Fundamental Physics

Physics represents a key area of study in the martial arts. No motion is possible without one or more fundamental laws of physics being involved somehow. Let’s explore a few of these fundamental laws and how they may apply to some common martial arts movements.

Newton’s Laws of Motion

Perhaps the most fundamental laws deal with inertia, force and energy. These are Sir Isaac Newton’s three famous fundamental laws of motion. Let’s discuss each law a bit.

  1. Law of Inertia. This law says that an object will seek to maintain its current inertial state. If something is resting it will not move from its current location unless some force acts upon the object. If an object is in motion, it will not stop, slow down, or change its direction unless some force acts upon it. In other words, an object will maintain its current behavior unless some external force interacts with it in some manner.
    • This is often seen when someone attempts to do a Mawashi Geri. If they try to move all parts of their body at one time the kick is delivered very slowly. It takes a good deal of energy and time to accelerate a resting body all the way around until it delivers a devastating round house kick. More time and energy is required by a larger person than a smaller one. It’s just fundamental physics.
    • If someone throws a punch at you it will require an equal amount of energy to stop it again. This is why you seldom see anyone attempt to directly intercept an incoming strike. It takes much less energy to redirect an object than it does to completely stop it. This is why most blocks deal with moving a strike out of the way, rather than intercepting it head on.
  2. Law of Force. This law states that the amount of force produced by an object is the product of its mass and the acceleration that was applied to it. Naturally, something large (according to the first law above) will require greater acceleration to get it to move than a smaller object.
    • A large object may move somewhat slowly, but it may have significant force since it took significant acceleration to cause it to move. A good example is a car. Even when moving at a very moderate speed it has substantial force that can do extreme harm to any unfortunate pedestrian who crosses its path.
    • A small object with little acceleration carries very little force. But a small object that has received high acceleration can have great force. Consider the case of a bullet. It does not have a lot of mass (certainly when compared to a car), but the much higher acceleration rate (when shot from a gun) means it will deliver very significant forces into the small area where it strikes.
    • A punch from a small person delivered at very high speed can have as much force as a punch from a large person delivered at a slower speed. This is one reason why we stress that the speed of delivery is a critical factor in the effectiveness of a strike.
  3. Law of Equal and Opposite Reaction. When a moving object encounters a stationary object (or any object, for that matter) it will impart energy into the stationary object. This is intuitively clear. But it is also important to recognize that the stationary object will impart exactly the same amount of energy, but in the opposite direction, into the moving object. If it did not, then the moving object, according to the first law above, would not slow down or change its behavior in any way.
    • When you punch someone an equal amount of energy is delivered into both your body and your opponent. If you are not correctly aligned mechanically and structurally then this energy may cause you injury and/or result in a sudden loss of balance or structural integrity. When you strike it is important to realize that you are being impacted just as much as your opponent. The only difference is the location at which the impact is occurring.
    • If someone is accelerating toward you then striking directly at them will impart more energy into their structure (and yours) than if they were standing stationary. How these forces are absorbed by you and your opponent is the only variable. The person who is charging forward seldom has the opportunity to dictate where these forces will be directed.

The Physics of Rotation

Other key physics concepts that you will encounter frequently in the martial arts are angular velocity (momentum) and tangential velocity.  These can best be described via a simple mental model. Assume you have an old phonograph record that is rotating at 33 RPM. Hopefully you’ve seen one of these in a museum somewhere.

If you place two small pieces of tape on the record, one at the outer edge (the outside tape) and one about midway between the spindle hole and the outside edge (we’ll call it the inside tape) then you can make the following observations.

  • When the record is spinning both pieces of tape make a full 360° rotation in exactly the same amount of time. Both pieces of tape have the same angular velocity. Both pieces of tape are traveling at just under 200 degrees per second.
  • The inside tape is moving around a much smaller circle than the outside tape. The circumference of the inside circle is much less than the circumference of the outside circle.
  • Since both pieces of tape are moving around their respective circles in the same amount of time, the outside tape must be moving around its circle at a faster speed than the inside tape is moving around its circle. The two pieces of tape have different tangential velocities.

There are two different types of velocity involved here. It is important that martial artists understand the differences and appreciate how they relate to movement and power. Something that is further away from the center of rotation will have greater tangential velocity than something closer to the center of rotation. This is why you might prefer to strike using the tip of a weapon. It simply has more force there due solely to its increased tangential velocity. It is also why you never block a swinging weapon near its attacking end. You always block such a weapon (or preferably close to the shoulder of the arm holding the weapon) near the center of rotation where it will have the least amount of energy and force. This is an important topic which we explore more fully in our topic on Angular and Tangential Velocities (please see the links at the bottom of the page).

This same concept is also applicable to energy conservation. If you maintain a very tight circle, and force your opponent to move in very large circles, they must expend more energy to move around the larger circumference. You meanwhile are using relatively little energy. This concept similarly applies to how broadly you move when employing circular strikes and blocks.

There are numerous other laws of physics that you will encounter over time. Periodically stop and think about the physics involved in a particular movement. It can be very insightful and may lead you to better understand how to protect yourself, minimize injury to an opponent, improve your movements, or stop an opponent instantly. Physics is your friend. An increased knowledge of physics will lead to a much better appreciation of martial arts principles.

See Also

Angular and Tangential Velocities


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