When a soccer player kicks the ball off-center, it as it flies. The spinning ball drags a thin of air around with it. On one , this air moves in the same as the passing air, while on the side it moves against it. The in air pressure pushes the ball , and its path . This is the Magnus effect, after the German who described it in 1852.

The Magnus effect appears in many sports. In tennis, players use topspin, in which the top of the ball rotates forward. The difference in air pressure pushes the ball downward, so a hard shot can clear the net and still drop inside the court. Table tennis players rely on the same principle, and in baseball, pitchers use different spins to make the ball move in ways that confuse batters.

Perhaps the most famous example in soccer came in 1997, when the Brazilian player Roberto Carlos took a free kick from about 35 meters out. At first the ball seemed to be heading far to the right of the goal; then it bent sharply back and went into the net. Scientists later explained that the kick combined great speed with strong spin.

The effect is not limited to sports. In the 1920s, the German engineer Anton Flettner built a ship powered by tall spinning cylinders instead of sails. As wind passed the rotating cylinders, the Magnus effect produced a force that moved the ship forward. The idea was not widely adopted, partly because engines running on cheap fuel were simpler, but rotor sails have recently returned on some cargo ships as a way to save fuel.