# Homework Help: Mechanics, degree of freedom question

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1. Oct 25, 2015

### yugeci

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. Oct 25, 2015

### andrewkirk

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?