When a force greater than the static friction between body B and the floor, and also greater than the static friction between body A and B, but less than their sum, is applied to B, it will begin to move. Once B starts moving, the situation shifts to kinetic friction, which is typically lower than static friction. The net force acting on B will be the applied force minus the kinetic friction force. If this net force exceeds the static friction between A and B, then A will also begin to move backwards. Therefore, the relationship between static and kinetic friction is crucial in determining the motion of both bodies.