【英语时差8,16】漩涡的形状

 

 

Paddling a canoe¹ and draining² the bathtub both produce that familiar, spinning hole called a "whirlpool"---wide at the top, narrow down below.   

The shape of a whirlpool comes from two forces acting³ against each other. First, there's the spinning of the water, which creates a force away from the center of the whirlpool. You can feel the same kind of force by swinging a ball in a circle on the end of a rope. In the case of the ball, the rope provides the second force, pulling the ball back into the center and keeping it from flying off in a straight line.

 

In a whirlpool there's no rope pulling the water back to the center. Instead the opposing force is created by the pressure of the surrounding water. So while the momentum⁴ of the spinning water acts as a force sending the water off in all directions, the surrounding water pressure forces it back to the center. The faster the water spins, the wider the whirlpool.

 

Water pressure doesn't change from one lake or river to the next, but the pressure is always greater under the water than it is on the surface. And that's why whirlpools are widest at the top.

 

A better analogy⁵, then, might be a ball swinging around on a long spring instead of a rope. On a weak spring, the ball would make a very wide circle because the spring exerts⁶ only a weak force. That's like the top part of the whirlpool where the water pressure is also very light. Down below, the pressure acts more like a strong spring, and so the circle is a lot tighter.

 

Beneath the whirlpool, the water still spins but the water pressure is too great to allow any air space at all.  

1 canoe   

n.独木舟；vi.乘独木舟，划独木舟

参考例句：

• They slid the canoe down to the water.他们使小舟滑到水中。
• It is only the second time he has been in a canoe.这仅是他第二次乘小游艇。

2 draining   

n.排水，泄水，排泄v.（使）流干， （使）逐渐流走( drain的现在分词 )；喝光，喝干；使（精力、金钱等）耗尽

参考例句：

• Draining mountains of everlasting snow, the river twists for nineteen hundred miles. 这条河把终年积雪的群山上的融雪带走，蜿蜒1900英里长。 来自《简明英汉词典》
• The old lady's strength is draining away. 老妇人的体力在渐渐衰竭。 来自《简明英汉词典》

3 acting   

n.演戏，行为，假装；adj.代理的，临时的，演出用的

参考例句：

• Ignore her,she's just acting.别理她，她只是假装的。
• During the seventies,her acting career was in eclipse.在七十年代，她的表演生涯黯然失色。

4 momentum   

n.动力，冲力，势头；动量

参考例句：

• We exploit the energy and momentum conservation laws in this way.我们就是这样利用能量和动量守恒定律的。
• The law of momentum conservation could supplant Newton's third law.动量守恒定律可以取代牛顿第三定律。

5 analogy   

n.类似，相似，类比，类推

参考例句：

• It is not always reliable to argue by analogy.靠类推法论证并不总是可靠的。
• A close analogy with the art of singing can be made.可以用歌唱艺术作类比。

6 exerts   

v.用（力）( exert的第三人称单数 )；尽（力）；运用；发挥

参考例句：

• He never exerts himself to help anyone. 他从未尽力帮助别人。
• Much as we may pride ourselves on our good taste, we are no longer free to choose the things we want, for advertising exerts a subtle influence on us. 尽管我们可能对自己的良好鉴赏力感到十分自豪，但我们不再能任意选择我们所需要的东西了，因为我们受到了广告的微妙影响。