Hello world. I am in the process of writing my first true college essay, a ten-page piece on some topic relevant to my University Physics I course, but I need a little help finding some information. Google hasn't been very helpful today, and I don't even want to think about combing our terribly organized library. Anyway. What I would like is to know the typical human's tolerance to being hit in the center of the forehead - by a thrown rock, for example. What amount of force would the rock have to have in order to kill an individual, or at least cause severe trauma? If I need to be more specific, then please let me know. All responses need to include some credible, cite-able source. Thank you.