Man jumps into a lake with a ball and the ball propels out In this video, a man throws up a ball and then jumps into a lake immediately followed by the ball. The ball then rockets out of the water with a tremendous speed. How does this happen?
My assumption was that the man jumps, breaking the surface tension of the water, and then hits the ball with his full power, such that his force and the water’s the buoyancy propel the ball upward.
However, many people in the comments believe that it is purely the pressure of the water that gave it such a high velocity. Is this correct?
 A: By hitting the water, the man displaces a lot of water, creating a hole in the water. Water rushes back from the sides, gaining momentum. Once the hole is filled, the water still has momentum and thus jets upward, having no other place to go. This jet hits the ball propelling it upwards.
Since the ball is much lighter than the man, you only need to transfer a fraction of the man’s initial positional energy to the man to propel it upwards that much.
I assume that you need several attempts to get this one right, which is arguably the main part of the trick: It’s not surprising that a person jumping into water causes considerable local water jets. You can see similar effects in slow-motion videos of stones dropping into water, e.g. this one. The surprising thing is that such a jet exactly hits the ball in the right moment. This surprise becomes diminished if you consider that you can just repeat the trick until you get it right.
Looking at the video in slow-motion confirms this: The man jumps directly underneath the ball (such that the water surge will hit the ball); you can see the hole in the water and how it is filled and this is finished in just about the time that the ball hits the water.
In addition, the man may hit the ball, but I consider that unlikely.
Buoyancy cannot account for what you see: At most the ball can bounce up as high as its highest point in the initial throw. Surface tension certainly doesn’t play a role in this.
