Phenomenological surface inertia in the MIT bag model

A phenomenological kinetic-energy term for the surface of the MIT bag is added to the Hamiltonian, and its consequences are studied for light-quark systems and heavy-quark systems. The value of the surface inertia must be less than approx.0.2 GeV in order to avoid a fifth S state in the portion of the UPSILON spectrum in which only four have been observed.