水珠在油面快速滑动的秘密（中）

And what they saw in these videos was that when the droplets were placed on the hot oil, they would propel themselves in random directions at very high speeds.

他们在这些视频中看到的是，水珠落到热油上时，会以极高的速度朝着任意方向散开。

Several things about this were very surprising.

有好几个点令人惊讶。

First, that the droplet propels itself. It was clear pretty quickly how this was happening.

首先，水珠推动自身滚动。这是怎么发生的很快就清楚了。

An easy way to think about this is it's called momentum transfer.

一个简单的理解方法，这是动量传递的结果。

So if you take a balloon and blow air in it, and you release it, the balloon just flies everywhere, right?

所以如果你拿一个气球，向里面吹气，然后放了气，气球就会到处飞，对吧?

Similar to the balloon, what was happening on the hotplate was that the oil was forming a thin layer around the drop.

和气球类似，在加热板上，油会包住水珠形成薄薄的油层。

The oil cloak acts as the balloon. The water inside boils and turns into vapor.

油层就像气球一样。而里面的水沸腾后变成蒸汽。

Eventually, this pocket of steam bursts through the oil, and much like letting go of the balloon this propels the drop.

最终，这一团蒸汽会冲破油层，就像放手的气球一样，这推动水珠跑动。

The second thing that confused them was that the drops went much faster than those levitating leidenfrost water drops. Ten to 100 times faster, in fact.

第二件让他们困惑的事是，这里水珠运动的速度远超悬浮的莱顿弗罗斯特水珠。事实上，要快10到100倍。

That was odd because the drop was still in contact with the oily surface.

这很奇怪，因为水珠仍与油层接触。

You might expect to slow it down compared to a levitating drop.

它的速度应该比悬浮的水珠低才对。

And so we were pretty stumped because the velocity of the droplet actually seemed that it moving on an infinite pool of liquid.

我们被难住了，因为水珠的速度看上去就像是在无限的液体池上运动。

That is Leon who ran the experiments.

做实验的是里昂。

He means that when he did the back calculations based on the speed that he saw the water drop was moving, the only way to make the calculation work out would be for the drop to be on an infinitely deep pool of oil.

基于所观察到的水珠移动速度进行反向计算时，他发现唯一能让计算进行下去的情况是水珠运动在无限深的油池上。

But in reality the oil was only 10 microns thick, which should cause the drop to stick--a lot.

但实际上，油层只有10微米厚，这应该会使水珠黏住——牢牢黏住。

From a physics perspective the amount of friction the oil surface should have is based on its depth.

从物理角度来看，油层表面摩擦力大小取决于其深度。

Think of it like pouring honey out of a bottle.

将其想象成从瓶子里往外倒蜂蜜。

The thin film is like pouring through the small opening in the cap -- the honey moves very slowly.

薄薄的油层就好比通过瓶盖上的小孔往外倒蜂蜜——蜂蜜流动的速度非常缓慢。

If you remove the cap entirely - the honey has less friction and pours more quickly.

如果你完全取下瓶盖，蜂蜜流动时的摩擦力会更小，倾倒速度会更快。

If you do the calculation for oil 10 microns thick the drop should move way slower.

如果按照10微米厚的油层来算，水珠的移速应该更慢才对。