英語(yǔ)聽(tīng)力文摘 燒開(kāi)水的秘密

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You may be surprised to hear that it’s actually easier to boil water on stormy days than it is when the weather is clear and sunny.

Can you guess why?

The reason is that the boiling point of water changes slightly in response to air pressure. High air pressure, found on sunny, clear days, means just what it sounds like: crowded air molecules are pressing down on the water in the pot, just like they press on the stove, the floor and on you. This causes the molecules that make up the water to be squeezed more tightly together, which means that the steam bubbles trying to form at the bottom of the pot have a harder job pressing outward. It’s somewhat like trying to stretch your arms in a crowded room: the more crowded it is, the harder it will be for you to stretch without being bumped back again by someone else.

On stormy days, the air pressure is relatively low; you have probably heard the weather person refer to a “low pressure system” moving in just before it rains. When there is low air pressure the water in your pot is not compressed as much by the air around it. Because it’s easier to displace that water, the bubbles of steam form more easily at the bottom of the pot; and voila — boiling begins.

There is a catch, however. Although the boiling point of water — 212 degrees — is reduced on stormy days, and thus water boils faster, the temperature of that boiling water is also lower. That means it will actually take LONGER to cook things — an effect that more than counters the ten seconds or so you save in waiting for the boil.

譯文：

你或許會(huì)覺(jué)得驚奇，在暴風(fēng)雨的天氣比在晴朗的天氣更容易把水燒開(kāi)。

你猜猜這是為什么呢?

原因就是水的沸點(diǎn)根據(jù)氣壓有細(xì)微的變化。高壓一般出現(xiàn)在晴好的天氣，就如聽(tīng)起來(lái)的那樣：擁擠的空氣分子擠壓在鍋里的水上空，就像它們擠壓在爐子，地板以及你的身上一樣。這讓構(gòu)成水的水分子擠壓的更緊，也就意味著在壺底形成的氣泡更難向外冒。這就像在一個(gè)狹窄的屋子里，你試圖伸展四肢：它越狹窄，你越難在不被什么東西撞回來(lái)的情況下伸展。

在暴風(fēng)雨的天氣，氣壓相對(duì)較低，你或許聽(tīng)到過(guò)天氣預(yù)報(bào)員報(bào)道下雨之前，“低壓系統(tǒng)”正在進(jìn)入。當(dāng)?shù)蛪捍嬖诘臅r(shí)候，壺里的水不會(huì)像周圍的空氣那樣被擠壓，所以水之間的更替的更迅速，蒸汽氣泡在壺底也更容易形成，瞧-已經(jīng)開(kāi)了。

但是仍有一個(gè)不好之處。盡管水的沸點(diǎn)-212度-在暴風(fēng)雨天氣會(huì)降低，水會(huì)燒開(kāi)的比較快，可是開(kāi)水的溫度也會(huì)相對(duì)較低。也就是說(shuō)煮東西的時(shí)間就會(huì)變長(zhǎng)-這就是在等待水開(kāi)過(guò)程中節(jié)約下來(lái)的那十秒時(shí)間而造成的一種負(fù)面效應(yīng)。