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Thread: Calculating center of gravity

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    Senior Member Butcher's Avatar
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    Calculating center of gravity

    Can this be done accurately from a photograph? I am doing a presentation on the analysis of the squat. I was thinking a portion of it would be photographs showing the upward shift of center of gravity as the bar has more weight on it. Is there any way to accurately figure this out without expensive computer software or extensive knowledge of physics? Or should I scrap the whole idea?

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    This is easy. There's a theorem where you can easily figure out the center of mass of two objects assuming you know each one individual one (I think it just works out to a weighted average). The center of mass of the barbell is self evident and for a person it can be easily calculated. (Hell I'd guess its in the center of your waist).

    You don't need photos, they won't help you anyway.
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    student of the game Runty's Avatar
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    I don't think the center of gravity actually shifts up. It will shift forward or backward. Do you mean upward as in up your torso? The increase in weight will allow for a greater moment or torque about your center of gravity. A moment is just a force multiplied by a distance. For the most part during a squat you keep the bar in as close to a direct line over your center of gravity as you can. The shift forward or backwards is inches or less. So as the weight goes up it increases the multiplier you use to calculate the moment.

    1in forward of center X 135lbs = 135in lbs of torque twisting you forward.
    2in forward of center X 400lbs = 800in lbs of torque twisting you forward.

    Both the distance from the center and the increase in weight itself produce a larger moment.

    The act of squatting is just using your body to produce a counter moment for that torque effect to move the weight along that center of gravity as best as possible.

    You could ball park the center of gravity using a picture but to be accurate you would need body density integrals and all that neat stuff.

    Sorry kind of got rambling there, hope this makes sense.
    Last edited by Runty; 04-13-2011 at 02:18 PM.
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    Senior Member Butcher's Avatar
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    Im thinking Im scrapping this specific idea. I was planning on simply using a front shot photo and calculate a 2 dimensional center of gravity for just my body, and then showing the change in COG as bar weight is increased. But it actually has to be intelligent and not just me saying this is my best guess as to where COG is and I donth think I would accomplish that.

  5. #5
    Senior Member Phenom's Avatar
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    Scrapping it is a good idea. What you wanted to accomplish is a very difficult thing to do unless you were going for a very crude estimate. The location of the center of mass of your body varies as your body position changes.
    Last edited by Phenom; 04-15-2011 at 06:51 PM.
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