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PHYSICS OF TANG SOO DO
Author: Jack Sanders-Reed
Whether your goal is to knock out an opponent or pulverize a brick, you have to deliver energy on target. It’s common knowledge that the more energy you dump, the greater the damage will be.
Just as important, however, are the time it takes you to transfer that energy and the area over which it’s spread.
This article will help you understand the roles of those additional factors so you can more efficiently execute the striking techniques of arts like tang soo do.
Energy
Kinetic energy is the energy of motion. It’s equal to one half the mass of the moving object multiplied by the square of its velocity.
Therefore, if you double the mass of your fist, you double the impact it makes when you punch. However, if you double the velocity of your fist, the impact jumps by a factor of four.
Obviously, increasing the speed leads to the production of more energy than does increasing the mass by the same factor.
When two objects collide—such as a car and a truck, or a fist and a nose—physics says that two quantities remain constant: total energy and total momentum. Ideally, you would like all your energy to be transferred to the target. We just saw that energy is one half the mass times the square of the velocity. Momentum is just mass times velocity.
Because a fist striking a nose is somewhat complex, we’ll start with a simpler example.
Think of two solid balls. The greater the mass of the striking ball, the more energy is delivered to the struck ball. If you’re driving your car and you hit a bicyclist, it will be bad for the bicyclist but you may not feel much inside your vehicle. On the other hand, if you hit another car, things will get worse for you, and if you hit a truck, the result will be much worse. Obviously, a larger mass will do more damage. The important concept with respect to momentum is, a more massive object is more efficient at transferring energy.
Time
The time during which you impart your kinetic energy is also important. If you shove an opponent with a strong push, you’ll move him backward but you probably won’t hurt him. On the other hand, if you deliver the same energy in a short impulse—such as with a punch—he could sustain a broken bone.
Think of dropping a glass on a concrete floor and dropping one on a soft bed. The bed deforms and spreads out the impact over a relatively long time, while the floor stops the glass almost instantly.
That’s the principle behind most automotive safety features: spread out the energy over time. The front fenders of your car are designed to crumple (like the bed) as opposed to being rigid (like the concrete floor) so it takes the passenger compartment —and you—longer to stop. If it isn’t restrained, your body will hit the dashboard and stop instantly, and thereby suffer more damage. But if you use a seat belt that stretches slightly and an airbag that gradually slows you down as you approach the dash, the energy decrease will be spread over a longer time. That means your body will have time to transfer the energy away from the area of impact.
Of course, if you’re on the offensive in the sparring ring, you’ll want to decrease the time it takes to deliver the energy on target.
Area
The area over which your energy is spread also affects the amount of damage you do. If it’s concentrated in a small area, more damage results.
A knife is dangerous because the edge is very narrow. If someone hits you with the side of a blade, it might sting, but it will do little damage. But if he strikes you with the point, all the energy will be concentrated at the tip, and your skin won’t be strong enough to resist.
Illustration
The following is another example that will shed some light on the physics of tang soo do strikes: When you drive a nail into a board, the hammer is the energy source. If you tap the nail, it won’t go in as deeply as it would if you were to swing the hammer down at high speed because a higher speed means more energy.
Similarly, if you use a lightweight hammer, the nail won’t go in as far as it would with a heavy hammer because more mass means more energy and a better transfer of that energy.
Now, what happens if you place something crushable, such as a piece of Styrofoam or rubber, on top of the nail? The blow is no longer about unyielding metal on unyielding metal. When the hammer hits the nail, the energy transfer is almost instantaneous. However, when the hammer hits the Styrofoam, the Styrofoam slows it gradually so the energy isn’t transferred as quickly.
The nail doesn’t go in as far.
Finally, note how the nail comes to a sharp point where it’s supposed to pierce the surface of the wood.
That allows all the energy of the hammer blow to be concentrated at a single point in a single instant. The wood cannot resist the energy, and the nail penetrates. However, if you use a blunt tip—maybe turn the nail over so the head is down—the nail no longer enters the wood.
Application
Based on these discussions and the equations listed in the sidebar, the essential principles are:
• Strike with maximum velocity. (That also implies quickness, which may prevent your opponent from blocking your strike.)
• Make the impact time short.
