Elastic collision
A collision in which kinetic energy is conserved (in addition to momentum). Both momentum and kinetic energy are conserved: Σp_before = Σp_after and ΣKE_before = ΣKE_after. Elastic collisions occur between hard objects like billiard balls, atoms, and fundamental particles.
Formula
Σ½mv² before = Σ½mv² after
Real World
Helium atoms bouncing off each other inside a sealed balloon behave as elastic collisions, which is why kinetic theory can predict gas pressure accurately.
Exam Focus
To prove a collision is elastic, calculate total KE before and after separately and compare — never assume without showing the calculation.
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