One of the big challenges in 2D is that you can’t tell how a design will interact until you build the first prototype. SolidWorks introduced Dynamic assembly motion several releases back to let you test component interaction in 3D before making a prototype. A user simply drags a part and mates act like joints and the parts interact.
Dynamic assembly motion in SolidWorks lets users visualize and find problems with component interaction. In SolidWorks 2007, users can design belts and chains in an assembly and represent that motion between pulleys or sprockets. A new rack and pinion mate can be used to translate rotary motion to linear motion and gear mates can now automatically obtain their ratio from the gear size.