英語聽力文摘477 地球為什么是圓的？

地球是太陽系從內到外的第三顆行星，也是太陽系中直徑、質量和密度最大的類地行星。它也經常被稱作世界。英語的地球Earth一詞來自于古英語及日耳曼語。地球已有44～46億歲，有一顆天然衛(wèi)星月球圍繞著地球以27.32天的周期旋轉，而地球以近24小時的周期自轉并且以一年的周期繞太陽公轉。迪士尼有同名紀錄片。

Why the Earth Is Round

地球為什么是圓的?

Our never-thought to ask question for today is: Why is the earth round? Why not a cube? A cube? No,that's silly. Is it? Why?

Because…,because really big things like to be round for some reason. Exactly right.And that reason is gravity.

Think of it this way. Suppose the earth were a cube. Then some points on its surface would be farther away from the center than others. The corners, for example, would be much farther out than the rest.

Since gravity works equally on everything, there would be a tendency to pull those uneven places down. The surface would even itself out. The only geometrical object in which every point on the surface is the same distance from the center is a sphere.

But wait a minute,I've seen pictures of asteroids that have all sorts of crazy shapes.Why aren't they round?

Only because they aren’t big enough for gravity to be a determining factor. If an asteroid were to suddenly become as big as a moon, it would indeed rearrange itself gradually into a sphere.

今天，我們“從未想過的問題”是：地球為什么是圓的?為什么不是方形的?方形?那太可笑了。是嗎?為什么?

因為……因為非常大的東西通常都是圓的。完全正確。這個原因就是重力。

我們這樣想，假設地球是一個立方體。而地球表面的某些端點離中間或其它端點比較遠。比如，立方體的各個角離得很遠。

由于重力對所有物質的作用是相等的，因此不均勻的地方會被向下拉。表面使其本身變得平均。唯一一個表面上的每個角

到中心距離都相等的幾何物體就是球體。

等一下，我看過很多行星的圖片，它們都是奇形怪狀的。它們?yōu)槭裁床皇菆A的?

那只是因為行星太小，重力不能成為其決定因素。如果行星突然變得和月亮一樣大，它就會真正重新安排逐漸變成一個球體。