STIRRING TEA
搅拌加热
Q. I was absentmindedly stirring a cup of hot tea, when I got to thinking, “Aren 8217;t I actually adding kinetic energy into this cup?” I know that stirring does help to cool down the tea, but what if I were to stir it faster? Would I be able to boil a cup of water by stirring?
Q．有次我在漫不经心地搅拌一杯热茶时突然想到：“咦，我不是在往这杯茶里输入动能嘛。”我知道搅拌能够加速茶的冷却，但如果我搅拌得快一些呢？我能不能通过搅拌的方式把一杯茶烧开呢？
——Will Evans
——威尔•埃文斯
A. NO.
A．不能。
The basic idea makes sense. Temperature is just kinetic energy. When you stir tea, you 8217;re adding kinetic energy to it, and that energy goes somewhere. Since the tea doesn 8217;t do anything dramatic like rise into the air or emit light, the energy must be turning to heat.
不过你说的基本原理是有道理的。温度其实就是（分子）动能的体现。当你搅拌茶的时候，你就在增加它的动能。这些动能总得有个去处，既然这杯茶没有从桌子上升起来也没有发光，那么这些动能最后肯定变成热了。
Am I making tea wrong?
一定是我泡茶的方式不对！
The reason you don 8217;t notice the heat is that you 8217;re not adding very much of it. It takes a huge amount of energy to heat water; by volume, it has a greater heat capacity than any other common substance.1
至于你为什么没有觉察到这些热量，是因为这些热量并不多。加热水需要大量热量，按体积来说，水的比热容比其他任何一种常见物质都要大。1
If you want to heat water from room temperature to nearly boiling in two minutes, you 8217;ll need a lot of power:2
如果你想要在2分钟内把水从室温加热到接近沸点，你需要有很大的功率：2
Our formula tells us that if we want to make a cup of hot water in two minutes, we 8217;ll need a 700-watt power source. A typical microwave uses 700 to 1100 watts, and it takes about two minutes to heat a mug of water to make tea. It 8217;s nice when things work out!3
上面的公式告诉我们如果你想在2分钟内变出一杯热茶，那么你需要有一个700瓦的热源。微波炉一般来说有700～1100瓦，用它的确只需2分钟就可以做出一杯热茶。理论和现实一致的感觉真好！3
Microwaving a cup of water for two minutes at 700 watts delivers an awful lot of energy to the water. When water falls from the top of Niagara Falls, it gains kinetic energy, which is converted to heat at the bottom. But even after falling that great distance, the water heats up by only a fraction of a degree.4 To boil a cup of water, you 8217;d have to drop it from higher than the top of the atmosphere.
将一杯水以700瓦的功率加热2分钟会使水吸收非常多的能量。当水从尼亚加拉瀑布顶端落下时会获得动能，到了瀑布底部这些动能变成了热能。但即使是下落了如此长的距离，水的温度也只是上升了0.12℃。4要把一杯水烧开，你需要让它从大气层顶部以上的高度落下来。