# Free-body diagram

For the following scenario: http://i14.tinypic.com/6jnvi3p.gif
why is the Force vector coming from the left only represented only in two of the three separate cases you can take. That is, te Force vector can only be represented in the case where you are considering a the system as a whole and the forces acting on the first object m1. However, if you do this for object m2 you obtain an incorrect normal force.