This is a question about the conservation of momentum:
If there were a cluster of billiard balls floating in space and the cluster was struck by one moving ball, the cluster balls would scatter in random directions and they would move with a velocity in proportion to their mass and the P transferred from the striking ball. The first cluster ball(s) struck by the moving ball would collide with other balls in the cluster and those would collide with other balls, etc. There would be a "chain reaction" of collisions. I understand this so far.
I also understand that the sum of the cluster balls' mass and velocity are equal to the mass and velocity of the striking ball. My question is: how is the linear momentum is conserved if the cluster balls move in scattered vectors (i.e., not in the direction of the striking ball's movement)?