Sliding weights

[Jeff D]

Hi All,

While it isn't a sliding weight, the sliding hilt does change the point of balance. This is from the Landesmuseum.

Jeff

[Jens Nordlunde]

Jeff, don't hold us waiting too long - which Landesmuseum?
There are several in the German speaking countries - so where is it?
BTW thanks very much for being the first to show a sword with a gliding weight

Jens

[Jeff D]

Originally Posted by Jens Nordlunde

Jeff, don't hold us waiting too long - which Landesmuseum?
There are several in the German speaking countries - so where is it?
BTW thanks very much for being the first to show a sword with a gliding weight

Jens

Oops Sorry Jens, this is the one in Zurich!

Jeff

[fearn]

Hi Jeff,

Neat sword! I think it's a solution to a different problem, though. There's a book out there (forgot the title) that's a translation of a late-medieval German swordmanship manual.

In that manual, they show the proper way to use a long sword (i.e. hand-and-a-half sword) against a foe in plate armor. Basically, you have to have gloves, on, because you grab the sword half-way up the blade and use the tip as a bayonet/pry-bar to attack the cracks in the armor at extreme close range. I say bayonet rather than short spear, because the the stance reminds me of the way one holds a rifle with for bayonet practice, as do the moves (short stabs and swings, using the pommel and guard in place of the rifle butt).

My suspicion is that this sword was designed with this half-sword grip in mind: Normally, one's finger holds the guard at the base, but at close quarters, you grab the pommel with the other hand, push the guard forward with the lead hand, and use it in a half-sword grip, without sacrificing the guard on the forward hand.

As far as swords with sliding weights, doesn't Stone's Glossary have a picture? I don't have my copy with me, but I have a memory that it does.

Fearn

[Rivkin]

In all honesty - I can imagine (barely) how one can use a movable weight in a throwing weapon, hoping to create some complex gyroscopic motion that would create a restoring force and stabilizing the trajectory as a result.

I can imagine using an adjustable grip or pommel to manage the balance and so on. I can imagine using an axe, the weapon with a high angular momentum.

I can't imagine any reasonable use for a moving mercury or anything in a sword. Suppresion of oscillations is most reasonably done by putting a tuned pitchfork into pommel. If this pitchfork is surrounded by an extremely viscous material, i.e. overdamped, you can have a very efficient transform of oscillations into heat (that's what they do in modern "professional" tools, like hammers). Another way is to design a sword in the way that all it's oscillations somehow negatively interfere with each other, so it basically damps itself (this method is way more complex, but that's what used in modern cameras to suppress the vibrations from shutter/mirror release).

Using a bottle of mercury for this purpose is rather strange.

[Jens Nordlunde]

Jeff, thanks a lot, I will try to have a look at it if possible.
Fearn, interesting what you write, but let us wait and see what I can come up with.
Rivkin, hold your horses till I - maybe can come up with something else.

Gentlemen it has been a pleasure

Jens

[Jim McDougall]

OK Fearn, I spent the better part of an evening thumbing through Stones, and didn't find any evidence of sliding weights or anything similar....but must say it was still enjoyable as always.I really love that book!! No matter how many times guys like to hammer away at Stone for the occasional errors, it's still fun to read so much very early data.He really set the stage for weapons research, and encouraged future researchers, such as us, to correct the inevitable errors with new evidence and revised data.
One thing I did find, and at the risk of mentioning something which applies only indirectly and is most probably irrelevant, I found:

"...Cestus: Heavy leather things, often weighted with lead or iron, wound around the hands and arms of Roman boxers to give additional weight to thier blows"
-Stone, p.168

Once again, leave it to the legacy of the ancients. Obviously, this note is purely speculative correlating the concept in dynamics and influences of many aspects of earlier cultures in application in later times. Clearly one would not need to seek such simplistic dynamics for the increase of force in a sword in ancient boxing, but the coincidence seemed worthy of note.

