The quality of a sword is often described by its metallurgical properties: the purity of the steel and the sharpness, hardness and resiliency of the blade. These are naturally important qualities for a weapon but the way it behaves when put in motion, how it responds to sudden changes in direction is equally or perhaps even more critical. A sword made of soft iron but with good balance will be a superior weapon to one that is made of fine steel of excellent temper but that is sluggish and unresponsive. It is often said that a good sword is like an extension of the arm, even though it would be more correct to say that it should be like an extension of the mind. This property of the weapon can be described as its balance. However, that word may bring to mind a balancing scale resting in static equilibrium which may not be the most apt image. Since swords are made for swift movements, we reach a better understanding by considering their dynamic properties. Some of the essential aspects that interact in establishing them are: mass, overall length, the proportion between blade and hilt, flexibility and perhaps most importantly how the mass is distributed along the length of the weapon.
Effects of mass distribution
To get an intuition of the effects of distribution of mass we may imagine two bars of identical length, weight and point of balance. The first one swells at the ends while the second swells at the middle with pointed ends. If we were to put a spin to them we would find that the dumbbell shaped bar demands the most effort, while the one with pointed ends is more agile. Conversely, the dumbell shaped object will hit with more mass and deliver more powerful, albeit slower blows. Swords show the same kind of difference though generally not in the same magnitude.
These aspects are undoubtedly less accessible to the eye than the external shape and typology of the sword. Nonetheless they can be documented and communicated with the help of careful measurements and dedicated tools. By entering measurements into our Weapon Dynamics Computer, you will be able to produce graphs similar to those published in the catalogue of the exhibit ‘The Sword, Form and Thought’. We have attempted to make the tool and diagrams as objective as possible, not favouring one aspect of mass distribution over the others.
The graphs demonstrate agility by an oval and hourglass shapes. The shape and size of the oval describes the relative ease by which the hilt can be accelerated in a straight line in different directions. The hourglass shape describes the agility of the sword in rotation around the hilt. The size of the arc increases with increased agility. Of course, the motion of the sword in use will most often be a combination of these two basic modes of motion. The diagrams also include a curve of effective mass. The effective mass in any given location is the amount of mass that must be displaced to set that part in motion or to stop it in defence or attack. At the point of balance, it is the total mass of the sword and it will decrease towards the pommel and point, at a rate that depends on mass distribution. The goal is to obtain a numerical and visual representation of a sword balance, which can be related to our tactile impression sword in hand.