Figure 2.1c Stress vector on an internal surface S with normal vector n. Depending on the orientation of the plane under consideration, the stress vector may not necessarily be perpendicular to that plane, i.e. parallel to n {\displaystyle \mathbf {n} } , and can be resolved into two components: one component normal to the plane, called normal stress σ n {\displaystyle \sigma _{\mathrm {n} }} , and another component parallel to this plane, called the shearing stress τ {\displaystyle \tau } .