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Everyone knows that a sharp knife cuts better than a dull one,but do you know why, exactly?
众所周知，锋利的刀刃的切割性远胜钝刀，但你知道确切原因吗？
The purpose of the cutting edge of a knife is to concentrate the force that's being applied at the handle.
刀刃的作用就是将人们用在刀把上的力集中起来。
When you push down on the handle of a knife you exert a force.
当你按下刀把时，实际上你施加了一种力。
The force on the handle and the edge are the same, but the areas in which the force is concentrated are quite different.
这种力无论是在刀把还是刀刃上都是等量的，但力的聚集区域不同，所产生的效果则有天壤之别。
At the handle your hand's force is spread over a wide area, but on the cutting edge it isconcentrated in a very small area, so therefore the pressure on the edge is much greater.
在刀把上，力会在一个较广阔的区域传播，但在刀刃上，力会聚集在一个非常小的区域，因此刀刃上的压力会剧增。
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.
只要借助一块橡皮泥、一枚宽头钉和一枚窄头钉，你很容易就能看到这一原理。
First hold the nail with the wide head by its shaft and push it head-first into theball of clay.
首先将宽头钉的杆竖起，将其头朝下推入橡皮泥球。
Then do the same with the small-headed nail.
然后对窄头钉做同样动作。
The small-headed nail goes into the clay much more easily than the wide-headed nail.
窄头钉比宽头钉更容易嵌入橡皮泥。
Since thehead of the small nail has less surface area than the big one, the force of your push isconcentrated in a smaller area, exerts more pressure on the clay, and so the nail goes in moreeasily.
由于窄头钉的头部面积比宽头钉小，你的推力将集中在一个更小的区域，对橡皮泥产生更大的压力，因此钉子更容易嵌入。
The same principle causes pointed high-heeled shoes to sink into a soft surface more easilythan flat shoes.
同理，尖高跟鞋比平跟鞋更易陷入表面柔软的物体。
By applying this principle to the knife you can see that with a keener edge there's a greaterconcentration of the pressure on the edge, so it takes much less force to make the knife cut.
将这一原理运用在刀上，你能看到，在锋利的刀刃上，压力能更好的聚集，因此切割起来更省力。
