# 태권도 물리: Lesson 4 – Size? Weight? Power?

What matters in martial arts? Size? Weight? Power? It may depend on the application. Since this series of blog entries focuses on a hard martial art, taekwondo, we can discard discussions on using leverage for throwing, body weight for grappling and wrestling, or baseball bats for the thug martial arts.

Size. Martial artists tend to use the “one-inch rule”. Punches involve an average of a one-inch contact area of the first two knuckles on the target. Kicks tend to have just over an inch squared of contact area. Weapons tend to have at most a square inch of contact area on the target as well. The majority of weapons available to a taekwondo martial artist adhere to the one-inch rule–the fist, the foot, the wooden staff (bo staff or jahng bong), fighting stick (bahng mahng ee or escrima stick), the wooden flail (nunchaku or ssahng jeol bong), et cetera.

Weight, or mass. Newton’s Second Law says it all, $F_{arm}=ma$. If a martial artist lacks mass, s/he must have acceleration. A more accurate way of stating this is $F_{arm}=\frac{d\rho}{dt}$. This implies that a martial artist must master momentum and time.

Power. Power is energy that is transformed. Note that in the formula, power comes from transferring mass as quickly as possible $E=\frac{1}{2}mv^2+mg_y$. This implies that a martial artist must master his/her own mass and transfer that mass to target with as much velocity as possible, and with the most efficiency.

In the next lesson we will investigate rotational physics in addition to the linear physics we have been studying thus far.

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