By Jikishin Kobudo, Jun 22 2016 11:30AM
Kobudo is a quasi-rigid body mechanical problem and ultimately the same mathematical laws that govern the motion of the planets and falling apples also govern the forces and motions of our body.
The most famous equation of which we are all taught in school is F=ma, Newton’s equation of motion (F being force, m = mass and a = acceleration). What is perhaps less well known is that integration of this equation yields the impulse equation I = Δmv, that is impulse is equal to the change in momentum of a ‘body’.
In Kobudo, the ‘body’ we typically care about is ‘the weapon’ and the impulse might be thought of as the amount of force we've 'paid in' to the weapon before our blow lands. If we push the weapon twice as hard or alternatively twice as long, we double the impulse.
Momentum is mass times speed and the laws of physics require it to be conserved. As such if a weapon strikes an opponent with great momentum, then the opponent must be moved by it.
However, if their stance is good they will remain rooted to the ground with the force of friction holding them still. The momentum of a blow will move them and the entire planet they are standing on (albeit an incredibly minute fraction) as the momentum is transmitted by their legs into the ground.
Kinetic energy on the other hand is needed to break or to do damage. Kinetic energy is the energy associated with a motion and is given by mass times the square of velocity. If one doubles the mass of an object, one doubles its kinetic energy. If one doubles its speed one has quadrupled its kinetic energy.
The transmission of power to our weapons is a smooth process that continues up to and beyond the moment a blow lands. Heavier weapons take longer to move but in the process of doing so they gather more impulse and a balance between speed and mass needs to be struck.
In Kobudo the same blow may be delivered different ways. Sometimes directly moving via the shortest path at other times wound back or circled to build momentum. The first way should in principal be faster, the second produce a harder blow.
Kobudo is not about learning to do techniques one way. It's about learning how weapons interact with the biomechanics of your body to do the same set of things well in lots of different ways as the situation demands. Similarly, it’s also not just about learning how to deliver blows it's about learning how to take them.
When an attacking weapon is blocked, its kinetic energy must go somewhere. If it connects with your weapon that energy may break your weapon. If it hits you it might break you. The ground generally doesn't bend or break under you when you take a blow and so the kinetic energy released must be converted into other forms of energy in the bodies and weapons involved. As a result, in Matayoshi Kobudo we generally avoid stopping weapons abruptly. Power is defined as dE/dt the rate of energy release over time. So by reducing a weapons kinetic energy gradually, a blow can be made less powerful even though it's initial energy remains unchanged.
By moving our own bodies and our weapon during an impact, more of that energy is turned into kinetic energy within ourselves. So by using the body in a flexible and fluid form we can transfer the energy of impact into the movement of our limbs. The heat of our muscles resists the motion without allowing our joints to be elastically compressed, pulled or sheared potentially beyond their tolerances. Similarly, we avoid vibrations and stresses in our weapons and bones that might break them.
Here at Jikishin Kobudo in Leeds, our scientists investigate the theoretical rigour behind the principles of power transmission. Many tend to think of martial arts in qualitative terms but the physical act of combat is most definitely quantitative and an understanding of the quantities involved can definitely improve our understanding of if not the practice of Kobudo. The old masters did not have the benefit of modern scientific theory to explain their techniques, but their insights and intuition were correct.