# Force

## 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.