from blackbeltmag.com - https://blackbeltmag.com/physics-and-kenpo/wrap-up
(part 1)
Every session in the dojo should be another step towards our ultimate goal, which is why we must take our training seriously. However, we also need to be able to appreciate moments of levity. That’s why I’d like to start today’s discussion with a quote from Master Ken regarding fighting a Kenpoist.
“In Kenpo, students are actually encouraged to hit themselves during a fight. Which means if you fight a Kenpo black belt long enough, eventually he’ll kick his own a**.”
This is, of course, a joke about the rebounding slap seen performed by Kenpoists all over the world. If you are a Kenpo practitioner, you are most likely aware of the reason behind this action of rebounding and its potential applications. If your art doesn’t employ this concept, then it may appear funny and foolish. To an outsider it can look like a guy slapping himself for no apparent reason, which may be true in some cases. However, a skilled and self-aware Kenpoist is conscious of their actions and uses rebounding to harnesses and immediately rerelease power.
“Harness and immediately rerelease power.” What does this mean?
Let’s take a moment to consider a baseball and what happens to it from pitch to a homerun hit. A pitcher throws a baseball at roughly 90mph. The batter swings his bat to strike the ball with a barrel speed of his bat around 80mph. There’s a loud cracking sound as the bat smacks the ball and, nearly instantaneously, the ball is sent off in a direction nearly opposite of its original path at over 100mph. Both the bat and the ball act upon one another. The heavier and continuously powered bat absorbs the energy of the ball and continues on its path. A homerun ball results from the bat’s massive force acting on the baseball creating huge acceleration of the ball opposite its original path when it left the pitcher’s hand.
Now that we have a visual example in mind, let’s get into the science of this action. A force from the bat is acting upon the ball to change its direction. The physics equations for what is happening in this example are as follows:
F=ma
Force = mass x acceleration
Force is equal to the mass of an object multiplied by the acceleration of that same object.
To deeper understand the resulting change of direction of the ball we must define “acceleration.” That is where the following equation comes into play.
a = (vf–vi)/Δt
Acceleration is equal to the change in velocity (resulting velocity – initial velocity) of an object divided by the amount of time it takes for that change to happen. We plug these pieces of the “Acceleration equation” into the original “Force” equation (F=ma) for “a” and end up with the following representation of the force exercised on the ball while it is in contact with the bat.
F = (mvf–mvi)/Δt
Here we are shown that the FORCE exerted on the ball by the bat is equal to the mass of the ball (m) multiplied by the final velocity (vf) of the ball minus the mass of the ball times the initial speed of the ball (vi). Pay special attention to how the positive and negative of the velocity affects the outcome. Because they are moving in opposite directions the initial velocity is considered a negative because it’s going in the opposite direction of where it ends up heading. The net result of the subtraction in the equation is that it is added to the first part of the equation. The (mvf-mvi) is then divided by the amount of time (Δt) the bat is in contact with the ball for our final understanding of the force used to create that change in speed and direction.
As we wrap our mind around these equations and how they relate to speed and acceleration, the overall take-home message I want to impart is the following:
The greater the change in directional speed of an object and the shorter the time frame in which the change of speed happens the greater the observed force must be.
The exact numbers for the speeds of the bat and ball are not the important part here. What is important is the overall concept. The speed at which the ball leaves the bat is enhanced and is greater than the speed of either object’s original movement. Imagine for a moment that the batter no longer had a bat. Instead, he was forced to catch the ball barehanded and, with the same hand, throw it back as fast as he could. He would have to decelerate the pitched ball’s speed by absorbing the moving ball’s force with his musculature and then reaccelerate it to throw it towards the outfield wall. It’s safe to say that it would take longer to get the ball moving towards the outfield and would also leave his hand with less velocity than in the previous example where it was hammered off the bat.
You may be wondering how this baseball analogy applies to Martial Arts. The idea of this parallel to baseball is to have us look at our torso compared to the bat and our hands to the baseball. After a hand strike is thrown, it returns to us. We don’t simply leave it out there for an attacker to grab or manipulate. So, as it returns toward the bulk of our body, we must instantaneously decide if it is to be deployed again or will it stay back in a fighting or checking position. If we’re deploying it once more, we can reduce the time out of battery and increase its velocity back into the fight by rebounding the hand off our torso. Like in the baseball example, the projectile bounces off the heavier object and it forced back towards whence it came.
