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Last update: 27/04/2010
A piece of science
Nunchaku is a soft weapon, which involves pros and cons. Its physical behavior is fairly complex and many questions have to be answered.
On this page, we answer the frequently asked questions concerning the physical behavior of the Nunchaku:
What force is generated by a Nunchaku ?
Can a Nunchaku break bones ?
Can a Nunchaku kill with a single blow ?
How does a Nunchaku react during a strike ?
Click on one of the questions to access directly the desired subject, you can also follow the article in the order.
What force is generated by a Nunchaku ?
All Nunchaku techniques are based on the weapon’s softness. When we hit with the Nunchaku, three forces sum up:
- The force generated by the torque of the arm creating the movement.
- The force generated by the torque of the body following the movement.
- The force generated by the torque of the Nunchaku resulting from the movement.
The sum of those three forces increases significantly the total inertia of the Nunchaku.
Measurements have been carried out during a basic attack using a Nunchaku weighing 180 grams: the tip of the free branch reaches a speed of 88 m/s, that is to say 316 km/h. It goes without saying: a shock at this speed can cause a lot of damage.
From this data, we can calculate the kinetic energy developed by this Nunchaku during a basic attack:
Ke represents kinetic energy, in joules units,
m denotes the mass of an object, in kilograms units,
v denotes speed in units of meters per second.
We take m = 0.180 / 2 = 0.09 or 0.09 kilograms because we investigate about only one branch of the Nunchaku: the free branch.
We have therefore Ke = 0.5 x 0.09 x 88² = 348.48 so about 350 joules.
The energy generated by a Nunchaku strike is 150 joules superior to the one generated by a flashball, is equivalent to the one developed by an explosion of 0.5 grams of TNT, and is equal to the one generated by a Colt M1911 bullet.
But, since a Nunchaku develops a similar force than a bullet shot from a Colt M1911, why doesn’t it go through a person when it hits ?
It's because of a physical phenomenon very easy to understand with the help of an example: press hard on your arm with one of your fingers. Of course, your finger is not going to get through your arm. Now, with the same strength, press a needle on your arm. There are significant chances for it to go through, although you had pressed with the same force. The only difference between the two situations is the area where the force is applied. Indeed: with the finger, the contact area is about 1.5 cm², whereas with the needle, the force is focused on a zone 1000 times smaller. It is due to this phenomenon that a Colt bullet, small and sharp, can easily go through a body.
Therefore a Nunchaku will not go though a body, but since it generates a lot of energy, it will nevertheless cause significant damage.
As shown on this picture, it is possible to break concrete cinder-block with a Nunchaku.
It is not without reason that the Nunchaku is considered as a wrenching weapon...
It's very important to understand the difference between the force generated by the Nunchaku and the one transmitted to the target during the shock (impact force):
- The force generated is due to the Nunchaku displacement, the higher the value is, the faster the Nunchaku goes. Theoretically, this force is entirely transmitted to the target during an impact, but it doesn't help to have any evaluation of damages caused.
- Impact force is represented by two parameters: a force and a surface. Indeed, this force depends of where it was applied onto, just as the needle phenomenon explained above. The more the force is applied on a large surface, the less damage will be caused. This force depends also of the target’s resistance, for example, if a target is soft, it will absorb a part of the energy.
Let us calculate the impact force of a Colt M1911 and of a Nunchaku:
The tip of a Colt M1911 has a surface of 25mm², so the impact force is 350 / 25 = 14 i.e. 14 joules per mm². If a hit is made with the side of the branch, we get a contact surface of about 1 cm² for a Nunchaku attack, the impact force is therefore of
350 / 100 = 3,5 i.e. 3,5 joules per mm².
The impact force of a Colt bullet is therefore 4 times superior to the Nunchaku one.
Those calculations have been carried out assuming a hard target, otherwise the impact force would be absorbed. We can manage to make more damage, by hitting harder, or by hitting with the tip of the edge, the contact surface is then very small and severe damages are caused. This is why Japanese Nunchakus are octagonal: if the strike hits with one of the corners, the contact area diminishes and damages are increased.
Can a Nunchaku break bones ?
