The coefficient of restitution (COR) is a measure of the elasticity of collisions between two objects. It quantifies how much kinetic energy remains for the objects after they collide, specifically in terms of their velocities before and after the collision.
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The restitution law applies to velocities of the actual contact points, including any rotational velocities of rigid bodies. A perfectly elastic collision has ; gives zero immediate normal separation speed, but does not by itself require all parts of colliding bodies to share the same velocity.
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