The “inertial mass” mi in the equation of motion to describe a carrier is usually m∗≠m0 where m0=9.1×10-31kg is the rest mass of an electron in free space. The aim of this paper is to study its “gravitational mass” mG and test the weak equivalence principle (WEP) mi=mG in condensed matter physics. First, the inertial forces in rotating systems are not 2miv×Ω and -miΩ̇×r. They should be 2mGv×Ω and -mGΩ̇×r. Secondly, we use the Sagnac effect and electromotive force (EMF) to determine the coefficient and compare with mi. Finally, the quantum energy levels caused by rotation are presented. The energies rely on the “gravitational mass”-to-“inertial mass” ratio mGmi=m0m∗≠1.