ANALYSIS AND COMPARISON OF SEVERAL DERIVATION METHODS OF MOTION MASS IN THE TEACHING OF SPECIAL THEORY OF RELATIVITY

In the teaching of special relativity, the derivation of motion mass is one of the core and difficult points. Current university physics textbooks often derive the formula for the mass of motion based on the processes of “two particle aggregation” or “single particle splitting”, which generally rely on the assumption of “conservation of mass”. However, at this stage, students only have knowledge of Lorentz transformation and relativistic velocity transformation, and have not yet been exposed to the relationship between mass and energy. They have a strong confusion about the contradiction of “mass changing with velocity but still conserved”. If the assumption of supporting the relationship between quality and energy is introduced in advance, it will undermine the rigor and coherence of the teaching logic, and reduce the persuasiveness of the deduction. In response to this issue, this article first rigorously derives the mass conservation relationship before and after particle splitting through coordinate system transformation; Furthermore, a simple derivation method is proposed that does not rely on specific physical processes and does not presuppose the conservation of mass and the relationship between mass and energy. This method only uses the definition of centroid velocity and the formula for relativistic velocity transformation to derive the relativistic mass formula. The derivation is simple, logically clear, and easy to understand, which is more in line with the teaching logic sequence of special relativity and helps students establish a correct relativistic spacetime view.