Final answer:
The question relates to the physics concept of stress and deformation in materials. Stress is the force per unit area applied to a material. A material remains in elastic deformation up to the yield point, after which it undergoes plastic deformation and will not return to its original shape once the force is removed.
Step-by-step explanation:
The student's question relates to the point when materials begin to flow, or deform, in response to stress, which is a fundamental concept in the study of physics, particularly in the area of material science and mechanics. Stress is defined as the force (F) applied per unit area (A) of a material and is measured in units of Pascal (Pa) or N/m². When stress is applied to a material, it initially undergoes elastic deformation, where the material will return to its original shape when the load is removed. However, if the applied force exceeds a certain threshold, known as the yield point or yield value (f), the material will begin to endure permanent, plastic deformation and will not return to its original form even after the force is removed.
Materials vary in their response to applied stresses and exhibit different types of deformation behavior, which can be characterized by stress-strain curves. In the elastic region, the relationship between stress and strain is linear, but after a certain point, called the elasticity limit (E), the relationship becomes non-linear, and further loading leads to plastic deformation until eventually the material reaches its fracture point.
This concept is closely related to Hooke's Law, which describes the initial proportional relationship between stress and strain (stress = Y x strain) for small, elastic deformations. Beyond the yield point, however, materials may behave non-linearly, and this relationship no longer holds. Engineers and scientists must understand these principles when designing with materials to ensure that structures can withstand the forces they will experience without failing.