The Physics of Karate

Regarding this wees column on the Phsics of Karate:

We are surprised, considering how lng we have ben a member, and how many times this has come up on the Messge Boards, that no one referenced these papers on THe Physics of Karate:
S.R. Wilk, R.E. McNair, and M.S. Feld
The Physics of Karate
American Journal of Physics 51 (9) 783-790 (1983)

M.S. Feld, R.E. McNair, and S.R. Wilk
The Physics of Karate Scientific American 240 (4) 150-158 (1979)

Not to mention the following on-line thesis:
We know one of the auhors realy well.

“We?” Whadaya mean, “We,” Kimosabe? You using the Royal We again? (looking at the list) 1979? Dude, it’s always nice to fine a Doper older than I. And if you aren’t, kindly humor me.

It’s the Peruvial “we”:

Fine. I wouldn’t mind trying to split a few 3/4" boards with the grain. Without even trying it, it doesn’t sound so difficult.

However, (the big however):

What about bricks? I hear they try to dry every last bit of moisture out of them to make them as brittle as possible but still…

Can you further your experiment by trying it on five bricks or is that asking too much?

If it makes you feel any better, I remember that article. Among other things, they attached white dots to the martial artist’s limbs and took strobe photographs to track his motions. Led to some freaky-looking pictures.

And no, I wasn’t reading Scientific American at two years old. The Villanova astronomy department had bound stacks going back to 1904 or so, and I would while away slack hours by reading them. The magazine really went downhill after Martin Gardner stopped writing the Mathematical Games column.

Actually, the dots were my idea. They weren’t white – they were yellow, made by using a hole punch on a roll of yellow plastic tape. I thought it’d be better to have well-defined points to measure the displacements with.

You should see the high-speed films of the strikes.

Further proof that a printed reference is not necessarily a citation.

An additional thought - one that may give Cecil some comfort - karate practitioners and other showoffs practice hitting hard things on a regular basis.

One of the desired effects is that the tendons that run over the tops of your knuckles migrate to the sides when punching. This prevents tendon rupture when your fist hits the bricks and also allows you to deliver a lot more force (I think).

Martial arts training really isn’t a mystery (referring to the striking martial arts like karate and tae kwon do). Breaking boards is even less, if you look at what a martial artist does in training. To begin, Force is equal to mass times speed squared. Forms, which is the stylized “dance” that the martial artist does for each belt, teaches the student to line up his or her mass behind a strike and to train the nervous system to react faster and more precisely to an attack. For the purposes of board breaks, if you hit something with just the weight of your fist, it would be a pound or two of force times however fast you hit squared, but if you hit with a quarter of your body weight by lining up your shoulders correctly with properly braced legs and just as fast, you could hit 20 or 30 times harder.

 The second major thing that martial artists do in training that helps them break boards is to practice striking.  In many martial arts that is done on bags and by sparring, sometimes (like in kung-fu) you strike a semi hard surface like a bucket of sand repeatedly.  This too has a few good reasons behind it.  First, sparring increases speed, endurance and recovery time.  Speed of course is the most important number in force, and endurance gives you the ability to continue practicing, thereby improving even more.  Sparring and punching sand also makes your bones stronger.  When you hit something hard, you can get tiny fractures in your bones.  If allowed to heal, they create greater calcification, which can help you not to break your knuckles or your arm when you make the harder contacts.

 Each martial art specializes in certain moves.  In Tae Kwon Do, we learned jump spin kicks, which admittedly don't hit nearly as much as a punch would, but consider this:  With my waste being 32 inches around, my truck's diameter is around 10 inches.  My inseam plus the length of my ankle and side of my foot is about 39 inches, which makes the diameter of my spinning kick around 78 inches plus the 10 inches for the trunk.  That would put the circumference of my spinning kick at about 276 inches.  This would mean that my foot would be traveling 8.6 times faster than my trunk, with the weight of my leg behind it.  When it hits, it is quite devastating, and if done right can break several boards with just a fraction of the force.

Force is mass times acceleration. Impulse is force times time. Momentum is mass times speed (actually, velocity). Energy is one half mass times speed squared. Which is most important depends on what you’re doing, and nothing in particular is mass times speed squared.

Well, some people do and some people don’t. I’ve heard rumors that when you see a demo where a guy has X number of bricks/boards in a row and he breaks the first and last couple, but leaves the ones in the middle untouched what’s actually happened is that he baked the outer bricks to let them break easier.

All that I can say to that is Doh! I must have misremembered the formula that the Sau Baum Nim had told us. I’m pretty sure that I have the rest of the stuff straight though (minus the math of course). Faster and massier is what breaks the boards.

You must be joking. Oprahs* are measured in Kg/d². Everyone knows that.

*Well known unit of weight gain/loss