Introduction to Kinematics

We begin the study of fluid mechanics by pointing out the differences be- tween fluids and solids, and by describing a fluid flow in terms of the motion of elementary fluid parcels. As the volume of a parcel becomes infinitesimal, the parcel reduces to a point particle and the average velocity of the parcel reduces to the local fluid velocity computed before the molecular nature of the fluid becomes apparent. The study of the motion and deformation of material lines and surfaces consisting of collections of point particles reveals the nature and illustrates the diversity of motion in fluid mechanics.