時(shí)差N小時(shí):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(jī)上的乘客開(kāi)始打哈欠，嚼口香糖，他們也許并不是因?yàn)槠v不堪而嚼口香糖，或許是為了防止高空耳鳴。當(dāng)飛機(jī)改變飛行緯度，氣壓會(huì)發(fā)生改變，使乘客的耳朵發(fā)生耳鳴。然而當(dāng)你在火車上遇見(jiàn)這樣的事，你會(huì)覺(jué)得奇怪，不知道發(fā)生了什么事。火車一般不會(huì)突然改變緯度，是嗎?那為什么在火車上也會(huì)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(dāng)然隧道外也有空氣。然而，當(dāng)火車不在開(kāi)闊的天地里馳騁，而是要穿過(guò)封閉的隧道時(shí)，情形則大不相同。在廣闊的平原上行駛時(shí)，火車只是簡(jiǎn)單地排開(kāi)空氣，然后駛過(guò)。在隧道內(nèi)將空氣排開(kāi)并是不那么容易。火車進(jìn)入隧道會(huì)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?yàn)橛兴淼缐Ρ趽醯馈?/p>

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(huì)沖過(guò)火車與隧道墻壁之間的狹小縫隙，來(lái)填補(bǔ)車后的空間?？諝獗粡?qiáng)制壓縮到狹窄的空間，會(huì)使空氣運(yùn)動(dòng)更加劇烈，正如水在漏斗里會(huì)加速下流一樣。實(shí)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(dòng)會(huì)吸住車身，從而減小車內(nèi)的氣壓，使乘客產(chǎn)生耳鳴。