Collisions

Science

Definition

Collisions occur when two or more objects exert forces on each other over a short time interval. In all collisions, total momentum is conserved. Collisions are classified as elastic (kinetic energy conserved) or inelastic (kinetic energy not conserved).

Examples

  • Billiard balls hitting each other approximate elastic collisions where both momentum and kinetic energy are conserved
  • A car crash is an inelastic collision—the vehicles crumple, converting kinetic energy to heat and deformation
  • Newton's cradle demonstrates conservation of both momentum and kinetic energy in elastic collisions
Key Fact

In all collisions: m₁v₁ᵢ + m₂v₂ᵢ = m₁v₁f + m₂v₂f (conservation of momentum).

Related Terms

Conservation of momentum Elastic and inelastic collisions Impulse and momentum Kinetic energy

Study This Concept

Practice collisions with free review games in these units:

Physics Unit 4: Momentum and Collisions