Like what difference does the cutting motion do compared to just pushing down a knife ?
In: Physics
It doesn’t need to be pulled back and forth. But the sawing motion can often make cutting easier.
There’s two basic versions of what’s going on when you cut something.
If there’s sawing motion going on, you’re sawing the object. On a microscopic level, a sharp knife still has tiny teeth. Google image search is your friend here.
Just pushing straight down also works, in that case the cutting is done by concentrating force is a really tiny area and overcoming the tensile (resistance to being stretched) strength of the material.
Which version of cutting is dominant or most useful depends on what you’re cutting.
Picture some cheese, an onion, and bread.
Cheese has very low tensile strength, and comparatively high compression strength, pushing straight through is easy and gets you a nice slice. Now look at stuff designed for cutting cheese. Often just a thin wire.
Bread is higher in tensile strength, low in compression. If you press straight down, you’ll crush the loaf before cutting it. Look at bread knives: they’re saws.
An onion is in between those two extremes. If you just want roughly chopped onion, slamming the knife into it is fine. But for thin uniform slices, the knife needs to slide a bit.
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