Explosion

•  Explosion is a phenomenon in which only internal forces are involved.
•  Nature of these forces are non conservative so just before and just after the explosion we can conserve the momentum of the system but we cannot conserve total mechanical energy of the system. 
• In all explosion kinetic energy of the system will always increase. Already external force by gravitational and frictional we can conserve linear momentum because magnitude of the process can be negative during explosion