Page 16 - Science Focus (Issue 017)

Imagine roaming around the frozen Arctic

all day, at –30 to –40 degrees Celsius with powerful winds
The Making of blasting around you. There are no trees or other materials
nearby to build a cozy wooden house, and all you see is
snow. But that’s exactly what you need to survive in this harsh
a Cozy Home… environment…by building an igloo!
Igloos have been the Inuit’s main shelter, allowing them to
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survive in the Arctic for 4,000 years [1]. Our intuition tells us that
With Snow igloos should not work — how could snow be used to build

such warm stable dome structures? This may be a mystery to
most people, but it can, in fact, be explained by simple physics!

極地愜意的家 ─ How to Build an Igloo?
Igloos are essentially built from a collection of snow
blocks, which are usually extracted from the ground using
冰屋大解構 long blades and knives. A skilled igloo builder stacks these
snow blocks in spirals. The builder will shave a slight incline
on the top of blocks so that they tilt inwards after each spiral,
until the entire dome-shaped structure is complete [2-4].
By Yasine Malki 馬建生 To construct a sturdy igloo, two aspects are critical. First,
the type of snow used has to be dense, dry and compressed
[5]. This tends to be deeper ground snow, between the very
fragile fresh snow and the heavy, dense ice.
The second is the shape of the dome: a stable igloo should
have a cross-sectional shape of a parabolic arch rather
than a semi-circle. A parabolic arch is perfectly optimized
to minimize structural tension and maximize compression,
which is vital for building with a weak material like snow. In
other words, its geometry ensures all the snow blocks exert a
force to squeeze themselves together, making it one of the

假如你在北極漫遊了一整天，北風在你身旁颼颼地吹著，溫
度只有大約攝氏零下 30 至 40 度。四周沒有樹，亦沒有其他材料讓你
興建一座愜意的小木屋。你眼前除了雪之外，也就只有雪。但這正是
你在如此嚴峻環境下所需要的救命稻草 — 就蓋一座冰屋吧！
冰屋一向都是因紐特人 的主要居所，使他們能在北極地區生活
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近四千年 [1]。然而直覺告訴我們：冰屋大概行不通吧 — 雪又怎能
夠被用於建造一座溫暖的拱形建築呢？不少人心裡仍抱有這樣的疑
惑，但其實我們可以用簡單物理解釋箇中原理！

如何蓋一座冰屋？
冰屋基本上是由一系列的雪磚蓋成的，當中的雪磚通常是用長
刀從雪地中切出來的。一名熟練的冰屋技工會把這些雪磚螺旋形地
疊起，他們會在雪磚的頂部切一個小小的斜面，令每一圈的雪磚疊
起來都會稍稍向內傾斜，直到整個圓拱形結構完成為止。
要興建一座牢固的冰屋，有兩方面是至關重要的。第一，使用的
雪必須是高密度、乾身和壓實的 [5]。這通常是雪地中稍為深的雪，
位置處於新鮮粉雪和高密度的冰之間。

第二是拱形結構的形狀。以一座結構穩定的冰屋來說，切面
形狀應該是像一條向上的拋物線，即稍為尖的半圓，而不是一個
均勻的半圓。拋物線狀的拱形能完美地把結構張力減至最小，並
使擠壓力最大化，這對於用雪這些脆弱材料來建屋是十分重要
的。換句話說，這種幾何形狀能確保每一層的雪磚都能施力把其
他雪磚壓得緊緊的，使其成為最穩固的形狀之一 [5]。相反，均勻
半圓的拱形結構當中含有一些高張力的位置（見圖一），當中的雪
晶（雪花）會被拉開，令冰屋很容易因為些微的外力而倒塌 [5]。