Sliding weights

Jeff D · 30th June 2005, 03:32 PM

Hi Jens,

As always you ask a interesting question. The purpose of a sliding weight (if it is indeed functional not decorative) is to move your point of balance down the blade. Essentialy converting a rapier (light blade with a point of balance closer to the hilt) into an axe. As you know the cutting ability has a lot of variables such as edge geometry, draw cut etc. However the sliding weights function would be to add mass to the point of impact thus increasing the kinetic energy which then gets converted into cutting energy. KE=1/2mv2 (kinetic energy = one half mass times the velocity squarded). The amount of mass added will then depend on where your sliding weight is in relation to the point of impact which ideally will be on the point of impact.

As a disclaimer I am not a physicist

Jeff

Jens Nordlunde · 30th June 2005, 03:44 PM

Hi Jeff,

Thanks for the kind words.
Would the effect not be bigger when, like I have done, let the glider pass the point of impact with a few cm?
My idea with this thread is not to get an exact answer, but to get an idea of, how much extra power a gliding weight did/could add to the sword.
I will comment on you quertion, 'The purpose of a sliding weight (if it is indeed functional not decorative) is to move your point of balance down the blade.' later, as I find this very interesting.

Jens

Jeff D · 30th June 2005, 03:56 PM

Quote:

Originally Posted by Jens Nordlunde

Would the effect not be bigger when, like I have done, let the glider pass the point of impact with a few cm?

Hi Jens

Yes, the effect should be increased as there is a rotational kinetic energy that should increase directly proportional to the distance past the point of impact squared (I=mr2).

Jeff

Jens Nordlunde · 30th June 2005, 04:16 PM

Hi Jeff,

I don't understand the formula, but I am relieved to say that I do understand what you write, and I find this interesting.
Now, if the blade was twice as long, and the glider could glide twice as long, but the point of impact would be the same - what then?

Jens

fearn · 30th June 2005, 04:19 PM

This is definitely a neat problem.

Just thinking about it, I'd break the contribution of the weights into two categories.

1) changing the centers of gravity and percussion. The best way to think of this is as a sliding weight that can be fixed in place. Fix it at the bottom of the slide, and the sword acts more as a back-weighted stabbing weapon. Fix the weight forward, and the sword acts better as a forward-weighted chopping weapon.

2) the sliding weight acts to increase the impact force by some amount. This gets weird. For instance, the weights could add a second impact to a stab. You use the blade to stab forward, and once the blade slams to a halt, the weights slide forward and add a second thump.

Conversely, when sliding, the weights move in an arc (potentially a straight line) out, from resting near the hilt to the outer end of the slide as the blade moves. Again, they add some force at the end of the slide, but it is at an angle to the cut. This might or might not be a good thing.

In both cases, there's a notable jerk or twitch when the sliding weight hits hits either end of the slide. This might or might not be a good thing.

The nice thing is that this would be relatively easy to dummy up. Put ball bearings (or whatever) in a closed pipe of the length of the slide, and attach this pipe to a practice blade (perhaps with duct tape?

). Some empirical experimentation would be informative, I think.

Fearn

Jens Nordlunde · 30th June 2005, 04:36 PM

Hi Fearn,

Your observations are very good. When I thought of the problem, before I started the thread, I wondered what the maximum weight of the glider might have been, if you did not want to loose your sword - torne from you hand by the force of the glider.
You write, 'In both cases, there's a notable jerk or twitch when the sliding weight hits hits either end of the slide. This might or might not be a good thing.' Yes there would have been, and if this jerk is too hard I don't think it is any good for the user, nor for the sword - therfor the slider must not be too heavy - but heavy enough to give the wanted effect. How heavy it that?

Jens

Rick · 30th June 2005, 06:23 PM

Wouldn't that be measured by a formula of the distance traveled by the weight , the mass of the weight and the speed of the swing ?
The important variable being the speed of the swing ?

Jens Nordlunde · 30th June 2005, 09:32 PM

Yes Rick, some can to day, but how could they do iot centuries ago?

Jens

fearn · 30th June 2005, 09:34 PM

Hi Rick,

With a perfectly frictionless slide and a perfectly rigid blade, you're right.

The problem is, it won't be frictionless, and since we're talking about steel, there's also the possibility of the weight rebounding off the end of the slide, plus some other weirdness with the sword flexing as it hits that we haven't even mentioned.

I'm wondering, at the moment, which is more important, the basic physics of a sliding weight on a frictionless surface and a rigid blade, or all the ugly complexities. Murphy's Law suggests that the ugly complexities might, be more important. But I'm a pessimist: either I'm right, or I'm pleasantly surprised.

Still, we need some physicists to speak up and point is to the right calculations.

