The Magnus effect is the name given to the physical phenomenon whereby an object's rotation affects its path through a fluid, in particular, air. It is a product of various phenomena including the Bernoulli effect and the formation of boundary layers in the medium around moving objects.

A spinning object creates a kind of whirlpool of rotating air about itself. On one side of the object, the motion of the whirlpool will be in the same direction as the windstream that the object is exposed to. On this side the velocity will be increased. On the other side, the motion of the whirlpool is in the opposite direction of the windstream and the velocity will be decreased. The pressure in the air is reduced from atmospheric pressure by an amount proportional to the square of the velocity, so the pressure will be lower on one side than the other causing an unbalanced force at right angles to the wind.

It is often referred to in the context of explaining otherwise mysterious but commonly observed movements of spinning balls in sport, especially golf, baseball, football and cricket. It is worth noting, however, that the Magnus effect is not responsible for the movement of a cricket ball seen in swing bowling.

German physicist Heinrich Magnus first described the effect in 1853.

External links

The Magnus Effect: or, Why do cricket balls swing and curveballs curve?