Set up Invariable Axiom of Force Equilibrium and Solve Problems about Transformation of Force and Gravitational Mass

Invariable axiom of force equilibrium is set up according to the common knowledge that force equilibrium is independent of observers. The transformation formulas of force in different inertial system are derived and the validity of these transformation formulas is affirmed via deducing the electric-field distribution of high speed moving charge. And through deduction, conclude that the gravitational mass of an object is not equal to its inertial mass.