i don't mean to be a science geek, but what is strength? define it with physical parameters.
the strength behind the screen door? do you mean the momentum
as p= mv? which enable said screen door to chop off cat's head. we have a couple of things we can take into account. the speed (or velocity) of the screen door, the mass of the screen door. the acceleration of the screen door. the force of gravity. friction. this is the sum of its forces. this is all its got. so what is the difference between chopping your cat and not? i would go with velocity. you whip the screen door hoping to inflict injury (barring stupid gismo which makes door close slowly), or you open and close it like a normal person. the rest are relatively fixed on a day to day basis. which brings me back nicely to my other point, which is getting punched by one of the twins would jack you up. high velocity equals ow.
mass is a factor but i don't think that shakes out to density. (area of impact isn't negligible but punching is punching and i don't think we want to nit pick about force/area) anybody who goes boating at clippy speeds can attest that a mosquito (which is probably not particularly dense) can hurt sting like a mofo.
i don't want to pee on anyone's cheerios but if we are going to argue imaginary beings let's do it properly! not really. i just get awfully excited about this stuff. seriously this is what i thought about in physics two the whole time, how does this parlay into comic physics?
hmm... and i wonder why i have landed a killer job in science yet......