Fluid movement

Need help to understand 8ii and b

8ii - think about direction of motion of surface of ball relative to fluid passing close to surface at top and bottom of ball, respectively.

8b - think about conservation of momentum.

This is the Magnus Effect.

https://en.wikipedia.org/wiki/Magnus_effect

I think any reasonable explanation based on the given information would get you the single mark

The force on the ball is because the ball is causing a net acceleration of the air in its wake in one direction (upwards in the diagram). air has mass and Newton tells us with his laws that you can't have a 'free push' on anything with mass - even air. so there must be an equal push on the ball in the opposite direction.

8B - due to the effective downward component of force due to spin of the ball, as the air passing the ball is downstream now due to the crosswind

8ii - think about direction of motion of surface of ball relative to fluid passing close to surface at top and bottom of ball, respectively.

8b - think about conservation of momentum.

8ii - First of all the direction of ball spin is in counterclockwise direction and the ball is moving to the left. The air flow is towards the right. As the air particles come in contact with the ball, a wake region is formed on the right of the ball. Within this wake region, any air particles will come in contact with the surface of the ball and the flow of air will be changed from laminar to turbulent due to the spin of the ball and the surface. The reason why there's more turbulent region of air on the top of the ball is due to opposite net effect of ball spin at the top as it is causing the air to move to the left. At the bottom the air particle in contact with ball's bottom surface is moving in the same direction as the air flow hence you will see less turbulence effect. This is as simple as it gets


Part B - As the air particle is in contact with the top or bottom surface, the will be an component of force acting downwards as the air particle hits to either left or right corners of the ball, leading to a downstream of air flow. The direction of this force is acting downwards.

This is the Magnus Effect.

https://en.wikipedia.org/wiki/Magnus_effect

I think any reasonable explanation based on the given information would get you the single mark

The force on the ball is because the ball is causing a net acceleration of the air in its wake in one direction (upwards in the diagram). air has mass and Newton tells us with his laws that you can't have a 'free push' on anything with mass - even air. so there must be an equal push on the ball in the opposite direction.

Thankyou much appreciated