In a collision, if the colliding objects deform and then remain in the deformed shape, the collision is INELASTIC. Inelastic collisions are typically characterized by objects hitting and sticking to one another. In ELASTIC collisions, objects spring back to their original shapes. A glass bead bouncing off a steel plate is highly elastic. Putty hitting the same steel plate deforms and does not return to its original shape (it also doesn't bounce) and is hence an inelastic collision.

Collisions - Elastic
Conservation of Energy
Conservation of Momentum

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