【英语时差8,16】硬币可以叠多高？（下）

 This is a problem because a low center of gravity is more stable than a high one. Think how much easier it is to tip over a long two-by-four board balanced on one end than a block of wood the same width but only six inches high. In order to stay standing¹, the center of gravity has to be over the bottom penny. If it moves out far enough so that a vertical² line going down from that point doesn’t hit the bottom penny, the whole stack falls. And every penny you add gives more wobble, making it more likely the center of gravity will stray outside that zone, even for a moment. When it does: crash.

1 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

2 vertical   

adj.垂直的，顶点的，纵向的；n.垂直物，垂直的位置

参考例句：

• The northern side of the mountain is almost vertical.这座山的北坡几乎是垂直的。
• Vertical air motions are not measured by this system.垂直气流的运动不用这种系统来测量。