科普为什么石头是圆的呢,石头圆

@人人能科普，处处有新知

不知道你有没有想过，为什么石头只有球形和扁平的两种呢？一起来找找答案吧...

想要"磨耳朵"的，可以移步至小月的”视频“观看哦~

Have you ever noticed that some rounded stones are almost spherical,

你是否注意过石头只有球形

while others are kind of flat like a bar of soap?

和扁平的两种

The spherical stones form that way because they never have the chance to settle into apreferred orientation:

石头会是圆的是因为它们没有明确的方向

they're either sloshing around in pot holes, or rolling along the bottom of a river,

这些石头要么陷在坑里要么在河底滚动

or if they're small enough, getting blown around by the wind.

如果足够小的话它们甚至能被风吹走

Since they have no preferred orientation,

由于没有明确的方向

these stones get weathered the same amount on all sides,

它们会在各个方向受到侵蚀

and they'll end up looking the same from all sides as well.

最终各个面会被磨得一样平

That's spherical symmetry!

也就成了球形

But for flat stones, even if they're a smooth disk perfect for skipping,

但对于扁平的石头而言尽管它们也会在河底滚动

there's obviously a preferred, or special, orientation -

但它们始终有一个固定的方向

the direction perpendicular to, or 'away from' the flat sides.

垂直于石头平面的方向

Where did this preference come from? And how do flat stones get flat?

这个方向从何而来而它们又是如何变平的呢

Gravity.

靠的是重力

It's kind of like the difference between dumplings and biscuits.

这就像是饼干和饺子的区别

A dumpling is a lump of dough dropped in a pot of water,

饺子就是煮在沸水的面团

and gravity doesn't really affect its orientation very much when it's rolling and bobbingabout.

而在煮饺子的过程中重力不会影响饺子的方向

A biscuit, on the other hand, is a lump of dough pulled down by gravity onto a baking sheet,

饼干则是放在烤盘上的面饼

so it tends to be flat and has a clear top and bottom.

所以它有明确的上下之分

And while the details are ultimately more complicated,

而在环境变得复杂时

when sedimentary rock forms, it forms layers,

比如沉积岩形成时

or when stones too heavy to roll are worn down by abrasion at the bottom of a river or lake,

或是石头沉在水底时

they tend to be worn a bit flat.

它们会被磨平

In both cases the preferred direction is dictated by gravity.

这两种情况都是重力造成的

And gravity is also why we build buildings in layers, with a basement, floors and a roof –

同时重力也是我们以层建造建筑并修建地下室和屋顶的原因

if we were in outer space without a preferred direction from gravity,

如果我们在没有特定重力方向的外太空生活

we'd probably just live in blobs.

我们很可能生活在泡泡