pingpong_slide1

When a ball is dropped into a puddle, momentum is exchanged between the impacting ball and the surrounding fluid, decreasing the rebound height. At impact, a radial jet and splash curtain are formed as fluid is instantaneously displaced by the falling ball. During rebound, the splash curtain is drawn in and a column of fluid is pulled upward. The formation of the fluid column is a manifestation of this beautiful momentum exchange. The gravitational force overcomes the inertia acting on the fluid column forming a pinch off point close to the ball (not shown) [1]. The now unre- strained ball continues to rise. As the fluid column falls, perturbations caused by pinch off give way to a Rayleigh-Plateau instability that propagates downward, eventually separating the column from the puddle. These images depict this momentum exchange with a ping pong ball falling into a puddle of water.