# Normal Stress

In a rectangular or Cartesian coordinate system (x,y,z), the

*stress tensor*τ is given by:
(1)

where i

_{x}, i_{y}and i_{z}denote unit vectors in the x-direction, y-direction and z-direction, respectively. The components of τ may be interpreted thus:- τ
_{xx}is the x-component of force per unit area exerted across a plane surface element normal to the x-direction; - τ
_{xy}is the y-component of force per unit area exerted across a plane surface element normal to the x-direction; and so on. (Precisely analogous interpretations can be given to components of stress in any orthogonal coordinate system.)

Each component with identical suffices (τ

_{xx}, τ_{yy}and τ_{ZZ}) is called a*normal stress*since it represents a force in a direction per unit area normal to that direction. Each other component with different suffices (τ_{xy}, τ_{yx}, τ_{xz}, τ_{zx}, τ_{yz}and τ_{zy}) is called a**Shear Stress**.