Fluid forces should be included for motion in water and for high velocity motions

It is low speed and the fluid hugs the object whilst the downstream flow is smooth

Occurs at higher speeds and is the flow that separates from the surface of the object and the wake contains eddies

As the velocity of a fluid increases, the pressure in that region decreases. High velocity= low pressure Low velocity= high pressure

It is always 90 degrees to the fluid force and is not necessarily always vertical.

It acts in the same direction that the fluid is moving relative to the object

The motion of the object in the air and its behaviour when it hits the surface

The ball makes a downward force on the air. By reaction the air makes a upward lift force on the ball- a magnus force

The buoyancy force is equal to the weight of the fluid displaced. The centre of buoyancy is nearer the head than the COM. The buoyancy force generates a torque about the centre of mass