英語聽力文摘489 船尾那條溫柔的尾流帶

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A Smooth Wake

平靜的尾流

(A smooth wake on today's moments of science)

Female: Donne and I are on a fantacy cruise. The sun has set and were standing on the rear deck. Look at the reflection of the moon.

Male: You might expect a ship's wake to be more agitated than the surrounding water. Instead, it's a smooth path through the waves that can extend for miles behind the ship. How come?

F: The wake starts out smooth because the passage of the ship destroys whatever wave patterns were there before the ship came through. The reason it stays smooth has to do with tiny organic molecules–such as decomposed plankton–on the surface of the water.

There are always some organic molecules on the ocean's surface, but as the ship pushes along, it plows these molecules to the sides. This leaves the wake something like a winter road that has just been snow-plowed, with piles of snow on both sides of the road.

The center of the wake is relatively free of organic molecules, but the two sides each have an accumulated pile-up. These stretch behind the ship on either side of the wake like ribbons.

M: Well, that's interesting. But how does this keeps wake smooth?

F: It turns out that a thin ribbon of organic molecules on the surface of water is really good at suppressing small waves. These two ribbons, on either side of the wake, act like guardrails, preventing small waves from entering and crossing the wake.

M: So that's why the wake stay so smooth

女：多恩和我正在進行著一場不可思議的巡游。太陽下山了，照耀在(船的)后艙。看，月亮的影子。

男：你或許還期望(船的)尾流要比四周的水更洶涌吧?相反，它卻是一條穿梭于海浪間的、可以在船尾延伸至幾公里的平靜軌跡。如何形成的呢?

女：尾流一開始就是平靜的，因為在船經(jīng)過之后，它的路徑變改變了之前波浪的路徑。尾流保持平靜的原因還與水面上微小的有機分子有關(guān)，比如說已分解的浮游生物。

海面上總是會有一些有機分子。但是隨著船只前行，它會把這寫分子推到一兩邊。這就讓尾流有點像在冬天里剛剛開通的雪路一樣，路兩旁是成堆的雪。

相對來說，尾流的中間就沒有了有機分子，而兩邊就堆積了很多。在船后面，兩邊倒偶像這樣延伸，就像兩條帶子一樣。

男：嗯，有意思!但是它是怎樣保持水流平靜的?

女：水面上薄薄的有機分子帶真的很能“鎮(zhèn)壓”周圍的小波浪。尾流兩邊的兩條帶狀物就像護欄一樣，阻止小波浪進入甚至橫穿過尾流。

男：這就是尾流如此平靜的原因啊!

【words & expressions】

rear deck：n. 后艙

decomposed：adj. 已腐爛的，已分解的