Thread: Angle of Attack

Originally Posted by joshearl

I'm not sure about the "crushing" you talk about, though. If you watch the National Geographic shaving video, they talk about a razor being so sharp that it just slides between the hair molecules. So regardless of whether or not it slices at an angle, you're breaking molecular bonds, not tearing them apart like a less fine edge would do.

Edit: the following is wrong - human hair is made of keratin, not collagen. Perils of posting under the influence. The truth, however, is even worse for the "sliding between molecules" theory. See the followup post.

Human hair is made of collagen. The basic collagen molecule is 300nm long and 1.5nm thick - basically a microscopic rope. Since a micron is 1000nm, this means the molecules are roughly 1/3 micron long.

Compare that to the grits we use for shaving. We can pop hair with a 6 micron hone. Obviously the fin is thinner than the grit size, but it seems unlikely that an edge that coarse is somehow missing the main body of these "ropes" and instead slides between the ends of adjacent "ropes" that are twisted together to make up a hair. It seems more likely that it really does tear these "ropes" as it cuts, or possibly just catches the molecules in front of the fin and pulls the hair in two, or some combination of the two.