The forces acting on a circular cylinder by a time-dependent flow are analyzed through the use of a potential flow model. The shear layers which spring from the sides of the body are replaced by a combination of line vortices and infinite number of vortex sheets which connect the nascent vortices to their respective feeding zones. The analysis is then applied to the prediction of the kinematic and dynamic characteristics of symmetric vortex separation on circular cylinders. The results compare favorably with the latest available experimental data. The development of the wake is also traced and the results show the primary and secondary roll-ups of the shear layers as represented by the line vortices and vortex sheets.