Martial Arts and Newton’s Laws of Motion

Intro to Newton’s Laws of Motion

To properly understand the concepts that Sir Isaac Newton studied and set down as the laws of physics concerning motion, one must first know what motion is and what causes it. Motion is mass that is changing position. Motion only exists if there is an unbalanced force. However, not just any force can move any object. In order to move or stop mass, you must first overcome its resistance to change, or inertia (Newton’s First Law). To correctly measure how much force is need, one must understand the relationship of mass and acceleration; the two components that you must have for force to be present (Newton’s Second Law). Now that the mass is
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moving, what happens to objects that it could encounter? Depending on the mass of the objects and whether they are in motion or not, there may be different results, but this is always the same: Energy is never gained or lost. You end with what you start (Newton’s Third Law). These laws are all around us; not as individual rules in a textbook, but interconnecting concepts that work all at once.

One of the very many examples of applied motion is that of martial arts. Martial arts are defined as a form of systematized combat training used to either defeat an opponent or defend against one. Whether used to attack or defend, all martial arts rely on motion and force; mainly ones pertaining to hand-to-hand combat. As such, martial arts offer an interesting and detailed example of individual instances of Newton’s laws and how they mesh together to form one cohesive whole: Motion.

Newton’s First Law: Inertia

In order to talk about motion, one must start at the very beginning: Getting an object to move. Newton’s First Law states that an object at rest, or not in motion, will stay that way unless acted on by an unbalanced force. A prime example would be bowling pins before being hit by a ball. Similarly, an object that is moving will keep moving unless another unbalanced force acts on it. An unbalanced force in this case means any force that is not the force pushing or pulling the object. Inertia is the force an object possesses that either keeps it in place or keeps it moving. In order to move or stop the object, the force must match the inertia of the object.

Martial arts applied to Inertia

In martial arts, this object that must be stopped or moved is almost always the opponent. The knowledge of inertia is enough to convince the defender to step aside when a larger opponent is charging towards them. His large inertia will overcome them and they will not stop him right away. Inversely, smaller opponents will be easier to stop due to their inertia being larger than the defender’s; the unbalanced force needed to stop them in their tracks. On the other side of this law, someone could be pushing the opponent instead. If they push on the larger opponent, he won’t move due to his larger mass, while a smaller opponent is easier to move. Keep in mind that this is true ONLY if the same amount of force is used every time. How can something be moved if its inertia is greater than the first object? Newton’s Second Law can be used to calculate what increase in what unit is necessary.

Newton’s Second Law: F=ma

Newton’s second law has to do with exactly what is needed to do to move anything. For force to exist, there must be mass and acceleration. When you multiply mass and acceleration, force is the product. To increase the amount of force, either mass or acceleration must be increased as well. However, due to mass and acceleration being inversely proportional, when you increase one of them, you must decrease the other. A good illustration would be a car or a bullet. Because mass cannot safely be added to a car while it moves, the only way increase the force is to increase the acceleration. In the bullet’s case, there is a gun that accelerates a bullet the same amount no matter what bullet it is. To increase force, one would acquire a larger bullet until the target force is achieved.

Martial arts applied to F=ma

In martial arts, a person usually does not have the means or the strength to add mass to their moving mass to increase force. The focus is increasing acceleration and hitting in an area that will be weak enough to harm under the force of the blow. So, a faster punch would equal a harder hit. Often, when in really close quarters, acceleration cannot be properly increased. To compensate for that, karate techniques are taught to end about an inch in the target, ensuring contact. That guarantees that it will hit with full force. However, a martial artist must be careful how hard they hit whatever it is their hitting; that’s because whatever hits them will hit them back as hard as they hit it.

Newton’s Third Law: Action-Reaction

Now that motion is achieved, what are the results of this motion? The two prior laws are dedicated to explaining why and how things move, but what are the results? What is the reaction to the action that is caused? With this mindset, we observe Newton’s Third Law: for every action, there is an equal and opposite reaction. Punching a wall with 450 N, for example, will not only cause someone to writhe in pain on the ground, but it will also make the wall hit back with 450 N. However, this does not apply to EVERY single instance. There are instances where the object hit can’t hit back with the force used on it, such as driving a golf ball down a range. The force exerted was so strong, it only hits back with however much force its inertia allows it to before it moves. Where does the rest of this force go? It is translated into force in the object’s movement. That ball is now flying with the force of the swing minus the force it took to move the ball.

Martial arts applied to Action-Reaction

If anything, this is the most important law to martial arts. With it, martial artists know what parts of the body to hit, how hard to hit them, and how to defend from those hits. The way kicks are delivered, martial artists are taught to whip their leg out to kick and quickly snap the leg back. This minimizes the time in contact with the opponent and the attacker experiences less damage from the reaction to his action. A clearer example would be the sword of a kung-fu practitioner. Let’s say he or she is told to cut down two trees with the same amount of force. One tree is a young sapling and the other is a large and old tree. They slash at the tree and the sword sticks, the force of their blow returning to the sword and ultimately, their arm. The sapling’s inertia, however, is too small to stop the blade and is quickly cut down; the sword only losing the force that was necessary to cut down the tree.

Martial arts and other applied physics

Ever since humans learned how to fight and defend themselves with these effective arts of combat, they have been using Newton’s Laws to their advantage; much before Newton was even born. But martial arts are not solely based on these laws of motion. Martial arts employ other areas of physics to their advantage. Among them are torque (used in throws and twisting of limbs) and potential and kinetic energy (employed in attacks such as the hammer blow and axe kick). For centuries, these worlds have lived without true knowledge of each other but in harmony. In recent year, martial artists have studied the physics of their arts and refined them further, such as United States Marine Corp Gunnery Seargent Bill Miller, the man who created the MCMAP (Marine Corps Martial Arts Program). The many kinds of martial arts that exist are proof of man’s ability to take three concepts and apply them to many forms of defending one’s self.