if you do get your hand on dan or one of the IP/IS folks, ask them to do a zero-inch punch, then see if you can explain that in term of F=ma. the m is easy to explain. the "a" is a bit harder since it's "m/s/s and m(distance)=0". try to figure out how to make "a" non-zero is quite interesting.
How far does that zero-inch fist travel into the target? Wouldn't that make a non-zero "a" easy?