The force of gravity pulls things towards the earth's centre.
地心吸力把物体吸向地心.
Professor gravity now seems to have become an unwanted fixture in the college.
格雷维蒂教授现在好像成了学院里的累赘.
He discoursed impressively on Newton's theory of gravity.
他讲述了牛顿的引力定律,给人以深刻的印象。