  We conclude that Special relativity effects are caused by a period of
acceleration in the past, before they are measure in uniform velocity. This can
be regarded as extension of the equivalence principle of General Relativity.We
define the notation tp for the acceleration time in the past and formulate the
equations for : space-time,velocities additions, mass and energy. The equations
give in some cases different results from the usuall special relativity.Our
results are obtained by experiments like Hafele and Kaeting experiment. We
deduce the existence a cosmological frame we call : Universal Inertial Frame.
