On the other hand the J knife might cut cardboard more easily, depending on just how blunted “dull” is. And the J knife would be a much better choice as a cheese knife.
Exactly.
Think of cutting ability as that which measures how much force a blade requires to make a cut. It all gets pretty simple then as there are three basic forces :
-the force right against the apex, some materials are very hard to start a cut (sharpness)
-the force to push material apart, some materials are very rigid (blade cross section)
-frictional losses, some materials are very sticky (this is related to but not equal to the second term)
A carrot does not take much to start a cut, you can even just push your thumbnail into it, thus a blade doesn’t need to be very sharp to cut it well. But a carrot is very rigid and thus a thick blade will break the carrot and requires more force. A carrot in general isn’t very sticky and thus there are no frictional concerns.
A piece of rope is very hard to start a cut, you will not be able to push your thumbnail into it (unless you emit gamma radiation). A knife has to be decently sharp to cut rope well. However rope tends to fall apart much more so than a carrot and thus cross section isn’t as critical. Rope isn’t very sticky at all.
A wet potato also isn’t hard to start a cut, but is very rigid and also sticky (starch is used to make glues). Thus a very thin convex profile works very well (or a relief hollow ).
Ideally you want a knife which is sharp, doesn’t bind and is resistant to sticking to cut a broad spectrum of materials well. But specialty knives can ignore 1 or even 2 factors if they just cut very few materials.
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As an aside, those properties of the materials are actually measured by the rupture pressure, Young’s modulus and coefficient of kinetic friction.
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