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Thread: Swordplay style physics...

  1. #1

    Swordplay style physics...

    Hi all!

    I got into a discussion on the Discovery Channel forums for Mythbusters, and I thought this was worth sharing. So, the discussion is basically regarding the difference between Eastern and Western swordplay. The original thread is here.

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    quote:
    Originally posted by thelightworks:

    quote:
    1) The attacker has to move his hand, then his body, then his foot in order to close the distance and attack. (The weapon has to move first to threaten your opponent, that's why the step is last.)



    the hand is the LAST to move. it's hips, shoulders, wrist. moving your hand first is like holding your fist out and then trying to run at your opponent in boxing.

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    That may be the case in the tradition of swordsmanship that you practice, but it is not the case in historical European swordsmanship (which Atrial and I clearly do practice).

    With German longsword, the basic blow is called a Zornhau - the actual action of throwing the blow is very similar to casting a fishing line. Done properly, the momentum of sword moving in its arc will pull you forward, and that's when you step forward and to the side, moving you off-line from your opponent's sword.

    So, what is the difference between the two traditions, and how does it matter? It's high school physics time (either "whee" or "run for your lives!", depending on how much you liked high school physics)!

    Basically, sword blows are all about Newton's first law - Force = Mass x Acceleration, or F=MA. Think of it like a golf swing - if you try to put power into it, your muscles will tense up, you will lose acceleration, and your ball won't go very far. So, in swordplay, in any given (non-thrust) blow, the acceleration of the sword is all-important. You need the point of impact on the sword moving as fast as possible to deliver the force upon impact.

    The Eastern style that Thelightworks described is using forward momentum to help generate A. That's a big reason why everything gets moving before the sword does. German longsword uses levering to generate A - that's why the sword moves first and everything follows.

    Now, a sword is little more than a big lever - it has a point of balance close to the hilt, and you don't need to swing the hilt around very fast to make the point of contact move with great speed. So, both Eastern and Western traditions in this case will get the sword moving at a sufficient speed to drop the opponent.

    Extending this to thrusts, there is something else going on, and here we do see a major difference in style. The Eastern swordsmanship way of moving on a cut does not necessarily make a big difference on force in comparison to the Western tradition - this is just because the blade is moving through an arc. If you want to put it this way, in the German tradition it is the flick at the beginning of body movement, and in the Eastern tradition it is the flick at the end of body movement. In a thrust, though, the body moving first has a serious impact on the force calculation.

    Taking our F=MA calculation into the thrust, what that body movement does is increase M from the mass of the sword alone to the mass of the sword + body. And this is very important when thrusting through armour (and we see this in the western martial arts in rapier fencing and spear, where the centre of the body - which might be armoured - is the primary target...in these cases, everything moves at once).

    German longsword, however, treats thrusts in a very different way. German longsword is a style originally used for judicial duels, and thrusts tend to be aimed at the head at the end of a bind - so, M is the sword plus the body, but there tends to be a relatively small A. And, the head is an unarmoured target in the primary style of judicial duel at the time when Talhoffer and Silver were writing their manuals. And, the required force to puncture the human body on a thrust is as little as 50 Newtons, according to the wonderful wacky internet.

    So, as far as the difference goes between the two styles, it is a bit apples and oranges, save one thing. Eastern martial arts have had a far greater continuity than Western martial arts. And, any martial art changes over time. It has been a VERY long time since anybody has had to use a longsword or samurai sword in a duel to the death (and God willing, it will be a long time before that ever happens again). So, with the lethal purpose no longer present, there is a degree to which the Eastern martial tradition has created certain artifacts and formalities in techniques that may not have existed if lives still depended on using them well (the blows used in Mythbusters, for example, would have gotten Adam and Jamie killed if they had tried them against any experienced swordsman).

    The Western traditions, such as German and Italian longsword, have only just recently been resurrected, and so the techniques are based on a time when lives did depend on using them well. As such, the German tradition (I don't practice the Italian tradition, so I can't speak for it) is very much about the attack and about striking blows quickly. The more that has to move before the sword does, the longer it will take the blow to land. So, I think it speaks volumes that when John Clements, who practices German longsword, entered into a Eastern martial arts swordfighting tournament, he cleaned house.