• Make the striking object massive.
• Make the striking object rigid so the delivery time is short.
• Ensure the impact area is small so the pressure is increased.
So how do you achieve these goals? Perhaps the easiest factor to deal with is the impact area. You already know the value of striking with a small, well-defined part of your body—for example, the first two knuckles of your fist, your flexed elbow or your heel. Compare those blows with an open-hand strike. A slap may sting, but it won’t break bones like a punch will.
Some techniques are a compromise.
For example, a ridgehand uses a larger striking surface than a spearhand—a line as opposed to a point. It’s like using the edge of a blade instead of the tip. The edge is sharp and can cut, but it doesn’t penetrate as well as the point does.
Nevertheless, both are useful.
There are several ways you can generate a high velocity for your striking object. You can slowly accelerate it over a long time or quickly accelerate it over a short time.
Conceptually, you could hold your fist out straight in front of your body and start running. The maximum velocity of your fist would equal the maximum speed at which you can run. However, it would take a relatively long time to get up to speed, and your maximum speed is limited.
Tang soo do teaches smarter ways of getting your fist up to speed more quickly—and, in fact, of getting it to move at substantially higher speeds.
Most power is generated from the abdomen, from hip rotation that drives your fist. (A rule of thumb is that 60 percent of your power comes from your abdomen, 30 percent from your legs and 10 percent from your arms.) You can do two things to achieve maximum velocity: First, you can accelerate your weapon over as great a distance as possible, thus maximizing the time during which it picks up speed. Think of the low block, which starts from a high position near your ear before traveling all the way down past your hip, and the high block, which begins near your waist and travels up past your head.
Second, you can maximize the acceleration itself. By remaining loose and letting your arms act like strings with rocks attached to the ends, then driving them with hip rotation, you can produce greater acceleration than if you simply tried to propel them with your arm muscles.
Deceleration
The next step in applying physics to the practice of tang soo do involves decreasing the time during which you deliver your energy on target, which is really the time it takes your fist or foot to decelerate.
You do that by making the striking object as rigid as possible so it transfers its energy instantaneously—like the aforementioned discussion of the concrete floor and the bed.
You must remember that your fists and feet are attached to the rest of your body, and that has several important implications. You can increase the effective striking mass of your fist by adding the mass of your body. However, that will require you to avoid absorbing energy back into your body; you must transmit it from your fist to the object you’re striking instead.
To implement this principle, start by forming a fist. If it’s loose, it will compress on impact, spreading out the time of the impact and lessening the force applied to the object. If, however, it’s tight, it will not compress when you make contact because it’s already compressed. The difference is akin to being hit by a rubber ball and being hit by a rock.
Now think of that rubber ball or rock as being attached to the end of a stick—much the same way your fist is attached to your arm. If you drive that stick into your opponent and it flexes, it will absorb energy and spread out the impact over the time during which the flexure occurs. On the other hand, if the stick is rigid, it won’t bend and the impact will be instantaneous.
Similarly, if you punch with a rigid fist and arm but a flexible body, your body will bend, thus increasing the duration of the impact. That’s why you learn to emit a kihap (spirit yell) in which you exhale compressible air and tighten your abdomen. Note that if you allow your legs to bend, you will extend the impact time as well.
Therefore, you should strive to stiffen your fist, arm, abdomen and legs so your body is one solid mass.
With a good stance that anchors you to the earth, you can completely transfer your energy to the target and do so instantaneously.
The same principles apply to kicking. When you execute a front kick, you strike with the ball of your foot after your foot has been extended. That provides a rigid line of bone from the ball through the foot to the ankle and up the leg. It’s linearity results in a rigid structure that won’t flex or spread the impact over time. Similarly, a properly executed side kick strikes with the heel. It’s the terminus of a straight line of bone that runs all the way up your leg to your hip. If, however, you perform a sloppy side kick and strike with the ball of your foot, your foot will flex backward at the ankle, reducing the effective mass and spreading the impact over time. The force will drop accordingly.
Obviously, studying physics can enhance your ability to execute more powerful striking techniques. Just as beneficial, however, is realizing that the teachings of the ancient Asian masters match up nicely with the principles of Western science. Perhaps that’s why they have withstood the test of time so well. ...
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