The Magnus effect (curved flight)

The first explanation of the lateral deflection of a spinning object was credited by Lord Rayleigh to work done by the German physicist Gustav Magnus in 1852. Magnus had actually been trying to determine why spinning shells and bullets deflect to one side, but his explanation applies equally well to balls. The mechanism that curves the flight of a ball in football is almost the same as in other sports; baseball, golf, cricket, tennis, etc.

When a ball is spinning about an axis perpendicular to the flow of air across it the air travels faster relative to the surface where the side of the ball is moving in the opposite direction to the airflow (bottom). The pressure is reduced because the air flow breaks away from the ball earlier than on the opposite side where laminar flow occurs. There is therefore an imbalance in the forces and the ball deflects.

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