  We investigate why the non-slip boundary condition for the velocity, imposed
in the direction of impressed magnetic fields, can contribute to the magnetic
inhibition effect based on the nonhomogeneous magnetic Rayleigh--Taylor (abbr.
NMRT) problem in non-resistive magnetohydrodynamic (abbr. MHD) fluids.
Exploiting an infinitesimal method in Lagrangian coordinates, the idea of
(equivalent) magnetic tension, and the differential version of magnetic flux
conservation, we give an explanation of physical mechanism for the magnetic
inhibition phenomenon in a non-resistive MHD fluid. Moreover, we find that the
magnetic energy in the non-resistive MHD fluid depends on the displacement of
fluid particles, and thus can be regarded as elastic potential energy.
Motivated by this observation, we further use the well-known minimum potential
energy principle to explain the physical meaning of the stability/instability
criteria in the NMRT problem. As a result of the analysis, we further extend
the results on the NMRT problem to the stratified MHD fluid case. We point out
that our magnetic inhibition theory can be used to explain the inhibition
phenomenon of other instabilities, such as thermal instability, magnetic
buoyancy instability, and so on, by impressed magnetic fields in non-resistive
MHD fluids.
