英語聽力文摘553 利刃特別在何處？
- 聽力原文
- 參考譯文
Everyone knows that a sharp knife cuts better than a dull one, but do you know why, exactly?
The purpose of the cutting edge of a knife is to concentrate the force that’s being applied at the handle.
When you push down on the handle of a knife you exert a force. The force on the handle and the edge are the same, but the areas in which the force is concentrated are quite different.
At the handle your hand’s force is spread over a wide area, but on the cutting edge it is concentrated in a very small area, so therefore the pressure on the edge is much greater.
You can easily see how this works with a piece of modeling clay, a nail with a wide head, and a nail with a small head. First hold the nail with the wide head by its shaft and push it head-first into the ball of clay. Then do the same with the small-headed nail.
The small-headed nail goes into the clay much more easily than the wide-headed nail. Since the head of the small nail has less surface area than the big one, the force of your push is concentrated in a smaller area, exerts more pressure on the clay, and so the nail goes in more easily. The same principle causes pointed high-heeled shoes to sink into a soft surface more easily than flat shoes.
By applying this principle to the knife you can see that with a keener edge there’s a greater concentration of the pressure on the edge, so it takes much less force to make the knife cut.
利刃特別在何處?
大家都知道鋒利的刀刃的切割性能勝過鈍刀，但您知道確切原因嗎?
刀刃的作用就是把人們用在刀把上的力集中起來。
當你按下刀把時，你施加了一種力。這種力無論是在刀把還是刀刃上都是等量的，但力的聚集區(qū)域不同，所產生的效果十分迥異。
在你手中的刀把上，力會在一個較廣闊的區(qū)域傳播，但在刀刃上，力會聚集在一個非常小的區(qū)域，因此刀刃上的壓力會劇增。
只要有一塊橡皮泥、一枚寬頭釘和一枚窄頭釘，你很容易就能看到這一原理是如何運作的。首先將寬頭釘?shù)臈U豎起，將其頭朝下推入橡皮泥球。然后對窄頭釘做同樣動作。
窄頭釘比寬頭釘更容易嵌入橡皮泥。由于窄頭釘?shù)念^部面積比寬頭釘小，你的推力將集中在一個更小的區(qū)域，對橡皮泥產生更大的壓力，因此釘子更容易嵌入。同理，尖高跟鞋比平跟鞋更易陷入表面柔軟的物體。
將這一原理運用在刀上，你能看到，在鋒利的刀刃上，壓力能更好的聚集，因此切割起來更省力。
