13.【运动的描述】x-t图像

....................../´¯/)

....................,/¯../

.................../..../

............./´¯/'...'/´¯¯`·¸

........../'/.../..../......./¨¯\

........('(...´...´.... ¯~/'...')

.........\.................'...../

..........''...\.......... _.·´

............\..............(

..............\.............\..