# 태권도 물리: Lesson 3 – energy and force, part 2b

Face Punch!

Ballistic impact to the forehead, zygoma, and mandible: comparison of human and frangible dummy face biomechanics.

Viano DC, Bir C, Walilko T, Sherman D.

Wayne State University, Bioengineering Center, Detroit, Michigan, USA. dviano@comcast.net

BACKGROUND: Currently, there is a greater use of nonlethal force in law enforcement and military operations. Because facial injuries have been observed, there is a need to understand the human response to ballistic impacts involving various regions of the face. This study aimed to establish blunt ballistic response corridors for high-speed, low-mass facial impacts to the forehead, zygoma (temple), and mandible (jaw). [1]

RESULTS: Law enforcement application of peak normalized force of 3.5 +/- 0.9 kN (kilonewton) (3500 J/ m) on the forehead and 3.0 +/- 1.0 kN on the mandible did not result in fractures, whereas an impact force of 2.3 +/- 0.5 kN on the zygoma caused anterior maxilla fractures. For those of you who only think in imperial units, 1 kilonewton = 224.609 13 pounds force.

SUMMARY: For the best face punch, aim for the temple or jaw, but not the forehead!

Now apply that force not to a person’s face, but to a wooden board or a plastic board. Multiple studies show the force required to break a 1 inch thick, 6 inch long, by  6 inch wide, pine board is 5 Joules [2,3]. Re-rebreakable boards are rated at about 300 re-breaks per board before they lose strength at an exponential rate.

Assuming the average hand/forearm weapon is about 1.3 kilograms, and the board is about 500 grams (0.5 kilograms), we can derive a hand speed of 5 meters per second (11 miles per hour for the American blokes). High speed photography has shown that even a novice can attain a hand speed of 10 meters per second (22 mph). Another variable with wooden boards is the grain of the board. Breaking along the grain only takes about 75% of the energy required to break against the grain (this can be calculated elsewhere with significant error bars).

SUMMARY: Plastic boards are actually harder to break than equivalent wooden boards for the first 300 breaks, and even a novice can break a 1-inch board.

Related:

References:

1. Ballistic impact to the forehead, zygoma, and mandible: comparison of human and frangible dummy face biomechanics. Viano DC, Bir C, Walilko T, Sherman D.
2. Kung Fu Science: http://www.kungfuscience.org/access.asp
3. The Physics of Martial Arts http://www.dontow.com/2008/06/the-physics-of-martial-arts-breaking-boards