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Gravitational Force Question

  1. Oct 1, 2007 #1
    My appologies for such a lame question, but it has been near 50 years since physics in college, and not much use since. A friend helped another to pick up a very large and heavy door. As the second person was taller than he, he was under the impression that he had the "heavy' end of the door (he was donwhill so to speak). I stated no, that both ends were equally "heavy" and both lifters were equally sharing the load. As the vertical lifting distance between them was approximately four inches I felt there was no significant difference in the gravitational force. I hope I'm right and someone can give me the logical explanation for this, may be even a formula?
  2. jcsd
  3. Oct 1, 2007 #2


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    You are correct that there is not a significant change in the gravitational force, no where big enough to be noticeable. But this doesn't explain the fact that the short person feels as if he is carrying more weight than the tall guy. This can be explained by the fact that the center of mass of the door is shifted closer to the shorter man due to the position of the door. So, he is supporting more weight than the tall man, but not because the gravitational force is stronger near him.
  4. Oct 1, 2007 #3


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    But hey, If you are picking up a heavy load for a friend and not getting paid for it, you have a right to *****!
  5. Oct 1, 2007 #4


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    Oh, that's interesting! my last word got censored! When did that start?
  6. Oct 2, 2007 #5
    For objects like a door, where the vertical dimension is small compared to the horizontal dimension, and where the angle of tilt is not too great, there is not much difference. For a door which has negligible thickness, there is no difference at all, except there is a tendency for the taller person to carry at his "normal" position which may cause the shorter person to slightly lift his end, and that position may not have as good a mechanical advantage. Bottom line: If the door is thin and they carry it tilted, no discernible difference.
  7. Oct 2, 2007 #6
    Thank you, gentelmen for your time to answer...
  8. Oct 10, 2007 #7

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    Knowing the way people carry things, the shorter person is definitely going to bear most of the load if the door is tilted. Without going into the math, we can see that the door tends to slide toward the shorter person, and he has to push back harder. Think if the taller person is very tall, the door will be almost vertical.

    But if the taller person actively pulls the door up, then it’s possible to share the load equally. It’s also possible that the taller person bear most of the load if he pulls harder and the door is effectively more like “hanging” from his hands than resting on the shorter person. Think as if you are carrying a door or something long and the other person is a little child. You would instinctively try not to rest the load on the child by pulling the load up.

    But under normal circumstances, the taller friend would probably be content to let the shorter person bear the brunt.
  9. Oct 10, 2007 #8


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    Halls, i thought they always censored particular arrangments of ASCII characters here (ever since this potty mouth had been posting). i've been in the habit of inserting an un_derscore or making a visual substitutions; judging from context and 5 asteriks, i think you meant "b1tch".
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