月球引力造成海平面周期性上升、降落、进退的现象叫做海洋潮汐，进时为潮涨，退时为潮退，是自然现象。
她在潮涨时被困住了。
牛顿认识到，为了使物体运动，无论是一个苹果从树上落下，还是海洋中的潮涨，都得有一种力存在。
Newton realized that in order to get an object to move, whether it was an apple that fell out of a tree or the tides that rose in the oceans, there had to be a force present.
那些在潮退时看似被石块盖掩着的杂草，在潮涨时却会变成彩色缤纷的珊瑚，与海葵一起随着水流荡漾。
What looks like rock-covered clusters of dark weeds at low tide will become a colorful coral with sea anemones waving in the currents at high tide.
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