# The Magnus force

The Magnus force FM arises from an asymmetry in the flow field, while the air stream against a rotating and yawing body interacts with its boundary layer and applies at the CPM. Depending on the flow field, the CPM may be located ahead or behind the CG. The Magnus force vanishes in the absence of rotation and in the absence of a yaw angle.

The Magnus force is usually very small and mainly depends on bullet geometry, spin rate, velocity and the angle of yaw. In exterior ballistics, the above expression is used for the Magnus force.