In which condition we apply special theoy of relativity

it is based on two postulates:
(1) that the laws of physics areinvariant(i.e. identical) in allinertial systems(non-accelerating frames of reference)
(2) that the speed of light in avacuumis the same for all observers, regardless of the motion of the light source
it only applies in thespecial casewhere thecurvatureofspacetimedue togravityis negligible.