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Initial Torque = 0

  1. Sep 7, 2011 #1
    Initial angular momentum = 0

    when we fall from a height, how does our head automatically reach the ground first than our legs though the initial angular momentum is zero???
     
    Last edited: Sep 7, 2011
  2. jcsd
  3. Sep 7, 2011 #2

    A.T.

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    Jump with head first? Seriously, what do you mean by "initial torque is zero"? The external torque is always zero during a fall, so the angular momentum is constant (aerodynamics aside). Did you mean: "initial angular momentum is zero"?

    See this thread:
    https://www.physicsforums.com/showthread.php?t=527460
     
  4. Sep 7, 2011 #3
    yes i meant initial angular momentum to be zero but not jumping with head at first!
     
  5. Sep 7, 2011 #4

    A.T.

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    Rotate your arms. See other thread.
     
  6. Sep 7, 2011 #5

    BruceW

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    Do you mean: 'why do people usually end up hitting the ground head first'?

    Given enough time, a person should be able to turn themselves any way they like (as a cat does).
    If a person is pushed off a roof (like in films), this means their upper body goes down first, then their legs follow. So this might be why you seem to think the head usually ends up hitting the ground first.
    Maybe there is a slight aerodynamic bias to going head first (since the legs flail about).

    But I think in general, any part of the body is as likely to hit the ground first. (especially if the person is spinning while they are falling).
     
  7. Sep 7, 2011 #6

    A.T.

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    That's a case of non zero angular momentum.

    No, people are like toast: They always land wrong way down.


    Cat_toast_swirl.gif
     
  8. Sep 7, 2011 #7

    BruceW

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    At least give a reason for why people always land the wrong way down.
     
  9. Sep 7, 2011 #8
    What about the weight of the head?? Doesn't that support the theory? If an object is thrown (or if it falls) the heaviest side is usually in the front (facing the direction in which it is traveling?)
     
  10. Sep 7, 2011 #9

    BruceW

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    You mean the head is denser than the legs? Yeah, that's probably true. Difficult to tell how important that factor is..
     
  11. Sep 7, 2011 #10

    A.T.

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    Murphy's law
     
  12. Sep 7, 2011 #11

    BruceW

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    I don't think Murphy's law applies in this case.
    If you're setting up a tv there are many ways for it to go wrong, but only one way to go right.
    But a person landing on his head first would be less probable than him landing on any other body part. (unless there is some other reason like hobblecookie's which explains why he would land head-first).
     
  13. Sep 7, 2011 #12
    Whenever I fall (off a bridge, off a diving board, off a trampoline, etc.) I always land on my feet. Perhaps the people who land on their head need more practice.
     
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