how does a drill work? Naively when I want to make a hole, I put a bit in the drill and press downwards and a hole is produced.  
Is it more complicated than that?  First of all every time I drill a hole in wood or any other material, shavings are produced, as well as a cylindrical empty space.  By conservation of matter, the shavings should have the same total volume as the volume of the hole I just made.
And there are other issues... how does a screw (or screw-shaped bit) remove the matter?  how much heat am I producing due to friction? what is rotation speed etc.
The main question that motivated me to ask on here, is why a drill requires vertical force, but a router uses only horizontal force.  From theoretical point of view all both objects do is rotate a screw and remove matter from a piece of wood or metal.  So I need a better approximation of how these two machines work.
 A: It sounds like you want to know what is going on at the tip of the drill bit. Well, I would say that scraping or gouging or digging, but in a circular motion, would best describe it in layman's terms. It's similar to what happens when you scoop out ice cream with with a twisting motion. It usually requires at least a little force in the direction of the hole, but sometimes the bit sort of pulls itself in, depending on the material.
Note this: A drill requires not only vertical force, but torque, or twisting force as well. Often you don't notice it because it doesn't require much, unless it gets stuck, then you'll definitely notice it.
Screws are different. A normal screw does not remove material, rather it deforms material by pushing it out of the way. It squeezes and wedges its way in. That's why sometimes you want to drill a smaller hole first so that the screw doesn't have to squeeze in too tight and crack the material.
Edit: Ha! I just gave myself an idea for a better ice cream scooper for very cold hard ice cream, which has always frustrated me.
