does the ball swing towards the shiny side
When the ball is older and there is an asymmetry in roughness the seam no longer causes the pressure difference, and can actually reduce the swing of the ball. Air turbulence is no longer used to create separation point differences and therefore the lift and pressure differences. On the rough side of the ball there are scratches and pits in the ball's surface. These irregularities act in the same manner as the dimples of a golf ball: they trap the air, creating a layer of trapped air next to the rough side of the ball, which moves with the surface of the ball. The smooth side does not trap a layer of air. The next layer of air outward from the ball will have a greater velocity over the rough side, due to its contact with a layer of trapped air, rather than solid ball. This lowers the static pressure relative to the shiny side, which swings the ball. If the scratches and tears completely cover the rough side of the ball, the separation point on the rough side will move to the back of the ball, further than that of the turbulent air, thereby creating more lift and faster air flow. This is why a new ball will swing more than an old ball. If the seam is used to create the turbulent air on the rough side, the tears will not fill as quickly as they would with laminar flow, dampening the lift and pressure differences.
Swing bowling