Bounciness

Bounciness is the tendency of a body to rebound after a collision. In physics and engineering, it is usually quantified by the coefficient of restitution, e, a dimensionless value between 0 and 1. A value of 0 corresponds to a perfectly inelastic collision where no rebound occurs, while a value of 1 corresponds to a perfectly elastic collision in which all normal components of relative velocity are restored. In practical terms, bounciness can also be described by bounce height: after dropping from a height h0, a body may rise to height h1, with h1 approximately equal to e^2 h0 when air resistance is negligible.

The bounciness of an object arises from how it stores and releases energy during impact. When the bodies deform, part of the kinetic energy is converted into elastic potential energy and then returned during rebound. Real objects also dissipate energy as heat, sound, or internal friction, reducing bounciness below that of an ideal elastic collision.

Factors that influence bounciness include material elasticity, surface hardness, and the amount of energy lost to deformation. Impact conditions—such as speed, angle, and alignment of the contact area—also matter. Temperature, wear, contamination, and surface texture can alter effective elasticity. Soft, highly elastic materials (e.g., rubber) tend to have higher e values, while stiff or damped materials, or rough surfaces, tend to be less bouncy. Air resistance and spin can modify the observed bounce as well.

Applications of bounciness considerations appear in sports equipment design, material testing and quality control, robotics and physics education, and safety analyses for vehicles or protective gear.