1. The problem statement, all variables and given/known data http://postimg.org/image/9fw7awqov/ The question is to write the Laplace transformed equations of motion for the system 2. Relevant equations 3. The attempt at a solution I am confused about a couple of things: why is an angle is not defined for the rotation of J2. Does it means J2 does not have linearly independent motion? And the fourth equation of motion (for the second J=0), I can understand the theta 4 term being due to the torques associated with it's motion but I don't get the other term.