Bones are made of a multitude of fibers, placed in a parallel manner across the bone’s length. Its composition gives the bone anisotropic properties:
- With a strike perpendicular to the fibers and a contact surface of 1cm², a bone can withstand 10000 joules without breaking.
- With a strike with an angle of less than 15 degrees and the same contact surface, the bone can withstand only 375 joules.
This is an average hardness, some bones are more resistant (elbows, knees, heels) and other more fragile (finger phalanx mostly).
As we saw in the previous chapter, the Nunchaku has an impact force of 3.5 joules per mm², i.e. 350 joules per cm².
According this data, with a strike angle superior to 15 degrees, a Nunchaku won’t be able to break a bone.
However, with an angle inferior to 15 degrees, a Nunchaku is very capable of shattering bones.
Nunchaku fighters like to target hands during fights: a hit on the phalanx is highly likely to break them. This area is also very sensitive, a hit provokes intense pain.
Hit the hand is very efficient to disarm an armed opponent, or simply to prevent him to use his hands during the rest of the fight.
Can a Nunchaku kill with a single blow ?
With a Nunchaku, it is theoretically possible to hit whichever part of the body, however very few of them are likely to cause death. Indeed, a hit in most of the zones under the neck will not lead to death, but rather to big bruises or broken bones.
Above the neck, it's possible to hit weak points and cause severe damages, and eventually death. Here are some weak points located above the neck:
- Temples: those are the skull’s most fragile zones, that’s also here that goes the maxillary nerve. A violent shock on these zones can fracture the skull, the brain is then directly hit, and death is quick to come. The maxillary nerve can also induce a K.O. if the shock is violently.
- Nose: a lateral strike on the nose can shatter the fragile cartilage that it's made of, a severe hemorrhage can occur, and then death if the bleeding is not quickly stopped. An upwards strike on the nose will displace the cartilage towards the inside of the skull, and should touch the brain, death is instantaneous.
- Jaws: a lateral strike in the jaws causes a violent movement of the head, causing the brain to move inside the skull and hit the head bones. As a function of the violence of the impact, damages can range from simple dizziness to instant K.O..
- Nape: the spine being an important nerve center, a hit on the nape can lead to instant K.O.. A too powerful shock can paralyze or kill.
Of course, a lot of experience is necessary to succeed hitting those zones in a fight situation. During training as well as during competition, a Nunchaku artist avoids hitting the head, to avoid any risk of lethal hit.
How does a Nunchaku react during a strike ?
The softness of the Nunchaku is a huge advantage in terms of striking force and speed. It's also a big inconvenient concerning the weapon’s control, which becomes difficult in some situations.
Generalizing, there are 3 types of strikes: a hit with the edge of the branch, a hit with the middle of the branch, and a hit with the part of the branch near to the rope.
The latter strike is, in general, totally useless: all the force will be absorbed by the rope. A such strike causes only little damage and stop the Nunchaku, forcing the artist to re-generate momentum for another strike or taking a guard position. This kind of strike is considered as a missed strike: not only it cause no damages, but also it makes the artist vulnerable during a short time.
The strike with the edge of the branch is often called whip strike. With a such strike, the movement of the free branch is only a little altered by the shock: during the impact, the Nunchaku will slightly bend, and continue its way normally, as if there had been no obstacle. Here, there is no energy loss and the damage is maximized.
The last type of attack, with the middle of the branch, is the most common. The two following pictures show how the free branch of a Nunchaku react in a such attack, the target is the shoulder of a dummy:
As we can see from this picture, the trajectory of the free branch after impact changes, and goes back towards the user. He will have to do something in order if he doesn't want his weapon to turn back on him.
During this move, the Nunchaku actually bounces off the target, a part of the energy is then transferred back to the free branch during the bounce, but such a strike remains nevertheless very powerful.
This second picture, as far as it is concerned, show the relative position of both Nunchaku branches: they tend to get closer from one to another after impact. Continue a move in these conditions can be very difficult.
It's because of this behavior than without proper training, the Nunchaku is as dangerous for the user as for the opponent. To be a good fighter with this weapon, you need to know how to handle the movement of the Nunchaku after impact. Martial arts using Nunchaku have therefore developed many techniques to counterbalance this lack of control after impact.