We watch sports everyday. Whether we’re watching David Beckham whipping in a free kick or Roger Federer smashing a topspin winner, we’re baffled by how the ball moves in the air, and so are their opponents!! Whether it is tennis, football, golf or baseball the Magnus effect is a crucial concept. This effect was discovered by its namesake Gustav Magnus when he was analyzing why cannonballs veered off their expected trajectories in the air. 
Consider the above depicted spherical object moving in the air. The object’s translatory motion is from left to right in the picture. The stream of air is flowing around the object in a direction opposite to its translation resisting it’s motion. This air resistance is experienced by any moving object. The object itself is rotating on an axis passing through its center in the clockwise direction.
Now we see that the stream of air along the lower surface is flowing in the same direction as the rotation of the object causing it to move along faster. The air closer to the surface gets pulled around the surface of the object rather than travelling in its straight stream-lined path.
The air flowing along the upper surface is opposed by the rotation of the ball slowing it down. Then the air getting pulled along the object’s surface exerts an upward force on the upper air stream. By Newton’s Third Law, every action has an equal and opposite reaction. Hence the air exerts an equal and opposite force known as the Magnus force in the downward direction as indicated in the diagram.
All ball games are dependent, even governed, by this powerful phenomenon. So a golfer would strike the bottom of a golf ball giving it a back spin, producing a magnus force in the upward direction hence giving the ball lift. A tennis player strikes the top of the ball giving it a top spin, producing a magnus force in the downward direction causing it to dip faster than the opponent would expect. Curling a football, swinging a cricket ball, pitching a baseball, serving a volleyball, they’re all based on this simple yet wonderful concept.