The search for the elusive sword with the slide continues

Best regards,
Jim

[Tim Simmons]

The sliding hilt is quite a good idea, how it worked in actual combat is another matter, but in theory it transforms a long thrusting weapon into something more general for close contact in the melee. Tim

[Jens Nordlunde]

Excelent Ian, but I think I on Google saw a training baseball bat with a sliding weight – only for training it said. It had some kind of sliding weight inside, but I am not sure what kind.

Imagine you had an arrow with a sliding weight on the haft. Before you took a shot, you pulled the weight back and when the arrow hit the target, the weight would make sure the impact was bigger than normal – would that work?

I hope to see the sword with the sliding hilt to morrow.

[Jens Nordlunde]

To day I went to Landesmuseum in Zurich, and found only very few weapons, and not the one Jeff show. When I asked where they were, I was told that they had packed them down, and no one knew when they would be on exhibition again, but to morrow a special exhibition would open with some weapons. I then went to the museums shop to ask after a book/catalogue showing weapons from the museums collection - no book, they had once had one, but it was sold out, and they did not plan another one.
Jens

[Ian]

Originally Posted by Jens Nordlunde

Imagine you had an arrow with a sliding weight on the haft. Before you took a shot, you pulled the weight back and when the arrow hit the target, the weight would make sure the impact was bigger than normal – would that work?

Jens:

I don't think this would have any effect, but perhaps it might if the weight shifted from the fletch to the head at the time of impact. Because we are talking about a piercing shaft, all energy would be concentrated at the point of impact, and the mass of the arrow lines up directly behind that point -- so however mass is distributed behind the point of contact would be immaterial, unless possibly if part of that mass is moving along the shaft at the moment of impact. Even then, I think the effect would be small and would need to be weighed against the effects of a rear-weighted arrow on its flight and accuracy. The small potential gain in penetrating power could well be offset by impaired accuracy.

Ian.

[Ian]

Here is what my engineering colleagues had to say about the question before us. I have translated from engineering-speak as well as I could.

The problem of a weight (mass) moving along a rod that in turn strikes another object is really quite complicated and we do not have enough information to answer your question. Here is a somewhat lay interpretation of the problem, which we have modified from The Physics of Baseball by Robert K. Adair.

Basically, the properties of a rod (sword, bat) relevant to striking another object squarely are defined by three weight distributions, or three moments.

1. The sum of the weight of each part of the sword, which is just its total mass (the zero moment)

2. The sum of the weight times distance, measured from the handle, of each piece of the sword (the first moment)

3. The sum of the weight times the square of the distance for each piece of the sword (the second moment or the moment of inertia)

There are three key positions along the sword that follow from these three moments.

a. The center of gravity
b. The center of inertia
c. The center of percussion

There are three additional factors that need to be considered.

d. The elasticity of the sword
e. The resonant frequency of the blade
f. The position of the vibrational node

Although the center of percussion and the vibrational node will be close to each other, they are not the same.

For a sword of fixed mass distribution, we can determine fairly simply the various points that correspond to the three moments.

The center of gravity is just the balance point. The center of percussion can be found by holding the sword lightly by the end of the hilt and striking the blade gently with a hammer; when the blade is struck at the center of percussion there is no detectable movement at the hilt. In most cases the center of percussion is very close to the vibrational node -- when the blade is struck at the vibrational node no vibrations are felt at the hilt.

The center of inertia can be determined by placing the sword on a frictionless surface (such as an ice rink) and pushed away. When the push is placed at the center of inertia the sword will move away without any appreciable rotation.

Each of the moments are manifest in obvious ways. The weight is felt by holding the sword vertically. The force required to hold the sword straight out in front of you at arm's length is proportional to the first moment. The force required to wave it back and forth vigorously when it is vertical is proprtional to the second moment. This second moment contributes most to the "feel" of the sword and is the factor most important to the user.

The elasticity is determined by the blade's resilience near the point of impact; a resilient blade may store energy upon impact and return that energy to the target.

