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Homework Help: Mechanics, degree of freedom question

  1. Oct 25, 2015 #1
    1. The problem statement, all variables and given/known data

    Calculate the DoF (mobility) of the following system:


    2. Relevant equations

    M = 3(L-1) - 2J1 - J2

    (where L = number of links, J1 is the number of full binary joints and J2 is the number of half joints.

    3. The attempt at a solution

    I am very confident about there being 9 links, and 1 half-joint (the pin in the slot above the L link) but I am unsure about the number of full joints which I numbered here.


    I know from 1-7 should be correct, but I don't know about the joints on the slider. Should there only be two binary joints for each like I put there? Which is basically one ternary joint... 2 on the rigid link 'L' and on the link to which the slider is attached.

    And if I am correct I take it there is only 1 DoF then, which is the rotational of the circle attached to the top?

    Help would be appreciated here.
  2. jcsd
  3. Oct 25, 2015 #2


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    I presume the straight lines are strings. What happens when two straight lines meet at a little circle? Is it a pulley? Is it a post to which they are knotted? What about when three strings meet at a little circle? Can the little circles move?
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