So yes, the atmosphere exerts a force of 100,000 newtons per square meter. A person's head, is obviously much less than a square meter (probably 0.15 meters on the side, which roughly translates to Pi*(0.15/2)^2 square meters). Anyways, for this matter this is irrelevant, as we are already in equilibrium with this force and so we're more concerned about extraneous forces. Now, I know this would depend *a lot* on where the force is exerted and how it's exerted. For this, I'm mostly curious about arbitrary falling objects (rather than, say, bullets). How many Newtons of force would it take to have, say, a 50% chance of killing a person? How many would it take to hurt a person?