    Now, all that said, as I mentioned before, nobody has had to use these swordfighting arts in a life or death duel in a very long time, and nobody on this board is likely to have to or see it happen in their lifetime, or even in the lifetime of their children and grandchildren. So, they are all fine traditions, and while I think comparison is helpful and enhances our understanding of them, I don't think there is any cause to disparage either one.
    Robert Marks
    Darksword Armory, Inc.
    www.darksword-armory.com

    "I'm not asking you to trade food for swords all the time, just food for THESE swords."

    "Sir, if we accepted your swords, then we'd have to accept EVERYBODY's swords..."
    - Home Movies

  2. #2
    Hello Robert,

    Could you please elaborate on the topic of this discussion here on the SFI? I.e. what is your question, your thesis etc. The discussions about east vs west are technically "dead horses" here and linking the discussion regarding a televison show on a different forum does probably not provide any new clues. So, what is it you would like us to discuss here?

    Regards, Thomas
    Erschrickstu gern /
    Keyn Fechten lern.

  3. #3
    Quote Originally Posted by T. Stoeppler View Post
    Hello Robert,

    Could you please elaborate on the topic of this discussion here on the SFI? I.e. what is your question, your thesis etc. The discussions about east vs west are technically "dead horses" here and linking the discussion regarding a televison show on a different forum does probably not provide any new clues. So, what is it you would like us to discuss here?

    Regards, Thomas
    Certainly - I thought it would be interesting to take a physics approach to the question of why we do what we do when we practice the historical European martial arts. It's more of an academic thing than anything else (I also hoped it would be a bit fun to share and discuss the physics with people who know more about it than I - my own physics background ends at high school science).

    So, for example, what happens when you bring both F=MA and edge geometry into play on a Zornhau, etc. And, can a better understanding of the physics of what we do make us better swordsmen/women?

    (I'm sorry if I'm not expressing this well - I'm fighting off a cold right now, and the decongestants I'm taking do make thinking a bit harder than usual.)

    Best regards to all,

    Robert Marks
    Robert Marks
    Darksword Armory, Inc.
    www.darksword-armory.com

    "I'm not asking you to trade food for swords all the time, just food for THESE swords."

    "Sir, if we accepted your swords, then we'd have to accept EVERYBODY's swords..."
    - Home Movies

  4. #4
    Quote Originally Posted by Robert B. Marks View Post
    So, for example, what happens when you bring both F=MA and edge geometry into play on a Zornhau, etc. And, can a better understanding of the physics of what we do make us better swordsmen/women?
    Hello Robert,

    The F=ma forumula has been intstrumentalized for many, many misinterpretations in about all martial arts circles. It isnt that simple at all:
    The kinetic energy of a sword is stored in its degrees of freedom, which is rotation, translation and vibration. For the math, only unidirectional rotation and translation apply.
    So technically if you add up both energies and factor in the contact speed, you have the impulse. Thats easy - and its application is easy as well. (if you like to play with maths - use widely available formulas for rotation of objects and those of calculating the energy of a pendulum at v(max) )

    However that does not factor in the reactive forces that occur upon impact, there its getting really fuzzy.
    The next big thing is the force your own body procuces over the time of delivery and during impact, and how much of that transfer to the target.
    For example, if you want your body to generate as much kinetic energy as possible, the movement will stop being compact because the generation of energy with joints, muscles and connective tissue needs more space and time. The reflex sets of the CNS do funny things for maximum force recruitment and that is very visible for the opponent.

    Here the sequencing of the body part hast great effect; for execution of any attack you have an alignment phase, a pre-stretch phase and a delivery/extrension phase.
    A swordman of good skill really tries to roll all these functions into one, so there is no latency in the attack itself. Achieving that does not allow the maximum possible tip velocity, because you need to
    shorten your swinging arc very much, ideally to zero (using the swords point of balance and that of your body as well)

    Then, in order to strike, cut or thrust different mechanics are necessary. A sword "strike" has a dominant percussive element, so it has a high impulse and a fast delivery of force.
    A cut OTOH can not be done too fast, because it would not cut well. A thrust again does neither need much speed nor impulse, but it needs continuus extension and be executed exactly in the support line of the blade.

    The next thing is how much energy you actually need to cause an effect, and thats not much at all - 3 Joule suffice for both puncturing and cleaving a skull with a decent blade.

