inelastic

Inelastic is an adjective used in science and economics to describe responses that do not readily reverse or change under a given stimulus. In common usage it contrasts with elastic, which implies a return to original state after a disturbance.

In physics, an inelastic process involves a loss or transformation of kinetic energy to other forms of energy, such as internal energy, heat, or deformation. Inelastic collisions conserve momentum but not total kinetic energy; some energy is absorbed by the bodies or converted to deformation. The degree of inelasticity is often described by the coefficient of restitution, e, defined as the ratio of relative speeds after and before impact along the line of contact. When e = 1 the collision is elastic; when e = 0 the bodies stick together, a perfectly inelastic collision. Inelastic deformation refers to permanent changes in shape or structure that do not fully recover when the applied force is removed.

In economics, inelastic refers to a market response where quantity demanded or supplied changes little in response to price changes. Price elasticity of demand, for example, measures this sensitivity; a demand is considered inelastic when the absolute value of elasticity is less than one. Examples include essential goods or goods with few substitutes. Elasticity can vary with time, income, and the availability of substitutes, with many goods becoming more elastic over longer horizons.

Other related concepts include inelastic scattering in physics, where incident particles exchange energy with a target, altering the outcome such as wavelength or energy states. Inelasticity thus denotes processes with irreversible or non-recoverable changes in energy or quantity.