The point of the longitudinal axis, at which the resulting wind force F1 appears to attack is called the centre of pressure CPW of the wind force (see figure), which, for spin-stabilized bullets is located ahead of the CG. As the flow field varies, the location of the CPW varies as a function of the Mach number. Due to the non-coincidence of the CG and the CPW, a moment is associated with the wind force. This moment MW is called overturning moment or yawing moment (see figure). For spin-stabilized projectiles MW tends to increase the yaw angle and destabilizes the bullet. In the absence of spin, the moment would cause the bullet to tumble:
