I'm a computational person, and I don't quite understand how rotational DoFs are manifested in the linear elasticity equations. I understand the translational DoFs are simply the displacement components. When specifying boundary conditions for linear elasticity simulations, we typically specify the displacement and/or traction boundary conditions at the boundaries. Where do the rotational boundary conditions come in? Are they manifested in the traction boundary conditions? 

This is not very intuitive to me and I was hoping someone can explain.