Newton's Laws of Motion

First Law of Motion

A body at rest tends to remain at rest and a body in motion tends to remain in motion, unless acted upon by external forces. This tendency to resist a change in state is called inertia. Since an opponent who is in motion tends to remain in motion, it is easier for a defender to use that motion in his or her favor rather than trying to stop the motion, such as pulling an opponent who is charging you. Since an opponent who is at rest tends to remain at rest, it is difficult for the opponent to avoid an attack quickly.

Second Law of Motion

When a force acts upon a mass, the mass acquires a certain acceleration proportional to, and in the direction of, the force acting upon it, and the acceleration is inverse to the magnitude of the mass. In other words, a large, heavy person has an advantage over a small, lighter person.

Third Law of Motion

For every action there is an equal and opposite reaction. Thus, when you punch an opponent with a certain force, an equal but opposite force is applied against you by the opponent's body. Therefore, you must have a tensed body and a firm, stable stance so you may withstand the force. Hopefully, the opponent will not be prepared and thus must absorb the full force of the punch. The third law also applies to technique execution. When one arm is pulled back quickly, an equal but opposite action occurs in the opposite arm. If that arm is executing a punch, the force will combine to increase the force of the punch.

Centripetal and Centrifugal Force

Two other forces that come into play during the practice of Taekwondo are centripetal and centrifugal force. Centripetal force is the force that draws objects into a spinning whirlpool. Centrifugal force is the force that throws objects off a spinning top. These forces come into play when using spinning kicks and releases that use a spinning motion.

Potential and Kinetic Energy

Potential energy is energy at rest; it is stored and available for use. Kinetic energy is energy in motion; it is consumed as it is used. When throwing an opponent, you use your kinetic energy to lift the opponent off the floor against gravity. At the peak of the throw, potential energy is stored within the opponent. To complete the throw, you release the opponent and the opponent's potential energy changes to kinetic energy as gravity forces the opponent to the floor.

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