The difference between roof jump and carriage jump: the people in the carriage are stationary relative to the train, so if you jump on the floor, it is not easy to change and still fall at the origin. The roof of the car reduces the speed of people's lateral fitness exercise. If it is lower than the train speed, it will fall behind the take-off point.

Physics:

Physics is a subject that studies the most common laws of motion and the basic structure of matter. Physics, as the leading discipline of natural science, studies the most basic motion forms and laws of all substances from the universe to elementary particles, so it has become the research basis of other natural science disciplines. Physics began in the era of Galileo and Newton, and now it has become a basic science with many branches. Physics is an experimental science, and it is also a science that advocates rationality and attaches importance to logical reasoning.