A stone on a string can move in uniform circular motion.
拴在绳子上的石头可以做匀速圆周运动。
In uniform circular motion, the speed is constant, but the velocity changes direction, so there must be centripetal acceleration toward the center.
在匀速圆周运动中,速率恒定,但速度方向不断改变,因此必然存在指向圆心的向心加速度。