One way of classifying different types of motion is according to their kinematic properties. For example, there is a large class of motions dealing with divergenceless fluids (commonly referred to as motion of incompressible fluids. Another class is motion wherein the vorticity is everywhere zero. This is referred to as irrotational motion. Motions of solid bodies, representing perhaps the most widely studied class in applied mechanics, falls under the heading of deformationless motion.