In Part 2, we will delve further into the practical application, the lab of the dojo if you will, and increase our understanding of the rebounding principle.
Salute,
Ian Lauer
B.A. Chemistry
from blackbeltmag.com - https://blackbeltmag.com/rebounding-for-speed-part-2
(part 2)
In Part 1 of “The Physics of Rebounding for Superspeed” we took an in depth look at the physics behind the force production necessary to change the direction of our hands and quickly create effective weapons. In case you have forgotten or missed Part 1, the take home message of all the fancy physics equations is:
The greater the change in directional speed of an object and the shorter the time frame in which the change of speed happens the greater the observed force must be.
Now that you’re here reading part 2, it means you intellectually understand this concept and are curious how to apply it to your Martial Arts training. Or you already use rebounding and wish to maximize its effectiveness. Allow me a moment to share the first experience I had of a rebounding happening in my body and me simply being along for the ride.
I remember it like it was yesterday. I had been told the principle before but still had to consciously think about how to apply it. It wasn’t something that just happened naturally. Because I was still thinking through each move within the attempt to rebound, everything was choppy without flow. That was up until around the time I was a purple belt working towards blue in American Kenpo. That’s when it changed for me. I was practicing the Parting Wings technique and I heard the rebound happen, and it occurred without conscious thought to make it happen.
For those unfamiliar with the Parting Wings technique, allow me to explain. An attacker tries to push you in the chest with both hands. In response, you step back with your right foot into a left neutral bow and do two simultaneous outward hand sword blocks. Then you settle into a forward bow with a right inward hand sword to the ribs. As the strike happens, your left-hand bounces from its previous block and recoils to your upper chest. It smacks against your chest at the same time your right-hand sword hits your opponent.
At the time of this smack, the body is rotating towards the attacker due to your transition from neutral bow to forward bow. The left hand then bounces off your chest with a smacking sound and is redeployed into battle and consequently very quickly strikes the adversary with an outward hand sword to the neck as you return to neutral bow. There is a more to the Parting Wings technique, but this was the very moment when my eyes were opened to rebounding and its potential applications.
After this realization, I started looking back at previously learned techniques and found that many of them also use this principle. For example, a few of my favorites that have rebounding applications learned at earlier levels in the American Kenpo curriculum are the purple belt technique Leaping Crane, orange belt technique Five Swords, and yellow belt technique Alternating Maces, among others.
If you are a Kenpoist and know these techniques, might I suggest you try working them through for a few reps and identify the rebounding opportunities. If you study an art that doesn’t utilize rebounding, revisit the described actions in the beginning phase of Parting Wings above and see if rebounding is something you can assimilate to enhance your hand speed.
Kenpoist or not, if you wish to incorporate this principle, it is important to keep an eye out for opportunities to effectively apply rebounding and practice, practice, practice. That’s what it takes to get good at any skill. And the greater our mastery of rebounding, the faster our strikes become and the more rapidly they can be consistently deployed. By digging back into our training techniques with rebounding in mind, we afford ourselves the opportunity to tighten up and improve our overall skill set as a Martial Artist.
After this realization, I started looking back at previously learned techniques and found that many of them also use this principle. For example, a few of my favorites that have rebounding applications learned at earlier levels in the American Kenpo curriculum are the purple belt technique Leaping Crane, orange belt technique Five Swords, and yellow belt technique Alternating Maces, among others.
If you are a Kenpoist and know these techniques, might I suggest you try working them through for a few reps and identify the rebounding opportunities. If you study an art that doesn’t utilize rebounding, revisit the described actions in the beginning phase of Parting Wings above and see if rebounding is something you can assimilate to enhance your hand speed.
Kenpoist or not, if you wish to incorporate this principle, it is important to keep an eye out for opportunities to effectively apply rebounding and practice, practice, practice. That’s what it takes to get good at any skill. And the greater our mastery of rebounding, the faster our strikes become and the more rapidly they can be consistently deployed. By digging back into our training techniques with rebounding in mind, we afford ourselves the opportunity to tighten up and improve our overall skill set as a Martial Artist.
Salute,
Ian Lauer
B.A. Chemistry
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