Elastic Collision
Definition
A collision in which both momentum AND kinetic energy are conserved — the objects bounce apart with no energy lost to heat or deformation.
Technical definition
A collision conserving both total momentum (Σmv) and total kinetic energy (Σ½mv²). Perfectly elastic collisions are rare at macroscopic scales; atomic and subatomic collisions (gas molecules, nearly billiard balls) approach the ideal.
Example
Two billiard balls colliding nearly elastically: one stops dead and the other takes off with almost all the energy — momentum and kinetic energy both carry over.
Common confusion
‘Elastic’ here does not mean stretchy like a rubber band — it means no kinetic energy is lost. A perfectly elastic collision is an idealization; even billiard balls lose a tiny fraction of energy as sound and heat.