Explain why objects moving in fluids must have special shapes.

When a body moves through a fluid, it experiences an opposing force which tries to oppose its motion through the fluid. Example, aeroplane in air, birds, ships in water etc.

This opposing force is known as the drag force. By giving objects a special shape, as shown in figure.

The force of friction acting on it can be minimized. Hence, it becomes easier for the body to move through the fluid.