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Help: The physics behind the throws of judo?

  1. Jul 28, 2014 #1
    I have been wanting to do an essay(4000 words) on the physics/biomechanics of judo and its throws. The only problem is I don't where to begin. Any help would be appreciated!
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  3. Jul 28, 2014 #2


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  4. Jul 28, 2014 #3
    Only problem is I have been searching for 2 days and I'm still not sure how everything fits together. The documents and sites that might be able to help me are behind pay walls so...

    I'm high school senior and I have been taking some physics and biology courses at school. So I have some basic ideas on how they interact to from biomechanics. Like how the forearm is lever and when the bicep contracts it applies a force to the tendons that connect to the forearm causing torque and the movement of your arm.
  5. Jul 28, 2014 #4
    That kind of answer dosent really seem to help things, I think OP would have already thought of that before coming here to post.

    Why not try to set out a series of questions about a throw? As in, "In order to throw a 75Kg opponent in a parabola over his shoulder, how much work would the judo master have to do?

    Then you could try to build 3 or 4 successively more intricate models of a human as both a mass and a lever.

    Maybe try to compare the energy the judo master actually expends compared to the most ideal situation?
  6. Jul 28, 2014 #5


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    It's a fine answer in this case. The PF rules (under Site Info at the top of the page) require that posters show some effort when asking schoolwork-type questions.

    @WizErnest -- Welcome to the PF. Have you taken Judo? If so, for how long and what belt level are you currently at?

    The Physics of Judo is not just calculating how high parabolic paths reach. The whole point of Judo is to minimize your effort in throwing, choking and pinning your opponent. "Balance, Momentum, Leverage" is one of the key mantras in Judo...
  7. Jul 28, 2014 #6
    Sorry, I just read it in my head as kind of talking down.

    Back on topic, maybe trying to model two whole people interacting is a lot (I'm a Sr physics major and that sounds daunting to me). Break things into little bits.
  8. Jul 28, 2014 #7
    Judo Novice - he would try try with all his might and not get to throw anybody.
    Judo Master - very little work as he knows that he will use the opponents momentum, centre of mass being off balance, and gravity to complete a move to success.
  9. Jul 28, 2014 #8
    This is true, but why not compare a judo master to a simple machine?

    * Also, I never meant to bring skill into the mix, I was just using judo master before beacuse it sounds better than "practitioner of judo" or something.
    Last edited: Jul 28, 2014
  10. Jul 28, 2014 #9
    One basic move in Judo is as follows:
    You and your opponent are holding on to each other and doing various shifts in position. You opponent suddenly pushes against you trying to unbalance you, thinking he will kick a foot out as you step back. Being a worthy Judo athlete, what do you do?
    You pull on his upper body, while at the same time dropping down, and sticking a foot ( or two if you are so inclined at the moment ) at his abdomen. What happens - your opponent is carried over you and lands on his back, and you, while that is occuring, grab onto the end of an arm, place a foot over his body and one under the arm for a pin winning the match and the title.

    Physics -
    Force - Newton's law - him pushing and then you pushing.
    Momentum - his forward movement continues throughout the throw.
    Lever - your foot is being used as a fulcrum
    Centre of balance - he cannot obtain a footing to re-balance himself
    Gravity- you dropping down, and him falling down on his back.
    Torque - he has rotated 180 degrees
    Force - pinning the arm and body disallows him to upright himself. Here you are using your body weight ( again gravity ) and prohibiting him from using any leverage to right himself.
    It could be I missed something.

    Try to see if you can evaluate the physics of other throws in a similar manner, such as the hip throw, or just a kick out of a leg.

    From a biomechanical point of view, I am not sure how to fit a description in there. Certainly, strength and size do not matter as much as some other factors.
  11. Jul 28, 2014 #10


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    Let's let the OP WizErnest reply before we give much more help here.... :smile:
  12. Aug 6, 2014 #11
    I'm a white belt and have doing it for about month now.
  13. Aug 6, 2014 #12
    Sorry, I've been away for a long time. I recently purchased a book: "The Secrets of Judo", which is very heavy on the mechanics and physics behind judo. So far I've got to stability and the mechanics of unbalancing an opponent, usually by moving is center of gravity beyond his/her base of support.
  14. Aug 7, 2014 #13


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    In contests between highly skilled opponents (like the olympics), there are weight classes since strength and weight are significant factors when both opponents are highly skilled. In the few times I've seen judo events on the olympics, its seems like there's a lot of effort involved in all the moves.
  15. Aug 7, 2014 #14


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    You have chosen the project because you like both the Judo and the Physics, and I can understand it's an attractive idea for you. The big snag is that Judo involves a very complicated set of moves, involving all your muscles and skeleton and a load of varied Physics ideas. You have definitely gone in off the deep end with this one and I would recommend (along with others) that you try to break the thing down into small parts and look at some chosen parts in detail. Write a list of all the mechanics topic you know and put the aspects of Judo that it could be relevant to next to each topic. Pick just one (the one with most in it, perhaps). That will be quite enough to be dealing with!
  16. Aug 7, 2014 #15
    Good Advice! Thank you all!
  17. Aug 8, 2014 #16


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    Don't forget to stay in touch when you have made your choices.
  18. Aug 8, 2014 #17
    yes, please, I'm quite interested.
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