Why can’t a bullet proof vest protect you from a knife stab?

Question

I mean, it’s designed to stop a bullet which delivers much more force than a human being can ever produce during stabbing

In: 784

Answer 1

Bullets and knives work on very different principals. Bullets use velocity to impart so much energy into an object that they overcome the tensile and compressive strength of and rip right through. Knives, on the other hand, use a sharp blade to minimize the area that the force is being exerted upon to overcome the shearing strength of whatever you’re cutting.

Basic bulletproof vests are made of Kevlar, which has a very high tensile and compressive strength but very low shear strength, making it difficult for a bullet to tear through but easy for a knife to pierce. More advanced armor uses metal or ceramic plates, which can also resist knives.