The Skeptical Teacher

Musings of a science teacher & skeptic in an age of woo.

Physics of Karate – No Woo Required

Posted by mattusmaximus on November 14, 2009

I’ve practiced martial arts of various styles for 20 years, and in all that time I’ve heard a number of very strange & woo-filled explanations for why people can accomplish the physical feats they can.  One such example is breaking wooden boards with the bare hands & feet – often people provide an explanation by referencing so-called “chi, ki, or qigong energy”. The whole concept of chi is more of a philosophical concept than anything else, and it is little more than a “dragon-in-the-garage” (an untestable notion that cannot be verified through scientific means).

karate chop

Well, I’m here to tell you that such physical feats as board breaking can be performed & explained simply by referencing the known laws of physics – no woo required.  Take a look at the video of me performing such a break with five pine boards at once…

How do I accomplish this feat?  Here’s how: I hit the boards really hard – the question is how do I generate such a large force of impact?  Read on…

1. Materials: First off, there’s a good reason why I’m hitting pine boards – they are a soft wood.  Whenever I’ve seen martial artists doing breaks such as these, they hit either pine boards or a brittle material like clay bricks or concrete slabs.  In addition, when striking wooden boards, successful strikes always go with the grain of the wood because the wood is structurally weaker in that orientation.  So, in a real sense, karate practitioners are kind of cheating by using these materials – if you really wanted to see something impressive & “supernatural”, perhaps someone could display slicing through a steel I-beam with the edge of their hand.  I think there’s a pretty good reason why we never see a “chi-master” doing that!  😉

2. Spacers: Notice the spacers that I’ve got placed in between the boards.  This is another common trick that is used whenever board breaking is performed.  By separating the boards like this, I really only have to break one at a time as opposed to one large, massive chunk.  In more technical terms, the momentum of my strike is slightly reduced by breaking only the top board, which allows the remainder of my hand’s momentum to continue to the next board, and the next after that and so on.  This works for the same reason why train cars are slightly decoupled from one another – once the engine gets moving, its momentum helps to move the next car when the coupling catches, and their combined momentum help to get the third car moving when its coupling catches, and so on.

3. Impulse-Momentum Theorem: the rest of it has to do with the physics of impulse & momentum. In equation form, this theorem (which is another way of expressing Newton’s 2nd Law) can be written as follows:

F Δt = m Δv


F = m Δv / Δt

where F is the force of impact, Δt is the time of impact, m is the mass behind the strike, and Δv is the change in velocity of striking hand (or foot).  In order to break the boards, one must maximize the force of impact, which can be done in a variety of ways…

*Maximize the mass: instead of merely hitting the boards with my fist, I turn & twist my entire body into the strike.  By doing so the mass (m) is greatly increased, and so too is the force.

*Minimize the impact time: the boards are placed onto solid supports (in this case the stools) which do not give under the impact.  Because the supports are not excessively elastic or bouncy, the time of impact is reduced to a minimum, which has the effect of greatly increasing the force of impact.

*Maximize the velocity: by dropping my body mass so dramatically, I convert a large amount of gravitational potential energy into kinetic energy. And since kinetic energy is proportional to the square of the velocity of an object, by doing so I provide a great deal of velocity (and therefore momentum) which can carry all the way through all five boards as previously mentioned.

So there you have it, folks – a thorough explanation of how such board breaking feats are done, without a mention of chi/ki/qigong or any other supernatural woo-woo.  This is a very good example of applying Occam’s Razor, and I thoroughly enjoy sharing this lesson with my students.

Sadly, there are those who would rather deny scientific reality & the laws of nature in favor of the delusion that they have some kind of mystical power over “chi energy” and can therefore do physically impossible things.  And even more sadly, these delusions can lead some people into serious injury.  Here are two examples of what I’m talking about…

*The first is of one of these so-called “chi-masters” who believes that he can throw people merely by “projecting his energy” at them, but – interestingly – he only seems to be able to perform these “throws” on his true-believing students.  What happens when he encounters someone who isn’t a true-believer in his abilities?  Take a look at this video to find out:

There is an entire group, almost cultish in nature, called Yellow Bamboo that purports to teach people how to “focus & project their chi” with equal levels of failure.  Just search Youtube and you’ll find plenty of videos of the Yellow Bamboo woo-meisters getting pwned.

*But if that isn’t bad enough, here’s a whole other level of fail… this next clown is so far down the “chi-master” rabbit-hole that he actually believes that by “focusing his chi energy” he can make himself impervious to blades. And to prove it, he hacks into his own arm with a razor-sharp machete!  How do you think it went? (Warning: not for the squeamish)

Folks, in my opinion, it just doesn’t get much more stupid than that.  The moral of the story is simple: when it’s you and your beliefs vs. the laws of physics, physics always wins.

28 Responses to “Physics of Karate – No Woo Required”

  1. Jake K. said

    The Science of Scams channel on youtube has a fun video about the tricks behind apparent use of “chi” in brick-breaking feats:

  2. […] The Skeptical Teacher goes where Patterson has gone before. You can peruse some of my past ramblings on the topic at this […]

  3. When Yan Xin went up against physics…physics lost. Of course, he actually studies the qigong, rather than studying martial arts while believing in qigong. Sadly, that distinction is lost on most believers and skeptics alike.

