Abstract: By taking relativistic effect into account,the elastic collision between two particles with equal rest mass,one of which is initially in the stationary state,is studied.It is shown that in the case of central collision,two particles will exchange their speeds after collision,which is the same as the result obtained based on the classical mechanics.However,for the case of non-central collision,the included angle between the speeds of two particles after collision is a sharp angle,which is different from the result obtained based on the classical mechanics.

Key words: relativistic effect, elastic collision