I'm not sure what the exact physical force needed to open a crown top is, but that would be an interesting experiment. You should ask a local university's physics department to figure that one out. I know as a college student, I'd be up for an experiment with beer!
My suggestion about easier ways to open them: get one of those long and wide openers bartenders use. They seem to pop off with little force using that. Simple physics. The further away from the fulcrum the less force/weight needed. You have much more leverage. Plus those put more pressure on the cap in a larger area than the small cheap openers.
Just some thoughts.
Michael
Primary: Palialia IPA
Secondary: EMPTY! (This needs to change)
Bottled: Wimpy's Christmas Cheer (Berry Cheer '05)
Next: Good question. Heify maybe?