It has always been explained to me that balls curve because a thin layer of fluid adheres to its surface as a boundary layer. This boundary layer retards the flow on one side of the ball and speeds it on the other. And then Bernoulli's principle is applied to make the pressure difference happen. But recently I have read that Bernoulli's principle plays little part in this effect because Bernoulli's principle cannot be applied to viscid flows which is essentially what is happening at the surface of the ball. The effect is instead explained with mass diversion which seems more logic. So if anyone is able to give a more thorough explanation of this effect and explain what part Bernoulli's principle actually plays, it would be greatly appreciated.