Boiling Water Under Boiling Clouds
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.
译文：
你或许会觉得惊奇，在暴风雨的天气比在晴朗的天气更容易把水烧开。
你猜猜这是为什么呢？
原因就是水的沸点根据气压有细微的变化。高压一般出现在晴好的天气，就如听起来的那样：拥挤的空气分子挤压在锅里的水上空，就像它们挤压在炉子，地板以及你的身上一样。这让构成水的水分子挤压的更紧，也就意味着在壶底形成的气泡更难向外冒。这就像在一个狭窄的屋子里，你试图伸展四肢：它越狭窄，你越难在不被什么东西撞回来的情况下伸展。
在暴风雨的天气，气压相对较低，你或许听到过天气预报员报道下雨之前，“低压系统”正在进入。当低压存在的时候，壶里的水不会像周围的空气那样被挤压，所以水之间的更替的更迅速，蒸汽气泡在壶底也更容易形成，瞧-已经开了。
但是仍有一个不好之处。尽管水的沸点-212度-在暴风雨天气会降低，水会烧开的比较快，可是开水的温度也会相对较低。也就是说煮东西的时间就会变长-这就是在等待水开过程中节约下来的那十秒时间而造成的一种负面效应。 |