i have a punching bag, say it weighs 70 lbs, hung by a chain. i duct tape an acceleromter (sparkfun) on the back of it, sampling at ~300 hz (is that enough?). punch the bag, i get a force in G force. how can i calculate this to say, foot lbs? i really am not sure where to start with this. any guidance in the right direction is appreciated. thanks!