- Joined
- May 11, 2005
- Messages
- 26
It has been my habit on other forums to post technical information on how and why swords perform well and I just posted this at Swordforum and though that I would share it here as well...
OK- I'm stronger on the concept than the specifics, and in fact have been using this term innapropriately! Thinking about it, when I have referred to a sword as having a "High Polar Moment' I believe that I should actually have been saying 'Low Polar Moment.' This isn't going to be a perfect description- we're still sussing some of this out...
So what the heck is 'Polar Moment?' With regards to swords the 'Poles' are the tip and tip of the pommel. If the sword's tip is 36" from the strong hand (the point of rotation) then the opposite pole is the tip of the pommel- usually only a few inches from the POR. The type and amount of distal and profile taper and the weight of the hilt (particularly the pommel) are what determines a swords 'Polar Moment.'
A case ito illustrate the point are two swords that I made recently- the Falchion and the Type XVII. Both swords have recently been seen on this forum so pics should be easy to find. The Falchion has a great deal of mass near the point because the blade actually gets wider towards the point- reverse profile taper. It does distal taper significantly, but not enough to off-set this expansion in width. The Type XVII has extreme profile taper and has a hex cross section for much of it's length. The Falchion weighs 2lb14oz and the Type XVII weighs 3lb4oz. Yet the Type XVII is universally percieved as being 'lighter' than the falchion. Both swords were handled by dozens of people and they all had the same reaction. This is because of Polar Moment. The Falchion with it's heavy tip and pommel has a high Polar Moment- it's mass is distributed more equally along it's length. The short distance from the POR (Point of Rotation) to the pommel decreases this effect but not significantly as there is relatively so much mass at the opposite pole (the tip of the sword.) This makes the sword slow in rotation. On the contrary the type XVII with it's extreme profile taper has only a tiny percentage of it's overall weight at the tip, and again the weight of the pommel is relatively close to the POR. This means that the greatest percentage of the sword's mass is located near the POR- the sword rotates easier as most of the mass that you are moving is close to the POR so you have good 'leverage.' Another way to say this is that the sword has a small 'Moment of Inertia' (MOI) towards the tip. The Type XVII has a Low Polar Moment, making it fell handier- thus it is percieved as lighter because it is easier to move and change direction of the point. Savvy?
So- take two swords with the same length of blade and the same weight and Center of Gravity (COG) For argument lets say that both swords have 32" blades and balance four inches from the cross. One sword is made from 3/16 inch stock and has little profile and no distal taper with a heavy pommel to draw the COG back to four inches. The classic 'sharpened bar' type of sword. The other sword is 3/8" thick at the base but has a good amount of profile and distal taper. This sword doesn't need a heavy pommel to draw the COG back because of the distal taper, so the swords are of equal weight. Despite both swords weighing the same and having the same center of gravity the second sword will feel lively in the hand, and the first sword will feel like a club. Since it has little profile or distal taper it has a much greater percentage of it's mass farther from the POR- it has a high 'Moment of Inertia' (MOI) at the tip compared to the other sword, so the tip moves slower making the sword feel heavy and clumsy. This sword has a High Polar Moment. The second sword's mass is concentrated near the POR- it has a low MOI at the point or a Low Polar Moment. It feels lively and quick in the hand, and most people will tell you that it is lighter than the first sword even if intellectually they know the swords are the same weight! The second sword could in fact be heavier than the first sword and still feel lighter to most people because of the ease of moving the point.
This is also why a shorter sword often feels 'handier' than a longer sword of the same weight- It has a shorter 'Moment Arm' which moves the tip's mass closer to the POR- reducing it's Polar Moment.
A note- when we say the tip moves easier and faster, what we are talking about is accelleration. An axe can move bloody fast at the end of the swing, but the mass of the head being at the end of the Momeent Arm means that it accellerates more slowly.
The practical effects of this from what Gus and I have observed- the sword feels lively in the hand, tends to be more forgiving in it's Harmonic Balance and tends to have a long COP. All good things...
