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Understanding Hammerthrow Forces, (no friction with ground)

  1. Aug 13, 2014 #1
    If I understand it correct during hammerthrow an athlete muscles cause Fcentripetal force on a ball and ball cause reaction Fcentrifual force on athlete.
    The athlete also cause Frotation on ball by rotating his body and ball cause Freaction on athlete.

    What would happen if athlete would try to throw the heavier ball than himself being in the air - by rotating his body (no friction between athlete and the earth - I mean the athlete and the ball are both in the air) ? Would it be even possible or would athlete rotate himself around ball(cause ball is heavier) ?
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  2. jcsd
  3. Aug 13, 2014 #2

    Orodruin

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    Hint: One of the basics of the hammer throw event is for the athlete to keep both feet in contact with the ground for as much time as possible. If you see a hammer throw in slow motion, notice how quick they are to put their feet back on the ground in the moments where they have to lift one of them.
     
  4. Aug 13, 2014 #3

    Drakkith

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    Friction on the ground (or something) is required in order for the athlete to spin the ball around himself. With no friction the athlete cannot even spin himself around.
     
  5. Aug 13, 2014 #4
    I can spin myself around in the air when I jump
     
  6. Aug 13, 2014 #5

    Drakkith

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    Sure, by pushing off the ground in a certain way. If I place you into zero g and you have nothing to push off of, you will not be able to turn around.
     
  7. Aug 13, 2014 #6

    rcgldr

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    Translation is not be possible, but rotation is possible because a person can rotate / swivel their arms and/or legs, and since the total angular momentum remains zero, the persons body rotates / swivels in the opposite direction. Once the person stops moving their arms and/or legs they will end up facing in a new direction (but no translation has occurred). If this method were used with a hammer, then the hammer could be released and thrown, but the person would end up traveling in the opposite direction (and with opposing angular momentum), and the center of mass of person and hammer would not move.
     
  8. Aug 13, 2014 #7

    Drakkith

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    Of course, but I don't consider this to be anything like what the OP was imagining in their original post with the athlete swinging the ball around themselves in midair. Unless I misunderstood the question.
     
  9. Aug 14, 2014 #8

    rcgldr

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    But that's the situation I had in mind. The person in midair, pushes the ball away from themselves, then starts swinging the ball in a circle while the persons body would rotate in the opposite direction. Swiveling of the legs could be used to reduce the person's rate of rotation and increase the hammer's rate of rotation. The person then releases the hammer and they both move away from each other, while the center of mass of person and hammer remains motionless, and angular momentum of person and hammer remains at zero.
     
    Last edited: Aug 14, 2014
  10. Aug 14, 2014 #9

    Drakkith

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    Okay, I can see that working. I was imagining both the athlete and the ball rotating with each other, which isn't possible given conservation of angular momentum.
     
  11. Aug 14, 2014 #10

    Orodruin

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    It will work to get the ball away, yes. Unfortunately, it is also quite unrelated to how the hammer throw event is performed where the thrower is actually rotating along with the hammer.
     
  12. Aug 14, 2014 #11

    jbriggs444

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    Not on-topic for this thread, but even with zero angular momentum throughout the exercise, one can contort and uncontort the body and thereby change orientation.
     
  13. Aug 14, 2014 #12

    rcgldr

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    It's how a cat can be dropped a short distance while initially paws up and manage to rotate it's body by swiveling about it's mid section so that it lands paws down.
     
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