垂直（法向）作用于某一平面的应力。（在此用法中，"法向"并不表示"通常"或"常见"。）正应力可以是拉应力，也可以是压应力。
A stress that acts perpendicular (normal) to a plane. (In this useage, "normal" does not imply "usual" or "common".) Normal stresses can either be tensile or compressive.