Fearn

30th June 2005, 06:23 PM	#7
Rick Vikingsword Staff Join Date: Nov 2004 Posts: 6,336	How Much Weight Wouldn't that be measured by a formula of the distance traveled by the weight , the mass of the weight and the speed of the swing ? The important variable being the speed of the swing ?

30th June 2005, 03:32 PM	#1
Jeff D Member Join Date: Dec 2004 Location: B.C. Canada Posts: 473	Hi Jens, As always you ask a interesting question. The purpose of a sliding weight (if it is indeed functional not decorative) is to move your point of balance down the blade. Essentialy converting a rapier (light blade with a point of balance closer to the hilt) into an axe. As you know the cutting ability has a lot of variables such as edge geometry, draw cut etc. However the sliding weights function would be to add mass to the point of impact thus increasing the kinetic energy which then gets converted into cutting energy. KE=1/2mv2 (kinetic energy = one half mass times the velocity squarded). The amount of mass added will then depend on where your sliding weight is in relation to the point of impact which ideally will be on the point of impact. As a disclaimer I am not a physicist Jeff

30th June 2005, 03:44 PM	#2
Jens Nordlunde Member Join Date: Dec 2004 Location: Europe Posts: 2,718	Hi Jeff, Thanks for the kind words. Would the effect not be bigger when, like I have done, let the glider pass the point of impact with a few cm? My idea with this thread is not to get an exact answer, but to get an idea of, how much extra power a gliding weight did/could add to the sword. I will comment on you quertion, 'The purpose of a sliding weight (if it is indeed functional not decorative) is to move your point of balance down the blade.' later, as I find this very interesting. Jens

30th June 2005, 04:16 PM	#4
Jens Nordlunde Member Join Date: Dec 2004 Location: Europe Posts: 2,718	Hi Jeff, I don't understand the formula, but I am relieved to say that I do understand what you write, and I find this interesting. Now, if the blade was twice as long, and the glider could glide twice as long, but the point of impact would be the same - what then? Jens

30th June 2005, 04:19 PM	#5
fearn Member Join Date: Dec 2004 Posts: 1,247	This is definitely a neat problem. Just thinking about it, I'd break the contribution of the weights into two categories. 1) changing the centers of gravity and percussion. The best way to think of this is as a sliding weight that can be fixed in place. Fix it at the bottom of the slide, and the sword acts more as a back-weighted stabbing weapon. Fix the weight forward, and the sword acts better as a forward-weighted chopping weapon. 2) the sliding weight acts to increase the impact force by some amount. This gets weird. For instance, the weights could add a second impact to a stab. You use the blade to stab forward, and once the blade slams to a halt, the weights slide forward and add a second thump. Conversely, when sliding, the weights move in an arc (potentially a straight line) out, from resting near the hilt to the outer end of the slide as the blade moves. Again, they add some force at the end of the slide, but it is at an angle to the cut. This might or might not be a good thing. In both cases, there's a notable jerk or twitch when the sliding weight hits hits either end of the slide. This might or might not be a good thing. The nice thing is that this would be relatively easy to dummy up. Put ball bearings (or whatever) in a closed pipe of the length of the slide, and attach this pipe to a practice blade (perhaps with duct tape? ). Some empirical experimentation would be informative, I think. Fearn

30th June 2005, 04:36 PM	#6
Jens Nordlunde Member Join Date: Dec 2004 Location: Europe Posts: 2,718	Hi Fearn, Your observations are very good. When I thought of the problem, before I started the thread, I wondered what the maximum weight of the glider might have been, if you did not want to loose your sword - torne from you hand by the force of the glider. You write, 'In both cases, there's a notable jerk or twitch when the sliding weight hits hits either end of the slide. This might or might not be a good thing.' Yes there would have been, and if this jerk is too hard I don't think it is any good for the user, nor for the sword - therfor the slider must not be too heavy - but heavy enough to give the wanted effect. How heavy it that? Jens

30th June 2005, 09:32 PM	#8
Jens Nordlunde Member Join Date: Dec 2004 Location: Europe Posts: 2,718	Yes Rick, some can to day, but how could they do iot centuries ago? Jens

30th June 2005, 09:34 PM	#9
fearn Member Join Date: Dec 2004 Posts: 1,247	Hi Rick, With a perfectly frictionless slide and a perfectly rigid blade, you're right. The problem is, it won't be frictionless, and since we're talking about steel, there's also the possibility of the weight rebounding off the end of the slide, plus some other weirdness with the sword flexing as it hits that we haven't even mentioned. I'm wondering, at the moment, which is more important, the basic physics of a sliding weight on a frictionless surface and a rigid blade, or all the ugly complexities. Murphy's Law suggests that the ugly complexities might, be more important. But I'm a pessimist: either I'm right, or I'm pleasantly surprised. Still, we need some physicists to speak up and point is to the right calculations. Fearn