# The Physics Behind Karate

Actions performed in Karate respond to exact laws of physics and mathematics. Karate specifically exploits these rules to obtain maximum power from human levers (arms and legs). Martial arts professors and students, while training in a dojo, spend a lot of time applying tricks and physical advice just to improve their stroke power. Let’s get acquainted with some of the phenomena that can be observed in Karate. Karate: A group of physical concepts Karate is probably the sport in which the concepts of physics are applied with the greatest precision and frequency. All movements and strokes that athletes make are not random but have been carefully studied to transmit maximum energy and inflict less severe injuries on their bodies. If shot correctly, it is potentially fatal and can even kill a person. This potential of the human body is well known by wrestlers. Some definitions Before starting the analyzes and simulations, it is helpful to remember some technical definitions. In physics, each word has a specific meaning and cannot be replaced by another: force (N) – the action that causes velocity to change Weight (N) – a quantity derived from the international system indicating the force with which an object is attracted by the force of gravity of the Earth’s mass (kg) – Inertia scale; That is, the resistance that the body opposes to all variations in its state of rest or movement. Velocity (m / s) – the speed at which an object’s position changes. In karate, the average speed corresponds to the speed at which the technique is executed, while the instantaneous speed corresponds to the speed of the impact. Acceleration (m / s2) – the speed at which velocity changes. If negative values ​​are assumed, then we have hysteresis. Work (J) – the transfer of kinetic energy to the body, which is performed by a force when the body moves energy (J) – the body’s ability to do the work of kinetic energy (J) – the energy that the body has due to the movement Center of gravity – the point at which each is applied Body weight pressure: (N / m2) – the ratio between the force perpendicular to a surface and its area. Speed ​​is an essential element in karate. Movement speed plays a fundamental role, and the most important results cannot be obtained if corpses move slowly. In other words, it is necessary to apply the maximum possible force at the moment of impact, and this can be achieved with such speed and precision at the same time, as shown in Figure 1. In this sequence of images, Bruce Lee said sends all his weight in one place with destructive results. All parts of his body move in harmony and maximize the ultimate energy. The system equates to an object of mass about 60 kg (Bruce’s weight) fired at a velocity of about 7 m / s, and has a kinetic energy of 1,470 joules and an impact force of tens of thousands of newtons. The bag weighing 60 kg, as you can see, was dumped from a distance. Figure 1: Bruce Lee’s destructive velocity. Had Bruce Lee been running at 1 m / s, his bag would have moved only a few centimeters, with poor results. Therefore, velocity is the real component of force, not mass. With speed doubling, the results would be horrific. Of course, the mass cannot be changed, as the body parts (hand grip and foot) are not adjustable. In Figure 2, we can see Bruce Lee hitting a 60 kg bag, at four different speeds: 1 m / s – the blow is barely perceptible and the bag only oscillates slightly. 2 m / s – the blow is a little stronger and the bag swings with a greater amplitude, it rises a few centimeters. 7 m / s – the blow is very strong and the bag rises to almost 2 meters from the ground. 10 m / s – the blow is very strong; The bag lifts up to several meters from the ground and also makes a revolution. This situation is within the limits of human potential. The yellow chart describes the vertical position of the luggage. Figure 2: Athletes should train their speed of movement more carefully. Now to see which of these situations has the most kinetic energy, remember that this is the energy that an object has due to its motion and is measured in joules. You have to choose between: Case 1 – a body of mass 4 kg at a speed of 10 m / s Case 2 – a body of mass 2 kg at a speed of 20 m / s Case 3 – a body of mass 2 kg at a speed of 20 m / s. A mass of 8 kg at a speed of 5 m / s is used to calculate the kinetic energy, the following formula is used: Results are as follows: As shown by the energy results, doubling of velocity is always preferred over doubling of mass. A very light object, weighing only 2 kg, and launched at high speed produces greater kinetic energy, and thus more damage (see Fig.3). The pistol bullet philosophy is based precisely on this point. Many fighters mistakenly believe that they “can strike more”. Strike energy can be increased by adjusting two variables: fist mass and velocity. Figure 3: Body velocity is more destructive than mass-effect dynamics. Impact is a violent collision between two objects, usually given speed. During collision, there is a mutual transfer of energy, in the form of heat, action, deformation, or noise. For the calculation it is necessary to determine the instantaneous slowdown; That is, the time the object goes from zero velocity. This is because every substance reacts differently. If the shock surface is smooth, then the impact time will be longer than the impact time on hard surfaces. To calculate the impact force, it is necessary to know: the mass of the object. Body speed. Duration of the effect. It is very difficult to calculate the cooldown time. It can range from a few hundred seconds for a net effect on a hard surface to a few seconds for a soft landing surface. It is necessary to consider the geometry and structure of objects to verify whether it is an elastic or inelastic collision, and to assess the impacts on objects and the relative deceleration due to the impact. To measure this in action, you can use special cameras with a very high “frame rate”, usually over 1000 frames per second. In other words, the impact strength will be different if it hits, for example, a piece of wood, iron sheet, face, or sponge. A good karateka grip can move at speeds greater than 10 m / s and can develop destructive force greater than 700 kg / force. To calculate the force of the impact, the following formula is used: the inelastic effect in an inelastic collision, momentum is conserved and the kinetic energy, on the other hand, is converted into deformation and heat. We can consider the blow to an athlete’s face as an inelastic effect (see Figure 4). Assume the following scenario: mass A (head): 5 kg velocity A: 1 m / s mass B (opponent’s punch): 0.6 kg velocity B: 15 m / s velocity units in two masses, understood Immediately they are about to collide with each other, which leads to surprising results. First, let’s calculate the kinetic energy of the two moving masses: the kinetic energy of the whole system before collision is equal to the algebraic sum of both bodies: Now it is necessary to calculate the velocity of the entire system after the collision, as the two bodies remain connected to each other, with the following formula: Finally, we can calculate the kinetic energy of the whole system after the impact: The measured kinetic energies are: the kinetic energy of the system before the collision: 70 J The kinetic energy of the system after the collision: 17.5 J You will immediately notice a difference in the kinetic energy between the system before the collision and after the collision. In an inelastic effect, this difference in kinetic energy (52.5 J) is converted into deformation and heat (with consequent pain and injury to the athlete receiving a blow to the face), in contrast to the elastic effect, in which the kinetic energy is preserved. The graph in the illustration shows an enormous slowdown in hitting speed, lasting only 0.03 seconds. The impact force is destructive – about 400 Newtons with an acceleration of about 60 g. Values ​​over 6 grams for a few seconds can cause very serious problems, from loss of consciousness to death. In any case, the problem is very complex and there are many variants in reality. The following table summarizes, in a very general way, the limits of human pressure above which it is possible to cause damage to the body: 10,000 Newtons (maximum force on the skull) 4000 Newtons (above this limit, the backbone fractures) 700 Newtons (maximum rib limit) Figure 4: System Headshot in inelastic effect. Conclusion The physics of Karate is a very broad topic and should be deepened in several aspects. One may, for example, study the concept of balance or spinning strokes. All human and natural actions are governed by strict physical and mathematical laws, and their knowledge allows us to know all the behaviors of the quantities involved and to predict their effects, even in the long term. Those who know karate moves have real human weapons and know that using them can be deadly. .

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