我們日常生活裏所看到的東西,没有一樣是老在動的,除非是受了外界的影響。例如風車,沒有風就停了;又如馬達,没有電也就停了。汽車火車,誰都知道沒有汽油或煤是動不了的。騎脚踏車,我們必須動腿,除非是下坡。球在地上滾,也許可以滾得很遠,但最終還是要停下來。鐘的擺倒是 Nothing we see in our daily lives is always moving unless it is influenced by the outside world. For example, a windmill stops when there is no wind; if it is a motor, it stops without electricity. Everyone in the car train knows that there is no gasoline or coal that cannot be moved. To ride a bicycle, we must move our legs unless it is downhill. The ball is rolling on the ground and may be able to roll far, but it will eventually stop. The swing of the clock is