Learning the Modern Dynamics of Judo

You may have the erroneous idea that force is not necessary in judo, especially when you see a sixty-year-old instructor throwing many young- and strong men seemingly without effort. Dynamics, however, denies this illusion. A body begins to move only when an external force works on it, as will be explained later. A human body is a physical entity. Therefore, if you want to break your opponent's posture and make him fall down or hold him down on the mat;, you must apply the proper force to him.

Newton's "three laws of motion" can be considered the foundation of modern dynamics. As a human body is a physical solid, its motion must be studied under these laws. Therefore a complete understanding of these law.-; may- well be the first step toward learning- the dynamics of judo.

First law of motion

What is force? A conception of it can be derived from the first law of motion. Newton states that a body at rest remains eternally at rest, and a body in motion remains eternally in uniform motion unless acted upon by an external force. When we push a book that rests upon a desk or stop a ball in motion with our hands, we receive resistance from these objects. This resistance is called inertia. Therefore, to give motion to a body at rest or to stop a body in motion, we must overcome the inertia of that body. We may define force as an action to overcome the inertia of a body.

According to the first law of motion, a rolling ball would continue eternally in motion after it had once been put in motion. Therefore, if we were to throw a ball at the moon, the ball would continue its flight until it reached the moon. In reality the ball eventually falls to earth. The reason for this is that the attraction of the earth's gravity acts on all objects in the same manner. How can we apply this law to judo? We know that if an opponent at rest makes a motion it is the result of an external force