OK- now for the questions and corrections...
OK- I'm stronger on the concept than the specifics, and in fact have been using this term innapropriately! Thinking about it, when I have referred to a sword as having a "High Polar Moment' I believe that I should actually have been saying 'Low Polar Moment.' This isn't going to be a perfect description- we're still sussing some of this out...
So what the heck is 'Polar Moment?' With regards to swords the 'Poles' are the tip and tip of the pommel. If the sword's tip is 36" from the strong hand (the point of rotation) then the opposite pole is the tip of the pommel- usually only a few inches from the POR. The type and amount of distal and profile taper and the weight of the hilt (particularly the pommel) are what determines a swords 'Polar Moment.'
A case ito illustrate the point are two swords that I made recently- the Falchion and the Type XVII. Both swords have recently been seen on this forum so pics should be easy to find. The Falchion has a great deal of mass near the point because the blade actually gets wider towards the point- reverse profile taper. It does distal taper significantly, but not enough to off-set this expansion in width. The Type XVII has extreme profile taper and has a hex cross section for much of it's length. The Falchion weighs 2lb14oz and the Type XVII weighs 3lb4oz. Yet the Type XVII is universally percieved as being 'lighter' than the falchion. Both swords were handled by dozens of people and they all had the same reaction. This is because of Polar Moment. The Falchion with it's heavy tip and pommel has a high Polar Moment- it's mass is distributed more equally along it's length. The short distance from the POR (Point of Rotation) to the pommel decreases this effect but not significantly as there is relatively so much mass at the opposite pole (the tip of the sword.) This makes the sword slow in rotation. On the contrary the type XVII with it's extreme profile taper has only a tiny percentage of it's overall weight at the tip, and again the weight of the pommel is relatively close to the POR. This means that the greatest percentage of the sword's mass is located near the POR- the sword rotates easier as most of the mass that you are moving is close to the POR so you have good 'leverage.' Another way to say this is that the sword has a small 'Moment of Inertia' (MOI) towards the tip. The Type XVII has a Low Polar Moment, making it fell handier- thus it is percieved as lighter because it is easier to move and change direction of the point. Savvy?
So- take two swords with the same length of blade and the same weight and Center of Gravity (COG) For argument lets say that both swords have 32" blades and balance four inches from the cross. One sword is made from 3/16 inch stock and has little profile and no distal taper with a heavy pommel to draw the COG back to four inches. The classic 'sharpened bar' type of sword. The other sword is 3/8" thick at the base but has a good amount of profile and distal taper. This sword doesn't need a heavy pommel to draw the COG back because of the distal taper, so the swords are of equal weight. Despite both swords weighing the same and having the same center of gravity the second sword will feel lively in the hand, and the first sword will feel like a club. Since it has little profile or distal taper it has a much greater percentage of it's mass farther from the POR- it has a high 'Moment of Inertia' (MOI) at the tip compared to the other sword, so the tip moves slower making the sword feel heavy and clumsy. This sword has a High Polar Moment. The second sword's mass is concentrated near the POR- it has a low MOI at the point or a Low Polar Moment. It feels lively and quick in the hand, and most people will tell you that it is lighter than the first sword even if intellectually they know the swords are the same weight! The second sword could in fact be heavier than the first sword and still feel lighter to most people because of the ease of moving the point.
This is also why a shorter sword often feels 'handier' than a longer sword of the same weight- It has a shorter 'Moment Arm' which moves the tip's mass closer to the POR- reducing it's Polar Moment.
A note- when we say the tip moves easier and faster, what we are talking about is accelleration. An axe can move bloody fast at the end of the swing, but the mass of the head being at the end of the Momeent Arm means that it accellerates more slowly.
The practical effects of this from what Gus and I have observed- the sword feels lively in the hand, tends to be more forgiving in it's Harmonic Balance and tends to have a long COP. All good things...
OK- now for the questions and corrections...
