ABSTRACT
Consider an elastic body B subjected to surface loads as in Figure 4.1. Consider a cutting plane N dividing B into two parts as shown in edge view in Figure 4.2.
Consider the equilibrium of one of the parts of B, say the left part BL, as in Figure 4.3. The figure depicts the forces exerted across the dividing plane by the right portion of B(BR) on the left portion (BL). Correspondingly, BL exerts equal and opposite forces on BR.
