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Lever math

  1. Aug 15, 2014 #1
    Forgive me if this is in the wrong category.

    I have a product I am working out - I am a programmer and electronic engineer by trade, which didn't include a lot of work with physics principles.

    I have a lever system which seems simple - but the trick is, my load is acting as a lever too. See the attached picture.

    In the bottom left is my load. It is 3 lbs. I want to attach it to the end of the lever in the bottom right. My assumption has been that I would find the center mass of my load to determine how much longer my lever arm becomes with the load attached.

    At the top of the picture, I sketch my 'assumed' equivalent system. I am right?

    If so, is it correct that I need 46x the force on the left side of the lever to raise my 3lbs => 138lbs

    Thanks in advance for the brainpower!

    Attached Files:

  2. jcsd
  3. Aug 15, 2014 #2


    Staff: Mentor

  4. Aug 15, 2014 #3
    I would like to clarify my description a little:

    The load is 3lbs - the load center mass is at 32"
    The unloaded lever system has a 1" arm and 14" arm on each side of the fulcrum.
    The load gets attached to the end of the 14" arm (extending it)

    I assume 14" (arm) + 32" (center mass) = 46" with 3lb load is the result.
  5. Aug 15, 2014 #4

    that doesn't help because my issue is understanding how the length of my load affects the equivalent system.

    I suppose the ultimate question is - do I take the center of mass of my load to determine where on the lever system it is applied?
    Last edited: Aug 15, 2014
  6. Aug 15, 2014 #5


    Staff: Mentor

    Yes, I think you take the center of mass of your load and its distance from the axis of the arm.
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