<human>:  What is the difference between stress and strain?
<bot>: Stress is the amount of force per unit area. Strain is the change in length per unit length. The two terms are often confused, but they are different. For example, if you bend a piece of metal, the metal will stretch and the strain will be the change in length divided by the original length. The stress will be the force applied divided by the original cross sectional area.