    So I would conclude that the "sword physics" is a very complex subject that goes far, far beyond F=ma. The questions must be asked very specific because, ultimately, there are several ways to do it "right" - depending on your intent. For example, for the purpose of my personal interpretation (and those that have adopted it) I found a specific way to apply "sword physics". But there are other approaches with different goals so the application there differs.

    Regards, Thomas
    Erschrickstu gern /
    Keyn Fechten lern.

  5. #5
    Herr Stoeppler speaks the truth. The effective mass of a striking weapon, even with good body mechanics, is much less than is often stated due to the body-weapon system not being perfectly efficient. Horsfall et al. imply that the best of their hundred or so police and military trainees could double the effective mass of a 600 g knife with an underarm stab to a vertical target at waist height, and triple it with an overarm stab to a horizontal target at waist height. So its not as simple as adding the weight of your arm, or of your body, to a strike. The physics of cutting are even more complicated!

    Edit: Beyond knowing that this is complicated stuff, I really don't understand physics, anatomy, or kinematics as well as I would like. This is important, because we tend to use pop Newtonian physics” like the sources use “pop Aristotelian physics,” and I wish I understood better. I don't understand the AES Calgary/The Forge or aikido striking mechanics that I have encountered either, other than that they are different than Fiore's.
    Last edited by Sean Manning; 10-19-2012 at 09:52 AM. Reason: Qualification

  6. #6
    Too much time considering mathematical formulas of force make you lose the basic understanding of why you put your blade before your body: Defense. Bringing your body into range without defense or a defense that can be blown through is not good for your health.

  7. #7
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    Quote Originally Posted by Johnny H View Post
    Too much time considering mathematical formulas of force make you lose the basic understanding of why you put your blade before your body: Defense. Bringing your body into range without defense or a defense that can be blown through is not good for your health.
    But it can help us know whether or not it is possible to strike as powerfully in true times as false times, which I instinctively suspect is so, otherwise true times would not exist. But I don't know the physics well enough to *prove* the point.

    I have noticed watching some Eastern swordplay that direct counters shown in many styles seem to be predicated on false times. "Blocking" the upraised hands with the edge of the sword as the opponent steps forward or a direct stab to the face against an overhead cut and the like-this sort of thing is more difficult against a cutting attack in true times.

  8. #8
    Quote Originally Posted by Matt Bailey View Post
    But it can help us know whether or not it is possible to strike as powerfully in true times as false times, which I instinctively suspect is so, otherwise true times would not exist.
    Hi,

    That goes into the direction which I mean by sequencing the body. Of course, a "ground-up" sequencing - which is technically a false-time motion (at least for the sake of this example) - does generate a far greater centripetal force and causes much greater impact. That is why you use a sledgehammer like that or throw a spear with this kind of move. However, impact and peak momentum are not the same thing as a more continuus transfer of energy, which you do generate by moving the other way round.

    So when talking about a "powerful strike" you may add up more elements, more degrees of freedom of several body parts that may result in a flatter power curve but have a greater likelyhood of transferring at the right (true) time. In addition to that, the rotation of the blade is quite independent from the larger motion model and being able to impart a rotational momentum during a strike(!) using true times causes massive Impulse, enough to knock the blade out of people´s hands.

    Regards, Thomas
    Erschrickstu gern /
    Keyn Fechten lern.

  9. #9
    Two things I have to add:
    • Cutting mechanics are not really detailed in source texts. This is a part that is very much reconstructed or borrowed from other arts. I personally doubt it was as simple or universal as "sword moves first". There are a few hints that point to a different sequencing, specifically with the foot landing at the same time as the strike or before, a timing that is of course found in many other arts.
    • People have a tendency to move differently when they demonstrate a strike, when they bout, when they hit something and when they cut something (with the last two being the most similar). When there is something to hit or cut, the so-called "true" timing is often the first thing that goes out the window. Most people intuitively revert to a swing of the sword around the hand(s), with the cut landing at the same time as the foot. My personal opinion is that this is because that is more efficient mechanically, in the sense that the energy expended goes mostly into the target.


    Regards,

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    Thomas, are you saying that true times hit harder than false times? And if so, what are baseball batters doing wrong?

    Cheers,
    Steven
    Athena School of Arms - Longsword & Highland Broadsword
    Fight with All Your Strength
    Swords of Chivalry - Youth Swordsmanship in Acton, MA

  11. #11
    Quote Originally Posted by Steven H View Post
    Thomas, are you saying that true times hit harder than false times? And if so, what are baseball batters doing wrong?
    Hi Steven,

    No - please read my posting again. The baseball players don´t do anything wrong, the workers using a sledgehammer dont do it wrong. The potential of force delivery(!) using true times is just greater, while the peak force is not. As for using a blade, it is far easier to impart rotational impulse like this than doing so with a bat or hammer so you can deliver excellent (in practical terms - sufficient) force during impact.

    Regards, Thomas
    Erschrickstu gern /
    Keyn Fechten lern.

  12. #12
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    Okay Thomas, I see the distinction you're making. Why do you conclude that total force over time is more useful than the peak force?

    Quote Originally Posted by T. Stoeppler View Post
    No - please read my posting again. The baseball players don´t do anything wrong, the workers using a sledgehammer dont do it wrong. The potential of force delivery(!) using true times is just greater, while the peak force is not.
    How does true times movement generate more force? By stepping and then turning the body I'm able to use passive force generation and the SSC.

    Quote Originally Posted by T. Stoeppler View Post
    As for using a blade, it is far easier to impart rotational impulse like this than doing so with a bat or hammer so you can deliver excellent (in practical terms - sufficient) force during impact.
    How does a blade make a it easier to impart rotational impulses?

    Thanks,
    Steven
    Athena School of Arms - Longsword & Highland Broadsword
    Fight with All Your Strength
    Swords of Chivalry - Youth Swordsmanship in Acton, MA

  13. #13
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    Baseball players and people working with a sledgehammer are generally standing in once place, not taking a step with their swing.

    I feel like while the initial part of extending to cut must be timed to the speed of the step, right before impact the hand(s) can impart to the already moving sword great velocity, combined with weight of your body movement behind it.
    Last edited by Matt Bailey; 10-27-2012 at 08:13 PM.

  14. #14
    Hi Steven,

    Quote Originally Posted by Steven H View Post
    Okay Thomas, I see the distinction you're making. Why do you conclude that total force over time is more useful than the peak force?
    Thats simply because you have to hit/bind/oppose holding the body in dynamic balance while the opponent does the same. So the time interval for potential delivery is longer. I find that useful.

    Quote Originally Posted by Steven H View Post
    How does true times movement generate more force? By stepping and then turning the body I'm able to use passive force generation and the SSC.
    I never said that "true time" motion generates more force.
    However, when relying upon passive forces, your opponent can see the buildup clearly (he sees you loading the shell), and the SSC is being brought into play with TT as well, though not with a complete prestretch along the full diagonal, as you would see being practiced in Meyer´s Zornhut. Thankfully, after a while thats not necessary because once the quality of neuromusular response has been learnt and the connective tissue is sufficiently trained, you can shorten the move.

    Quote Originally Posted by Steven H View Post
    How does a blade make a it easier to impart rotational impulses?
    Compared to a hammer, the mass is closer to the hands. The lever affecting the mass is shorter, therefore the body can induce it with less neuromuscular latency.

    Regards, Thomas
    Last edited by T. Stoeppler; 10-28-2012 at 01:55 AM.
    Erschrickstu gern /
    Keyn Fechten lern.

  15. #15
    Thomas,

    Could you or rather will you elaborate on these quotes from you?

    "the generation of energy with joints, muscles and connective tissue"

    "for execution of any attack you have an alignment phase, a pre-stretch phase and a delivery/extension phase"

    "the reflex sets of the CNS do funny things for maximum force recruitment and that is very visible for the opponent."

    "However, when relying upon passive forces, your opponent can see the buildup clearly (he sees you loading the shell), and the SSC is being brought into play with TT as well, though not with a complete prestretch along the full diagonal, as you would see being practiced in Meyer´s Zornhut. Thankfully, after a while thats not necessary because once the quality of neuromusular response has been learnt and the connective tissue is sufficiently trained, you can shorten the move."


    Thank you,

    Patrick

  16. #16
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    Patrick, I'm not Tom, but I know most of the stuff you're asking about (and I brought it up to begin with).

    It has to do with 3 kinds of force generation that your body is capable of.

    The first is active force generation, that is the contraction of your muscles.
    The second is passive force generation. Your muscle tissues, and tendons are stretchy like a rubber bands. What this means is that if you pre-stretch the tissues you will get more force, active+passive. This is why people will reflexively pull back before punching, it pulls the chest muscles, stretching out the "rubber bands" first.
    The third is Stretch Shortening Cycle (SSC). This is a neurological phenomenon where stretching the muscle causes a reflex action that contracts the muscle. This reflex also adds to force generation when there is a prestretch.

    This prestretch is, of course, visible to the opponent. It's telegraphing when done in the usual way. And a lot of people do it unconsciously, especially when they are new to the material.

    The "full diagonal" refers to making the prestretch along the entire diagonal of your body from the right arm to the left leg. Since the muscles are interconnected the rubber band aspect of them actually stretches all the way across the body. This is the same reason why a big kick in football (both kinds) will be proceeded by the player stepping out and flinging their non-kicking side arm back.

    This is a trainable characteristic. Both the neuromuscular component and the connective tissue aspect - the tendons actually become stiffer*, too loose and they don't work like rubber bands. What happens is increased capacity for passive/SSC force generation. So if my max force is n before I start and 2n after I train for 12 weeks, then when I use this characteristic a movement half as big will still generate n additional force.

    Cheers,
    Steven


    * too stiff is also bad, there exists a sweet spot in the middle
    Athena School of Arms - Longsword & Highland Broadsword
    Fight with All Your Strength
    Swords of Chivalry - Youth Swordsmanship in Acton, MA

  17. #17
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    Meyer and Biomechanics

    I also think that a lot of Meyer's stuff indicates that he understood this and wished to make use of it. I think he has drills and techniques that are meant to maximize the passive/SSC force generation without it being telegraphic.

    Cheers,
    Steven
    Athena School of Arms - Longsword & Highland Broadsword
    Fight with All Your Strength
    Swords of Chivalry - Youth Swordsmanship in Acton, MA

  18. #18
    Quote Originally Posted by Patrick De Block View Post
    Thomas,

    Could you or rather will you elaborate on these quotes from you?
    Hi Patrick,

    Steven explained a lot of it already (Thanks )

    So I just pick up those two:

    Quote Originally Posted by Patrick De Block View Post
    "for execution of any attack you have an alignment phase, a pre-stretch phase and a delivery/extension phase"
    Thats simple - caveman first look at mammoth, then draw back arm, then cast spear at mammoth.
    The example is how all attacks in us are structured - in the alignment phase you usually turn towards the opponent, fix the attacking point and and your whole posture adjusts. This is a subtle and entirely subconscious movement, sometimes only a micro-motion is there. Then you do a pre-stretch (see Steven´s post) of sort; somtimes big, sometimes small but its always there in the kinematic chains. Then you release and extend to the fixed point of contact, delivering your attack. This kind of pattern is there, always, sometimes more and sometimes less visible. Even the most artfully executed rapier lunge bears artifacts of this.

    Quote Originally Posted by Patrick De Block View Post
    "the reflex sets of the CNS do funny things for maximum force recruitment and that is very visible for the opponent."
    These are associated motions; if the CNS expects to exert a peak force there are a lot of associated motions throughout the body, like, clenching teeth, drawing up shoulders, there are many of these and they affect the way people move in a certain manner.

    Regards, Thomas

    (P.S. though slightly off-topic: Steven, I guess Meyer indeed offers lots of practical exercises for functional force development, especially in longsword and staff sections)
    Erschrickstu gern /
    Keyn Fechten lern.

  19. #19
    Steven and Thomas,

    Thank you both and since you said, Steven, you brought it up and I was puzzled, I've been reading your blog. Now I'm trying to digest it.


    Patrick

  20. #20
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    Don't have anything to say about physics, but to this silly East/West debate I'd like to say that there is no eastern tradition of cutting, moving or breathing... at least not a unique one. The eastern (which you probably meant Japanese) is a very complex tradition with some arts using oral teaching coupled with manuscripts, other being modern developments, competitive sports and other being just plain BS. You would be very good to give a united theory of all this. My style for example recognizes what would be called "true time" and uses it.

    And John Clements moping the floor with "Eastern" martial artists amounts to a big nothing. Except if he took part in Gekkiken, which I am sure he didn't, he probably did not face a single legit Japanese school as few would take part in such an event.

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