(N/A) $(i)$ Ball moving without spin:
When a ball moves through a fluid without spinning,the streamlines of the fluid are symmetric above and below the ball. The velocity of the fluid at corresponding points above and below the ball is the same,which results in zero pressure difference according to Bernoulli's principle. Therefore,the air exerts no net upward or downward force on the ball.
$(ii)$ Ball moving with spin:
When a ball spins,it drags the air along with its surface due to viscosity. If the surface is rough,more air is dragged.
Consider a ball spinning clockwise as it moves through the air. On the side where the rotation is in the same direction as the airflow,the velocity of the air increases. On the opposite side,where the rotation opposes the airflow,the velocity of the air decreases.
According to Bernoulli's principle,regions of higher fluid velocity correspond to lower pressure,and regions of lower fluid velocity correspond to higher pressure.
Consequently,the crowding of streamlines above the ball indicates higher velocity and lower pressure,while the sparse streamlines below the ball indicate lower velocity and higher pressure. This pressure difference creates a net upward force on the ball,causing it to deviate from its straight path. This phenomenon is known as the Magnus effect.