英語(yǔ)聽(tīng)力文摘477 地球?yàn)槭裁词菆A的？

地球是太陽(yáng)系從內(nèi)到外的第三顆行星，也是太陽(yáng)系中直徑、質(zhì)量和密度最大的類(lèi)地行星。它也經(jīng)常被稱(chēng)作世界。英語(yǔ)的地球Earth一詞來(lái)自于古英語(yǔ)及日耳曼語(yǔ)。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(zhuǎn)，而地球以近24小時(shí)的周期自轉(zhuǎn)并且以一年的周期繞太陽(yáng)公轉(zhuǎn)。迪士尼有同名紀(jì)錄片。

Why the Earth Is Round

地球?yàn)槭裁词菆A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(guò)的問(wèn)題”是：地球?yàn)槭裁词菆A的?為什么不是方形的?方形?那太可笑了。是嗎?為什么?

因?yàn)?hellip;…因?yàn)榉浅４蟮臇|西通常都是圓的。完全正確。這個(gè)原因就是重力。

我們這樣想，假設(shè)地球是一個(gè)立方體。而地球表面的某些端點(diǎn)離中間或其它端點(diǎn)比較遠(yuǎn)。比如，立方體的各個(gè)角離得很遠(yuǎn)。

由于重力對(duì)所有物質(zhì)的作用是相等的，因此不均勻的地方會(huì)被向下拉。表面使其本身變得平均。唯一一個(gè)表面上的每個(gè)角

到中心距離都相等的幾何物體就是球體。

等一下，我看過(guò)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?yàn)樾行翘?，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(huì)真正重新安排逐漸變成一個(gè)球體。