In mechanics, stress is defined as the internal resistance force acting within a deformable body per unit cross-sectional area. Quantitatively, it is calculated as the applied force divided by the area over which that force acts. The nature of stress determines how a material will deform, and types include tensile stress, which attempts to pull a body apart, and compressive stress, which attempts to squeeze it together. Stress analysis is critical for determining structural integrity, as the magnitude of the stress, in conjunction with the material's properties, dictates whether the structure will undergo plastic deformation or fail entirely.