I know nothing about physics but so far i have determined at least 6 factors
Speed of the punch
strength of/weight behind the punch
physical area of the attacking body (the smaller the better)
physical area of the recieving body (the smaller the better)
vulnerability of the area hit
hardness of the attacking body
By attacking body i mean the part that actually makes contact, like the knuckle. Recieving body is the area that recieves the impact.
I was watching some documentaries on martial arts and this is supposedly how they do their stunts like having little kids breaking concrete, they try to maximize all these factors, and it made me think about the subject and what all goes into maximizing the force.
those martial artists that can break wood and concrete without breaking their arms train a lot for a very long time. Basically if you punch a solid object on a regular basis, gradually increasing the force behind the punch, your bones respond to the constant stress by becoming thicker and stronger, and less easily broken.
If you do everything correctly, wood and bricks are surprisingly easy to break. It’s more about building confidence than anything else.
I would think the biggest factors would be the speed of the striking object, along with how well it managed to transfer kinetic energy to the target. You see this in boxing. Glancing partially dodged blows do almost nothing for all their fury; yet one well connecting blow to a vital area can end the fight at any point.
With regard to the “hardness of the attacking body”
I once witnessed a program which claimed that the wearing of boxing gloves actually allowed the boxer to deliver more destructive energy to his blows by protecting the hands.
Everything you have listed are all factors.
I would also two additional factors:
- transference of energy. You want to deliver all of your energy to the target
- penetration of the target. You want your energy to penetrate into the target
With specific regards to brick and board breaking, something that I do very regularly, technique is very important. Bricks are actually easier to break in mass quantities then boards. Once I’d mastered 4 bricks I quickly progressed to 5 then 6 and more. However, several boards is still very very difficult for more. Boards are much easier in low numbers though. One thing I should point out before the masses come in here and call me crazy (it’ll happen anyway) but I break boards all together and bricks with spacers which probably is why boards are harder for me. If I used spacers boards would probably be easier.
Where you strike the brick or board matters. For some techniques you have to hit at the edge, for others in the centre. It is vital to centre yourself over the board and brick as well for overhead strikes, or for other breaks centre your energy so as to maximize the hit.
Confidence is a big factor. I can still remember my first brick break. I had a lot of doubt as to what was going to happen. In my mind, human beings couldn’t break concrete. Still broke it but it was much easier after that.
Essentially, it all comes down to learning how to do it and doing.
Note, that it is easy to cheat at breaking too.
For boards, you can pre-break them and then glue them back together.
For bricks, you can cook the bricks or you can make your own with less gravel in it. You can spot either cheat easily because when the break is made there will be a puff of dust.
Would the area (in square inches) be a factor? If I punched you in the arm it might not hurt, but the same force onto a smaller area like a chin could increase the damage.
Yes, and those were both listed in the OP.