inelasticity

Inelasticity denotes a property or behavior in which a system's response to an applied stimulus is neither proportional nor fully reversible. The term appears in physics, materials science, and economics to describe phenomena where energy dissipation, permanent deformation, or reduced responsiveness occur relative to the input.

In physics, an inelastic collision is one in which kinetic energy is not conserved, though momentum remains conserved. After impact, bodies may collide and stick together or separate with reduced velocity. The degree of inelasticity is commonly described by the coefficient of restitution, e, which ranges from 0 (perfectly inelastic) to 1 (perfectly elastic). The missing kinetic energy is converted to heat, sound, or deformation energy.

In materials science, inelastic behavior includes plastic deformation, where permanent shape change remains after the load is removed, and viscoelastic or damping responses, which depend on time or loading rate. Materials exhibit a yield point beyond which unloading does not retrace the original path. Inelasticity is important in processes such as forging, stamping, and creep in polymers and metals.

In economics, price inelasticity describes a limited change in quantity demanded or supplied when price changes. Price elasticity of demand is the percent change in quantity demanded divided by the percent change in price. If the absolute value is less than one, demand is inelastic. Determinants include whether a good is a necessity, the availability of substitutes, its share of a consumer's budget, and the time available to adjust.