Some interesting sites to check out -

http://www.fas.harvard.edu/~scdiroff/lds/NewtonianMechanics/KarateBlow/KarateBlow.html

"A detailed description of the physics of karate has appeared in a Scientific American article. 1 We will only present the salient features here relevant to the impulse momentum theorem. First we estimate the momentum of the fist. Its effective mass is greater than just the hand ... after all, you're swinging the whole arm to which your fist is attached. Resting the forearm on a scale suggests an effective mass somewhere between 2 and 4 kg. The viewing of a videotape showed the hand swinging through 1/2 meter in the time between frames (1/30 sec) thus establishing a velocity 2 of 15 m/sec and a momentum of 45 kg m/s.

Wood is a fairly elastic material and a 30 cm long board typically requires about a centimeter of deflection before breaking; 500 Newtons will deflect it to that extent. If we assume that a 2 cm thick board actually stops the swing of the fist, the action takes place over a distance of 2 cm + 1 cm = 3 cm and the time of this interaction will be the distance divided by the average velocity of the fist = (vi + vf)/2 = 7.5 m/sec. Thus t = 0.03 m ÷ 7.5 m/sec = 4 millisec. In this time the momentum of the fist would change by 45 kg m/s. That's equivalent to 2250 lbs! Of course the board breaks with this kind of force and does not stop the fist.

The boards are stacked on top of one another and kept slightly separate with pencils placed between them; rupture can proceed successively through the boards with each rupture involving a smaller force than if a single thick board were used. This also has the effect of the momentum of the downward-moving broken pieces of the top board helping to break the board beneath it, and so on down the stack. Thus the peak force to break, say, eight boards is less than eight times the force needed to break one board."


http://academic.reed.edu/physics/courses...ysicskarate.pdf

http://www.kungfuscience.org/assets/kungfuscience.swf

E=mc2

That's the only geeky thing I could think of

I never did any breaks in karate, but aren't you supposed to drop your weight through the strike? So it would be more than just the weight of your arm. Bah, I don't have enough physics to critique this properly but I am almost certain Johnny TKD can't produce 2250 pound of force with that hammer fist if the average boxers right cross hits for ~1000

If you are striking down. It is different with the strike and where you are striking. You have to use energy from more than just what you are strking with to get a good break.
For example to get maximum power with a reverse (front) punch you should use momentum from your hips and turn on your heels to get full power. Doing this will make things a lot easiery

Hmmm...I've never studied karate, but i have studied physics XD

So do you guys think it would give it more force if you jump up, and keeping ur balance, strike when falling back down?

That is correct, of couse depending on the break your wieght is dropped. The same thing would happen if your were striking someome after a take down. Your weight would drop vs bending over to punch your opponent.

Pretty good post. Good food for thought. The most interesting thing is towards the end. The tid bit about the crab. If there isn't already, there should be a Crab Form.

When I put my rice bag on the brick pillar in the attic that goes through the center of my house, with my wushu I can make my punches resonate through 2 of 3 floors of my house. I'm using internal short range Fut Sao punches.

I'm working on making it through the first floor.

http://www.youtube.com/watch?v=G89IcZ3PluE
http://www.eurekalert.org/multimedia/pub/1632.php?from=82660

I was trying to look up the name of that crab but I only found this crazy ant. Check it out.