The resonant frequency is a measure of the energy loss when a target is struck at a point along the blade away from the vibrational node. A higher frequency indicates a larger (i.e., longer) "sweet spot." Swords with longer blades and thicker handles will display higher vibrational frequencies and long sweet spots.

This is what we know about items that have a fixed mass distribution. When you add a varying mass distribution, the problem becomes more complex. When the weight distribution shifts, all of the moments change.

A sliding mass would create a tip-heavy sword, moving the centers of gravity, inertia and percussion away from the hilt. Depending on the fraction of the total mass that is moving and its final resting place along the blade, the respective moments may well be centered quite close to the tip, and essentially one would have a club. Such a shift in mass would likely make a clumsy and slow weapon.

We will think some more about this problem but it seems that any substantial shift in mass would produce a sword that could be difficult to control and would probably slow its action. How much of an effect would depend on the fraction of total mass that was shifting and the distance it traveled away from the hilt.

[Rivkin]

This list seems popular among the sword community - it's not the first time I've seen similar ideas expressed concerning the waves for example.

My problem is that for example it's hard for me to understand why the center of gravity is going to be a node for all waves (it should not be for at least for the waves with an odd number of halfwavelengths). Concerning the hilt, it seems more like a boundary condition to me, rather than a center of gravity. Concerning longer swords having higher frequencies and wider diaposon, it seems counter-intuitive to me - I would expect smaller swords to have larger frequencies and bigger separation in between of individual modes, but that's just my guess.

I'll be honest, I don't understand some of the ideas expressed above. Concerning the sliding mass question, again, what are the possible benefits of this construction vs. simply high momentum fixed mass weapon - nothing simple comes to mind.

[Ian]

Originally Posted by Rivkin

... My problem is that for example it's hard for me to understand why the center of gravity is going to be a node for all waves (it should not be for at least for the waves with an odd number of halfwavelengths).

The center of gravity is a balance point and the centers of inertia and percussion are located at different points along the blade. The respective centers are features of the weight distribution and mechanical properties of the sword (which mostly comprises the blade and the tang).

Waves do not originate from any of these centers. Waves are set up at the point of impact and spread out from that point. The further away the point of impact is from the vibrational node, then the more vibration will be transmitted along the blade and will be felt in the handle.

Originally Posted by Rivkin

... Concerning the hilt, it seems more like a boundary condition to me, rather than a center of gravity. Concerning longer swords having higher frequencies and wider diaposon, it seems counter-intuitive to me - I would expect smaller swords to have larger frequencies and bigger separation in between of individual modes, but that's just my guess.

The tang is continuous with the blade and would not be a boundary condition. Depending on the properties of the handle covering materials there may be some dampening of the vibration transmitted from the tang to the hand. My colleagues assure me that physics dictates that the longer the blade, the longer the sweet spot and the higher the frequency of vibrations.

Originally Posted by Rivkin

... Concerning the sliding mass question, again, what are the possible benefits of this construction vs. simply high momentum fixed mass weapon - nothing simple comes to mind.

I cannot see any real benefits to a sliding mass. That was the conclusion of my esteemed colleagues also -- they are skeptical that any greater force could be achieved, and the sliding mass would introduce unpredictable and inconsistent properties of the sword depending on how it was wielded.

Ian.

[Rivkin]

Hi Ian,

I don't think rod vs. string makes too much of a difference.

1. Equations are basically the same - they are basically the same for all oscillations. What is important is that we have oscillations around the equilibrium. Exapnding potential in Taylor's series, and taking derivative with respect to the displacement (which is going to give us force), we'll se that constant force is not there due to the equilibrium requirement (there are no forces in equilibrium, the derivative of energy is zero), force linearly proportional to the displacement is what gives us oscillations, force proportional to the displacement squared exist only in anisotropic bodies (asymmetric problem), cube will give us a nonlinear oscillator, and that is something we don't whant to deal with.

So it's always restoring force linearly proportional to the displacement.

2. Now the shape determinces boundary conditions - but if something is very long in one dimension, since if it would be infinite, it would have plane waves as a solution, if it's just long it has something similar to plane waves - sin or cos (basically sum of 2 plane waves propagating in the opposite directions).

