Trying to determine the "Safe" properties of Face Guards I work in a sports science laboratory and I've been set the task of trying to create a simple and inexpensive test to determine which face guards are safe when two field hockey players clash heads (one wearing a face guard the other unprotected). You have to excuse me if my question has a simple answer or if my terminology is a little out, its been many years since I've had to use physics in anger. Here is the state of play so far: I have or can get data relating to injurys and what pressures can cause bone/facial damage. I am therefore looking to express a safety rateing based on pressure levels in combination with the hardness of material and shape of face guard. The last two items I can already determine but I'm struggling with the pressure part. I can assess the pressure exerted using a pressure sensitive photo film easily enough but this method is not ideal because it is very expensive and only gives results for one or two points on each face guard. A simpler and much cheaper method is to drop the face guard into clay and measure the depth of penetration. I know the kinetic energy at the point of impact and I can work out the impact force but I'm not sure how to convert this into a pressure value. I know this should be easy as pressure has a direct relationship between force and impact area but due to the shape of each face guard its not so easy working out what the impact area is. Any suggestions would be most appreciated.