Sliding weights

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

Rick · 30th June 2005, 10:48 PM

Quote:

Originally Posted by Jens Nordlunde

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

Jens

Hi Jens , since you brought this subject up are we discussing a sword that actually exists ; or are we just brainstorming over the possibility of making a sliding weight cutter ?
In your initial post you refer to "sliding weight claymores" , does such a beast actually exist ?

If we are talking about a sword with metal balls i.e. 'tears of the afflicted' in my opinion that feature is entirely for show .

Jim McDougall · 1st July 2005, 02:22 AM

Wow! I had no idea that the clearly established knowledge of the members here included such command of physics!! I'm afraid I'm pretty much lost in this dynamic discussion, but its fascinating to see the potential and plausibility of such an interesting feature as the sliding weights on sword blades.

Actually this topic was discussed several years ago in a query about a much storied Scottish hero of the 17th century, whose claymore was said to have a 'ten pound weight on the back of the blade to add force to the cut'. While the hyperbole here is obvious, further research found no examples of such a feature on the back of sword blades. It seemed a bit useless to add any weight to the already heavy enough claymore let alone trying to control such a sword with moving weight changing the balance.
It seems that another tale similar describes a medieval falchion with a weight termed in literary fashion 'the apple' or 'pear' on a shaft at the back of the blade for the same express purpose of adding force to the cut.

Clearly the 'tears of the wounded' feature on Chinese and Persian edged weapons aesthetically correspond to this moving feature, but are generally considered to be ceremonial or parade weapons. There have been some accounts of blades containing mercury enclosed in a channel for the purpose of movement of force in the use of the blade, but again these tales appear to have literary origin rather than practical.

What I would like to know is if anyone has ever seen or heard of an actual weapon with a shaft and sliding weight, again without reference to the 'tears of the wounded' pearls or bearings.

Having asked that, I hope the discussion on the actual dynamics of this feature continues! Its fascinating to see how this feature would have been applied and helps in understanding possibilities. Excellent observations!!

Best regards,
Jim

Ian · 1st July 2005, 05:09 AM

It is some years since I addressed problems in physics, but the mechanics of this problem seem both simple and complex. We are dealing with a rigid bar traveling through an arc, which approximates the segment of a circle having the shoulder at the center of that circle. The radius of that circle is the length of the arm plus the length of the blade (or, more precisely, the distance to the point of impact along the blade).

The energy from the blow will depend on the angular momentum at the point of impact. So far, so good.

If this were a problem with a ball at the end of a weightless string it would be easy to solve (think of a yo-yo or a ball flail). But we have a bar with mass along its length, and we want to add a variable mass distribution to that situation. One way to address this variation in weight distribution is to consider several scenarios, with the two extreme cases being the variable weight at each end of its travel. I'm not sure how to address the question of mass distribution along a bar. Perhaps this requires an analysis of the moments around a fulcrum (which is the point of impact), although the "fulcrum" in this case is not an immovable object but yields with the blow.

I'm sure all of these issues have been worked out previously but it is a matter of finding a reference to the solution. Presently I'm traveling but will be back in the office next week and will talk with some engineering colleagues who have far more skills in mechanics than I do. The final solution may well include calculus, so be warned.

Ian.

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

fearn · 30th June 2005, 09:41 PM

A side thought:

I keep thinking about an exotic Chinese weapon I've read about: the "seven stars" rod. Basically, it's a bamboo rod of seven segments. This is a "special species" of bamboo, which I take to mean that the bamboo has pretty thick walls.

The reason it's relevant here is that each of the seven segments is half-filled with mercury and sealed. Basically, it's got sliding weights all throughout the rod.

If someone knows how to make one of these suckers, please speak up. I'm too transfixed by the vision of the rod splintering and spraying mercury everywhere to want to make one of these things.

However, a simple version of it could be made with PVC and marbles (put small, closed sections of PVC pipe inside a bigger one, and secure them with glue or whatever.

Just a side thought, but it's a possible design for any one who wants to experiment with sliding weights.

