personally
| found quite hard to break with, particularly when jumping. Two
| boards, no spacer, palm strike was much easier for me.
| WalterBright wrote:
| That's why laminates, with the layers running in different
| directions, are so strong.
|
| You won't see a piece of plywood being broken this way.
| licebmi__at__ wrote:
| >In short, this stuff is 90% magic trick.
|
| I would say, kinda but not entirely. IME as a practitioner in
| my youth, I would say that breaking the mental barrier to throw
| a good punch is a thing that needs to be broken as part of the
| martial arts training. Another thing that a good training gives
| you and not many people understand is the preparation to
| receive a punch, not cower in fear and still keep a sound mind
| to try to recover and react.
| bluedino wrote:
| I did martial arts for years and often helped out with the
| classes as an adult. We used to buy the cheapest concrete
| brick/paver we could get for breaking. Something similar to this:
|
| https://www.homedepot.com/p/16-in-x-8-in-x-1-75-in-Pewter-Co...
|
| There is a lot of variance in bricks. And honestly a lot of the
| cheap ones would break if you dropped them, or loading and
| loading them in the van...
|
| Not to mention people would accuse us of baking them, or freezing
| them, leaving them outside for months or years, all kinds of
| stuff. But honestly we would buy a bunch of them from the home
| improvement store on the way to the demo at the mall or a school.
| You'd be surprised at how easily you can break one with the
| simple tap of a claw hammer.
|
| It's just physics. The longer the brick, the easier it will
| break. Some demo rocks are much longer. The trick is to hit it
| fast, use the smallest impact point you can, and follow through.
| If you don't follow through you won't even be able to break a
| pine board. Theres some kind of psychological thing prevent most
| people from punching through a target, whether it's a brick,
| punching bag, or a board.
|
| Drywall, however, is an exception to this rule.
| Cthulhu_ wrote:
| Drywall is a funny one; anyone "punching a hole" in it
| carefully prepared where they will hit it so they don't hit a
| 2x4.
|
| Don't ever believe anyone claiming they "got so mad they
| punched a hole in the wall"; they would not have punched a wall
| if it was solid.
|
| Notable exception is a friend of mine who punched a wall in a
| rage and broke his hand, lol.
| polygamous_bat wrote:
| I assume selection bias is in play: for every post on the
| internet there are many more who did break their hand and
| ended up in ER, they were just too ashamed to talk about it.
| drivers99 wrote:
| I punched a wall while mad and put a hole in the drywall. I
| didn't plan where I was going to hit it. I'm not proud I did
| that though. Firstly, for losing my temper, which is not who
| I strive to be. Secondly, it's obviously weak material. I'm
| sure a lot of people have.
| simonbw wrote:
| Walls generally have studs that are 1.5" wide every 16", so
| more than 90% of points on a wall are not in front of a stud.
| You do need to punch a few inches away from the stud to
| account for the width of your hand and to get enough leverage
| to break the drywall, so maybe expand the width of the hand-
| break-zone from 1.5" to 8", and you've got around a 50%
| chance that punching a random spot on the wall avoids a stud.
|
| Just felt like doing the math on that one.
| exe34 wrote:
| I used to have a rage problem until about 5 years ago. I
| broke a number of phones in the few years before that, so I
| bought a rugged one. In my last ever bout of rage, I threw
| the phone at the wall. I expected the phone to break, but
| instead it made a hole in the wall. I spent ages researching
| how to fix it and in the end ended up using quickfill and
| painting over it several times. From that point onwards, I've
| always preferred handstand pushups when I'm feeling agitated.
| aidenn0 wrote:
| One of my friends had the "brilliant" idea of playing
| "drywall roulette." In a room about to be demoed, run
| headfirst into somewhere near the center of the wall. First
| person to hit a stud loses.
| bigstrat2003 wrote:
| > Don't ever believe anyone claiming they "got so mad they
| punched a hole in the wall"...
|
| Yeah that's not true man. You can get lucky and not hit a
| 2x4, it's not like it's impossible to punch a hole in drywall
| without advance prep.
| zeristor wrote:
| What?!
|
| Ronald McNair, laser physicist and astronaut? Even more
| impressive.
|
| I did not expect his name to pop here, I need to read up on what
| other amazing things he did.
|
| https://greensboro.com/news/local/30-things-you-should-know-...
|
| or here:
|
| https://archive.is/5Oy2u
| cuddlyogre wrote:
| When I was in martial arts, breaking landscaping blocks with a
| palm strike was not difficult at all, but did sting like a hard
| high five. The trick is a stiff hand, but not so stiff as to be
| inflexible, and hitting mostly with the meat of your hand.
|
| A regular punch or knife hand is much more prone to injury
| because of the more fragile bits being closer to the action.
| gnicholas wrote:
| Anyone have any suggestions for youtube videos on breaking
| concrete? My kid has an upcoming TKD black belt test and the
| master said she can do the concrete if she wants, but doesn't
| have to (she's 10 and very small for her age). I've watched a few
| youtube videos about this, but all of the demonstrators are grown
| men, and the seem to jump and use their body weight as they're
| coming down.
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