Elastic and inelastic collisions

Science

Definition

In elastic collisions, both momentum and kinetic energy are conserved, and objects bounce apart. In inelastic collisions, momentum is conserved but kinetic energy is not—some energy is converted to heat, sound, or deformation. A perfectly inelastic collision is one where the objects stick together.

Examples

  • Two billiard balls colliding approximate an elastic collision
  • A car crash where the vehicles crumple is an inelastic collision—kinetic energy converts to deformation
  • Two clay balls that stick together after colliding is a perfectly inelastic collision
Key Fact

Elastic: KE conserved (KE_before = KE_after); Inelastic: KE not conserved; Perfectly inelastic: objects stick together (maximum KE loss).

Related Terms

Collisions Conservation of momentum Kinetic energy Impulse and momentum

Study This Concept

Practice elastic and inelastic collisions with free review games in these units:

AP Physics 1 Unit 4: Linear Momentum and Collisions