Fearn

30th June 2005, 06:23 PM	#3
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 ?

1st July 2005, 05:09 AM	#7
Ian Vikingsword Staff Join Date: Dec 2004 Location: The Aussie Bush Posts: 4,361	Interesting question It is some years since I addressed problems in physics, but the mechanics of this problem seem both simple and complex. We are dealing with a rigid bar traveling through an arc, which approximates the segment of a circle having the shoulder at the center of that circle. The radius of that circle is the length of the arm plus the length of the blade (or, more precisely, the distance to the point of impact along the blade). The energy from the blow will depend on the angular momentum at the point of impact. So far, so good. If this were a problem with a ball at the end of a weightless string it would be easy to solve (think of a yo-yo or a ball flail). But we have a bar with mass along its length, and we want to add a variable mass distribution to that situation. One way to address this variation in weight distribution is to consider several scenarios, with the two extreme cases being the variable weight at each end of its travel. I'm not sure how to address the question of mass distribution along a bar. Perhaps this requires an analysis of the moments around a fulcrum (which is the point of impact), although the "fulcrum" in this case is not an immovable object but yields with the blow. I'm sure all of these issues have been worked out previously but it is a matter of finding a reference to the solution. Presently I'm traveling but will be back in the office next week and will talk with some engineering colleagues who have far more skills in mechanics than I do. The final solution may well include calculus, so be warned. Ian.

30th June 2005, 04:19 PM	#1
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	#2
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	#4
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

1st July 2005, 02:22 AM	#6
Jim McDougall Arms Historian Join Date: Dec 2004 Location: Route 66 Posts: 10,192	Wow! I had no idea that the clearly established knowledge of the members here included such command of physics!! I'm afraid I'm pretty much lost in this dynamic discussion, but its fascinating to see the potential and plausibility of such an interesting feature as the sliding weights on sword blades. Actually this topic was discussed several years ago in a query about a much storied Scottish hero of the 17th century, whose claymore was said to have a 'ten pound weight on the back of the blade to add force to the cut'. While the hyperbole here is obvious, further research found no examples of such a feature on the back of sword blades. It seemed a bit useless to add any weight to the already heavy enough claymore let alone trying to control such a sword with moving weight changing the balance. It seems that another tale similar describes a medieval falchion with a weight termed in literary fashion 'the apple' or 'pear' on a shaft at the back of the blade for the same express purpose of adding force to the cut. Clearly the 'tears of the wounded' feature on Chinese and Persian edged weapons aesthetically correspond to this moving feature, but are generally considered to be ceremonial or parade weapons. There have been some accounts of blades containing mercury enclosed in a channel for the purpose of movement of force in the use of the blade, but again these tales appear to have literary origin rather than practical. What I would like to know is if anyone has ever seen or heard of an actual weapon with a shaft and sliding weight, again without reference to the 'tears of the wounded' pearls or bearings. Having asked that, I hope the discussion on the actual dynamics of this feature continues! Its fascinating to see how this feature would have been applied and helps in understanding possibilities. Excellent observations!! Best regards, Jim

30th June 2005, 09:34 PM	#8
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

30th June 2005, 09:41 PM	#9
fearn Member Join Date: Dec 2004 Posts: 1,247	A side thought: I keep thinking about an exotic Chinese weapon I've read about: the "seven stars" rod. Basically, it's a bamboo rod of seven segments. This is a "special species" of bamboo, which I take to mean that the bamboo has pretty thick walls. The reason it's relevant here is that each of the seven segments is half-filled with mercury and sealed. Basically, it's got sliding weights all throughout the rod. If someone knows how to make one of these suckers, please speak up. I'm too transfixed by the vision of the rod splintering and spraying mercury everywhere to want to make one of these things. However, a simple version of it could be made with PVC and marbles (put small, closed sections of PVC pipe inside a bigger one, and secure them with glue or whatever. Just a side thought, but it's a possible design for any one who wants to experiment with sliding weights. Fearn