When the body is subjected to external surface forces or contact forces F {\displaystyle \mathbf {F} } , following Euler's equations of motion, internal contact forces and moments are transmitted from point to point in the body, and from one segment to the other through the dividing surface S {\displaystyle S} , due to the mechanical contact of one portion of the continuum onto the other (Figure 2.1a and 2.1b). On an element of area Δ S {\displaystyle \Delta S} containing P {\displaystyle P} , with normal vector n {\displaystyle \mathbf {n} } , the force distribution is equipollent to a contact force Δ F {\displaystyle \Delta \mathbf {F} } exerted at point P and surface moment Δ M {\displaystyle \Delta \mathbf {M} } . In particular, the contact force is given by