Acting States of Force

Principle of Transmissibility of Force

Forces of equal magnitude and direction applied along a straight line will produce the same effect, no matter where they are applied along the line. If an opponent pushes you in a certain direction, you should pull or push him or her in the same direction. The force you apply will have the same effect whether it is applied as pull to the opponent's hand or as a push to the opponent's elbow, as long as it is applied along the line of the push and in the same direction as the push. When executing a punch, forces from different parts of the body are applied along a straight line through the fist to the target, e.g. the forces of the dropping mass of the body and the arm muscles are applied along the punching arm.

Summation of Forces

Many muscle groups are involved in the execution of a Taekwondo technique. If all the involved muscle groups contract at the same instant, the final force would be limited by the weakest muscle group. However, if each muscle group contracts sequentially, their forces are added sequentially to produce the strongest final force. The strongest muscle group should contract first and the other groups should contract sequentially down to the weakest group. Each succeeding muscle group should contract at the moment of greatest velocity resulting from the preceding contraction. This coordination of muscle contractions is accomplished by repetitiously performing a technique during years of training.

Composition of Forces

This is the combining of forces to create a greater force. You may not be able to pull a much larger opponent down or resist his or her push, but, if instead of pushing back against a pushing opponent, you pull, then your pulling force will combine with the opponent's pushing force and result in a combined force you may use to pull the opponent down.

Decomposition of Forces

The longer the rope, the easier it is to pull a heavy load because of the decomposition of forces. It is easier pull an opponent off balance by pulling the hand of the opponent's extended arm than it is to pull on the opponent's shoulder.

Time and Distance

The longer a force is applied to an object, the greater its final velocity. The greater the distance a force is applied to an object, the greater the time the force is applied, and the greater its final velocity. The final velocity desired in a strike depends on the situation. In point free-sparring, quickness is desired without a strong final force, while in a self-defense situation, a stronger final force may be desired. Therefore, in a self-defense situation, a technique may be cocked to provide a greater distance for the technique to travel, while in a free-sparring situation, the short, quick, less powerful technique is desired.

Moment of Force

A moment of force occurs when a force is applied anywhere except at the center of mass. It is what makes a fulcrum work. The product of the acting force and the distance between the axis and the line of action of the acting force is called the moment of force. For example, to lift a rock with a board, you slide one end of the board under the rock, place a small log under the board, and push down on the other end of the board. The closer you place the log to the rock, the greater the moment of force, and the easier it is to life the rock. To lift a standing opponent, pull the opponent's upper body forward with one arm, lean in and grab the opponent around the waist, and continue to pull the opponent over onto your shoulders so you may lift the opponent off the ground. The lower you grab the opponent below the waist, the greater the moment of force and the easier it will be to lift the opponent.

Moment of a Couple

A couple is two forces equal in magnitude and opposite in direction acting on a body. It is similar to equal forces pushing in opposite directions on the ends of the two blades of a propeller. The moment of a couple is the product of one of the forces and the distance between lines of action of the two forces. When you punch, if you pull one arm backward as you punch forward with the other arm, the body rotates along its vertical axis and the moment of the couple adds to the power of the punching arm.

Surface Area

The striking pressure of a technique is inversely related to the surface area of the striking object (pressure = force/area). If two objects strike a body with equal force, the object with the smaller striking surface area will strike with the greater pressure and thus be the more effective blow. In other words, the smaller the striking area of a blow, the greater the damage to the opponent. A strike with the outer edge of the foot is more effective than a strike with the sole of the foot.

Dissipation of Force

The person on the receiving end of a strike may reduce the effect of the blow by absorbing the force of the blow over a distance. For example, if you try to catch a falling, heavy object with rigid, outstretched arms, you may injure yourself or drop the object. However, if you bend your arms and let the arms slowly stop the object over a distance, you may avoid injury and successfully catch the object.