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High jump - Fosbury Flop

  1. Aug 4, 2010 #1
    It is said that jumping with the Fosbury Flop technique, one's center of mass stays significantly under the bar. What if, instead of the bar, one tryed to jump over a wall? It looks as though there's no difference between the bar and the wall, but the wall is a potential barrier for the center of mass and so the jump should be unsuccessful. What's the difference between the two cases and why is the Fosbury Flop tehcnique successful?
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  3. Aug 4, 2010 #2

    Andy Resnick

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    Why is the wall a potential barrier for the center of mass? Is the center of mass always located at a material point within a body during that maneuver?
  4. Aug 4, 2010 #3
    No offense, but this is just rubbish. Unless air flow has influence on successful FF jump, there is absolutely no difference between the two.
  5. Aug 5, 2010 #4
    The trajectory of a body is determinated by the motion of the center of mass. If the energy of the body is not large enough for the center of mass to go over the wall, then the wall should be a barrier for the motion.

    Also, one obvious difference between the wall and the bar is that you can put your arms/legs under the bar while jumping and maybe that's what makes the key difference.
  6. Aug 5, 2010 #5

    Vanadium 50

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    If you have a hard time seeing how a body can travel over a wall with it's COG always below it consider a Slinky.
  7. Aug 5, 2010 #6

    There is also a lot more give to a bar than a wall. It is possible to land partially on the bar, or to otherwise strike it, without knocking it out of place. Walls are...less forgiving. There is a higher margin for error when jumping over the bar, meaning a higher chance for success.

    Psychologically, there is a huge difference. However it's very difficult to judge how the psychological difference between a wall and a bar will affect performance without testing it.
    That was the perfect thing to say to make the concept "click" in my head. Awesome.
  8. Aug 5, 2010 #7
    So, you're saying that a slinky can travel over the wall with it's COM always below it? So, I'm mistaking about the barrier for the motion?
  9. Aug 5, 2010 #8

    Doc Al

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    Yes and yes. Try it and see.

    Since no part of the object (man or slinky) passes under the bar, it doesn't matter if it's a bar or a wall.
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