The formula for strain is change in length divided by original length. What does this measure?

The formula for strain is defined as the change in length divided by the original length. This measurement expresses how much a material deforms in response to applied forces, regardless of whether the material is being compressed or stretched.

Strain is a dimensionless quantity that can be valid for both compressive and tensile loading, as it quantifies the relative deformation of the material. It does not differentiate between the type of loading but rather informs us about the deformation that occurs in response to those loads.

The correct understanding of this concept is that strain fundamentally describes how materials react to all types of loads. Young's modulus, which is a property of material that indicates its stiffness, is derived from the ratio of stress (force per unit area) to strain in the linear elastic region of a material's stress-strain curve. However, strain itself is independent of the specific type of loading, making it suitable to measure deformation due to either compressive or tensile forces.

Thus, while the question may suggest a specific relationship to Young's modulus, strain itself measures deformation that can apply to both types of loading scenarios. The answer reflecting both compressive and tensile loading provides a more comprehensive understanding of strain in different contexts.