main

Commentary

The Magnus Effect

September 3, 2010 — by Sean

A new article on the physics of free kicks linked back to this gem of a piece from a 1998 issue of Physics World. The Roberto Carlos strike in question is still one of the most fantastic goals ever recorded.

Head over to the Physics World site for the full article. And just to whet your whistle:

The drag force, FD, on a ball increases with the square of the velocity, v, assuming that the density, r, of the ball and its cross-sectional area, A, remain unchanged: FD = CDrAv2/2. It appears, however, that the “drag coefficient”, CD, also depends on the velocity of the ball. For example, if we plot the drag coefficient against Reynold’s number – a non-dimensional parameter equal to rv D /μ, where D is the diameter of the ball and μ is the kinematic viscosity of the air – we find that the drag coefficient drops suddenly when the airflow at the surface of the ball changes from being smooth and laminar to being turbulent