就说香水吧 let's say I have perfume.
我拿着一瓶香水坐这儿 I have a jar of perfume and I sit it here,
假设教室是绝对静止的 if the room was perfectly still
香水分子会慢慢扩散出瓶子 the molecules of perfume would diffuse out of this jar
飘向整个教室 and they'd start moving through the room
第一排的同学 and those of you in the
马上就能闻到 first row would smell it within a few minutes,
过一会下一排才能闻到 sometime later you'd smell it one row back,
再过一会-- sometime later - and the
距离越远 闻到的越晚 farther away you get the longer it takes. 561