ABSTRACT
Let P be the total force applied to the surface element. In general this force will be inclined to the surface, but it can be resolved into (i) a normal component Nnn, acting perpendicular to the surface, and (ii) a shear component Snr, acting tangential to the surface. To obtain all component forces parallel to the Z, m and n axes, the shear force Snr may be resolved into two components Sn£ and Snm. Two subscripts are attached to each force component; the first (n) indicates the direction of the normal to the plane, while the second gives the direction of the component. For the normal component, the second subscript is the same as the first, and this unnecessary duplication is avoided by dropping the second subscript, replacing Nnn by Nn.
