In any kind of collisions, we always have conservation of linear momentum, whereas, we do not necessarily always have conservation of energy. Types of collisions: ​

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• Elastic collisions: Total momentum and total kinetic energy are both conserved: Total momentum before collision = Total momentum after collision ; Total kinetic energy before collision = Total kinetic energy after collision.

• Inelastic collisions: Total momentum is conserved but total kinetic energy is not conserved; the bodies separate after the collision. Some of the total kinetic energy is dissipated to sound, heat and/or permanent deformation of the bodies. Total momentum before collision = Total momentum after collision; Total kinetic energy before collision ≠ Total kinetic energy after collision. 

• Perfect inelastic collisions: The bodies stick together after the collision and move with a common speed v. Total momentum before collision = Total momentum after collision; Total kinetic energy before collision ≠ Total kinetic energy after collision. Some of the kinetic energy is dissipated to sound, het and/or permanent deformation of the bodies. 

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