Normal stress is a measure of the internal forces acting within a material when it is subjected to an external load. It is defined as the force applied per unit area and is typically expressed in units like Pascals (Pa) or pounds per square inch (psi). Normal stress can occur in two forms: tensile stress, which pulls the material apart, and compressive stress, which pushes it together. Understanding normal stress is crucial in fields such as engineering and materials science, as it helps predict how materials will behave under different loads. By analyzing normal stress, engineers can design structures and components that can withstand the forces they encounter during use, ensuring safety and reliability.