What Is Fluid Mechanics

To decide what we mean by the word fluid, first we have to consider the idea of shear stress.lt is easiest to discuss shear stress in comparison with tensile stress and compressive stress see Fig. 1.1.  

In Fig. 1.1 (fl) a rope is holding up a weight. The weight exerts a force which tends to pull the rope apart. A stress is the ratio of the applied force to the area over which it Is exerted. Thus the stress in the rope is the force exerted by the weight diyided by the cross-sectional area of the rope. The force which tries to pull things apart is called a tensile force and the stress it causes is called a tensile stress. 

Comparison of tensile, compressive, and shear stresses, (a) The rope is in tensile stress ( ) the column is in compressive stress (c) the glue is in shear stress. 

A more detailed examination of these examples would show that all three kinds of stress were present in each case, but those we have identified are the main ones. (For more information on this topic, see any text on strength of materials.) 

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