From practical experience, it's obvious that a sharp non-serrated knife will cut items with more ease if the user attempts a sawing motion.
The intuitive reasoning for how a non-serrated knife cuts - the blade is sharpened to just several atoms thick on the edge and whatever is being cut simply can't hold up to forces applied across such a small area - obviously breaks down here. (Experimentation!)
The most logical explanation that occurs to me is that the knife is imperfectly sharpened, leading to micro-serrations that assist cutting. To utilize these imperfections, one must use a sawing action while slicing.
Can anyone explain what's going on here?