PhySP18SS5.1.29 Conservation of momentum in a “strike” in pool. The initial momentum of the cue ball is transferred to all those numbered pool balls. No momentum is lost. It is all just transferred. That blew me away in college at first until, one night I was laying in bed staring at the ceiling and it finally hit me. MOMENTUM IS A VECTOR. Which simply means the big initial arrow of the cue ball (containing its mass and velocity) gets transfomed into 16 different arrows. How can this happen? Because much of those arrows cancel each other. Check out this picture. If you assume the cue ball is originally moving ONLY in the y direction, all the x components are going to cancel each other. All the final momentum y components will add up to the original momentum of the cue ball. I was so excited by my epiphany that I got out of bed and did a naked glorious jig in my bedroom.