The figure shows a prismatic bar whose right end is an inclined plane. The angle between the normal to the inclined surface and the horizontal is theta. The cross sectional area of the bar on vertical and inclined planes are shown at the bottom right for comparison. The area of the inclined surface is larger.

As the angle θ of the inclined plane increases in magnitude, the exposed area An also increases. Correspondingly, both the normal and shear stress magnitudes will be directly affected by the orientation of the plane.