The Physics of Power
The application of physics to the human endeavor of karate can be murky. The human body and how it interacts with another human body is far from the perfect conditions of a physics laboratory. However, understanding even in a superficial sense some of the words of physics that we use so freely in karate class can help us improve the effectiveness of our techniques. For example, power. The word power is often misused by all but the physicists among us.
In physics, power is defined as the rate at which work is done.
P = W/Δt
In other words, power is a measure of how quickly energy is being transferred or transformed. To understand power we must first understand energy and work.
Energy
Kinetic Energy
KE= 1/2 mv2 where m is mass and v is velocity (or, very loosely speaking, weight and speed)
The equation for kinetic energy clearly shows that both mass (m) and velocity (v) are necessary to produce kinetic energy. In other words, only mass that is moving can exert kinetic energy.
- Kinetic energy is directly proportional to the mass of the object.
If the mass is doubled the kinetic energy is doubled; if the mass is tripled the kinetic energy is tripled. - Kinetic energy is proportional to the square of its velocity.
If the velocity is doubled the kinetic energy is increased four fold; if the velocity is tripled the kinetic energy is increased nine fold.
Therefore, when you punch or kick, rather than using just your arm or leg, involve your whole body in the punch or kick. Only then can you adding the most mass to the energy equation. If you double the mass of your attack by using your body you deliver twice the energy to your opponent.
The kinetic energy equation also shows the importance of speed. If you are able to develop twice the velocity you actually deliver four times the energy to your opponent.
Summary: For the most power, you have to be both strong and fast.
Work
But work is defined as force times displacement
a force does work if the application of the force displaces an object in the direction of the force. In other words, work is equivalent to the application of a force over a distance. The amount of work a force does is directly proportional to how far that force moves an object. The general formula for work and for determining the amount of work that is done on an object is:
W = Fs
Force
Force is an external agent capable of changing a body’s state of rest or motion. It has a magnitude and a direction.
F = ma
How much force you can deliver to an opponent is dependent on two factors: mass and acceleration.
Work
So the amount of force done in a given distance equals the amount of energy used, which is work.
When you deliver a punch or kick, you want to take the energy of your movement (your kinetic energy) and deliver it to your opponent as a forceful blow. The more kinetic energy the more force can be delivered to the opponent. In other words, the more work you have done on your opponent.
Energy is needed for a force to do work.
Work and energy are equal in magnitude.
So:
ForceForce×distance=Workdistance=Work
Work=Energy Work=Energy
So
ForceForce×distance=Energy
Chūkyū punches, unlike shokyū, often do not come from pulling back the fist back to the side but rather are launched from kosa uke. To be as fast as possible in the shortened distance from your fist to your opponent you need acceleration. Lots of acceleration. Follow through is important, too. You want to be still accelerating as you contact.
Force Is a Vector
A force has both magnitude and direction. Energy needs to be delivered in the right direction to be perform work on the opponent. A forceful kick that angles up the body does not deliver all of its energy to the opponent. The remaining energy is wasted.
Strength
When you exercise by lifting weights you are attempting to increase your body’s ability to do work. In other words, you hope to make yourself capable of producing great force that you can apply to another person’s body.
Chūkyū punches, unlike shokyū, often do not come from pulling back the fist back to the side but rather are launched from kosa uke. To be as fast as possible in the shortened distance from your fist to your opponent you need acceleration. Lots of acceleration. Follow through is important, too. You want to be still accelerating as you contact.
Acceleration
Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity. Acceleration measured as the change in velocity in a particular direction.
Another way to write the above equation is:
KE = ma where a is acceleration
What is not important to the amount of kinetic energy at the moment of contact is the how long it took you to get to that velocity. A punch delivered straight out of kōsa uke can reach the same velocity as a punch from hikite, but you need more acceleration to reach that velocity in the distance available. If you develop explosive speed, then you can deliver power without hikite, making you a more formidable opponent.
Potential Energy
| inyō | 陰陽 | |
| in | 陰 | equivalent to yin negative female dark |
| yō | 陽 | equivalent to yang positive male light |
As you punch out the opposite shoulder will naturally move back, setting you up to deliver the next punch, This increases potential energy for the next punch by giving you more distance to accelerate through.
In the more Asian way of thinking, apply the concept of dual forces (inyō) to punching. Inyō is the Japanese word for the Chinese concept of yinyang. The forces of the universe are paired: black/white, male/female, light/dark, up/down and so on. How does this apply to punching? Where there is in, there is yo. Therefore, as you punch out the opposite shoulder moves back.
Elasticity
To increase the mass delivered to the opponent, use the whole side of your body and not just your arm. Tighten on contact to deliver all of that force to the opponent. Make the collision as inelastic as possible. In other words, you don’t want to bounce off like a ping pong ball hitting a billiard ball.