Bounce

Bottle Setup

No Bounce

Bounce

Ball does not bounce if bottle is not allowed to bounce.

My current hypothesis is that the container bounces up right after hitting the table and in turn causes the water and hence the ping pong ball to bounce upwards.  If I bring the bottle down hard, but without letting it bounce up, then the ball does not fly upwards.  The ball bounces higher than if it were bounced on a hard surface, so the motion of the water is contributing to the energy of the ball.  The ball must be centered to bounce high, which is where the motion of the water is the greatest.