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The human leg

  1. May 28, 2008 #1
    When kicking off the ground, what is the maximum amount of force that human's can exert?
    Any references?
     
  2. jcsd
  3. May 29, 2008 #2
    rough estimate: 2000N

    the world high jump record is 2.45m. A good high jumper can actually have his center of mass pass under the bar by arching around it, so say his center of mass rose to 2.40m. The dude who did it is 1.94m tall. The center of mass of a man is about .56 his height (hypertextbook.com/facts/2006/centerofmass.shtml), so that's 1.09m. So he jumped 1.31m. I don't know what he weighed, but 80kg is a reasonable guess. The impulse would have to have been 406 kg*m/s.

    To figure out over how long a time that impulse was delivered, imagine he bent his knees to 90 degrees, then straightened them, lifting himself .5m before taking off. If his acceleration was constant in that time, it would have taken him .20 seconds, yielding a force of 2000N.
     
  4. May 29, 2008 #3
    on second thought, it should be more. people can deadlift 455kg, so that's 4500N right there.
     
  5. May 29, 2008 #4
    What exactly do you mean by kicking?

    meichenl gives two examples - a high jumper and a deadlifter. Personally, I'd classify both movements as pushing, not kicking...
     
  6. May 29, 2008 #5
    isn't a kick just a type of push?
     
  7. May 29, 2008 #6
    well, I suppose it could be. But, when I 'hear' kick, I thinking of kicking a soccer ball or a football. I think we'd all agree that that movement is different than a pushing type movement...
     
  8. May 29, 2008 #7
    Hmm, In a way I see what you mean. When one kicks a ball properly (football=soccer ball to me I'm afraid) one stops applying force on contact with the ball and lets the transfer of momentum from the foot to the ball move the ball forward. However it really is a very related question.

    vinny11 why do you assume he bent his knees to 90 degrees? High jumpers always start with a run so this assumption might be the problem with your calculation i.e I think the actual impulse lasts way less than 0.2 seconds.

    check out this guy for instance:



    even in slow mo his foot is in contact with the ground for far less than 0.2s.
     
    Last edited by a moderator: Sep 25, 2014
  9. May 29, 2008 #8
    jbunten,

    maybe it's less than .2 sec, although just by watching the video i can't tell. is there an easy way to count the number of frames it takes him to take off, and divide by the frame rate?
     
  10. May 29, 2008 #9

    DaveC426913

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    Gold Member

    In fact, it's the same question. Over a duration approaching zero (i.e. before gravity is a significant factor), kicking a soccer ball is the same as kicking off a much much MUCH larger ball. :biggrin:
     
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