## 태권도 물리: Lesson 5 – Jerk!

In martial arts, perhaps it pays to be a jerk! In kinematics, jerk is defined as the change in acceleration over time. Jerk or jolt is useful in designing roller coasters for the maximum, well, jolt in order to give the rider the best bang for the buck in terms of roller coaster rides. Jerk with respect to force is shown by:

$j=\frac{dF}{mdt}$.

Recall Newton’s Second Law$F_{kick}=ma$. 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, but we can also relate force and mass to the desired jolt that we want to impart on an opponent, say with a kick or punch. In this case, it pays to have less mass and to be fast, for mass and dt are inversely related to the change in force and the jerk. In other words, if you are faster and smaller, you can be a bigger jerk!

In Lesson 4 we figured out that a 45 kg (100 lb) martial artist could impart 478.8 N of force through his/her 10 kg fist or foot traveling 0.3 m at 4 m/s. Plugging this in we get a jerk of about $j=\frac{d478.8}{45d0.075}=141.9\frac{m}{s^3}$ or 14.4 g/s. Note that it only takes about 10 g/s to cause a concussion!

## 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.

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

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, and mandible.

RESULTS: Peak normalized force of 3.5 +/- 0.9 kN 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.

Kn = kilonewton.

1 kilonewton = 224.609 13 pounds force

Studies show the blackbelt board:
Board took 366.387 lbs. to break
The boards used for the test are brand new re-breakable plastic to maintain consistency for each test. Each full board takes about 70 lbs. of pressure to break. These boards are harder to break than wood!

Using the formula:
2.3 * 13 pounds force = 29.9
3.0 * 13 pounds force = 39.0
6.0 * 13 pounds force = 78.0

2.3 +/- 0.5 kN of power on the zygoma caused anterior maxilla fractures.

So (2.3 Kn * 13 pounds force) = 29.9.

That is well within the 70 pounds or 366 psi required to break a blackbelt rebreakable board.

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

In lesson 1 we started with:

$E=\frac{1}{2}mv^2+mg_y$ and $F_{arm}=ma$

• Let m = mass of the fist and arm of a 45 kg (100 pounds) martial artist, approximately 10 kg (22 pounds).
• Let v = velocity of the fist in the horizontal, or x direction only. Assume $5 \frac{m}{s}$
• Note: In lesson 2 we discovered that the actual $velocity_{arm} = 4 \frac{m}{s}$.
• Inserting values we have $E_{arm}=\frac{1}{2}(10kg)(4\frac{m}{s})^2-(4\frac{m}{s})(9.8\frac{m}{s^2})=80J-39.2J=40.8J$ and $F_{arm}=(10kg)(9.8\frac{m}{s^2})=980N$

This is about 220 pounds of force, if the entire arm is treated as a solid body. In actuality, the entire arm does not travel through the target. Assuming proper extension of the fist through the target zone, at most only 10% of the arm’s force will be delivered to the target.

• Let l = length of fully extended arm, approximately 0.3 m
• Let m = 10 kg, the mass of the fist and arm
• Let v = 4 m/s, as calculated in lesson 2

$F_i=\sum_{i=1}^{10 }m_i\frac{iv}{10t}=478.8N$

Note that by treating the fist as one-tenth of the total arm, we find a more accurate assessment of the force delivered to target. In this case, one-tenth the size yields one-half the force, 108 pounds of force instead of 220 pounds.

Again, this assumes only linear motion. What about rotational motion enacted by twisting the fist during the punch? Let us save that for the next lesson.

## 태권도 물리: Lesson 2 – velocity and force

First, we start with $v=\sqrt[]{\frac{2K}{m}}$

• Let m = mass of the fist and arm of a 45 kg (100 pound) martial artist, approximately 10 kg (22 pounds).
• Let K = kinetic energy solved in lesson 1, $E_{arm}=\frac{1}{2}(10)(5)^2-(5)(9.8)=125J-49J=76J$

Next, plug and chug: $v=\sqrt[]{\frac{2(76)}{10}}=3.9m/s$

This shows that the initial assumption of 5 m/s was close enough. We can re-visit lesson 1 and show the difference in energy and force.

