It IS acting on everything with equal force. But the bottom of the slinky is actually the end of a spring that is compressing while it is being dropped. So the bottom is coming up at the same rate it is dropping, which makes it seem that it isn't moving at all because the forces are being cancelled out - until the top of the spring "catches up" with it, finishes the compression, and the whole thing drops.
The MORONS who made this video spouting off about "gravity messages not reaching the bottom of the spring" are either too stupid to live, or are educational disinformation agents.
Consider - the speed of gravity is FASTER than the speed of light. And this is easily proven. It takes light over eight minutes to reach the earth from the sun, yet the earth follows an exactly curving eliptic gravitational path of constant adjustments every micro-second to follow that ellipse, rather than simply go flying off into space.
So the sun "communicates" it's gravity to earth that fast, but gravity can't manage to "communicate" to the bottom of a slinky?
Like I said, too stupid to live.
I can't remember the time it took in (split) seconds for the top of the slinky to make its way to the bottom without watching the video again, but that seems to be the key.
Slo-mo plays with our minds a bit. The bottom does move, but not until the top reaches a "critical mass" point. The bottom is connected to the top, after all.
The slinky is a whole object, but its mass is "spread out" by design, the physicists discuss this - the same thing happens with a "solid" object (say, a lead bar), just quicker.
Like I said, my math skills are mediocre.