  4. Nice post! I’m a fellow skeptic and a martial artist. I’ve added your blog to my Google Reader. I’ve blogged about chi and the martial arts on several occasions. If you search “chi debunked” on my blog you can read the old posts. Alternately, you can just follow this link:

    Be sure to click on “older entries” to see my better posts.

  5. Riayn said

    Thank you, thank you for posting this. Like Bob, I am also a skeptic and a martial artists and at a recent training camp we did Tai Chi in the mornings complete with all the woo about meridians and chi energy and how the chi energy generated from Tai Chi was supposed to make your hands tingle. I would prefer the Tai Chi as a nice way to get the blood flowing in the morning without all the woo.

  6. […] 18, 2009 · Leave a Comment The Skeptical Teacher’s recent post on this very topic got me to pondering ki once again. For those of you that are new to this blog, ki is a topic I […]

  7. I cam here from the 124th Meeting of the Skeptics Circle because I want to support a fellow skeptic. Now, I always thought that karate was physics. Now I can point woo-pushers here. Not that they will be convinced, but at least you debunk it right!

  8. Alex said

    Hi – I stumbled on this oage by mistake. I was looking in Bing for Antivirus software that I had already purchased when I came upon your site, I must say your page is pretty informative, I just love the theme, its amazing!. I don’t have the time this minute to fully read your site but I have bookmarked it and also signed up for your RSS feeds. I’ll back around in a day or two. thanks for a great site.

  9. Chloe said

    These are all different forms of martial arts. The UFC has become extremely big over time. Mixed Martial Arts has overtaken boxing in terms of tickets being sold.I would like to know your opinion on this

  10. […] woo.  Specifically, I performed three impressive physical feats: walking barefoot on broken glass, breaking five wooden boards with my fist, and laying between two beds of nails while a concrete cinder block is crushed on my chest. Talk […]

  11. […] that many times I’ve stated publicly on this blog that, whether you’re talking about breaking boards, laying on beds of nails, or walking barefoot on glass shards, such amazing physical feats have […]

  12. […] It might surprise many people to know that pretty much anyone can break boards with little training – in order to do more challenging breaks like that pictured here takes more training, though the basic principles are still the same. But in the end there is *nothing* mystical involved – no chi or “life energy” or any of that rot. With proper body mechanics and good use of mass (twisting the body), velocity (dropping to convert GPE into KE), and a low time of impact (solid supports that won’t give) one can make lots of kindling out of boards. Oh yeah, and the spacers are a nice trick as well For a fuller explanation, see my previous blog post on the subject. […]

  13. […] Board Breaking & Karate – This is another subject on which I have written before (click the link).  However, […]

  14. Okay, I know I’m like, really late posting on this… but you missed part of the physics equation for breaking boards… it isn’t just Force…. force alone doesn’t break a board; it’s pressure.

    Pressure=Force/Area. Increasing force increases pressure and increases likelihood of a break, but proper striking technique should also decrease the area contacting the boards during the strike and increase pressure as well…

    At least that was part of the lesson when MY black belt Physics Teacher did his board breaking physics lecture in high school.

    • mattusmaximus said

      This is correct. However, I also left out another aspect of physics – torque. Many boards or bricks that are broken are broken in the middle of a relatively long lever arm, making it even easier to break a board.

  15. […] Physics of Karate – No Woo Required (Skeptical Teacher) […]

  16. Julia said

    I have researched and spanned the internet to find that there is more physics than skill in doing this. Many martial artists, esp Karate, tend to get offensive when people try to explain that these feats are no true test of skill.

  17. Fightclub said

    I could not agree more, very good post

  18. Bri said

    I’m a martial artist as well, and my teacher never taught us that board breaking comes from some kind of “internal energy”. We were taught that its just one of many tools (just traditional) to help with technique and to understand how to generate power using body mechanics n’stuff.

  19. Bri said

    Also to kinda of mentally prepare a person for striking and to go through your target, but of course there are more safer ways to do this.

  20. Aaron Zorn said

    Leibniz originally called kinetic energy vis viva or the living force. Niels Bohr had a Yin and Yang symbol on his coat of arms. Newton’s laws of motion describe objects possessing energy but Taoism describe objects as energy.

  21. Scott Chrisman said

    I really enjoyed the article. I was especially pleased to see you mention the use of spacers. All too often I hear someone arguing that the use of spacers makes it harder, not easier. I groan every time I hear it. Also, I understand the desire to roll one’s eyes when listening to topics like chi or meridian points. But, I would caution people against blind dismissal. Are the effects being generated in a mystical fashion? No, of course not. Does this this mean they aren’t actually being generated? Again, the answer is no. Just because someone says they’re performing an action through mystical means, doesn’t mean they aren’t perform an action, only that the true mechanics for the action are likely not understood. After all, that’s how we get mysticism in the first place, as an explanation for that which is not understood. So don’t discount arts like Tai Chi as ineffectual, or parlor games, but instead ask yourself this: What is the practitioner actually achieving through their actions? Next, how can this be explained and replicated?

  22. John said

    Nice simple physics explanations here, thanks! It appears to me that it hurts more when the board doesn’t break, I figure this is because there is a greater impulse on the hand as it stops suddenly. However the force cannot be greater, else the board would break…does this mean the force on your hand acts over a longer time period and this makes it hurt more than of you break the board?

    • mattusmaximus said

      No, it has more to do with energy transfer. Basically, if the boards break, much of the kinetic energy generated in the strike goes into breaking the boards; however, if they don’t break, much of that kinetic energy goes back into the striker’s hand – ouch.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: