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A shinai's center of mass

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  • A shinai's center of mass

    I am just curions, where is the center of mass there the shinai should be balanced on, let's say, a pin? (It weights 550g and it's an adult one)

    For some reasons, mine is very hard to maneuver compare to some others, or it could be that my arms are just not strong enough to hold one

    I tried to balance mine and it lies somewhere 2 inches above the Tsuka, close to largest part of the bamboo.

  • #2
    Basically there are two main types of shinais based on balance....one where the weight of the shinai is spread equally over the "blade" portion, making it good for basic practice and swings...the other is where the weight of the shinai is focused on the tsuka or handle of the shinai. this makes the tip lighter and allows you to make strikes faster. Thats what i know about shinais...there shape and other such things but im not the person to ask about all that.

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    • #3
      Crap...now you got me thinking Physics (I have a final next Wednesday).

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      • #4
        There is an article on Arma webpages about balance and swinging of western swords from a newtonian POV. The applicability of the article in question to swinging of shinai is of course not clear. Perhaps some physics student would be kind enough to review it?

        http://www.thearma.org/spotlight/GTA...nd_impacts.htm

        Sakari Jokinen

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        • #5
          I see, but as a beginner should we be using the one with the mass spread all over the blade(which is hard to control) or the other one where the center is right before the Tsuka?

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          • #6
            Originally posted by x_ouch
            I see, but as a beginner should we be using the one with the mass spread all over the blade(which is hard to control) or the other one where the center is right before the Tsuka?
            It's largely a matter of personal preference, and something that will tend to change over time as you become more experienced. Some people like dobari type shinai (center of gravity closer to the tsuba) because it allows for quick techniques. But it's not necessarily true that the koto style shinai (more even weight distribution) is harder to control. Just a different feel.

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            • #7
              Neil Gendzwill-sensei?

              This is a job for Neil Gendzwill-sensei, or Obukan's Murosako-sensei (but I don't think he reads this forum).

              If Murosako-sensei is at practice tonight I'll ask him, he does enjoy talking about the Physics of Kendo...

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              • #8
                So it's not a rule or anything? Then I perfer the one closer to the tuska

                How is it possible to find out which one is which? Does it usually say on the tag?

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                • #9
                  Shinai with the mass near the tsuka are called Dobari type shinai. They have a thicker middle part and a slimmer tip. They are usually more expensive and fragile (slimmer tip). Many (like me) use them for special occasions like competitions or gradings. I use normal shinai for practices because they are cheaper to replace and when I do use thge dobari it is even easier to use.

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                  • #10
                    Center of Mass

                    Here are two examples, both size 39 (about 47") with leather, no tsuba.

                    Akatsuki - balance point about 26.5" from tip.
                    Kunimasa (e-bogu) - balance point about 27.5" from tip.

                    By profile the Kunimasa is more dobari. (Akatsuki shinai, being one of a kind, are sold by dimensions, not a particular classification.) I don't have a scale appropriate for weighing them, so my comments are subjective. The Akatsuki is slower to handle. It feels heavier but, as we should all have a sense for, the farther the mass is from the point of rotation (somewhere around your shoulders for the swing and somewhere in the tsuka for the strike) the heavier it feels. If we assume that these two shinai are about the same mass, the one inch difference in center of mass makes a big difference in how it feels.

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                    • #11
                      An inch makes some differences, but what about the prices?

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                      • #12
                        Originally posted by x_ouch
                        An inch makes some differences, but what about the prices?
                        Dobari shinai are usually more expensive and may break easier (the striking part is slimmer)

                        For actual prices look at vendor websites (e-bogu, eguchi, etc) in the shinai section.

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                        • #13
                          Originally posted by x_ouch
                          I am just curions, where is the center of mass there the shinai should be balanced on, let's say, a pin? (It weights 550g and it's an adult one)

                          For some reasons, mine is very hard to maneuver compare to some others, or it could be that my arms are just not strong enough to hold one

                          I tried to balance mine and it lies somewhere 2 inches above the Tsuka, close to largest part of the bamboo.
                          Hmm....when you say hard to control, how do you mean ? hard to pick it up ? hard to cut ?

                          hard to cut repeatedly ?

                          I'm in no authority on this but one of my seniors who cut super quickly repeatedly just basically say its all a matter of practice on suburi.

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                          • #14
                            Sorry, missed this earlier - as a beginner, just get whatever shinai in the correct length. You won't be able to tell the difference. The el-cheapo Taiwanese ones are often more durable than good Japanese shinai anyways - much better to break a $40 shinai than an $80 one.

                            As far as dobari/chokuto goes - most of the cheap ones are somewhere in the middle. Most people like dobari better for tournaments due to the quicker action for small movements - with a little experience, you will notice the difference in balance. If you like to do a lot of oji-waza the balance lets you move the tip more quickly. The wider bit near the tsuba can help with suriagi-waza, but unless you have quite a bit of experience you can't take advantage of it.

                            A true chokuto shinai isn't often seen. Usually when people talk about them they mean one of what I think of as a normal shinai. Chokuto are really straight, thick tip, usually heavier than normal, with the balance quite even. To an experienced hand, they feel really sluggish and tip-heavy, especially if you prefer dobari. They are intended for a more mature style of kendo. If you like to keep the pressure on and then hit men, you might like chokuto. I've never seen any cheap ones - mostly they are handmade.

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