Insert corrected values: $E_{arm}=\frac{1}{2}(10)(3.9)^2-(5)(9.8)=76J-49J=27J$

Note that with a 1.1 m/s change in velocity, there is about a 50J change in energy delivered, but the force applied does not change! Force is a product of mass and acceleration, not velocity!

## 태권도 물리: Lesson 1 – energy and force

First, we start with $E=\frac{1}{2}mv^2+mg_y$

• Let m = mass of the fist and arm of a 45 kg (100 pounds) martial artist, approximately 10 kg (22 pounds).
• Let v = velocity of the fist in the horizontal, or x direction only. Assume 5 m/s.

Second, plug and chug: $E_{arm}=\frac{1}{2}(10)(5)^2-(5)(9.8)=125J-49J=76J$

Next, let us find the actual force: $F_{arm}=(10)(9.8)=980N$

This is about 220 pounds of force, if the entire arm is treated as a solid body. Later we will try to verify that 5 m/s is a good assumption on velocity.

## 2012 ATA World Championships Videos and Photos

Here are all the Victory Martial Arts San Antonio videos that I have from ATA World Championships and ATA Worlds Tournament at Little Rock, Arkansas from 21-23 June 2012.
• Team Victory Legacy
• 2nd place in Team Demonstration Competition [VIDEO][PHOTOS]
• Team Legacy video library [LINK]
• Rissa Kilar
• World Champion in Traditional Forms for the 2011-2012 season [VIDEO][PHOTOS][PHOTOS]
• 4th place in traditional weapons for the 2011-2012 season [VIDEO]
• 3rd place in traditional weapons for the 2012 ATA Worlds Tournament [PHOTOS]
• 1st in traditional forms for the 2012 ATA Worlds Tournament [PHOTOS]
• 3rd in extreme forms for the 2012 ATA Worlds Tournament
• 4th extreme weapons for the 2012 ATA Worlds Tournament
• 2nd in extreme forms for the 2011-2012 season [VIDEO]
• 2nd in extreme weapons for the 2011-2012 season [VIDEO]
• JR Kilar
• 4th in extreme forms for the 2012 ATA Worlds Tournament [VIDEO]
• 3rd in sparring for the 2012 ATA Worlds Tournament
• Jose Guzman
• 4th in ATA Creative Weapons for the 2011-2012 season [VIDEO]
• Mr. Evan Turner
• World Champion in Extreme Weapons for the 2011-2012 season [VIDEO]
• 2nd place in Extreme Forms for the 2011-2012 season [VIDEO]
• Sean Mills
• Lexi Mills
• ATA Worlds 2012 Tournament [PHOTOS]
• Kenzie Mills
• 3rd in extreme forms
• 4th in extreme weapons
• Mills Family
• Pictures by the H.U. Lee Memorial Gate [PHOTOS]

## Week 8 of 213: Look at life through the windshield, not the rear view mirror [1]

Cubicle Warrior’s blog, Week 8 of 213 until AF retirement (?). It is hard to believe that it has been 8 weeks since I moved to LA. The past week in San Antonio and Little Rock with my San Antonio and ATA friends have been a bittersweet mix of joy and sadness… Today’s blog was quite cathartic. The past couple weeks have been an emotional roller coaster, and I needed a release. Here it is…for all three readers of my blog.

You never really leave a place or person you love. Part of them you take with you, leaving a part of yourself behind [2]. The pain of leaving so many good friends still has not worn off. I lived in San Antonio from 2006 to 2012, the longest I had lived anywhere on Earth. I will think of my friends fondly, and hope for a happy reunion. I carry with me all the positive impacts and happy memories from each of my friends, as I hope they do for me.

It is not the mountain that we conquer, but ourselves [3]. Rissa earned the title of World Champion in traditional forms for the 15-17 year old, 2nd/3rd degree black belt girls! She also finished 2nd in extreme forms and weapons and 4th in traditional weapons! The world champion title was the culmination of 11 years of training–4 years of top ten finishes in world rankings. On this day, her preparation, determination, and execution paid off. Congratulations, Rissa. Take your one day of rest and get back to work. ATA Strong! Victory Strong!

