Fluid Mechanics-Fluid Kinematics

In the previous three chapters we have defined some basic properties of fluids and have considered
various situations involving fluids that are either at rest or are moving in a rather elementary
manner. In general, fluids have a well-known tendency to move or flow. It is very
difficult to “tie down” a fluid and restrain it from moving. The slightest of shear stresses will
cause the fluid to move. Similarly, an appropriate imbalance of normal stresses 1pressure2
will cause fluid motion.
In this chapter we will discuss various aspects of fluid motion without being concerned
with the actual forces necessary to produce the motion. That is, we will consider the kinematics
of the motion—the velocity and acceleration of the fluid, and the description and visualization
of its motion. The analysis of the specific forces necessary to produce the motion
1the dynamics of the motion2 will be discussed in detail in the following chapters. A wide
variety of useful information can be gained from a thorough understanding of fluid kinematics.
Such an understanding of how to describe and observe fluid motion is an essential
step to the complete understanding of fluid dynamics.
We have all observed fascinating fluid motions like those associated with the smoke
emerging from a chimney or the flow of the atmosphere as indicated by the motion of clouds.
The motion of waves on a lake or the mixing of paint in a bucket provide other common, although
quite different, examples of flow visualization. Considerable insight into these fluid
motions can be gained by considering the kinematics of such flows without being concerned
with the specific force that drives them.