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Understanding Newton's three laws of motion is the first
step to
learning the dynamics of Judo
Learning the Modern Dynamics of Judo
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 laws 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—that is, of something already independent and
separated from his will—even if originally produced by his own
will. Therefore you can exploit the force of your opponent if you
have a good understanding of the nature of force.
For instance, assume that your opponent moves to his left with
the object of making you lean to your right front corner. Suppose
that the force with which he moves is equal to five units and
that you can throw him in the same direction by adding a force of
five units to his five. Then the total force of ten units will
throw him easily, even if he tries to resist. To keep from being
thrown, he must exert additional force against the force of ten
units that is being placed on his body. We know that there is a
force that can be exploited whenever the opponent makes a motion.
Second law of motion
Newton states in the second law of motion that when a force acts
on a mass, the mass acquires a certain acceleration proportional
to, and in the direction of, the force acting on it and that the
acceleration is inverse to the magnitude of the mass. The law can
be easily understood by means of the following experiment.
Suppose that there are two balls placed on the floor. One is made
of iron and the other of wood. Now let us roll the balls
simultaneously by applying two forces equal in magnitude and
direction. The wooden ball goes farther than the iron ball
because its velocity is greater. Try the experiment again, this
time exerting a larger force than before. The wooden ball will
roll proportionately farther and faster.
Now let us see how this law works in judo. You know that if you
exert a force on your opponent and that if his body weight is
less than yours, you will be able to make him move or fall with
comparative ease. On the other hand, if he is heavier than you,
you will have more difficulty in moving him and breaking his
posture.
If you throw him with a larger force, he will fall faster to the
mat. If he strikes his body against yours to push you down
backward, the larger his body, the more difficult it becomes for
you to stop his body's movement before he applies his throw.
These phenomena are all due to the second law of motion. It is
this law that shows us why a large man has an advantage over a
small man in competition.
Third law of motion
The third law of motion is called the law of reaction. The law
states that to every motion there is a reaction. We find numerous
examples of this in our daily experience. If a man in a rowboat
pushes another rowboat, the pushed boat moves in the direction of
the force applied, while the pushing boat simultaneously makes a
corresponding motion in the reverse direction.
Again, if a man in a boat pushes the shore with a pole, his boat
gets clear of the shore. If a person standing in a natural
posture before a pillar pushes it with his hand, he will tend to
fall backward. This is due to the force of reaction that the
pillar exerts against his force.
The third law of motion—the law of reaction—proves that a
dynamically produced force is more important than the force of
the muscles in breaking the posture of the opponent and making
him fall as the result of a fast and powerful movement of your
body.
In grappling, why is it difficult for your opponent to get up
when he is turned over on his back? It is because he has nothing
to push against effectively with either of his feet.
Consequently, he can use only the force of his arms and
shoulders, but this is not enough to make all parts of his body
cooperate.
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