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It's midnight and all is still, except for the soft skittering of a gecko hunting a spider.
在午夜，一切都静止着，除了捕捉蜘蛛的壁虎飞掠发出的轻微的声音。
Geckos seem to defy gravity, scaling vertical surfaces and walking upside down without claws,
壁虎看似是无视地心引力的，爬上垂直的表面不用爪子也能倒着爬，
adhesive glues or super-powered spiderwebs.
像有强力胶或超强蜘蛛网。
Instead, they take advantage of a simple principle: that positive and negative charges attract.
但其实它们利用了一个简单的原理：正负电荷相吸。
That attraction binds together compounds, like table salt,
吸引力把化合物绑在一起，就像食盐
which is made of positively charged sodium ions stuck to negatively charged chloride ions.
它是由正电钠离子和负电氯离子黏在一起组成的。
But a gecko's feet aren't charged and neither are the surfaces they're walking on.
但壁虎的脚不带电，它们爬行的表面也不带电。
So, what makes them stick?
那么，是什么使它们粘在一起呢？
The answer lies in a clever combination of intermolecular forces and stuctural engineering.
答案是分子之间的作用力与结构工程的巧妙结合。
All the elements in the periodic table have a different affinity for electrons.
元素周期表中的所有元素对电子都有不同的亲和力。
Elements like oxygen and fluorine really, really want electrons,
像氧、氟这样的元素真的真的很想要电子，
while elements like hydrogen and lithium don't attract them as strongly.
而电子对氢、锂这样的元素就没有那么强的吸引力。
An atom's relative greed for electrons is called its electronegativity.
一个原子对于电子的相对贪欲叫做负电性。
Electrons are moving around all the time and can easily relocate to wherever they're wanted most.
电子在不停地运动而且可以移到它们最被需要的地方。
So when there are atoms with different electronegativities in the same molecule,
所以当一个分子内的原子带有不同的负电性时，
the molecules cloud of electrons gets pulled towards the more electronegative atom.
分子的一团电子会被拉向负电性最强的原子。
That creates a thin spot in the electron cloud where positive charge from the atomic nuclei shines through,
这样一个电子云中的薄薄的小点就产生了，原子核的正电穿过这个点，
as well as a negatively charged lump of electrons somewhere else.
带负电的电子也在别的地方聚集。
So the molecule itself isn't charged, but it does have positively and negatively charged patches.
这个分子本身并不带电，它只是有带正电和负电的区域。
These patchy charges can attract neighboring molecules to each other.
这些区域性电荷会吸引周围的分子。
They'll line up so that the positive spots on one are next to the negative spots on the other.
它们会连成一条线，让一个分子的正点区域挨着另一个分子的负电区域。
There doesn't even have to be a strongly electronegative atom to create these attractive forces.
甚至根本不需要强负电的原子去创造这些吸引力。
Electrons are always on the move, and sometimes they pile up temporarily in one spot.
电子在不停地运动，有些时候它们暂时堆积在一个点。
That flicker of charge is enough to attract molecules to each other.
那一瞬间的电荷足以让分子互相吸引。
Such interactions between uncharged molecules are called van der Waals forces.
这种不带电分子的相互运动被叫做范德华力。
They're not as strong as the interactions between charged particles,
他们没有带电分子间的作用力那么强，
but if you have enough of them, they can really add up.
但是如果有足够的量，它们的积累也能十分可观。
That's the gecko's secret. Gecko toes are padded with flexible ridges.
这就是壁虎的秘密。壁虎的脚趾上有易弯曲的凸起。
Those ridges are covered in tiny hair-like structures, much thinner than human hair, called setae.
这些凸起的表面被头发般的细小结构覆盖着，这种比人类头发还要细得多的结构叫刚毛。
And each of the setae is covered in even tinier bristles called spatulae.
这些刚毛被更小的多叫做匙突的结构覆盖。
Their tiny spatula-like shape is perfect for what the gecko needs them to do: stick and release on command.
这些小铲子似的形状完美对地承担了壁虎的需求：粘牢和释放的命令。
When the gecko unfurls its flexible toes onto the ceiling,
当壁虎在天花板上展开它柔韧的脚趾时，
the spatulae hit at the perfect angle for the van der Waals force to engage.
匙突与墙壁会形成能产生范德华力的完美角度。
The spatulae flatten, creating lots of surface area
匙突变平，形成的很多表面积，
for their positively and negatively charged patches to find complimentary patches on the ceiling.
使其正电和负电区在天花板上找到相对应的区域。
Each spatula only contributes a minuscule amount of that van der Waals stickiness.
每个匙突只有微乎其微的范德华力的黏力。
But a gecko has about two billion of them, creating enough combined force to support its weight.
但是一个壁虎有大约二十亿的匙突，这产生足够支持其体重的作用力。
In fact, the whole gecko could dangle from a single one of its toes.
实际上，壁虎甚至可以整个吊在一根脚趾上。
That super stickiness can be broken, though, by changing the angle just a little bit.
当然，如果角度有一丁点的改变，这些强大的粘力就会消失。
So, the gecko can peel its foot back off, scurrying towards a meal or away from a predator.
所以，壁虎可以抬起它的脚，冲向一顿美餐或者逃离捕食者。
This strategy, using a forest of specially shaped bristles to maximize the van der Waals forces between ordinary molecules
这种用一丛丛特殊形状的刷毛，让两个普通分子之间的范德华力最大化的策略
has inspired man-made materials designed to imitate the gecko's amazing adhesive ability.
启发了很多人造的、试图模仿壁虎超凡的黏合能力的材料。
Artificial versions aren't as strong as gecko toes quite yet,
人造版本目前还不像壁虎的抓力那么强，
but they're good enough to allow a full-grown man to climb 25 feet up a glass wall.
但是它们已经不错了，可以让一个成年人有能力爬一个25英尺高的玻璃墙。
In fact, our gecko's prey is also using van der Waals forces to stick to the ceiling.
事实上，壁虎的猎物也是在用范德华力粘在天花板上。
So, the gecko peels up its toes and the chase is back on.
于是，壁虎抬起脚趾，一场追逐又开始了。
