Manu with a Ball: Water Entry of Two Tandem Sphere

The popular diving maneuver in New Zealand known as “manu bombing” is not only fun for the loud sound it makes, but also creates quite the splash. This cannonball like dive is able to create an air cavity in the pool which displaces the water into the form of a jet, better known as a Worthington jet. When a manu is paired with a ball in hand, the ball can ride the jet into the sky. Though this is a fun trick to observe, there is no quantitative research on the criteria it takes to optimally transfer energy from the diver’s Worthington jet to the ball, until now. We can model the ‘manu with a ball trick’ as a water entry of two tandem spheres. The research conducted involves experimenting with two spheres aligned concentrically to obtain scaling laws, regime diagrams and predict the height of the top sphere. With these newly discovered scaling laws, future manu bombers will be able to enjoy bigger splashes and even higher-flying balls.