The coefficient of restitution (COR) is a number that tells us how “bouncy” a collision is between two objects. It measures how much kinetic energy remains after they collide compared to before the collision.
When two objects collide, some of their kinetic energy might be lost as sound, heat, or deformation. The COR ranges from 0 to 1:
- A COR of 1 means a perfectly elastic collision where no kinetic energy is lost — the objects bounce off each other without losing speed.
- A COR of 0 means a perfectly inelastic collision where the objects stick together, and maximum kinetic energy is lost.
By comparing the relative speeds of the objects before and after impact, the COR helps engineers and scientists understand the efficiency of collisions in everything from car crashes to sports balls bouncing.