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  1. #106
    Senior Member Radialhead's Avatar
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    Quote Originally Posted by Wing 11 View Post
    MFP exist and it is not hard to prove,but problem is that MFP is just internal force,internal force can not cause any type of board movement,yaw,roll,pitch,forward motion,beckward motion
    Both you & Basher keep saying this, & it simply isn't true. An internal force cannot move *the centre of mass* of the system, but it most certainly can move parts of the system. If MFP from a leaning rig pushes the nose down & at the same time the rig pivots more to the vertical, the centre of mass can stay the same whilst the board pitch changes. But it's also irrelevant to the original question as you're not talking about raising or lowering the boom whilst moving.

    So when considering the effect of boom height, instead of thinking of MFP as pushing the nose down, try thinking about how it prevents the nose coming up. Then you have your balanced forces preventing movement from a given starting point, & that starting point may be different depending on boom height.

  2. #107
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    Quote Originally Posted by Navegante View Post
    Sorry but sounds like a whole load of nonsense.

    Internal force? Internal to what?
    It's Newtonian physics. You define a 'system' (in our case the board, rig & sailor), then any forces generated within that system cannot move the system's centre of mass. A classic example is a person inside a cardboard box in space. No matter how hard they push against or kick one end of the box, it won't move.

    They can however change the shape of the box - dent it or twist it etc. In the same way that MFP can change the shape of our windsurfer system by moving the board & sail in relation to each other, without actually moving the whole system in any direction. Hence why I said back at the start of this thread that talk of internal vs external forces is irrelevant.

  3. #108
    Senior Member Radialhead's Avatar
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    Easy, just straighten your legs. Or get a big sledgehammer & whack the other end. Or get a saw & cut it. You're trying to manipulate the problem to match your (mis)understanding of the physics involved. If you're going to continue to maintain that an internal force cannot move parts of the system within which that force exists, you'll never get anywhere & you're just wasting everybody's time.

  4. #109
    I did not say that mast foot pressure was an internal force.
    Now back in the UK.

  5. #110
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    Quote Originally Posted by basher View Post
    I did not say that mast foot pressure was an internal force.
    Nice bit of selective dismissal there.

  6. #111
    I'm just correcting something you wrote. (In post #142)


    I have written a lot on this which you may not have had time to read. (It's all still there)

    I do believe that MFP exists but it also varies as we sail along and varies from gear to gear.

    There are also sometimes multiple loads on the mast foot/U/J but some of those forces – such as the sideways leverage one – are effectively neutralised as we sail along. The neutralised forces can be described as internal forces.
    Last edited by basher; 24th November 2017 at 07:19 PM.
    Now back in the UK.

  7. #112
    Senior Member Radialhead's Avatar
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    Quote Originally Posted by Wing 11 View Post
    Your examples are frivolous ,cut with saw,sledgehammer?!!Are you kidding me!You know what I am asking ,so be serious.
    Just out of interest, how old are you?

    Quote Originally Posted by Wing 11 View Post
    On example saftey ropes are in tension,pointing slightly upright,but it will not lift "nose" ,bacause it is just internal force

    (Please dont sombody ask me now,how red foken rope can represent sail forward force or this is on beach not in planning)

    Attachment 15781
    Why are the safety ropes in tension? Are you saying the upwards vertical force from the brown rope is greater than the downwards vertical force imparted by leverage from the red rope?

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