Final answer:
The force-extension graph for rubber shows linear behavior (Hooke's law) up to the linearity limit, then becomes nonlinear but still elastic up to the elasticity limit. The area between the loading and unloading curves represents the energy stored in the material. Beyond the elasticity limit, permanent or plastic deformation occurs.
Step-by-step explanation:
The force-extension graph for an elastic material like rubber illustrates how the material responds to increasing and decreasing forces within its elastic limit. Initially, the graph depicts a linear behavior, following Hooke's law, where the deformation (ΔL) is directly proportional to the applied force (F). This linear relationship continues until the material reaches its linearity limit at point H.
Beyond point H and before reaching the elasticity limit at point E, the graph becomes curved, indicating a nonlinear elastic region. The deformation is still fully recoverable if the force is removed—the rubber band would return to its original length, indicating its elasticity. When the load is removed at any point before E, the curve retraces its path back to the origin.
The area between the loading and unloading lines is significant, as it represents the energy stored in the material during deformation, which is released upon deloading. Past the elasticity limit (E), permanent deformation or plastic deformation occurs, signifying that the material will not return to its initial state when the force is removed. Beyond the elasticity limit, the material ultimately reaches its fracture point, concluding its behavior on the graph.