Thursday, June 15, 2006

How Knives Work

Have you ever wondered how a knife works? How is it that a machine as simple as a blade of metal is able to accomplish things so elegantly that we could only do with brute force?

Take, for example, a steak knife. If you want to eat a steak, you have the option of picking it up in your fingers and ripping off bite-size pieces to put in your mouth. But isn’t it much more neat and convenient to have a knife neatly slice through the meat, giving it a clean edge and a perfectly sized piece? How does it do that?

Everybody knows that a knife is better when it’s “sharp”. What does “sharp” mean? It means that the edge comes to a definite point instead being rounded.

Consider it this way. When you push down on a knife, you exert force through the knife onto the piece of meat. Let’s say that’s a force of, oh, five pounds or so. But it’s not just five pounds. That force is spread over the surface area of the meat where the knife meets it.

Hang in there. We’re getting close to understanding how this works.

Suppose you lay the knife on its side and push down. That five pounds of force is now spread over the surface of the knife blade — perhaps two or three square inches. Not much cutting power there, huh? Just a mushed-up piece of meat.

Now turn the knife on its sharp edge. Push down with the same force. That same five pounds of force is still being exerted on the meat. But instead of being spread over two or three square inches, the force is concentrated. Let’s see — how much area do you think is represented by the edge  of the knife as opposed to the side?   Infinitesimal, don’t you think? And the sharper the knife is, the less surface area is represented by the edge and the more concentrated the force is.

Knives work not because they are strong, but because they concentrate all their strength in a very small area.

There’s a lesson to be learned from this. When we are in a struggle, it often isn’t important how strong we are — individually or collectively. What really makes us effective is when all our strength is concentrated in a small area. The greater the concentration, the more effective our relative strength.

“Sharpening” our skills doesn’t refer to making us stronger, smarter, or better. It means learning how to effectively utilize the skills that we already have — concentrating them in a small area — to get the job done.

5 comments:

Pastordeshon said...

I once read in a novel, written by and about an engineer, an explanation of how padded plate mail (armour) works, which is really the opposite of how a knife, or in this case a sword, works. He explained that it is really transfering the force of the blow through both time and space. The armour spreads the blow over a larger surface area (space) and the padding slows the weapon, spreading the force also over time. The novel is "The Cross-Time Engineer" by Leo Frankowski, and is full of similar explanations. Michael Crichton is especially good at this, as is Tom Clancy to a lesser extent.

Robert Wainblat said...

who on earth wrote this it's almost like a computer generated the sentences.....did you translate it from another languages?

Joe DeShon said...

Nope. I'm a real human being. But thanks for asking. -- Joe

Anonymous said...

What "Robert Wainblat" actually meant was:


Wow, neat article - made me think about things in a different way

Thanks for posting it :)

Bill Phil said...

Yeah, it's based on the surface area of the blade. Less area results in more pressure for the same applied force. Also, the wedge shape forces the two sides apart.