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May14-11, 11:58 AM
P: 3,387
You make the edge of the metal as fine as possible.

By doing so, you decrease the area of the edge of the blade which in turn increases the pressure.

A blunt blade has a large surface area on the edge of the knife, a sharpened blade has a small surface area on the edge of the blade.

Pressure = Force / Area

Now in both cases, force can be the same. But the smaller the area value the higher the pressure.

Example (numbers exaggerated):

Let's say you have a knife that is blunt. The area of the blunt edge is 20cm2. You apply 100N of force. This gives a pressure of 100/20 = 5N/m2.

Now you sharpen it, the area reduces to 5cm2. You apply 100N of force again. This time you have a pressure of 100/5 = 20N/m2.

Basically, you are removing atoms from the material with each pass.