【英语时差8,16】火车上也会发生耳鸣

 If an airplane's passengers start yawning¹ and chewing gum², they might not be over-tired chewing-gum executives–they might be trying to keep their ears from popping. When an airplane changes altitude, air pressure changes often make peoples' ears go pop, and yawning or chewing can help. If you saw this same thing on a train however, you might wonder what was up. Trains aren't supposed to change altitude rapidly, are they? Why would your ears go pop on a train? The answer is tunnels, and the air inside them. Of course there's air outside the tunnel too, but very different things happen when a train moves through the closed-in air of a tunnel instead of the usual, open air. Traveling across an open plain, a train simply pushes the air aside to allow its passage. In a tunnel, things aren't so easy. When a train enters a tunnel, it compresses³ the air in front of it like a piston⁴. Unlike outside air, air in a tunnel can't be simply pushed aside–the tunnel walls are in the way. Some of the air is pushed forward, all the way down to the tunnel's other end, but most of it rushes through the narrow space between the train and the tunnel walls, to fill in the area behind the train. Being forced into this narrow space makes the air rush faster, exactly as water speeds up at the base of a funnel⁵. In fact, this tunnel air can rush backward much faster than the train's forward speed! This fast moving air creates a kind of suction on the train, lowering the air pressure inside and making your ears go pop.

1 yawning   

n.打呵欠adj.张着大嘴的，打哈欠的v.打呵欠( yawn的现在分词 )；张开，裂开

参考例句：

• Yawning is often contagious. 打哈欠常易于感染。 来自《现代英汉综合大词典》
• I felt so sleepy I couldn' t stop yawning. 我感到很困，止不住地打呵欠。 来自辞典例句

2 gum   

n.牙龈；口香糖；树胶

参考例句：

• We can stick these pictures into the book with gum.我们可用胶水把这几张画粘贴在书里。
• Americans like to chew gum.美国人喜欢嚼口香糖。

3 compresses   

参考例句：

• An electronic device that compresses the volume range of a signal. 一种压缩信号量范围的电子装置。 来自辞典例句
• They alternate hot and cold compresses. 他们使用冷热交替压缩法。 来自辞典例句

4 piston   

n.活塞

参考例句：

• They use a piston engine instead.他们改用活塞发动机。
• The piston moves by steam pressure.活塞在蒸汽压力下运动。

5 funnel   

n.漏斗；烟囱；v.汇集

参考例句：

• He poured the petrol into the car through a funnel.他用一个漏斗把汽油灌入汽车。
• I like the ship with a yellow funnel.我喜欢那条有黄烟囱的船。