It looks like the same concept as driving in reverse with your tail gate open and abruptly stopping causing what ever is in the bed of your truck to fly out. But that's just me I'm probably wrong.
It's just an application of momentum.
(mass of slide+mass of frame)velocity backward = (mass of slide)velocity of the slide cocking movement -(mass of frame)Velocity forwards.
A little math rearrangement: V_slide initial -(mass of frame/mass of slide){(V_slide initial) - (V_frame final)}=V_slide final
This tells me that a heavier frame makes cocking the weapon like this difficult, and a heavier slide makes cocking the weapon easier (which I think explains why it's easy to do on Hipoints, super heavy slide because it's just a lot of mass delaying the blowback).
Whether or not the slide opens is a question of forces, not momentum... if the derivative of the equation (or better yet, a rearranged version of it) above is taken with respect to time (velocity is meters per second, and the derivative of that is acceleration... so F=ma.
Umm... my minimal physics knowledge doesn't tell me where to go from here.
Is it this force being greater than spring force+friction that cocks the gun?
or when sufficient work is done by this force to equal the work required to cock the gun, counteract friction and work done by the spring force...
ANYWAYS; simple test to see if my ideas hold true: anyone want to clamp something rather heavy on their glock and see if this makes inertia cocking easier?