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Formula Problem

  1. Jun 22, 2006 #1
    Hi folks, this isn't homework, but its a homework type question so I thought this was the best place to post it.

    I am in the process of constructing something that requires me to figure out the force exerted at a certain point on a pivoting object. It is a fold away bed.

    The matress and the frame it sits in all need to pivot on a steel bar, folding up to the wall and down from the wall. To make the motion less dangerous I am using two gas springs to cushion the weight of the bed in movement. To order the Gas Springs I need to let the manufacturers know the force that will be exerted on them so they can be made to spec.

    I am looking for some help with regard to how I figure out the wieght, with regard to the location of the pivot point, that is exterted. Hopefully this picture will help.

    Thanks in advance,

    http://www.phatjerusalem.com/files/bedexample.jpg [Broken]
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jun 22, 2006 #2


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    Staff Emeritus
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    Gold Member

    You need to google for "Moments" or "Torques" :smile:
  4. Jun 22, 2006 #3


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    Staff: Mentor

    The torque that Hoot is referring to is the force multiplied by the distance from the pivot. So to lift the bed, it takes twice as much force if you are lifting at the hafway point of the bed as opposed to lifting it at the foot.

    And for your gas springs, since they are much closer to the pivot point, they will have to provide a larger force than if they were somehow located at the foot of the bed. So for an initial SWAG at the spring values, measure the force that it takes to lift the foot of the bed, cut that in half (so the springs will support half of the bed weight when it is horizontal), and then ratio that force up by the ratio of the distance from the pivot to the foot of the bed divided by the distance from the pivot to the spring connection point.
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