How does the curve ball drag air around it? In cricket or baseball there is a type of ball called the curve ball.

This is the top spin of the ball.I read that due to spin the ball drags the air around it due to friction in the way shown above.Can you please explain why??
 A: In this case, fluid molecules near the surface of the ball, to good approximation, are essentially dragged along with the local surface motion.  The reason the fluid is dragged along is that the ball surface on a molecular level is not perfectly smooth.  You can read about Brownian motion if you want to understand this more in detail.  Near the surface, in the boundary layer, the physics driving fluid motion is dominated by viscous forces.  The arrows that are drawn in your diagram are more appropriate for describing the fluid motion outside of the boundary layer, which is governed by pressure and momentum.
A: Extending on the answer of SimpleLikeAnEgg;
Magnus effect(http:/en.m.wikipedia.org/wiki/Magnus_effect) would work for rotating body and like friction the viscous force (also a type of fricton) would cause the effect of curve ball dragging force.
What happens is that the part of the ball having velocity(tange bntial velocity due to rotation) in direction of motion of ball would then have a resulting velocity greater than that on the other side where there is velocity in opposite directions, due to this effect the air friction (viscous drag/air drag) would be different on the two parts of the ball, similarly due to action-reaction force the friction on nearby air would also be different. Since air is not fixed like ground, it moves under the influence of this friction and as a result we get magnus effect resulting in curve balls dragging air, and producing little alterations in vertical acceleration (due to lift related phenomenon)
