Elasticity is the ability of a solid to return to its original shape and size after it has been deformed by a force. All solids have some elasticity. Familiar materials that have elasticity include the steel in automobile springs and the rubber in basketballs.
Solids return to their original shape and size if the stress (deforming force per unit of area) does not exceed a value called the elastic limit. If the stress applied to a solid exceeds the solid’s elastic limit, the solid will not return to its original shape after the stress has been removed. In the inch-pound system of measurement customarily used in the United States, stress is measured in pounds per square inch. In the metric system, pascals (newtons per square meter) are used to measure stress (see Pascal).
Stress is related to strain. Strain measures how much a given dimension of a solid changes under stress. In many solids, including metals and minerals the stress below the elastic limit is in direct proportion to the strain. The greater the stress, the greater the strain. The ratio of stress to strain, called the elastic modulus, is a measure of how well a solid resists deforming forces. A solid with a high elastic modulus, such as steel, has a stronger resistance to stress than a solid with a low elastic modulus, such as rubber.
