Not So Silly Geese
雁群为什么总排成“一字”或“人字”形队伍飞行呢？这是因为大雁飞行的路程很长，它们除了靠扇动翅膀飞行之外，也常利用上升气流在天空中滑翔，使翅膀得到间断地休息空隙，以节省自己的体力。当雁群飞行时，前面雁的翅膀在空中划过，膀尖上会产生一股微弱的上升气流，后边的雁为了利用这股气流，就紧跟在前雁膀尖的后面飞，这样一个跟着一个，就排成了整齐队伍。但是“头雁”就没有这股气流优势，所以相对而言头雁比较容易疲倦，因此我们就可以看到雁队很经常地变换队形，更换头雁。
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”!
译文：
如果你看过自行车比赛，你或许注意到自行车手们都一个跟着一个排成一队。
自行车手们耗费了很大的能量来克服风的阻力，所以这样的排队方式是很合理的。如果你直接骑在对手的后面。他能够为你阻挡空气的阻力，为你冲刺终点保留体力。对于自行车手适用的道理也同样适用于其他方面的事情。以直线的队列行进是克服风阻力的最好办法。
这让我们想到了那些愚蠢的大雁！就如自行车手们那样，大雁们以节省能量的队形飞行。然而它们喜欢的队形却是“V”字形。这是怎么回事？难道大雁是傻瓜？
不是这样的。记住，大雁不仅需要担心空气阻力-他们同样也需要停留在高空。为了做到这一点，大雁的翅膀如弯曲的锥形的飞机机翼一般，表面凸起向上，底部保持平整。空气很快从其翅膀顶部凸起的部分掠过，这就造成了一种向上的吸力，此现象就叫做“牵引”，这就是大雁能够停留在高空的秘密。
然而“牵引”是一种很特殊的东西。大多数的引力牵引着大雁向上，一些引力则以上升气流的形式从翼尖流出。这些残留的上升气流像船的尾迹一样在大雁的身后呈V字形伸展开。如果另一只大雁也在这样的上升气流中展开翅膀，它会获得额外的升力来助推自己。什么样的队形能够最好地利用这个优势？不是直线，而是“V”字形。 |