Abstract: In the study of special relativity, “simultaneous relativity” is a difficult point, and beginners are easily confused when transforming time and space between different reference frames. Especially deeply rooted daily experiences can bring a lot of confusion to the understanding of “simultaneously”. This paper designs two spacecraft flying towards each other and an observer on the ground. By comparing the clock timings of the three spacecraft, the common difficulty in understanding “relativity of simultaneity” in learning is demonstrated. In the analysis of the case, not only detailed calculations were carried out in different reference frames through Lorentz transformation, but also the effect of the principle of the constancy of the speed of light was intuitively demonstrated through the flashing experiment of the clock.

Key words: special theory of relativity, simultaneous relativity, teaching