Final answer:
Stress and strain are related quantities in physics that describe the response of a material to an applied force. They have a linear relationship within the linearity limit, but become nonlinear when stress exceeds this limit.
Step-by-step explanation:
Stress and strain are two related quantities in physics. Stress is the ratio of force to area, and it is measured in N/m². Strain, on the other hand, is the ratio of the change in length to length and is a unitless quantity.
Both stress and strain are related through the concept of elasticity. When stress is low, the deformation it causes is proportional to the stress value, and the proportionality constant is called the elastic modulus.
While stress and strain have a linear relationship within the linearity limit, they become nonlinear when stress exceeds this limit. In this case, the material exhibits non-elastic behavior.