Stress: The simplest definition of stress is that stress is equal to force per unit area. Therefore, the
units of stress are pounds per square inch or newtons per square meter (pascals). However, stress is
not a single value. There are normal stresses in all three directions. Normal stresses cause a material
to stretch or contract. There are also shear stresses in all three planes. Shear stresses cause a
material to warp or distort. These six stress components are often combined to find principal
stresses.