The ultimate victory in competition is derived from the inner satisfaction of knowing that you have done your best and that you have gotten the most out of what you had to give [4]. Team Victory Legacy finished 2nd in the world for demo team. It was a great run, winning back-to-back world championships in 2010 and 2011. The team members were a great family over the past three years, and I will miss them all terribly. The coach, Mr. Evan Turner, did an excellent job leading this goofy group of goobers. I was fortunate enough to meet his parents. I hope to see Mr. Turner and his parents again at ATA Fall Nationals.

The ultimate victory is that the team did its best, and that their good friends from Team Edge won. The picture below, taken by my friend, Roger, is a very appropriate way to say goodbye to an era…Team Victory Legacy…

The healthiest competition occurs when average people win by putting above average effort [5]. On the first day of the 2013 competition season, JR finished 3rd in sparring. Rissa finished 1st in traditional forms, 3rd in traditional weapons. JR’s sparring looked a lot better than it has in the past, and it looked as if he actually enjoyed it. That is a good start to the new season.

Those whom we support hold us up in life [6]. This was a bitterweet tournament week as we wrapped up the 2012 TKD season, closed one chapter of our lives in San Antonio, and prepared to open a new chapter out in Los Angeles. We were able to talk to several of our former instructors from Florida, say goodbye to some of the Texas area judges, and meet some of our potential new instructors for the upcoming season. Many of our good friends from San Antonio will say that our departure leaves a large void in their lives, and they will not only wonder why we left, but by we gave so much without expecting anything in return. We support the kids’ taekwondo endeavors, because they enjoy it. ATA has been the one constant in our lives since 2001, starting with Mr. Edelson’s ATA Black Belt Academy at Shaw Air Force Base, South Carolina, continuing in Pensacola, Florida with “drunken master”, and then Victory Martial Arts San Antonio.

Miscellaneous:

• I have been thinking of the wildfires in Colorado Springs. That area is so beautiful. I went running not far from the wildfire area just a couple weeks ago. I hope they manage to control the fire soon. I will probably be taking a lot of trips out there, and I would like to run on more trails and take in the beautiful scenery.
• A battalion commander was killed at his own safety briefing at Fort Bragg. The Soldier that killed him immediately committed suicide. This is absolutely tragic.
• The Air Force is investigating reports of military training instructors (MTIs) having inappropriate relationships with recruits, sometimes even raping them. The sad thing is is that most military members have heard these stories, but could never verify the veracity of the stories. Apparently many of the rumors and stories were true.
• Today’s count: 1,407 days.

[1] Jim Hinkle

[2] Anonymous

[3] Sir Edmund Hillary

[4] Howard Cosell

[5] Colin Powell

[6] Baroness Marie von Ebner-Eschenbach

## 2012 Legacy Gathering Videos

Here are my first set of videos from the 2nd Annual Legacy Gathering, hosted by Evan Turner and Team Victory Legacy. For videos without hyperlinks, please check back later. Links will be inserted once I have uploaded them to YouTube.

## San Antonio Karate Demonstration Team Finds Victory in Dallas Tournament

January 14, 2010 – Dallas, Texas. Team Legacy, a seven-member martial arts demo team from San Antonio earned 1st place at the American Taekwondo Association Black Belt National Tournament and the right to defend its title as World Champion Demo Team at world championships this summer. Team Legacy overcame some technical difficulties during competition to win the gold in a high flying, dizzying display of martial arts prowess, “extreme tricks”, and entertaining showmanship.

The captain and coach of Team Legacy is Mr. Evan Turner, 4th degree black belt and former “Extreme Martial Arts” world champion. Also on the team are students Rissa Kilar (3rd degree black belt and Texas state champion), JR Kilar (3rd degree black belt), John Healy (3rd degree black belt), JoJo Guzman (3rd degree black belt), Cristian Perez (2nd degree black belt), Van Asher Chandler (2nd degree black belt). Congratulations, Team Legacy, and good luck at World Championships in June!