Within the framework of the drift theory and ideal magnetohydrodynamics (MHD), we consider the analogy between gravitation and effects of the curvature of the magnetic field lines (rule of correspondence) which are used in astrophysical applications for estimation of a growth rate of the flute type instability. On the basis of the linearized MHD equations, an analytic expression for the change in potential energy of a system with the sharp plasma—plasma boundary is obtained. It is shown that the MHD forces determine the development of the surface flute type instability. Conditions of application of a rule of correspondence is discussed.