  Inertial mass of a skyrmion arising from spin-phonon interaction is computed
exactly within a toy model of the magnetoelastic coupling in a ferromagnetic
film. The mass scales as the square of the strength of the magnetoelastic
coupling, as the square of the film thickness, and as the first power of the
lateral size of the skyrmion. For nanometer skyrmions it is in the ballpark of
a few electron masses but may be significantly greater in materials with large
magnetostriction. These findings are expected to stand for any complex
structure of spin-phonon interaction in real materials. They must be taken into
account when addressing the speed of information processing based upon
skyrmions.
