Area of Inclined Surface Depends on θ  
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The figure shows a prismatic bar whose right end is an inclined plane. The t axis is taken along the surface and the n axis is taken perpendicular to the surface. The angle between the n axis and the horizontal x axis is theta. The cross section of the bar is shown on the bottom right and a caption to its left reads: The cross sectional area of the bar is denoted by A. The inclined surface taken through the bar is shown on the bottom right and a caption to its right reads: The area of the inclined surface depends on the angle theta. A subscript n equals A over cosine of theta.

Stress is defined as force per area; therefore, the magnitude of the normal stress and the shear stress depends on the area of the inclined surface.