What does the Magnus effect describe?

The Magnus effect refers to the phenomenon that occurs when a spinning object moves through a fluid, which can be a gas or liquid. The rotation of the object creates a difference in pressure on either side of it, leading to a force that acts perpendicular to the direction of the object's velocity. This effect is particularly significant in sports, such as how a spinning soccer ball curves in the air or how a baseball can gain lift and change direction due to its spin.

In this context, the correct option highlights that the Magnus effect is specifically related to an object that is both spinning and traveling through a viscous fluid. This understanding is essential for pilots and instructors as it can influence the behavior of aircraft and other objects moving through the atmosphere, where air acts as the viscous fluid.