One of the aspects of martial arts that is widely practiced but certainly misunderstood is breaking stuff. This usually refers to breaking boards and concrete slabs, although I'm sure just about anything that can be broken has probably been tried before. Myths usually revolve around breaking stuff like glass, metal or other hard objects. Although I have resisted mentioning specific physics, there is something that has to be mentioned here to discuss breaks with any scientific accuracy. Newton's Third Law states that for every action there is an equal and opposite reaction. Remember the Third Law.
The reason that martial arts include board breaks is because they teach students to focus strikes on specific points and use full power. No matter how powerful a student is, if he or she can't hit a target (and boards are usually still, but that doesn't always help) then they can't effectively use their strikes. If they can always hit something but don't know how to apply power, they're no better off. There's a lot of technique to breaking boards. It's also assumed that you can break bones if you can break boards. Although that's not quite true, it is a good start. Besides, it's also a lot of fun. (Don't do it unless you know how, though!)
Whenever you hit something, Newton's Third law says that there will be a force equal and opposite to your strike. The harder you hit something, the more the opposite force. To break a board, you must subject the striking point to this force. This puts a limit on how hard you can hit something. Whenever your body can no longer withstand this force, damage will occur. As we have already shown with falling monks, there is no force known to modern science that can actually shield your body from an opposing force. There are ways to improve how your body takes it, but no mental state, harmony of thought, or any other pseudoscientific force exists that can absorb it. If you are inclined to believe there are, you could make a lot of money if only you could reproduce it. The military of every nation would literally kill to get it, and if it had really been discovered by ancient Chinese masters, they would have used it to conquer the Earth. Your only recourse is that such knowledge has somehow stayed in the possession of only benevolent people through history. Considering an honest study of Human history, I don't believe this is a defensible position. We're stuck with Netwton's laws.
So how much can a martial artist break? The answer is not quite as easy as it sounds. There are many ways to hit something. There are myriad weapons, from fists to shins to feet, that can be directed at a target. It would not be practical for me to list each striking point and estimate how many boards, bricks, or other breakable items that each of them is capable of breaking.
It is better to get a general feel for how powerful a strike can be, and then generalize from there. I will use orders of magnitude. The estimates are included to give an idea of general significance. Because this section is based on ancient knowledge, I will focus on what you can expect a martial artist to be able to break, not what Master Powerful Fist managed to break seven centuries ago from sheer luck.
I will start by estimating the force of a normal punch. One of my own punches can generate about 3400N or force, or about 764lbf (foot pounds). I would estimate that a good board probably requires about 1000-2000N to break, for a general comparison. (Boards can vary by quite a bit, from weak, dry boards that will break if you look at them to moist, high-quality boards filled with sap that break hands, so those are just rough estimates.) I can't claim to have a record-breaking punch. If I can generate 3400 N on average, what about the world's best striker? We can be generous and say that perhaps this striker is three times more powerful than me, which would be about 8100 N on the target. This can be achieved by being faster or being heavier. In the Physics section, I cover this in more detail, but I will go over the results here. I generate 3400 N by punching with an estimated 3 kg hand (plus arm) traveling at 15 m/s. The equation for force requires momentum, and in order to increase momentum, you can either increase your speed or your mass. So, the ultimate striker could be three times heavier than me. At roughly 540 lbs, this striker is probably too fat and slow to have an effective punch. (If a human is that heavy and is all muscle, be very afraid.) We'll assume that this striker can be heavier, but not an order of magnitude heavier. This leaves speed. Could the ultimate striker perhaps punch as fast as a speeding bullet? A good average for the velocity of a bullet is about 900 m/s. This would be 60 times faster than my own punch, which is about 3240 kph, and a few times faster than the speed of sound. Clearly, the ultimate striker can't go that fast. If we assume 3 times faster, then the striker's hand is going 37.5 m/s, or 135 kph. That's pretty fast for a punch, and it does not strain our imagination to assume that someone might have had a punch that fast.
You can certainly argue over my arbitrary selection of only a factor of three times for the ultimate striker, although I think that is a fair estimate. A factor of three is actually quite significant, from a punch going 45 kph to a punch going 135 kph. That would be a valid argument that maybe I'm being too generous. But how far can you go and still be plausible? Could a human be five times better? Either this striker would be so heavy he or she couldn't walk, or the striker would be able to throw a 225 kph punch. Is it possible? I doubt it, but we're talking about the ultimate striker. By asking this type of question we can begin to believe how powerful of a strike a human is capable of throwing. We probably can't possibly calculate exactly what can be broken and how much force a human can generate, but we can ask this type of question and begin to understand what is plausible. This is one of the most important aspects of critical thinking. When confronted with an extraordinary claim, how do we go about evaluating it?
If you hear about a martial artist that can break concrete blocks, you probably have either seen someone break them or heard about it (or look at the previous image - Fun with concrete.), and you incorporate this experience into your interpretation of the event. If you hear about someone breaking 270 degree Kelvin dihydrogen monoxide blocks with their bare hands, you may be doubtful, even skeptical. This is the essence of critical thinking. If you heard that story from a master or a friend, and didn't stop to think about, you may believe it without verification. If you happened to look it up, though, you would find out that it is just ice, and be inclined to believe them. You took a critical step, though, and verified the claim. This is how a lot of martial arts breaking myths get propagated. There are a lot of people that do not verify these claims, perhaps because they are inclined to believe them, they want to believe them, and they don't want to think their instructor/friend is wrong, or they're just inclined to believe anything.
In general, breaking requires knowledge of the item being broken. If you are breaking concrete, you probably lay it flat and make sure nothing is underneath it. If you are breaking baseball bats on the shin, you will probably not have someone swing the heavy, thick end at your leg. Instead, you'll strike it so it breaks at the middle where it is narrower. Skilled martial artists can perform some truly impressive breaks. Sometimes they appear to defy the laws of physics. Stacks of concrete can be broken with palms and feet, and highly skilled masters can break with their forehead. If you're breaking concrete with a palm strike, you need to hit it straight down (no sideways movement), and with the palm of your hand. If you use too much of your palm and slap it, you dissipate the force of the blow and the concrete will not break. How you move your arms and hips to generate enough power takes quite a bit of practice. As described above, all these techniques are bounded by a certain limit, inherent to us as living organisms. Almost all breaking involves this type of knowledge, and thus it is only limited by our creativity. If something requires enough force to break bones, and there is no technique or way to hit it that will negate this constraint, then there is no inner knowledge, no ancient secret that will prevent your bones from breaking. What separates stupidity from a demonstration of skill is the specific knowledge about the techniques and the target. Sometimes it isn't easy to spot the difference unless you know what you're doing. Anyone can break stuff, but those that are skilled can do it without hurting themselves.
- Serway, R. Physics for Scientists and Engineers. Philadelphia, PA: Saunders College Publishing, Fourth Edition, 1996
- Giancoli, D. Physics Principles with Applications. Upper Saddle River, NJ: Prentice Hall, Fifth Edition, 1998
- TKDTutor.com: Breaking Mechanics: http://tkdtutor.com/12Breaking/BreakingMechanics.htm