The line between a “sharp knife” and a “dull knife” is finer than you’d think. When talking about how sharp a knife is or how it all works, you have to delve in almost microscopically to the very edge of the knife. “Cutting” is literally separating a fused substance into two parts.To do this, the very edge of the knife, which you can consider as an edge, is pushed forward into the substance, say a tomato. The edge is pushed against the surface of the tomato, and if you look at it microscopically, the foremost atoms of the knife edge slip in between and push aside the molecules of the tomato, so they are no longer bonded together. To imagine a two-dimensional image of a perfectly sharp knife, edge up, point facing you, would be like a triangle made up of pixels, which are the grains of particles of steel. The edge, at the top of the pyramid, would be the smallest possible size, one particle, or one pixel. This single pixel is stacked and bonded to two more just beneath it, which are bonded to three beneath them, and so on. Imagine a cloud of tomato pixels or particles, descending down onto the point of the triangle. One tomato pixel comes down and touches on top of the topmost steel pixel. The tomato pixel is pushed by more pixels behind and around it, and it cannot be pushed back upwards, so it takes the path of least resistance, to say the right of that steel pixel, breaking the bond with the adjacent tomato pixel, which pushes to the left of the steel pixel. As the cloud of tomato pixels continue to push down, the tomato pixel just above the first, also comes into contact with the topmost steel pixel, and separates to one side. Because the bonds between the steel pixels are stronger than those of the tomato pixels, the very first tomato pixel is pushed to the right of the second steel pixel, rather than left and in between the first and second steel pixels, pushing it further away from the original partner tomato pixel, on the other side of the steel triangle. This continues, pushing the cloud of tomato atoms into two parts, until it has reached the end of the cloud, at which point the cloud of tomato atoms is to completely separate parts. This is an ideal perfectly sharp knife.
Now imagine the same situation, the triangle of steel pixels with the cloud of tomato pixels descending on it once more, but this time with instead of one single pixel at the top of the triangle, there are two (with three below them, four below those, and so on). When the cloud descends down, the nearest tomato pixel pushes against the top two, nestling in the valley between, but not slipping in between them because the steel pixels are too close and will not separate due to extremely strong bonds. The tomato pixels behind and around the first are not separated, rather they just push onto the triangle like a finger against a balloon. Eventually, they only separate from the first tomato pixel because they are stretched so far down the sides of the triangle. However the above situation would be rare, as the chance of that tomato pixel coming down perfectly on top of the two steel pixels is extremely minute. More likely the tomato pixel would separate to one side or the other, especially as tomato particles do not pack as closely together as steel particles. But imagine now if you had five steel pixels as the top layer. In this case they will almost definitely push against the cloud until the tomato bonds break because of stretching. This is an example of a dull knife. Quite often, depending the strength of the material being cut, such as bread, the bread particles will just be pushed upwards, breaking all bonds with the particles to either side. A dull knife cutting is just squishing whatever material is in it’s path, away.
Serrated knives on the other hand, cut by digging away a trench, like a row of shovels. When non-serrated knives are dulled, it is because those few topmost particles on the triangle have been moved to the side, bent out of the way because of tough resistance. Some particles will remain in the original space, while others bend to either side, causing jaggedness, like small serrations. This is why when people accidentally cut themselves with a super sharp knife, they sometimes don’t feel it, or don’t bleed immediately, even though the cut is fairly deep, as opposed to when they cut themselves with a dull knife. The sharp knife has not destroyed tissue, it simply separated the skin into two parts, which touch and are closed again as soon as the knife is removed. A dull knife rips away the tissue in its path, leaving a gaping gash, through which blood will flow freely.
Well, that was longer than I had intended. Hopefully that gives you a detailed knowledge on exactly how a blade cuts, how it dulls, and under what ways it performs and stays performing best.