Coefficient of Restitution

The ratio of separation speed after a collision to approach speed before it — a measure of how bouncy the impact is.

The coefficient of restitution is an empirical parameter describing how elastic a collision is, usually written e, and it traces back to Newton's laws of impact: e equals the relative separation speed of the two bodies after the collision divided by their relative approach speed before it. e = 1 is a perfectly elastic collision with no kinetic-energy loss; e = 0 is perfectly inelastic, with no bounce at all; real collisions fall somewhere in between. In robotics it shows up mainly in two places: modeling the impact when a legged robot's foot lands or a gripper grasps an object, and as a material parameter in physics engines — Isaac Lab's rigid-body materials include a restitution value alongside static and dynamic friction coefficients, and training runs commonly randomize all three together so the policy doesn't overfit to one particular bounciness of ground or object.

ExampleA ball dropped from 1 m and bouncing back up to 0.64 m has e = √(0.64/1) = 0.8. Isaac Lab's randomize_rigid_body_material function samples static friction, dynamic friction, and restitution randomly within given ranges.

Also called

COR, Restitution

Related

Impact · Physics Engine · Contact Model · Domain Randomization · Dynamics Randomization · Friction Coefficient (Coefficient of Friction)

Sources

Wikipedia: Coefficient of restitution
Isaac Lab API: isaaclab.envs.mdp（randomize_rigid_body_material）
Isaac Lab API: isaaclab.sim.spawners（RigidBodyMaterialCfg.restitution）