A Knife Is A Machine

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zignal_zero

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Apr 16, 2008
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ok, this might be a lot less profound to everyonelse than it is to me, but i (recently) made this observations that has really stuck with me.

i'm sure most of you know the 3 basic machines: a lever, a pulley, and an inclined plane.

a machine simply concentrates force. like if the end of the lever you're pushing on is 5 feet long and the end on the other side of the fulcrum is 1 foot long, the force is the same. you've just condensed 5 feet of movement into 1 foot making it more concentrated. well, i was rebeveling a blade and noticed the little inclined plane that is the edge :) the knife is just one of the simple machines that takes the force exerted by my arm and condenses it down (using inclined plane) into a much more concentrated area.

maybe i'm too easily amused, but this seems so cool to me :D

is it just me?
 
maybe i had a similar epiphany about how changing one thing could change the whole substance such as Sio3 is quartz if its in a hexagonal structure, however those same elements also make a form of glass if the pressure is irregular change the structure to random patterns, this can also be applied to metals and anything else with a molecular form, it kinda blew my mind
 
Looking at it the way you did is very good and helps you to further your understanding of sharpening. You also made a good example of how too much pressure results in excessive metal deformation. You also made a good example of how bevel thickness can have a effect on downward force applied to the edge without a change in hand pressure.





your not alone ;)
 
Yep, force divided by area equals pressure. It takes high pressure to mechanically sever chemical bonds, which is what cutting is. The sharper the edge the lower the area there, so the higher the pressure for a given force.

Physics is cool.
 
I was actually thinking about this the other day when thinking about cuts I've done that used the back of the spine as a fulcrum. Hadn't really considered the aspect that I was using a fulcrum to pass two inclined planes through an object.
 
It's a simple tool that is complex in nature.
 
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Bill1170 said:
Yep, force divided by area equals pressure. It takes high pressure to mechanically sever chemical bonds, which is what cutting is. The sharper the edge the lower the area there, so the higher the pressure for a given force.

Physics is cool.
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Chemical bonds, or aggregate bonds? I don't think cutting causes chemical reactions. An aggregate is a collection of (usually) solid material. That's what you're breaking when you cut.
 
The 6 simple machines are the wedge, inclined plane, pulley, lever, screw, and wheel + axle. So a knife is a complex machine combining inclined planes, wedges, screws, wheels + axles, etc. A machine is an object that makes work easier to do for people so yes, a knife is a machine.

I always thought about knives in physics.
 
Heiheit said:
The 6 simple machines are the wedge, inclined plane, pulley, lever, screw, and wheel + axle. So a knife is a complex machine combining inclined planes, wedges, screws, wheels + axles, etc. A machine is an object that makes work easier to do for people so yes, a knife is a machine.

I always thought about knives in physics.
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it was a LONG TIME ago, so mabye they've changed what they teach, but they told us that the wedge & screw WERE inclined plane. the wedge for obvious reasons and the screw because if you follow the path up it, it's an inclined plane.

i do see how "wheel and axle" stand alone, though, can't really push them into the "pulley" catagory.
 
rayban said:
I suppose next you're gonna tell us, "life is a highway":jerkit:....
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no because that would be both a metaphor and an opinion (some might compare it more to a sandbox), whereas what i said was neither a metaphor nor an opinion. it's a fact that the simplest knife imaginable (fixed blade, no handle material) qualifies as a "machine" by definition. i find it intresting how little is required to qualify as a machine. that's significantly different than saying "life is a highway" :rolleyes:
 
zignal_zero said:
i do see how "wheel and axle" stand alone, though, can't really push them into the "pulley" catagory.
Click to expand...

wheel & axle are a modified form of lever.

When someone want to borrow your knife it is important to understand what kind of machine they need, if it is a lever then your knife is not that kind of machine and they shouldn't be allowed to borrow it. I have widgy bars that are suitable as levers and I don't want some twit snapping the tip off my inclined plane when I could have lent them a lever if I knew that was what they needed.

There is much physics in knife use:
For chopping there is a reason why a longer knife or an axe works better than a shorter knife and why a heavier knife or axe chops harder than a lighter one - it's all physics! A machete can bite deep due to the mechanical advantage of its length multiplying the speed that your hand is moving - the end of a machete can be moving really quick when it strikes the vegetation.
When you choke up on a knife while carving you are reducing speed to increase force.
It's all physics if you think about it - unlike guns which use physics + chemistry.
 
You guys and your fancy talk...you are all wrong. A knife works because there are little evil demons in the blade casting spells on what you are cutting. These spells result in stuff falling apart.

Everyone knows that God created Earth, so the spells are powerless against stone...and stones knock some of the little demons out of the blade.

Don't you guys know anything....sharpening is the work of the Devil
 
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