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B How does a Triple Beam Balance work?

  1. Dec 8, 2016 #1
    so I understand that it balances both sides of the scale but why does it have to be horizontal? in other balancing systems the beams do not have to be horizontal but in this system they do. I know it has to do with torque but can't seem to understand how the balance can be close to the right mass and not be moving but it is not correct unless it is horizontal.
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  3. Dec 11, 2016 #2

    Simon Bridge

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  4. Dec 11, 2016 #3


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    For any balance to be stable, the suspension point has to be slightly above the CM of the suspended mass. Only when the beam is horizontal is there no moment acting due to the horizontal displacement of the CM. Imagine an exaggerated arrangement consisting of an inverted T, with the suspension at the top. A perfect T will hang with the leg vertical but, put unequal masses on the arms and the T will still balance but with the leg not vertical. Only when the leg is vertical can you say that the masses are equal. The triple beam balance, likewise, needs the (very short) hanging 'leg' to be vertical and the arms horizontal. Then the moments on each side can be said to be equal.
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