Define the limit of proportionality in the context of stretching an elastic material.

The limit of proportionality is the maximum extent to which an elastic material can be stretched while still obeying Hooke's law, where the extension is directly proportional to the applied force. Beyond this limit, the material will not return to its original length.

This answer effectively defines the limit of proportionality and connects it to Hooke's law, demonstrating a clear understanding of the relationship between force and extension in elastic materials. The question assesses the student's ability to recall and explain key physics concepts.