Now for other dimensions - if it's a rod, it's most likely going to have a Bessel function or something like this (since it's like a drum). I think the problem is somewhere in the books on diff. equations.

I think plank is more suitable than rod in case of swords, but again - we are interested in transverse oscillations along the longest dimension.

Concerning additional b.c. - I meant that the tang is coupled to a human hand, so it's either unmovable, but under stress, or it's coupled to an oscillator.

I still don't agree to the rest of the things...

Sincerely yours,

Kirill Rivkin

[Ian]

Kirrill:

I have taken this way beyond my knowledge or comfort zone and cannot address your latest comments.

Much of what I have presented comes from the book that I referenced above by Robert Kemp Adair. He is presently Sterling Professor Emeritus of Physics at Yale University. You can find his contact information at http://www.yale.edu and using the search function for people on the home page.

Much of what you disagree with is cited in his book, including the comment that the resonant frequency of a baseball bat is related to its length and the thickness of the handle. He also points at that the centers of gravity, percussion and inertia are not the same and occur at different points along the length of a baseball bat.

BTW, Adair's book is available on the web for $1.00 plus shipping through this site http://www.abebooks.com

Ian.

[Jens Nordlunde]

In ‘The Indian Antiquary’, August 1873, page 217, W.F.Sinclair writes:

A common weapon among Hindustanis and Musalmans is a long steel rod with three or four small rings sliding on it. These, slipping forward as the weapon descends, add force to the blow, which is far more severe than might be supposed from the slender appearance of the weapon. It is also a good guard against sword-cuts.

[Andrew]

Hi Jens.

Interesting. Have you ever seen such a weapon?

How was your trip?

Best,
A

[Jens Nordlunde]

Hi Andrew,

I am not sure, as I seem vaguely to remember such a weapon. If I have seen one, it is very long ago, but from the description I think it must be a mace without a head, only with a rather long and slender haft with sliding weights. The weapon Sinclair describes is interesting, but if they made such a weapon, why not a mace with sliding weights?

The trip was terrific, we saw the reserves at V&A, but it is with time like with fire, it is a good servant but a brutal master. When we arrived we had hours ahead of us, but suddenly the time was running out fast. We did however see a lot of things, amongst other the Kitchener collection, which is fantastic. We met Robert Elgood and Jonathan Barrett, but again, the time – rather frustrating I must say. I hope to see them again next year when we go to England once more.

At the V&A I did notice something about some weapons from Kutch, and will write about it later.

Oh yes, I forgot to mention, how can a trip like that not be a success, when you have the best guide of all.

Best

Jens

[kronckew]

this thread was linked to in another thread today about a blade with sliding balls incorporated.

as i read this thread (post 31) there appeared a rapier with a sliding section hailed as a sliding weight sword example. this is incorrect as it was actually created to solve a completely different problem.

as rapiers became fashionable, they increased in length to almost silly proportions.m some wielders went accompanied by a servant that would help them draw and re-sheath the blade as needed.

numbers of gentlemen carrying these long swords were quite a tripping hazard and cumbersome to manoeuvrer in crowds, and could actually provoke duels. laws were passed to limit blade lengths. i recall london set a maximum BLADE length of 40 inches.

guards at the city gates would actually measure blades, and if found too long the owner could be fined and/or his blade snapped off to make it fit the regs.

this sword posted earlier was a design to circumvent the law, as it's long blade was slid back to allow it to be sheathed without requiring a servant while also becoming a regulation blade length with a long grip to bypass the regs - which did not specify an overall length.

if drawn in anger, the blade was slid out and locked in place rather them sliding in and out freely.

overly long rapiers with thrusting only type blades were an affectation of society that died out fairly quickly - that's why so few examples exist. they didn't really work well in a duel, gentlemanly rules of engagement which covered the flaws thankfully were rarely carried over to military blades that stuck to a more practical carry & use length suitable for the no rules melee of hand to hand desperate combat.