Normal and Shear Force Components  
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The figure shows a prismatic bar whose right end is an inclined plane. The loads on either end have magnitude P and are directed leftwards and rightwards respectively. The t axis is taken along the inclined plane and the n axis is taken perpendicular to it. The angle between the n axis and the horizontal x axis is theta. The projection of the force P along the t and n axes are V and N respectively.

The perpendicular component (acting in the n direction) is termed the normal force N:
N=P cos θ

The parallel component (acting in the t direction) is termed the shear force V:
V=-P sin θ

When working with planes, the orientation of the plane is specified by the normal to the plane. The inclined plane above is referred to as the n face because the n axis is the normal to this surface.