Which property of a material allows it to resist a change in shape or size when a load is applied?

The property of a material that allows it to resist a change in shape or size when a load is applied is stiffness. Stiffness is a measure of how much a material deforms under a given load; it reflects the ability of the material to maintain its original shape when subjected to external forces. The stiffer a material, the less it tends to deform or change its shape when a load is applied, making it a critical factor in engineering applications.

While elasticity refers to a material's ability to return to its original shape after removing the load, stiffness specifically addresses the extent to which a material resists deformation. This means that a material may be elastic yet not very stiff, as it can deform significantly while still returning to its original shape.

Plasticity is the property that describes how a material can undergo non-reversible deformation when the yield strength is exceeded, and toughness indicates a material's ability to absorb energy and plastically deform without fracturing. However, neither of these properties directly relates to resisting deformation under load in the same way that stiffness does.

Understanding stiffness is essential for designing structures and mechanical systems, as it helps ensure that components can support the expected loads without undergoing unacceptable deformation.