Comments by "EebstertheGreat" (@EebstertheGreat) on "This Ball is Impossible to Hit" video.

  1. It's similar physics to the wiffle ball. The other factor is the seam. You can swing bowl by pointing the seam in the direction you want the ball to swing. When air hits the ball head-on, it will curve around it, forming a boundary layer. On one side, this boundary layer is laminar, and it quickly reaches zero velocity and separates from the ball. On the other side, air hits the seam, which induces turbulence. This turbulent boundary layer loses velocity more gradually and separates from the ball later, because velocity is constantly replenished by other layers of turbulent air. Because of this asymmetry, the air is exerting different forces on either side of the ball, and in different directions. One way to look at it is to consider the wake. If air is separating from the ball close to the front on one side and close to the back on the other, the wake will be pointing in the direction of that first side. So by Newton's third law, the ball must be accelerated in the opposite direction, toward the seam. For rough vs. smooth, the same principle is in effect, but it is the roughness of the ball causing the turbulence instead of (or typically in addition to) the seam. Apparently more complicated things happen at high speeds though.
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