Why are plane windows round? This seems like a simple question, but let's take a look.
機窗為什麼是圓的？這似乎是個簡單的問題，但讓我們來看看。
As passenger planes became more popular, planes needed to fly higher. Flying high means less drag because the air density is lower in the upper atmosphere, so less fuel is wasted. And flying high also means a more comfortable flight because the plane can now fly above the turbulent lower atmosphere. But some design changes need to be made to allow this.
隨著客機變得越加普及，飛機需要飛得更高。飛高代表較少阻力，因為空氣密度在高層大氣中較低，所以會浪費較少燃料。而飛高也代表更舒適的飛行體驗，因為飛機現在可以飛在氣流不穩的低層大氣之上。不過得做一些設計更改才能讓這發生。
First, the cabin has to be pressurized to create a survivable environment for the passengers. Second, the cabin must be cylindrical in shape because a cylinder can resist the new internal pressure. But one design flaw was not corrected when cabin pressurization was first introduced. The windows remained square. So why is this a problem?
首先，機艙得被加壓來替乘客創造出一個可生存的環境。第二，機艙的形狀必須是圓筒狀，因為圓筒可以抵抗新的內部壓力。不過機艙加壓首度問世時，有一個設計瑕疵未被修正。窗戶仍是方形的。這為什麼是個問題呢？
As the plane increases in altitude, the external atmospheric pressure lowers more than the internal cabin pressure. This creates a pressure difference between the inside and outside of the plane, causing the plane to expand ever so slightly. When a material changes shape like this, stress is created in the material. As the material is stretched more and more, this stress begins to rise. Eventually this stress can rise so high that the material breaks.
當飛機高度增加，外部大氣壓力會比機艙內部壓力下降得還要多。這產生飛機內外的壓力差，使飛機極細微地膨脹。當一個材料像這樣改變形狀時，應力就在其中產生。隨著材料越來越伸展，應力開始增加。最終這種應力會升到非常高，以致材料斷裂。
And there are a lot of factors that can elevate this stress. One of them is the shape of the material. In planes, the shape of the windows has a huge effect on the level of stress. Stress will flow smoothly through material, but if an obstacle is placed in its path, like a window, it needs to change direction, and this causes the pressure to build in certain locations. This is called stress concentration.
有許多能升高這種應力的因素。其一是材料的形狀。飛機中，窗戶的形狀對應力程度有極大影響。應力會順利流經材料，不過若有個障礙在應力行進的路線上，像是一扇窗戶，應力就需要改變方向，而這會使應力在某些位置累積。這就稱作「應力集中」。
Comparing modern-day oval windows and square windows, you can see that the square windows provide a larger barrier through the smooth flow of stress. And this means that the stress builds in the sharp corners of the window. This elevated stress created by the square windows actually caused cracks to form in the de Havilland Comet, causing three tragic crashes. The investigations that followed led to our greater understanding of stress concentration, and that is why all plane windows are now oval in shape.
將現代橢圓窗戶和方形窗戶相比，你可以看到方形窗戶在流暢的應力流動中會提供較大的屏障。而這代表應力在窗戶的尖角累積。方形窗戶造成這種升高的應力實際上真的使裂縫在哈維蘭彗星型客機內形成，造成三場不幸的墜機意外。後續的調查讓我們更加了解「應力集中」，而那就是為什麼現在所有飛機的窗戶都是橢圓形的。
- 「非常、極其」- Ever So
This creates a pressure difference between the inside and outside of the plane, causing the plane to expand ever so slightly.
這產生飛機內外的壓力差，使飛機極細微地膨脹。 - 「導致、通往」- Lead To
The investigations that followed led to our greater understanding of stress concentration, and that is why all plane windows are now oval in shape.
後續的調查讓我們更加了解「應力集中」，而那就是為什麼現在所有飛機的窗戶都是橢圓形的。
