英語(yǔ)聽(tīng)力文摘 大雁的“V”字形
雁群為什么總排成“一字”或“人字”形隊(duì)伍飛行呢?這是因?yàn)榇笱泔w行的路程很長(zhǎng)，它們除了靠扇動(dòng)翅膀飛行之外，也常利用上升氣流在天空中滑翔，使翅膀得到間斷地休息空隙，以節(jié)省自己的體力。當(dāng)雁群飛行時(shí)，前面雁的翅膀在空中劃過(guò)，膀尖上會(huì)產(chǎn)生一股微弱的上升氣流，后邊的雁為了利用這股氣流，就緊跟在前雁膀尖的后面飛，這樣一個(gè)跟著一個(gè)，就排成了整齊隊(duì)伍。但是“頭雁”就沒(méi)有這股氣流優(yōu)勢(shì)，所以相對(duì)而言頭雁比較容易疲倦，因此我們就可以看到雁隊(duì)很經(jīng)常地變換隊(duì)形，更換頭雁。
If you’ve ever seen a bicycle race, you might have noticed the riders lining up behind each other in straight columns.
Bicycle racers spend much of their energy overcoming wind resistance, so this lining up makes good sense. If you ride directly behind your opponent, she’ll cut through the air resistance for you, letting you save up energy for the finish line. What’s true for bicycle racers is true for other things too. Going in straight line formation is the best way to overcome wind resistance.
Which brings us to those silly geese. Like bicycle racers, geese fly in formation mainly to save energy. The formation they prefer however is shaped like the letter “V.” What’s going on? Are geese just plain dumb?
Not at all! Remember, geese don’t only need to worry about air resistance—they need to stay aloft as well. To do this, goose wings are curved and tapered like those of an aircraft. The top surface bulges upward while the bottom stays flatter. Air rushes more quickly over the wing’s bulging top, and this creates a kind of upward suction. This phenomenon is called “lift,” and it’s a goose’s secret for staying aloft.
Lift, however, is a peculiar thing. While most of it tugs upward on the goose, some of it spills away from the wing tips as a kind of updraft. This lingering updraft spreads out behind the goose in a V-shape like the wake of a boat. If another goose puts its wings inside this updraft wake, it gets an added upward boost itself. What’s the best formation to take advantage of this? It’s not a straight line, it’s a “V”!
譯文：
如果你看過(guò)自行車比賽，你或許注意到自行車手們都一個(gè)跟著一個(gè)排成一隊(duì)。
自行車手們耗費(fèi)了很大的能量來(lái)克服風(fēng)的阻力，所以這樣的排隊(duì)方式是很合理的。如果你直接騎在對(duì)手的后面。他能夠?yàn)槟阕钃蹩諝獾淖枇?，為你沖刺終點(diǎn)保留體力。對(duì)于自行車手適用的道理也同樣適用于其他方面的事情。以直線的隊(duì)列行進(jìn)是克服風(fēng)阻力的最好辦法。
這讓我們想到了那些愚蠢的大雁!就如自行車手們那樣，大雁們以節(jié)省能量的隊(duì)形飛行。然而它們喜歡的隊(duì)形卻是“V”字形。這是怎么回事?難道大雁是傻瓜?
不是這樣的。記住，大雁不僅需要擔(dān)心空氣阻力-他們同樣也需要停留在高空。為了做到這一點(diǎn)，大雁的翅膀如彎曲的錐形的飛機(jī)機(jī)翼一般，表面凸起向上，底部保持平整。空氣很快從其翅膀頂部凸起的部分掠過(guò)，這就造成了一種向上的吸力，此現(xiàn)象就叫做“牽引”，這就是大雁能夠停留在高空的秘密。
然而“牽引”是一種很特殊的東西。大多數(shù)的引力牽引著大雁向上，一些引力則以上升氣流的形式從翼尖流出。這些殘留的上升氣流像船的尾跡一樣在大雁的身后呈V字形伸展開(kāi)。如果另一只大雁也在這樣的上升氣流中展開(kāi)翅膀，它會(huì)獲得額外的升力來(lái)助推自己。什么樣的隊(duì)形能夠最好地利用這個(gè)優(yōu)勢(shì)?不是直線，而是“V”字形。
