時差N小時:嚼口香糖防止耳鳴

If an airplane's passengers start yawning andchewing gum, they might not be over-tired chewing-gum executives—they might be trying to keep theirears from popping.When an airplane changesaltitude, air pressure changes often make peoples'ears go pop, and yawning or chewing can help. If yousaw this same thing on a train however, you mightwonder what was up. Trains aren't supposed tochange altitude rapidly, are they? Why would yourears go pop on a train? The answer is tunnels, andthe air inside them.

如果飛機上的乘客開始打哈欠，嚼口香糖，他們也許并不是因為疲憊不堪而嚼口香糖，或許是為了防止高空耳鳴。當飛機改變飛行緯度，氣壓會發(fā)生改變，使乘客的耳朵發(fā)生耳鳴。然而當你在火車上遇見這樣的事，你會覺得奇怪，不知道發(fā)生了什么事?；疖囈话悴粫蝗桓淖兙暥?，是嗎?那為什么在火車上也會發(fā)生耳鳴?答案就在隧道，以及隧道里的空氣。

Of course there's air outside the tunnel too, but very different things happen when a trainmoves through the closed-in air of a tunnel instead of the usual, open air. Traveling across anopen plain, a train simply pushes the air aside to allow its passage. In a tunnel, things aren'tso easy. When a train enters a tunnel, it compresses the air in front of it like a piston. Unlikeoutside air, air in a tunnel can't be simply pushed aside—the tunnel walls are in the way.

當然隧道外也有空氣。然而，當火車不在開闊的天地里馳騁，而是要穿過封閉的隧道時，情形則大不相同。在廣闊的平原上行駛時，火車只是簡單地排開空氣，然后駛過。在隧道內(nèi)將空氣排開并是不那么容易?；疖囘M入隧道會壓縮車身前方的空氣，就像活塞一樣。與外面不同的是，隧道內(nèi)的空氣不能被推到兩邊——因為有隧道墻壁擋道。

Some of the air is pushed forward, all the way down to the tunnel's other end, but most ofit rushes through the narrow space between the train and the tunnel walls, to fill in the areabehind the train. Being forced into this narrow space makes the air rush faster, exactly as waterspeeds up at the base of a funnel. In fact, this tunnel air can rush backward much faster thanthe train's forward speed! This fast moving air creates a kind of suction on the train, loweringthe air pressure inside and making your ears go pop.

部分空氣從隧道一端直接被推到另一端，但大多數(shù)空氣會沖過火車與隧道墻壁之間的狹小縫隙，來填補車后的空間?？諝獗粡娭茐嚎s到狹窄的空間，會使空氣運動更加劇烈，正如水在漏斗里會加速下流一樣。實際上，隧道里的空氣向后沖撞的速度比火車前行的速度更快。這樣快速的空氣流動會吸住車身，從而減小車內(nèi)的氣壓，使乘客產(chǎn)生耳鳴。